A3-128-12,000-L180 TEXAS AGRICULTURAL EXPERIMENT STATION B. YOUNGBLOOD, DIRECTOR COLLEGE STATION, BRAZOS COUNTY, TEXAS BULLETIN NO. 377 FEBRUARY, 1928 DIVISION OF ENTOMOLOGY Hibernation 0f the Cotton Flea Hopper AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS T. O. WALTON, President ADMINISTRATION: _ *B. YoUNGRLooD, M. S., Ph. D.,_ Director . B. CoNNER, M. S., Acting Director . E. KARPER, B. S., Acting Vice-Director . M. SCHAEDEL, Secretary ~ . P. HOLLEMAN, JR., Chief Clerk . K. FRANcKLow, Assistant Chief Clerk HESTER HIccs, Executive Assistant . B. NERLETTE, Technical Assistant flfl~g~w> CHEMISTRY: _ G. S. FRAPs, Ph. D., Chief; State Chemist S. E. AsRURY, M. S., Assistant Chemist E. C. CARLYLE, B. S., Chemist WALDo H. WALKER, Assistant Chemist VELMA GRAHAM, Assistant Chemist R. O. BROOKE, M. S., Assistant Chemist T. L. OGIER, Assistant Chemist J. G. EvANs, Assistant Chemist _ ATHAN J. STERGES, B. S., Assistant Chemist G. S. CRENSHAW, A. B., Assistant Chemist JEANNE M. FUEGAs, Assistant Chemist HORTICULTURE: Chief H. NEss, M. S., Berry Breeder RANGE ANIMAL HUSBANDRY: ‘J. M. JoNEs, A. M., Chief; Sheep and Goat Investigations J. L. LUsR, Ph. D., Animal Husbandman; Breeding Investigations t , Wool Grader ENTOMOLOGY: F. L. TIIoMAs, Ph. D., Chief; State Entomologist H. J. REINRARD, B. S., Entomologist R. K. FLETCHER, . A., Entomologist W. L. OWEN, JR., M. S., Entomologist FRANK M. HULL, M. S., Entomologist . C. GAINEs, JR., M. S., Entomologist . J. ToDD, B. S., Entomologist . F BIRRY, B. S., Entomologist _ . E. McGREcoR, JR., Acting Chief Foulbrood Inspector . B. KENNERLY, Foulbrood Inspector ILLIs GRAIIAM, Foulbrood Inspector RONOMY: _ . B. REYNoLDs, M. S., Chief . B. CoNNER, M. S., Agronomist; Grain Sorghum Research . E. KARPER, B. S., Agronomist; Small Grain Research C. IVIANGELSDORF, Sc. D., Agronomist; in charge of Corn and Small Grain Investi- gations _ . T. KILLQUGH, M. S., Agronomist; Cotton Breeding . E. REA, B._S., Agronomist; Cotton Root Rot Investigations . C. CUsRINc, B. S., Assistant in Cro s R. JOHNSON, B. S., Assistant in Soi s 53> V110“ A Wm m U W w >m@ STATION STAFFT VETERINARY SCIENCE: **M. FRANcis, D. V. M., Chief _ H. SCHMIDT, D. V. M., Veterinarian J. D. JoNEs, D. V. M., Veterinarian PLANT PATHOLOGY AND PHYSIOLOGY: J. J. TAURENRAUs. Ph. D., Chief _ L. J. PEssIN, Ph. D., Plant Pathologist and Laboratory Technician W. J. BACH, M. S., Plant Pathologist_ J. PAUL LUsK, S. M., Plant Pathologist} B. F. DANA, M. S., Plant Pathologist FARM AND RANCH ECONOMICS: L. P. GABRARD, M. S., Chief *B. Y0UNGRL00D, M. S., Ph. D., Farm and Ranch Economist _ G. L. CRAWFORD, M. S., Marketing Research Specialist C. A. BoNNEN, M. S., Farm Management Research Specialist _ V. L. CoRY, M. S., Grazing Research Botanist ***T. L. GASTON, JR., B. S., Assistant; Farm Records and Accounts ***J. N. TATE, B. S., Assistant; Ranch Records and Accounts RURAL HOME RESEARCH: JEssIE WmTAcRE, Ph. D., Chief _ MAMIE GRIMEs, l\I. S., Textiles and Clothing Specialist SOIL SURVEY: ***W. T. CARTER, B. S., Chief E. H. TEMPLIN, B. S., Soil Surveyor T. C. REITcR, B. S., Soil Surveyor BOTANY: H. NEss, M. S., Chief PUBLICATIONS: A. D. JAcKsoN, Chief SWINE HUSBANDRY: FRED HALE, M. S., Chief DAIRY HUSBANDRY: , Chief POULTRY HUSBANDRY: R. M. SHERWOOD, M. S., Chief ****AGRICULTURAL ENGINEERING: MAIN STATION FARM: . T. McNEss. Superintendent APICULTURE (San Antonio): . B. PARKs, B. S., Chief A. H. ALEX, B. S., Queen Breeder FEED CONTROL SERVICE: F. D. FULLER, M. S., Chief . D. PEARcE, Secretary . H. RoGERs, Feed Inspector . H. WooD, Feed Inspector . L. KIRKLAND, B. S., Feed Inspector . D. NORTHCUTT, JR., B. S., Feed Inspector SIDNEY D. REYNOLDS, JR., Feed Inspector P. A. MooRE, Feed Inspector II éxéum SUBSTATIONS No.1, Beeville, Bee County: R. A. HALL, B. S., Superintendent No. 2, Troup, Smith County: W. S. HOTCHKISS, Superintendent No. 3, Angleton, Brazoria County: R. H. STANSEL, M. S., Superintendent FRANK M. HULL, M. S., Entomologist No. 4, Beaumont, Jeflerson County: R. H. WYcRE, B. S., Superintendent No. 5, Temple, Bell County: HENRY DUNLAvY, M. S., Superintendent B. F. DANA. M. S., Plant Pathologist H. E. REA, B._S., Agronomist; Cotton Root Rot Investigations No. 6, Denton, Denton County: P. B. DUNKLE, B. S., Superintendent No. 7, Spur, Dickens County: R. E. DIcKsoN, B. S., Superintendent No. 8, Lubbock, Lubbock County: D. L. JONEs, Superintendent FRANK GAINES; Irrigationist and Forest Nurseryman 9, Balmorhea, Reeves County: J. J. BAYLEs, B. S., Superintendent Z .° No. 10, Feeding and Breeding Station, near College Station, Brazos County: , R. M. SHERWOOD, M. Animal Husband- man in Charge of Farm L. J. McCALL, Farm Superintendent No. ll, Nacogdoches, Nacogdoches County: H. F. MORRIS, M. S., Superintendent ***No. 12, Chillicothe, Hardeman County: J. R. QUINRY, B. S., Superintendent '**J. CL STEPHENS. M. A., Junior Agronomist No. 14, Sonora, Sutton-Edwards Counties:- W. H. DAMERON, B. S., Superintendent —————-—— , Veterinarian V. L. CORY, M. S., Grazing Research Botanist ***O. G. BARcocK, B. S., Collaborating Entomologist O. L. CARPENTER, Shepherd No. 15, Weslaco, Hidalgo County: W. H. FRIEND, B. S., Superintendent , Entomologist W. J. BACH, M. S., Plant Pathologist No. 16, Iowa Park, Wichita County: E. J. WiLsoN, B. S., Superintendent J. PAUL LUsK, S. M., Plant Pathologist Teachers in the School of Agriculture Carrying Cooperative Projects on the Station: w. ADRIANcE, M. S., Associate Professor of Horticulture BILSlNG, Ph. D., Professor of Entomology COATES, A. E., Professor of Agricultural Engineering G. S. Y). LEE, Ph. D., Professor of Marketing and Finance RI P. SMITH, M. S., Associate Professor of Agricultural Engineering TAR-of January 1, 1928. *On leave. **Dean, School of Veterinary Medicine. ***In cooperation with U. S. Department of Agriculture. ****ln cooperation with the School of Agriculture SYNOPSIS The dormant or inactive period in an insect’s life cycle is called hibernation. Cold weather in the fall kills all stages of the cotton flea hopper except the eggs, which remain dormant throughout the winter and hatch the following spring when the mean temperature reaches 58 or 60 degrees F. This Bulletin reports the results secured in the hiberation ‘studies on the cotton flea hopper during the seasons of 1925-26 and 1926-27. The average period of hiberation of this insect extends from October 1 to May 1. The time at which the overwintering eggs begin to hatch in the spring varies from year to year and depends largely on prevailing climatic condi- tions. In 1926 emergence from hibernation began on March 7, and continued over a period of 13 weeks; in 1927 it began on February 16, and extended over a period of nearly 20 weeks. When climatic conditions are optimum, emergence of the in- sects proceeds very rapidly. In the spring of 1926, 73 per cent of all the insects emerged from April 5 to April 26. In "1927, 79 per cent of the total emergence was completed from March 17 to April 7. There is a definite relation between the time of maximum emergence and the extent of injury to cotton. Normally the heaviest emergence of insects from hibernation occurs before young cotton is up in the field and little or no injury to the crop is the result. When climatic conditions de- lay emergence of the insects from hiberation in the spring, and cotton is planted at the average date, conditions are favor- able for extensive injury to the crop by the cotton flea hopper. Data are presented on emergence of the insects from 19 species of winter host plants which were collected locally and in several other localities in the State. During the season 1926-27 goatweed at College Station, and primrose at Wharton, contained the greatest number of cotton flea hopper eggs; averaging about 215 insects per plant. Fourteen new winter host plants of the insect have been discovered. These include many of our most common weeds and have a wide range of distribution over the State. CONTENTS PAGE Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5 Methods of Conducting Hibernation Studies . . . . . . . . . . . . . . . .. 