~ _ - Y‘ n n ~ W ______ August 1966 PAUSE oou wtevn common omporison of two methods TEXAS A8cM UNIVERSITY Texas Agricultural Experiment Station R. E. Patterson, Director, College Station, Texas Summary Insecticidal control of fall populations of boll weevils in the High and Rolling Plains during 1964 and 1965 made it possible to com- pare the relative effectiveness of two types of diapause control programs. Both programs dealt with reducing the overwintering boll weevil population. The 1964 program utilized six applica- tions of malathion in an attempt to kill the potential overwintering adults during the feed- ing period after they had emerged from in- fested squares or bolls but before they had left the cotton fields for nearby overwintering sites. This program produced a 9O percent reduc- tion in the fall population. However, a great many weevils survived to infest the 1965 crop. The 1965 program combined control of the last reproductive generation of boll weevils in September with control of potential dia- pausing survivors in October and November. The 1965 program proved greatly superior to the 1964 program. The adult boll weevil population was reduced approximately 99 per- cent, and several times fewer weevils survived to enter hibernation than following the 1964 program. Contents THE EIGHT-COUNTY CONTROL AREA Summary ................................................ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 2 Introduction ________________________________________________________________________ __ 3 Plan of Attack for 1964 Program ______________ __ 4 Results of the 1964 Program _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 5 1965 Population Increases by 1964 Survivors . _ . . . _ _ _ _ __ 6 Basis for 1965 Program ________________________________ __ ' 7 Plan 0f Attack for 1965 Program _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 8 Results 0f 1965 Two-phase Program _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 3 Conclusions- _ _ _ _ _ _ _ _ _ _ , , _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 10 Acknowledgments ___________________________________________________________________________________________ __ 11 Literature Cited ______________________________________________________________________ __ 11 PAUSE oou WEEVIl commot. mporison of two methods Perry L. Adkisson D. R. Rummel W. L. Sterling W. L. Owen, ]r.* THE WINTER CLIMATE of Temperate Zones offers an extreme hazard to many insects. The boll weevil, Anthonomus grandis Boh., minimizes this hazard by overwintering in a state of dormancy, called diapause. Although the diapause phenomenon has been recog- nized in insects since 1869 (Duclaux, 1869) it was not known for the boll weevil until 90 years later when Brazzel and Newsom (1959) discovered that this species overwinters as a diapausing adult. The diapause syn- drome of adult boll weevils is characterized by the cessation of gametogensis and atrophy of gonads, in- crease in fat content, decrease in water content and decrease in respiratory rate (Brazzel and Newsom,“ 1959). The diapausing adults typically occur in the fall population. They apparently feed for a few days after emerging from infested squares or bolls, after which they migrate from the cotton fields to nearby woody or brushy areas in search of suitable overwintering sites. Once the insects find a suitable site they settle into the leaf litter near the soil surface where they become sedentary. The weevils apparently remain in these sites until the following spring. Diapause is terminated at this time and the weevils leave the woody areas to enter cotton fields. These weevils become reproductive and produce the first generation of the new season (Brazzel and Newsom, 1959; Brazzel et al., 1961; Lloyd et al., 1964; Mitchell and Mistric, 1965). Not all adults present during the fall enter dia- pause. Many continue to reproduce, thereby increas- ing the population. The final diapause status of the boll weevil adult apparently depends on the environ- mental conditions, mainly day length and tempera- ture, experienced by the individual insect. If the environmental conditions are appropriate for diapause after the egg is laid, the subsequent adult will be of the diapause type; if these conditions are inappro- priate the insect will not diapause but will produce yet another generation (Earle and Newsom, 1964; Sterling and Adkisson, 1966). The overwintering period has been recognized as a potential “weak link” in the seasonal cycle of the boll weevil which might be exploited for purposes of controlling the pest. As early as 1895, Townsend recommended that stalks be burned immediately after harvest in an attempt to destroy food and breeding sites of late fall populations. Malley (1901), who was among the first to make recommendations for boll weevil control in Texas, advocated a cultural control program involving stalk destruction and plowing in *Respective1y, professor, area Extension entomologist, research associate and associate entomologist, Department of Entomology, Texas A8cM University. t11e fall t0 reduce overwintering