5 Duration of Hibernation Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 8 Climatic Conditions During Hibernation Period . . . . . . . . . . .. 9 Emergence from Hibernation . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10 Rate and Time of Emergence . . . . . . . . . . . . . . . . . . . . . . . .. 11 Peak of Emergence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16 Effect of Climatic Conditions on the Beginning and Rate of Emergence from the Overwintering Eggs . . . . . . . . . . . . . .. 18 Dissemination at the Time of Emergence from Hibernation. . . 20 Relation Between the Time of Emergence from Hibernation and the Extent of Injury to Cotton . . . . . . . . . . . . . . . . . . .. 21 Winter Host Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 23 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 25 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5 BULLETIN NO. 377 FEBRUARY, 1928 HIBERNATION OF THE COTTON FLEA HOPPER H. J. REINHARD With the approach of cold weather in the fall of the year, insects gen- erally become less active and are either killed by the occurrence of low temperatures or find shelter in which t0 pass the winter. This period of inactivity is called hibernation or the dormant period in an insect’s life cycle. From the time that activity ceases in the autumn until its recurrence in the following spring insects do not multiply or require any food. They are dead to all outward appearances. Yet the im- portance of the hibernating stage in the life cycle of any major insect pest will be appreciated when it is realized that this is the only means by which the insect can pass through the cold season successfully and appear again with the advent of warm weather in the spring. ' Hibernation may occur in various stages of the development of an insect. The boll weevil, for instance, passes through the winter as an adult or mature insect in practically any available shelter from ‘the cold. On the other hand low temperatures kill all stages of the cotton flea hopper except the egg, which alone remains the source of infestation the following year. Aside from its scientific interest, a knowledge concerning the hiberna- tion of an insect pest often has a practical bearing on developing effective methods for its control. In fact, it has been demonstrated that some of the common destructive pests are most vulnerable during the in- active period of their life cycle. ' In searching for effective methods to control the cotton flea hopper, the hibernation of this insect has been studied for the past two years at the Texas Agricultural Experiment Station. The data which have been accumulated in these studies are presented in this Bulletin as a contribution to our present knowledge of this insect with special refer- ence to conditions affecting the extent of infestation and injury to cotton in Texas. METHODS OF CONDUCTING HIBERNATION STUDIES Hibernation studies on the cotton flea hopper were begun during the fall and winter of 1925 and 1926 and have been continued up to the present time. The methods devised for conducting these studies are described briefly below. It has already been pointed out that all the active stages of the cotton flea hopper are killed by cold weather in the fall and winter. Hence, all observations on the hibernation of this insect are necessarily con- fined to the egg stage. Since the eggs are laid within the host plants it is not possible to determine which are most heavily infested or how many eggs may be present in any single plant or lot of plants, except 6 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION by the numbers of insects emerging from them. This makes it difficult. to secure data on the extent of mortality during hibernation; however, a comparison of the results secured in these studies from year to year will be a valuable index in this connection. To determine the extent of the period of hibernation and emergence‘ therefrom in the spring, common weeds suspected of being winter host plants of the cotton flea hopper Were gathered at varying dates during the fall and early winter. The plants were either cut close to the ground= or pulled up and tied in loose bundles, which were kept under field con- ditions standing upright to prevent undue decay. Some time before the- eggs were expected to hatch the Weeds were placed in cages for observa» tion on the emergence of the young insects. The weeds were installed in the cages in an upright position as nearly" intact as possible. In order to secure representative data on any species of host plant, a lot consisting of 100 average-size plants was selected“ as the minimum unit of installation. It was found necessary to break up the large varieties of plants to get the required number into a cage~ and in some cases they were packed tightly together. The possible- effect of this procedure on the results secured will be referred to in a, later paragraph. The material used in these studies was collected at College Station~ and at several other localities in the State, viz., Wharton, Weslaco, Troup, San Antonio, and Corpus Christi. A' complete record of the~ winter host plants collected and installed in the emergence cages is given in Table 3. _ The cage designed for these studies is a wood frame constructed of 1 by 4 material and measures 2x2x3 feet. The sides and top are cov~ ered with one thickness of black percale to darken the interior and at the same time maintain ventilation, temperature, and humidity conditions as nearly natural as possible. A series of 28 vials (25x100 mm.) are inserted around the top and half-way down one edge on each side to~ admit light from all directions for the purpose of attracting the young insects as they hatch from the weeds within the cage. The vials are- held securely in place by a cork Washer which is fitted and glued in the frame exactly flush on the inner surface. As the insects enter the vials» they can be readily removed and counted at any time without disturbing the contents of the cage. The emergence cages are illustrated in Fig» ures 1 and 2. The principal sources of error introduced which affect the results secured in the hibernation studies by the use of the cage and methods described above are: first, breaking the plants which may destroy some of the eggs present; and, second, packing the plants closely together in a cage, which increases the hazard of the young insects, especially those hatching in the center of the mass of plants, in reaching the vials. How-e ever, since all cages received the same treatment the error is assumed to be relative and in effect reduces the number of insects emerging from- all the different host plants caged for observations. The data presented HIBERNATION OF THE COTTON FLEA HOPPER 7 Fig. 1. The type of cage used for making observations on emergence of the cotton flea hopper in the spring of 1927 Fig. 2. A series of the emergence cages used_ in the hibernation studies on the cotton flea hopper 111 8 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION on the following pages is therefore considered a conservative index to the emergence from hibernation 0r the hatching of overwintering eggs under natural conditions. DURATION OF HIBERNATION PERIOD Since practically all observations on this point were made at College Station, the data presented refer especially to that locality. Undoubt- edly both seasonal variations and latitude affect the limits of the period. To establish the extent orduration of the hibernation period of the cotton flea hopper, seven 100-plant lots of goatweeds were cut in the same locality at intervals of two weeks, beginning August 1, during the late summer and fall of 1926. These weeds were placed in separate cages for observations on the emergence of insects from each lot of weeds during the following spring. The data secured in this connec- tion are given in Table 1. It Will be noted that very few insects emerged from the weeds cut on August 1, August 15, and September 1, indicating that the eggs in these Weeds hatched some time before con- ditions were favorable to effect dormancy. However, there was a de- cided increase in the number of insects emerging from the lot of weeds cut on September 15, showing that an appreciable per cent of the eggs Table 1.——Emergence of the insects from 100 goatvveeds cut at various dates in the late summer . and fall of 1926 Total Cage Number Date Cut ' First Last Number Emergence Emergence Emerged 1926 1927 1927 l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Aug. 1 Feb. 16 Mar. 30 9 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aug. 15 Mar. 19 April 28 2O 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sept. 1 Feb. 17 May 1 82 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sept. 15 Feb. 17 May 20 _ 1380 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sept. 3O Feb. 16 June 28 14714 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Oct. 15 Feb. 16 June 14 15324 7 . . . . . . . . . . . . . . . . .' . . . . . . . . . . . . . . . . . . Nov. 3 Feb. l6 June 29. 17275 were dormant on that date. There was very little variation in the number of insects emerging from the weeds cut on dates subsequent to September 15, and the data presented above show that practically all the eggs were dormant on September 30, during the season of 1926-27. The results of a similar experiment conducted during the season of ‘ 1925-26, reported in Texas Experiment Station Bulletin 356, page 2'7, ' indicate that about 3' per cent of the cotton flea hopper eggs were dor- mant on September 15, and approximately 22.5 per cent were dormant on October 1. According to these observations it may be stated that the hibernation» period of the cotton flea hopper in this latitude begins about September" 15. Although complete hibernation may not be efiected until about the time that the first killing frosts occur. In the spring of 1926 the first insects hatched from the overwintering HIBERNATION OF THE COTTON FLEA HOPPER 9* eggs on March '7, while in 1927 first hatching occurred on February 16.. By May 15 emergence from the winter host plants was practically com- pleted although a few insects continued to hatch in the emergence cages. over a period of 3 to '7 weeks thereafter. At College Station, the average period of hibernation may be said to- extend from approximately October 1 to May 1, or over a period of about 7 months, while the extremes of the period may possibly range,- from 4 to 8 months. Climatic Conditions During Hibernation Period The principal climatic factors affecting the overwintering eggs of the cotton flea hopper during the dormant seasons of 1925-26 and 1926-27 are given in Table 2. Since enormous numbers of eggs were carried successfully through both of these dormant seasons it is evident that the eggs were not affected unfavorably by the prevailing climatic con- ditions. It will be observed that the monthly mean temperatures dur- ing the fall and winter of 1925-26 were consistently below the normal; however, the only apparent effect was delayed emergence in the spring. In 1926-27 the monthly mean temperatures more nearly approached the normal and the result was an earlier spring emergence. The minimum. .Table 2.-—Climatological data affecting the hibernation period at College Station during the seasons of 1925-26 and 1926-27 Temperature, Degrees F. Departure Rainfall, Departure Distributioil Month Year — from Inches from of Rainfall Max. Min. Mean Normal Normal Days 1925 99 65 82.0 +2.8 2.41 —0.39 September 1926 100 57 82.8 +3.6 1.10 -—1.70 9 v 1925 95 35 66.8 +2.9 12.21 +9.48 13 October 1926 97 46 73.6 +3.9 6.61 +3.88 10 1925 s0 s2 57 .4 +1.6 5. e7 +2 .27 9 November —— 1926 80 30 56.6 -—2.4 2.50 —-0.90 1925 76 2O 45.8 —~7.1 0.88 ——2.91 December . 1926 80 26 51.5 —1.4 8.02 —4.41 11 1926 70 25 46.2 ——5.2 4.53 +1.27 10 January 1927 78 24 52.2 +0.8 1.28 —1.98 5 1926 79 36 58.2 +5.2 0.13 -—-2.68 February 1927 85 26 58.4 +5.4 6.10 +3.29 9 1926 79 32 56.0 —-4.4 8.03 +5.34 17 March 1927 87 31 60.6 +0.2 2.20 +0.49 1926" 8O 41 62.9 ——5.1 5.97 +2.10 April 1927 88 43 72.2 +4.2 5.09 +1.22 3 10 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION temperature at which the eggs are killed was not determined. During December, 1925, an average minimum temperature of 24 degrees F. pre- vailed over a period of four days, With 12 degrees below freezing obtain- ing on two successive days. These lOW temperatures apparently did not produce a high rate of mortality since the eggs hatched in large numbers during the following April. There is no evidence available which indi- cates that the excessive rainfall which occurred in October, 1925, March, October, and December, 1926, or February, 1927, affected the hiberna- tion of the insect directly except possibly in being a factor influencing early spring emergence during 1927. Emergence from Hibernation The time at which emergence begins varies from year to year and depends largely upon the prevailing temperatures. When conditions are favorable, as was the case early in the season of 1927, hatching of the overwintering eggs may begin by the middle of February. Emerg- Table 3.