populations. How- ever, many of these early efforts did not meet with great success. This probably was because substantial numbers of diapausing adults developed in the fields during the harvest period before the stalk destruction programs could be initiated (Brazzel and Hightower, 1960). To overcome this difficulty, Brazzel (1959) con- ceived the idea of reducing diapausing boll weevil populations by repeated applications of methyl para- thion at 10- to 14-day intervals during the harvest season. This method of reducing overwintering popu- lations, termed “diapause boll weevil control,” has been tested by several laboratories (Brazzel ct al., 1961; Lloyd et al., 1964; Cleveland and Smith, 1964; Smith et al., 1965). In each experiment, the potential over- wintering boll weevil population was reduced, but in no case was eradication achieved. The boll weevil was first reported in the High Plains of Texas in 1936 (Owen, personal communi- cations). However, infestations great enough to pro- duce substantial crop damage did not appear until the early part of this decade. Weevil damage in the High Plains in 1963 and 1964 caused much concern to area cotton producers. They requested assistance from Texas A8cM University, Plant Pest Control and Entomology Research Divisions, USDA and the Texas Department of Agriculture in an attempt to stop the westward migration of the boll weevil. A diapause boll weevil control program was recommended as offering the best and most economical means for accomplishing this task. Subsequently, the first diapause control program " in the High Plains was initiated in late September 1964. As will be shown later, an improved control program was developed during 1965. Thus, the results obtained in the High Plains afford an opportunity to compare the effectiveness of two types of diapause boll weevil control programs. PLAN OF ATTACK FOR 1964 PROGRAM Very little was known in 196,4 concerning boll weevil behavior in response to the environment of the High Plains. Because of this, a fall control pro- gram similar to the one tested by Brazzel (1961) in Presidio was planned for the High Plains. This program was based on the premise by Brazzel (1961) that “an insecticide program of two to four applica- tions applied immediately before and during the harvest season, followed by destruction of food and breeding sites by frost, chemical or mechanical means, will materially reduce and possibly eradicate the over- wintering boll weevil populations.” This type of 4 program was designed to kill diapausing adults the feeding period after they had emerged f; fested squares or bolls but before they left i fields for nearby woody or brushy areas for hibernation. Accordingly, a diapause control program u‘ four applications of malathion was planned. i to be applied by the low volume method at t of 12 fluid ounces of 95 percent technical in per acre. The insecticide was applied by aid flying at an altitude of approximately 20 at swath-width spacings of 100 feet. Howeve the first two applications, the rate was incre 16 fluid ounces per acre by decreasing the swath to 75 feet. This adjustment was made beca tremendous size of the boll weevil populati manded an extremely high level of control. Treatment was initiated September 16, 196, applications made at intervals of 10 to 14 da i‘ the end of the fourth treatment, it was evide most producers were not going to terminate thei i with desiccants or defoliants. Also, at this ti weather was quite warm, furnishing no indica an immediate killing frost which would termina" crop, thus rendering it unsuitable for further __ and reproduction by the boll weevil. In ad boll weevil numbers still were high. For these r _ two additional applications of malathion were, but because of limited funds only the areas 1 the greatest infestations were treated. A Briscoe, Hall, Floyd, Motley, Crosby, Di Garza and Kent Counties were included in the c zone. All the infested cotton acreage, almost acres, were sprayed at the beginning of the dia control program. Total acreage treated durin 1964 and 1965 fall programs is reported in Ta More specific detail previously was report‘ Adkisson et al., 1965. if TABLE l. TOTAL NUMBER OF ACRES TREATED? APPLICATION DURING THE 1964 AND 1965 DIAL BOLL WEEVIL CONTROL PROGRAMS IN THE HIG ROLLING "PLAINS Application — — '— — Acres treated — — —-1 number 1964 1965,13 1 294,846 241,9 is 2 296,147 251, s 242,526 255,1 , 4 196,992 252, if, 5 88,620 23821 6 18,666 202,7. 7 None 63,3 v Total 1,136,663 1,509 4' zULTS or THE 1964 PROGRAM umber of fields were monitored in the center fwhere the greatest infestation occurred so that j iency of the insecticidal treatments could be I . All monitored fields were in Dickens County. i a were collected by examining all squares and p1 plants growing on 150 t0 300 feet of randomly i? rows. The number of adult weevils were p, collected and finally dissected to determine ffapause status. Untreated fields were used as , A detailed report of these records was made _'sson et al. (1965). pical results produced by the 1964 program fwn in Table 2. Two of the three fields were with malathion. The untreated field used for of comparison was adjacent to both treated l Results show that, following the fourth mala- treatment, the boll weevil population had been f1 to an estimated 211 weevils per acre on one ‘ farm (Haney’s) but was quite high, an esti- j 2,574 adults per acre, on the other treated farm find's). Of course, the populations on the treated were considerably smaller than on the untreated i he first killing frost occurred almost a month the fourth malathion treatment on October 22. 