—Data on collection of winter host plants of the cotton flea hopper Host Plant _ Cage Date Locality No. Collected Collected Scientific Name Common Name 1 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed. . . . . . Aug. 1, 1926 College Station 2 Croton capitalus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Aug. 15, 1926 College Station 3 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed. . . . . . Sept. 1 , 1926 College Station 4 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Sept. 15 , 1926 College Station 5 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Sept. 30, 1926 College Station 6 Croton capitalus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Oct. 15, 1926 College Station 7 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Nov. 3, 1926 College Station 8 Gossypium hirsutum . . . . . . . . . . . . . . . . Cotton . . . . . . . . . Nov. 23, 1926 College Station 9 Gaura brachycarpa . . . . . . . . . . . . . . . . . Primrose . . . . . . . Oct 19, 1926 Wharton 10 Solarium elaeagnifolium . . . . . . . . . . . . . Horse Nettle... . Oct 19, 1926 Wharton 11 Ambrosia psilosiachya. . . . Ragweed . . . . . . . Dec 7, 1926 College Station l2 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Feb 15, 1927 College Station 13 Amphiachyris dracunculoides . . . . . . . . Broomweed. . . . . Feb 15, 1927 College Station 14 Xanthium speciosum . . . . . . . . . . . . . . . Cocklebur . . . . . . Feb 17, 1927 College Station 15 Helerotheca subaxillaris . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feb 17 , 1927 College Station 16 Eupatorium compositifolium . . . . . . . . . Dog Fennel. . . . . Feb 17, 1927 College Station 17 Aster sp . . . . . . . . . . . . . . . . . . . . . . . . . . Wild Aster. . . . . Feb 19, 1927 College Station l8 Gossypium hirsutum. . . . . . . Cotton . . . . . . . . . Feb 19, 1927 College Station 19 Ambrosia aptera . . . . . . . . Ragweed . . . . . . . Feb. 21 , 1927 College Station 20 Amqranthus Torreyii . . . . . . . . . . . . . . . Careless weed. . . Feb. 21 , 1927 College Station 21 Atriplex sp . . . . . . . . . . . . . . . . . . . . . . . . Orach . . . . . . . . . . Feb 17, 1927 Weslaco 22 Helianthus Maximilianii . . . . . . . . . . . . Sunflower . . . . . . Feb 17, 1927 Weslaco 23 Ambrosia artemisiifolia 7 . . . . . . . . . . . Ragwee . . . . . . . Feb 17, 1927 Weslaco 24 Gossypzum hzrsutum . . . . . . . . . . . . . . . . Cotton . . . . . . . . . Feb 17, 1927 Weslaco 25 Heleiiium tenuifolium . . . . . . . . . . . . . . Bitterweed. . . . . Feb. 26, 1927 College Station 26 Leptzlon Can adense . . . . . . . . . . . . . . . Horseweed . . . . .. Feb. 26, 1927 College Station 27 Ambrosia psilostacliya . . . . . . . . . . . . . . Ragweed . . . . . . . Feb. 20, 1927 Troup 28 Croton capitatus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Feb. 20, 1927 Troup 29 Monarda sp . . . . . . . . . . . . . . . . . . . . . . . Horsemint . . . . . . Feb. 20, 1927 Troup 3O Gossypium hirsutum . . . . . . . . . . . . . . . . Cotton . . . . . . . . . Feb. 20, 1927 Troup _ 31 Gossypium hirsutum . . . . . . . . . . . . . . . . Cotton . . . . . . . . . Feb. 21 , 1927 San Antonio 32 Ambrosia aptera . . . . . . . . . . . . . . . . . . . Ragweed . . . . . . . Feb. 17 , 1927 San Antonio 33 Heliantlius anmius . ._ . . . . . . . . . . . . . . Sunflower . . . . . . Feb. 17, 1927 San Antonio 34 Ambrosia artemzsiifolza . . . . . . . . . . . . . Ragweed . . . . . . . Feb. 16, 1927 San Antonio 35 Solarium elgzeagmfolzum . . . . . . . . . . . . . Horse Nettle. . . . Feb. 21 , 1927 San Antonio 36 Crolon capitafus . . . . . . . . . . . . . . . . . . . Goatweed . . . . . . Feb. 23, 1927 San Antonio _ 37 Gossyplum hzrsutum . . . . . . . . . . . . . . . . Cotton . . . . . . . . . Mar 1 , 1927 Corpus Christi 38 Croton capitatus . . . . . . . . . . . . . . . . . Goatweed . . . . . . Mar 1 , 1927 Corpus Christi 39 Solanuni elaeagmfolium . . . . . . . . . . . . . Horse Nettle. . . Mar 1, 1927 Corpus Christi 4O Parthemum Hysterophorus . . . . . . . . . . . . . . . . . . . . . . . . . Mar 5, 1927 Corpus Christi HIBERNATION OF THE COTTON FLEA HOPPER 11 ence, however, is a slow process until optimum conditions occur, at which time the insects hatch in enormous numbers over a period of two or three weeks. After the period of maximum emergence there is a sharp decrease in the number of insects hatching from the overwintering eggs. However, they may continue to hatch in small numbers over a period of two or three months after emergence has been practically completed. During the season of 1926, emergence of the cotton flea hopper ex- tended from March '7 to June 10, or over a period of about 13 weeks; while in 1927 the period of emergence comprised approximately 20 weeks extending from February 16 to July 3. Climatic factors appear to have a direct influence upon the rate of emergence and consequently also affect the limits of the period from year to year. This subject will be discussed in a later paragraph. . In Table 4. are presented the data secured on the emergence of the cotton flea hopper at Weekly intervals from the various kinds of winter host plants which were caged for observation during the season of 1927. It will be noted that the date of first emergence in most cases occurred from February 25 to March 25, and apparently the time at which the eggs begin to hatch is little, if at all, affected by the character of the host plant in which they are laid. There also appears to be little or no difference in the rate of emergence from the different types of host plants. The last insects emerged from ragweed and bitterweed on July 3, from goatweed and primrose on June 29, while several other widely related host plants yielded insects up to the latter part of May. A summary of the data secured in these studies on the emergence of the cotton flea hopper from the overwintering eggs in 19 different species of host plants collected at College Station and in other localities of the State is given in Table 5. These data illustrate the numerical pro- gression of emergence by months from each lot of host plants. The duration of the composite emergence period averaged about '74 days, ranging from 16 to 134 days. The number of insects emerging during June was very small and in only three instances did any emerge after July 1. It will be noted that the maximum number of insects hatched during March, although large numbers continued to emerge throughout April from practically all species of host plants. The total number of insects emerging from each lot of host plants is a definite indication as to the plants preferred by the insects, and their importance in connection with hibernation of this insect. Rate and Time 0f Emergelwer The rate at which the insects emerged from all the host plants under observation in the spring of 1927 is illustrated graphically in Figure 3. Beginning on February 16, the insects emerged in small numbers during the following four weeks; in fact, less than 5 per cent of the total emergence was completed on March 16. From that date hatching of the overwintering eggs proceeded very rapidly and by April 6, three weeks later, about '79 per cent of the total 12 BULLETIN NO.37Z TEXAS AGRICULTURAL EXPERIMENT STATION w whm¢mmwmm»mmw~wwom@gN@cmo~¢mmh~wm -_. U.) l-QP1c'J@¢3X§Dv-4C\1 CQF-ilf-I-i l\v-41 B E - H I [\-b-l\l‘wl\l\l‘-l\l\b-l\l‘-l\l\lf-l\l\l\l\l\l\b-l‘-l\l\ 'l\l\l*l\l\l\l\ CQCQCQCQCQCQICQCW$FNINN$NCQNNCQOIDIQINOICQX "CQCQCVNNCQX ‘Q3 O56‘;OQC90>OQ@CFO50>O>UQC>O>O>O>C>OQO505UPO5UI@OQ '@O’IO5@O50>C> a: v-iv-lv-IwfllPiFli-ll-lv-iFir-li-ii-1l-lr1v-iv4i-lv-iv-iv-li-lPiv-lv-l ‘I—(V—1I—1I—|I_.I—|U—| Aw ----...-.-..-....-.-...-.I.-..... 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QQCQMNQEQ WGTHDQ wowHwEm mHovmHH~ m0 nQQEDZ Quark 30E ummH docomuwfiv wsiam =0 H33. Ho %nmEE-m|||.m BHHNF 14 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION PER CENT I00 Q0 80 70 b0 ‘50 £10 50 lbZ5~2 9 162550-6 52027-11 ll l8Z5-l 8 P522295 FEB MARCH APRIL MAY JUNE JUL Fig. 3. Accumulative emergence 0f insects at weekly intervzgls from nineteen different species of winter host plants, during the sprmg 1927 PEROgENT 90 8O 70 b0 50 40 50 Z0 lbZ5'2 Q lé2550~é 52027-4 ll I825~| 8 I522 29-5 FEB MARCH APRIL MAY JUNE JUl Fig. 4.—-Accumulative emergence of insects at weekly intervals from goatweed during the spring 1927 . 15 HIBERNATION OF THE COTTON FLEA HOPPER er words, out of a total of 53,137 in- emergence was completed. In oth sects which emerged in the cages, 41,956 of them hatched from March 17 to April 7, a period of 21 days. The significance of this fact may be out that this number of insects emerged from Under field conditions where oftentimes many host plants of the cotton flea hopper the hich may hatch during a comparatively emphasized by pointing It will be noted that few insects only 3,200 host plants. acres are literally covered with owing the period of enormous number of insects W few weeks is beyond computation. immediately foll the rate of emergence again increased hatched during the two weeks maximum emergence; however, rapidly from April 20 to May 4. On May 11 emergence was prac- tically completed. PER CENT A... IOO 9o l /: l 8O / I l I 7o ,- l l I l I l l l I l l l b0 l 5O l A10 l / .- 50 .‘ l / .- 20 =' - f / : l O ,- ¢"J' ’ nnn —' FEBRUARY MARCH APRIL MAY JUNE Accumulative emergence of insects by months during the spring of 1926 and 1927. The broken line represents emergence in 1926; the solid line in 1927. aragraph refers to the composite Fig. 5. The discussion in the preceding p rate of emergence from all host plan xima undoubtedly is the closest appro ts caged for observation. tion of the rate of emergence under ting to note that the rate at which the strated in Figure 4, is practically from all the natural conditions, it is interes umerical rate of emergence it will be observed that a corresponding insects emerged from goatweed, as illu In comparing the n the same. cages, as indicated in Table 4, 16 BULLETIN NO. s17, TEXAS AGRICULTURAL EXPERIMENT STATION curve, with possibly a few eXce ptions, will represent the rate of emerg- ence from any of the important host plants included in this list. The rate and time of emergence during the spring of 1926 and 1927 are illustrated graphically in Figures 5 and 6. In the spring of 1927 emergence began on February 16 about three Weeks earlier than in the previous season, and by April 1, more than 71 per cent of all the insects had emerged. On the same date in 1926 less than 4 per cent of the total emergence had been effected. However, hatching continued at a very rapid rate during April and on May 1 practically 95 per cent of the PER CENT I00 9O 8O 7O co !\\ i l / \~* 50 1 i / ‘l: so ll i \\ i Z0 / . \‘~=. _J ....... --l' ' \ FEBRUARY lhARcH APRIL MAY JUNE JULY Fig. 6. Total emergence of insects by months during the spring of 1926 and 1927. The broken line represents emergence 1n 1926; the solid line in 1927. total emergence was completed. The inter in this connection is the early later but even more rapid eme i esting and significant point heavy emergence in 1927contrasted by a rgence in 1926. this difference in rate and time of emergence a explanation for the heavy infestation of the cott The effect produced by in 1926 and the contrasting lack or compara which occurred durin ppears to be the logical on flea hopper on cotton tively light infestations g 1927. This subject is discussed more fully on "Peak of Emergence: vals, from all the host page 21. The per cent of total emergence at Weekly inter- plants Which were caged for observation during ~ HIBERNATION OF THE COTTON FLEA HOPPER 17 PER CENT 4O 5b 52 Z8 Z A lb Z5'Z 9 lb Z5 50% l5 Z0 27-4 l| I8 ZS-I 8 l5 ZZZQ'5 FEB MARCH APRIL MAY JUNE JUL Fig. 7. Total emergence of_ insects at weekly intervals from nineteen different species of winter host plants during spring of 1927 PER CENT 4O 5b 52 Z8 Z4 Z0 IbZErZ Q lbZ550'b 52027-4 ll l8Z5-l 8 ISZZ 29'?) JUNE FEB MARCH APRIL MAY JUL Fig. 8. Total emergence of insects at weekly intervals from goatweed during the spring of 1927 18 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION the season 1927, is illustrated graphically in Figure 7. It will be ob- served that the peak of emergence, or the time when the insects hatched in greatest numbers, occurred during the Week beginning March 24. About 33 per cent, or 17,715 out of a total of 53,137 insects, emerged from 3,200 host plants during the brief period of 7 days. The per cent of total emergence at weekly intervals from goatweed is shown in Figure 8. The peak or time of maximum emergence oc- curred during the week beginning March 17, Which was a week earlier than the corresponding period in the composite emergence from all host plants. Over 38 per cent of the total emergence was effected from March 17 to March 24. In other words out of a total of 21,895 insects 8,413 emerged in 7 days. On the basis of these data some conception may be gained of the count- less myriads of young cotton flea hoppers which may appear suddenly in fields where host plants are abundant. For example, assuming that an acre of ground contains 20,000 goatweed plants from which the insects are hatching over the period of maximum emergence at the rate indi- cated above, then 1,700,000 insects may emerge per acre area during the course of one week. Since these figures are considered very conservative they may be taken as a concrete index to the immensity and rapidity of emergence under natural conditions. The data which have been accumulated on the emergence of the_ cotton flea hopper during the season of 1926 and 1927 are summarized by months and illustrated graphically in Figures 5 and 6. During the , month of March in 1927, it will be observed, about 69 per cent, or 36,719 out of a total of 53,137 insects, had emerged. For the same period in 1926 only 1,706 out of a total of 44,363 insects, or less than 4 per cent, had emerged. However, this was followed by a very heavy emergence in April, during which month about 91 per cent of the total number of insects emerged. In other words, in 1927 the peak of emergence from the winter host plants had been attained at a time when emergence had hardly begun in 1926. Undoubtedly this wide difference in rate and time of emergence was due to the influence of prevailing climatic conditions. Eifl"ect of Climatic Conditions on the Beginning and Rate of Emergence from the Overwintering Eggs Since the studies on the emergence of the cotton flea hopper from hibernation have extended over a period of only the last two seasons, the data available are insufficient to formulate any final conclusions regard- ing the effect of climatic conditions on emergence of the insects. How- ever, a comparative study of the emergence periods for 1926 and 1927 is of special interest with respect to the influence of climatic factors, since these were contrasting seasons so far as the time of beginning and the period of maximum emergence of the insect are concerned, and with respect to injury produced by the insect. HIBERNATION OF THE COTTON FLEA HOPPER 19 Table 6.