1g this time the population on the Haney farm increased greatly, and just before frost an estimated 1,056 adult boll weevils per acre were present. On the Ragland farm the population was reduced from an estimated 2,574 adults per acre on October 21 to 1,848 on November ll. This number of adults sur- vived in the two fields even though they were treated with six applications of malathion. Population trends from October 24 to November ll showed the impor- tance of treating undefoliated fields until frost. One can only imagine what the population increase would have been if treatment of these fields had been termi- nated with the fourth application on October 22. There is little doubt that if the fifth and sixth appli-' cations had not been made, the reductions produced by the first four treatments would have been largely negated. These results show that, under the environ- mental conditions and present management practices in the High Plains, insecticidal treatments of a dia- pause control program should be continued until frost. It appears likely that six or more applications of insecticide will be required during "most falls, unless the first killing frost occurs at a very early date. The overall effect of the six malathion treat- ments, as measured by the seasonal means, was to reduce the potential overwintering populations which developed in treated fields by more than 90 percent (Table 2). Although this was a substantial reduction, there was still an average of more than 200 potential 0' 2. 2A COMPARISON OF THE NUMBERS OF POTENTIAL OVERWINTERING BOLL WEEVILS IN TREATED AND TED FIELDS SHOWING THE EFFECTIVENESS OF THE 1964 CONTROL PROGRAM. THE TREATED FIELDS RECEIVED SIX APPLICATIONS OF MALATHION DURING THE PROGRAM (ADKISSON, ET AL., 1965) Estimated number Estimated number Percent reduction adults Percent potential overwintering over adjacent per acre diapause adults per acre untreated field Untreated farm 16 5,800 40 2,320 21 9,108 40 3,643 24 18,480 80 14,7 84 6 21,120 29 6,125 12 6,600 48 3,168 12,221 47 6,008 Treated farm No. 1 (Haney) 1 16 528 12 63 97 21 0 0 0 100 24 211 9 (est.) 19 99+ 6 5,808 5 290 95 ll 1,056 37 391 88 1,521 l3 153 96 Treated farm No. 2 (Ragland) 1 16 528 12 63 ' 97 21 2,574 l0 257 93 j 24 M Y 1,372 4 55 99+ 6 " 3,432 1s 61s 90 ' 11 ‘ 1,848 19 240 92 Mean 1,951 11 247 94 treatment schedules for these fields were as follows: .111 uid-ounce-per-acre rate. first application, 12 fluid ounces per acre of malathion, September 17-22; nd application, 12 fluid ounces per acre of malathion, October 1; third application, October 13; fourth application, October 22; i1 application, November ll; and sixth application, November 20. The last four applications of malathion were made at the overwintering adult boll weevils per acre which sur- vived in treated fields. Examinations of leaf litter taken from woody and brushy land suitable for hibernation by the boll weevil were made in January, 1965. Samples were taken across the control zone. A summary of these data, reported in Table 3, confirm the population records made in treated cotton fields. The hibernating boll weevil population averaged an estimated 281 adults per acre of hibernation quarters, a reduction of 89.4 percent over the population of the previous year when no fall control was practiced, and confirmed the field records presented in Table 2. 1965 POPULATION INCREASES BY 1964 SURVIVORS Surveys were initiated in June 1965 to study the rate of population increase following the 1964 pro- gram. The surveys were begun in June as the seedling cotton emerged to a stand. This research was con- fined to Dickens County, the area of heaviest infesta- tion; this also was the area which had received the six malathion treatments in the fall of 1964. Nine fields were selected for surveys. Four fields were irrigated and five were dryland. Five fields were treated by the producers in July and August for boll weevil control while the other four were left untreated. For the most part, the treated fields received malathion applied by the low volume technique at rates of 8 to 12 fluid ounces per acre per application. These fields were treated at intervals of approximately 6 to 7 days from July l0 to the first week of September; The nine fields were located so as to be representative ' of the entire area and so that the population estimates might be made on a county basis. Records were made at weekly intervals during the season by making whole plant examinations at six randomly selected locations in each field. Fifty feet of row was examined at each location to provide a TABLE 3. ESTIMATED NUMBERS OF HIBERNATING BOLL WEEVILS PER ACRE IN THE LEAF LITTER OF WOOD AND BRUSH LAND IN THE CONTROL ZONE BE- FORE AND AFTER THE DIAPAUSE CONTROL PROGRAM Estimated Percent Date of fgggfd number of reduction hibernating produced Month Year weevils by diapause per acre control program‘ January 1964 2,650 January 1965 281 89.4 January 1966 48 98.2 lPercent reductions in overwintering boll weevils were calculated for both 1965 and 1966 on the basis of the uncontrolled hiber- nating population of January, 1964. 6 TABLE 4. ESTIMATED SIZE OF THE BOLL . POPULATION IN DICKENS COUNTY, TEXAS DURI Estimated number of a Date inspected Per acre Dickens t June 18 l0‘ 529, 25 20‘ 1,058 July 2 5‘ n‘. 264, 9 341- =1 1,800 , 16 15 794, 23 20 1,058 30 0 ~. August 6 20 1,058 " l3 27 1,429 , 18 207 10,959 l“ 27 264 15,977, T September 3 129 6,830, 10’ 116 6,141, , 15 495 26,408 ‘ p 20 1,386 73,3831 , 28 710 37,591,, October 8 248 13,130 ="' 12 578 30,605] 18 339 17,948, f 28 358 18,954, ~ November 1 242 12,812, ». s 22 1,164.8 16 154 8,153, l. 21 158 8,365, ~ ‘Overwintered weevils. . “First phase of diapause control program was initiated on- tember 7, 1965. Entire population after this time was f treatment with malathion. total sample of 300 feet of row per field. The n -i of adult boll weevils on the 300 feet of row' recorded and the data converted to form estii of number of adults per acre. ’ Population records, summarized in Table 4, that the average number of overwintering boll w surviving to infest seedling cotton in the spri 1965 ranged between 5 and 34 per acre. Overwin weevils were present in the fields from June If July 9. The first generation of boll weevils beg _ emerge during early July. After this, it was". possible to identify the collected weevils accordin parent or generation number. f The boll weevil population during July and I August remained relatively stable, barely maintai its numbers. There was _ no population in l attributable to the first (F1) generation. The mated numbers of adultsper acre ranged from I 27 during the period July 16 to August 13. The of increase by the boll weevil during this time p‘ ably was attributable to insecticidal treatment of irrigated fields and to hot, dry weather, high ‘ temperatures and lack of shade in the dryland fi since the cotton plants in these fields were still -f small in July. These conditions will cause high 1 tality in immature forms of the boll weevil in sq ' which fall on unshaded ground. i ‘The population increased approximately 10-fold ' g the last half of August. For example, on i_ st l3, the population was estimated at 27 adults gacre while on August 27, the average was 264 its per acre. This increase probably was due to (‘emergence of another generation of boll weevils. §f ould be noted that this increase occurred even _, h five of the nine surveyed fields were being larly treated with insecticides for weevil control. The boll weevil population made an additional _ ase of approximately 5-fold from late August to " September. For example, there was an average 64 adults per acre in the fields on August 27. By ' ember 20, the number had increased to an average ,386 adults per acre. This increase occurred even V h all the surveyed fields were treated with three ilications of low volume malathion at the l6-fluid- ce-per-acre rate at 5-day intervals between Septem- T‘ 7 and September 20, 1965. These results show the tremendous reproductive iacity of the boll weevil. During the growing season weevils increased to relatively great numbers, even ugh the overwintering population was quite small. i ch of this increase occurred despite regularly sched- (I I insecticidal treatments which have been found able of killing from 80 to more than 90 percent {the adults in the fields at time of treatment (Adkis- ‘i! et al., 1965). _ adult boll weevils in Dickens County during the " ‘,1 season (Table 4). The estimates, although gross, ‘ ish some indication of the tremendous numbers boll weevils that might be present in a relatively ii ll area. The population ‘increased during a 3- inth period from an estimated 529,460 adults on " e 1s in seedling cotton to 73,333,156 individuals _.~ September 20. Such magnitude shows the ex- mely high efficiency that must be obtained in any iv of boll weevil suppression or eradication pro- i . A diapause control program which killed iproximately 90 percent of die adult boll weevils p‘ Dickens County during the fall of 1964 still left great number of survivors to infest the county in e5; * “These results clearly show that although the 90 rcent population reduction obtained in 1964 might considered excellent, this level of control was not {fficient to prevent crop damage during the subse- uent growing seasonj However, the 1964 diapause ntrol program offered an excellent adjunct to the ular control practices conducted by producers. It moved much of the normal population pressure and jfas responsible for the small populations that were ., ident until late in the season. It is obvious, how- Estimates also were made of the total