—Climatological data affecting spring emergence at College Station during the seasons of 1926 and 1927 . Departure Departure Nlonth Year Temperature from Rainfall, from Mean Normal Inches Normal “b; i 1926 58.2 U +5.2 0.13 _ E268 February - m _ 1927 58.4 +0.4 6.10 +3.29 T‘ _4’ 1926 56.0 +4.4 8.03 +5.84 March - 4— - 1927 60.6 +0.2 2.20 +0.49 _IM_ '9 1926 62.9 ~51 5.97 _2.10 April 1927 72.2 +4.2 5.09 +1.22 H’ 1926 72.3 ~17 2.26 #180 May 1927 79.2 +5.2 1.97 -2.78 1926 81.0 +0.1 0.68 —2.60 June ' 1927 80.9 0.0 5.43 +2.15 The mean temperature, total precipitation, and the departure from the normal for each month during the emergence periods of the past two seasons are presented in Table 6. The apparent influence of these factors on hatching of the overwintering eggs will be considered briefly, by pointing out differences or approximations in temperatures and pre- cipitation for various months in connection with the per cent of total emergence attained, as illustrated in Figure 6. It will be observed that the mean temperatures for February, 1926, and February, 1927, were practically the same and slightly over 5 degrees F. above the normal. In 1926 the rainfall for the month was only 0.13 inches, while in 1927 the total was 6.10 inches distributed over 9 days. These amounts of rainfall represent marked departures in both direc- tions from the normal. During February, 1927, 2.4 per cent of the total emergence had been completed, indicating that an average mean temperature of 58.4 degrees F. becomes effective when rainfall is abundant. No insects emerged during February, 1926, although the average mean temperature was 58.2 degrees F., and the rainfall was very light. In other words, present knowledge indicates that the rainfall has an important influence on the hatching of the overwintering eggs after the effective mean temperature has obtained for several weeks. During March, 1926, the mean temperature was 56.0 degrees F., or 4.4 degrees below the monthly normal. The rainfall on the other hand was 5.3-1 inches above normal, 8.03 inches being recorded over a period of 17 days. March, 1927, approached normal conditions very closely with respect to the mean temperature and the rainfall. The climatic conditions which prevailed during March, 1926, were closely approximated in February, 1927. The per cent of total emerg- ence effected during these months is practically the same, indicating 20 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION that mean temperatures of 56 to 58 degrees F., with abundant rainfall, are effective factors in the emergence of insects from overwintering eggs. The small per cent of emergence which occurred during March, 1926, with an average mean temperature 4.4 degrees F. below the normal, is contrasted by the peak of emergence which occurred during March, 1927, with practically a normal temperature and rainfall. Ap- parently a mean temperature of-60 degrees F, with a normal well- distributed rainfall, is near the optimum conditions for the procedure- of maximum emergence. Further evidence concerning this point is presented in the following paragraph. Since the period of maximum emergence in 1926 and 1927 occurred during April and March, respectively, a comparison of the climatic conditions which prevailed during these months is pertinent to the optimum conditions which effect maximum hatching of the overwinter- ing eggs. The mean temperature for April, 1926, was 62.9 degrees F.,. which was 5.1 degrees below the monthly average mean. The rainfall for the month was excessive, totaling 5.97 inches distributed over a period of 9 days. During March, 1927, the mean temperature was 60.6 degrees F., or practically normal. Similarly, the rainfall for the month closely approached the normal, a total of 2.20 inches occurring over a period of 8 days. Obviously, April, 1926, was an abnormal month and the climatic conditions which prevailed, it will be observed, approxi- mated the normal for March. In other words, these observations indi- cate that the period of maximum emergence of the cotton flea hopper from the overwintering eggs is effected during March whenever the mean temperature and rainfall for the month approximate the normal. The apparent effect of climatic conditions on the emergence of the cotton flea hopper in the spring of 1926 and 1927 may be summarized briefly as follows: In the spring of 1926 hatching of the insects from the overwintering eggs was retarded during March by abnormal climatic conditions, and the period of maximum emergence occurred in April, which was subsequent to the time when cotton was up generally in the field. On the other hand, climatic conditions in March, 1927, were nearly normal and maximum emergence of the cotton flea hopper was effected during that month, or at a time before practically any cotton had been planted. Dissemination at the Time of Emergence from Hibernation The immensity of the generation of insects emerging from the over- wintering eggs has been‘ described in the preceding paragraphs. Often vast numbers of the insects emerge from weeds located on waste-lands or uncultivated fields which may be remotely situated from any fields of young cotton. It is therefore interesting to consider how the young insects are disseminated or spread over the surrounding territory from the centers of spring emergence. - ' Winds are probably the most important single factor effecting the HIBERNATION OF THE COTTON FLEA HOPPER » 21 wide dissemination or spread of the cotton flea hopper at the time of emergence from hibernation. The newly hatched insects are very deli- cate and fragile. In size they compare favorably with tiny particles of dust 0r sand which even moderate breezes could carry over considerable distances. It is also significant that the period of heaviest emergence normally occurs during a time when Winds are usually blowing at a maximum average rate. Large fields of preferred host- plants of the insect frequently are left unmolested until the period of maximum emergence occurs. At that time the young insects, present on thedried- up or dead host plants of the previous season, are doubtless scattered far and wide in prodigious numbers by the prevailing strong winds. Thus far all the preliminary tests made to prove this point definitely have yielded only negative results. However, there is an abundance of indirect evidence which supports the theory of wind distribution in case of the cotton flea hopper, and further studies in this connection will undoubtedly show that the insects are commonly spread in this manner. Relation Between the Time of Emergence from Hibernation and the Extent of Injury to Cotton It is significant that practically all the serious outbreaks of the cotton flea hopper in this State are in accord regarding the time when most of the injury to the cotton crop is accomplished. Invariably it has occurred early during the growing season. The evidence which has been accumu- lated on the activities of this insect indicates that the generation hatch- ing from the overwintering eggs is responsible for making the greatest inroads on the crop. It is a well established fact that cotton is an acquired food or host plant on which the insects, under normal conditions, do not multiply as rapidly as they do on the preferred host plants. Yet in the early part of the growing season large numbers oflthe insect may be encountered in cotton fields, which apparently could not have developed on the plants. Furthermore, as the season advances, the cotton flea hopper population decreases and usually by the end of June the number. of in- sects remaining on cotton is practically insignificant. It therefore ap- pears logical to assume that the early destructive infestations of the cotton flea hopper are composed principally of individuals which emerged from the overwintering eggs. To illustrate the importance of the generation of insects emerging from the overwintering eggs, as a potential source for the origin of infestations during the early part of the growing season, a few data secured from individual emergence cages are presented below and used as the basis for some precise calculations on the extent of emergence. On March 22, Cage No. 9 containing 100 host plants, Gaura brachycarpa, yielded 4,438 insects in 8 hours; and 12,959 insects in '7 consecutive days, March 22-28. On March 22, Cage No. 12 containing 100 goat- weed plants yielded 3,386 young insects in 8 hours; and 12,300 insects 22 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION from March 22 to March 28. More data in this connection could be cited, but these are sufficient to illustrate the point. Assuming that an acre of ground contains 20,000 preferred host plants from which the insects are emerging at the maximum rate indicated above, it will be noted that 887,600 cotton flea hoppers may hatch per acre area in a single day; 2,591,800 in a week or at a daily rate of about 370,000 for 7 con- secutive days. Obviously, in localities where the preferred host plants abound, the number of cotton flea hoppers which may emerge from the overwintering eggs is beyond comprehension. According to the figures given above, theoretically the number of insects which may hatch during one week on an acre of preferred host plants if transferred to an acre of cotton with a normal stand ranging from 15,000 to 20,000 plants would result in a ratio of approximately 150 insects to each cotton plant. For- tunately, however, such severe infestations do not occur, because a vast majority of the insects never reach young cotton plants in the spring. The principal limiting factor in this connection is the relation between the time at which maximum emergence occurs and the status or develop- ment of the current cotton crop. Emergence depends largely, as has already ‘been shown, upon the mean temperature and precipitation prevailing during February, March, and April. The observations made at College Station in this connection have added greatly to our knowledge of the relation between the time of maximum emergence and the extent of injury to cotton. In the spring of 1926 a late‘ heavy emergence of the cotton flea hopper was followed by widespread infestations and considerable injury to the crop in nearly all cotton-producing regions of the State. In 1927, although the emergence of the insects was fully as great as during the previous spring, an early heavy emergence occurred before cotton was planted and practically no injury to the crop resulted anywhere in this State. The lack of injury to cotton was the direct result of a late emergence of the insects in 1926, contrasted with an early emergence of the insects in 1927, as illustrated in Figure 5. In other words, the time at which maximum emergence occurs in relation to the growth of cotton largely determines the extent of injury that is produced by the cotton flea hop- per. This is a very significant point. To illustrate, if the time of maximum emergence of the insects is delayed, by abnormal conditions, to or after the time when young cotton is ordinarily’ up in the fields, then the plants are subject to infestation and subsequent injury results. These were precisely the conditions which existed generally throughout this State during the early part of the growing season in 1926. The result was widespread infestations of the insect accompanied by unprec- edented injury to the crop. On the other hand when maximum emerg- ence occurs at the normal time, as was the case in the spring of 1927, cotton, except that planted unusually early, is not available as a source of food. In fact, during 1927 much of the seed was not planted at the time when the insects were hatching in greatest numbers. In the absence of cotton the young insects must necessarily turn to other sources HIBERNATION OF THE COTTON FLEA HOPPER 23 of food and very likely vast numbers of them perish before reaching suitable food plants. According to these facts and observations made during the past two seasons, the general indications are: that Whenever a normal mean temperature and precipitation prevail during March, the cotton flea hopper Will do little, if any, injury to cotton ;_ When the monthly mean temperatures for March and April are 4 or 5 degrees F. below the normal, with the rainfall for each month Well above the average, and cotton is planted at the normal time, conditions are favorable for flea hopper infestations on cotton and considerable injury to the crop is likelyto be the result. WINTER HOST PLANTS In these studies much valuable information has been accumulated concerning the winter host plants of the cotton flea hopper. Heretofore only 5 or 6 different species of plants Were known to be concerned in the hibernation of this insect, and the information available on the relative importance of these was very limited. In addition to securing more complete data on the number of eggs carried through the dormant season in these plants, 14 new Winter host plants of the insect have been discovered. The data secured in the observations on emergence of the insects from these plants are presented in Table 5. It will be observed that this list of winter host plants contains many Widely related forms. These plants, however, agree generally in having a semi-Woody texture which hardens at maturity and results in rather tough Woody plants which readily Withstand the elements during the Winter months. The present list of Winter host plants is not considered inclusive or nearly complete. Undoubtedly there are many other species of plants, not yet discovered, which are important factors in the hibernation of this insect. The importance of any Winter host plant is determined, not only by the number of eggs Which it carries through the Winter, but also by its abundance and by the extent of its distribution. For example, the various species of Croion, or goatWeed, are Widely distributed over this State and in some sections at least rank among the commonest Weeds. On the other hand, Atriplex, or orach, While also abundant in some localities, is not generally distributed over the State. Both Croton and Atriplecc wherever they occur arepreferred by the insect for food and reproduction. Assuming that they may contain approximately the same number of eggs, per unit of measure, during the dormant season, it will be appreciated readily that Atriplesv is an important Winter host plant only in the local areas Where it is indigenous, While Croton assumes the status of being an important factor in hibernation over a vastly larger territory. To illustrate further, by accurate count the number of in- sects which emerged from 100 primrose plants, Gama, brachycarpa, collected at Wharton, Texas, and from 100 goatWeed plants, Uroton capitatus, collected at College Station, Was 21,617 and 21,895, respec- tively. Evidently the number of eggs contained in these Weeds during 24 BULLETIN NO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION the Winter of 1926-27 Was approximately the same. However, primrose plants of this species are confined in distribution principally to southern Texas, and Wherever the plant abounds in that section it undoubtedly is an important Winter host of the cotton flea hopper, While goatweed, With approximately the same number of eggs per plant, by the virtue of its Wide distribution and abundance, is a preeminent Winter host of the insect. It Will be observed that the number of insects emerging from the overWintering eggs in bitterWeed, ragweed, dog fennel, horseWeed, horse nettle, careless Weed, H eterotizecct subaixiZ/aris, and others, are not as impressive as the number emerging from primrose or goatWeed. Fig. 9. Two common species of goatweed plants, (A) Croton capitatus, (B) Croton Engel- mannii. These plants are preferred by the cotton flea hopper for food and as winter host plants. Nevertheless, many of these are very common Weeds With a Wide range of distribution over the State and hence must be considered as potential factors in the hibernation of this insect. It is interesting to note that out of a total of 19 different species of plants principally common Weeds Which were collected during the Winter of 1926-27 and placed in emergence cages, only one, H elilanthus annuus, failed to contain any overWintering eggs of the cotton flea hopper. This singular fact illustrates a remarkable flexibility in the habits of the in- sect When choosing its Winter host plant. As these studies are con- tinued, the list of plants concerned Will very likely be extended to in- HIBERNATION OF THE COTTON FLEA HOPPER 25 clude other common weeds that may prove to be equally as important in the hibernation of the insect as any of those which have been dis- covered up to the present time. ACKNOWLEDGMENTS The Writer is indebted to several members of the Station Staff for assistance rendered, especially to Dr. F. L. Thomas, Chief, Division of Entomology, for helpful suggestions in conducting the experiments and in the preparation of the manuscript; to Messrs. W. L. Owen, Jr., Entomologist, and H. E. Parish, Assistant Entomologist, for aid in recording the data on emergence; to Mr. H. Ness, Chief, Division of Botany, for determination of all plants submitted to him; and to Messrs. H. B. Parks, San Antonio, and W. S. Hotchkiss, Troup, who kindly collected and sent in material for study from their respective localities. SUMMARY 1. The hibernation period of the cotton flea hopper at College Station may begin as early as September 1 to 15, although the eggs are not dormant generally until October 1. ' 2. In the spring of 1926 the first insects hatched from the over- wintering eggs on March 7, While in 1927 first hatching occurred on February 16. Emergence from the winter host plants was practically completed on May 15; however, a few stragglers continued to hatch up to June 10, 1926, and July 3, 1927. 3. The average period of hibernation at College Station extends from approximately October 1 to May 1, or over a period of about 7 months. The extremes of the period may range from 4 to 8 months. 4. Minimum temperatures of 20 degrees F. in December, 1925, did not kill the dormant eggs. . 5. The time at which emergence from hibernation begins varies from year to year and depends largely upon the prevailing temperatures. 6. _During the season of 1926 emergence of the cotton flea hopper extended from March 7 to June 10, or over a period of about 13 Weeks. In 1927 the period of emergence comprised approximately 20 weeks extending from February 16 to July 3. 7. There is little or no difference in the rate of emergence from the different types of winter host plants. 8. The duration of the emergence from all winter host plants under observation in 1926-27 ranged from 16 to 134 days, and averaged about 74. days. 9. When climatic conditions are optimum, emergence proceeds very rapidly. In 1926, 73 per cent of the total emergence was effected from April 5 to April 26. In 1927, about 79 per cent of the total emergence was completed from March 17 to April 7. 26 BULLETIN VNO. 377, TEXAS AGRICULTURAL EXPERIMENT STATION 10. The peak of emergence in 1926 occurred during the week be- ginning April 12 after cotton came up ; in 1927 it occurred during the week beginning March 24 or before cotton was planted. 11. A mean temperature of 56 to 58 degrees F., with normal rain- fall, becomes effective for emergence of the insects from the winter host plants. Maximum emergence occurred in mean temperatures of 60 to 62 degrees F. 12. Winds appear to be the most important single factor effecting dissemination at the time of emergence from hibernation. 13. There is a definite relation between the time of maximum emergence and the extent of injury to cotton. Normally the heaviest emergence of insects from hibernation occurs before cotton is ordinarily planted or at least before much young cotton is up in the fields. When climatic conditions delay emergence of the insects in the spring, and cotton is planted at the average date, conditions are favorable for ex- tensive injury to the crop by the cotton flea hopper. 14. Fourteen new winter host plants of the cotton flea hopper have been discovered. Data on the emergence of insects from each are presented. These new host plants include many of our commonest Weeds and have a wide range of distribution over the State.