numbers I ever, that the 1964 program fell far short of eradica- tion; and, in fact, the population suppression was not sufficient to prevent some migration in September. In view of these results, research was expanded in an attempt to develop a more efficient control program for 1965. BASIS FOR 1965 PROGRAM Knipling (1963) discussed several approaches for reducing diapausing boll weevil populations. He advanced the hypothesis that a program aimed at killing the last reproductive generation of weevils» would be considerably more effective than schemes designed to kill diapausing adults before they leave cotton fields for overwintering sites. In 1964, experi- ments designed to provide the information needed to implement this approach were initiated. Sterling and Adkisson (1966) studied environ- mental factors causing diapause of the boll weevil in laboratory and field experiments. They developed a technique, using adult boll weevils reared from in- fested squares, for determining more exactly the time when diapause is first initiated under fields condi- tions. Sterling and Adkisson showed that on the High Plains in 1964 the first potential overwintering boll weevils of the season developed from eggs that were laid from mid-August to early September. The last reproductive generation, for the most part, occurred in September. Females present in September appar- ently produced the majority of the eggs which gave rise to the diapausing, or overwintering adults. These studies were continued in 1965. The inci- dence of diapause was studied in field-collected adults and in weevils reared from infested squares and bolls. The adults were taken at random by hand-picking weevils off infested plants in Dickens County. Also, weevil-infested squares and bolls were collected weekly from fields near Spur during the summer and fall. These were held in an open insectary until the adult weevils emerged. These adults were fed for 20 days, then dissected and examined for diapause. Results, summarized in Figure 1, closely paralleled those reported for 1964 by Sterling and Adkisson (1966). These data again show the advantages of rearing boll weevils from squares and bolls for de- termining the seasonal incidence of diapause. A number of the square- and boll-reared adults that emerged in August attained diapause. However, the combined data indicated that September probably was the most important month for the development of the diapause broods. Most eggs laid in September developed into adults of the diapause type. PLAN OF ATTACK FOR 1965 PROGRAM The above studies provided the basis for cl1ang- ing the diapause control program in 1965. The plan of attack was simple. A two-phase program was de- signed along the lines suggested by Knipling (1963). Phase 1 utilized three applications of malathion de- livered at 5-day intervals during early and mid- September. The objective of this phase was to break the reproductive cycle of the boll weevil, thereby preventing the females from laying the eggs that eventually develop into diapausing adults. Calcula- tions indicated that if the insecticide killed 90 percent of the females, the size of the overwintering brood also would be reduced by 90 percent, even if no further control was practiced. However, phase 2 was designed to deal with this problem. Four applications of malathion were made at 10- to 14-day intervals through October and November until frost. The objective of these applications was to kill any adult boll weevils that might have escaped the Phase 1 treat- ment or that might have developed from eggs laid in late August or the first few days of September before the insecticidal applications were initiated. RESULTS OF 1965 TWO-PHASE PROGRAM The 1965 control program was conducted as planned under the supervision of the Plant Pest Con- trol Division, USDA. Seven applications of malathion were applied by the low volume technique at a dosage of 16 fluid ounces of 95 percent technical malathion per acre per application. The insecticide was applied 100' f I by airplane at swath widths of 100 feet. The a9 treated per application in the eight-county area 1965 are given in Table 1. The first application of Phase 1 was ini September 7, 1965. The next two applications delivered on schedule, 5 to 6 days apart. Sev fields which were relatively heavily infested wit, weevils were selected at randonf across the enti i‘ trol zone for monitoring. These fields were c ~i at weekly intervals. All the plants on 50 feet y, randomly selected rows were examined an number of weevils recorded. Weevils were c0 , and examined the same day to determine thei, pause condition. In addition, the number y punctures and immature weevils in the squar bolls of the plants on the two samples were rec The effectiveness of the Phase 1 treatme breaking the reproductive cycle of the boll we, shown in Figure 2. These data furnish a comp of the estimated number of immature weevils- were present in fields which had been treated d“ the summer months by the producers as oppo fields which were not treated during this period)‘ of these fields -were treated with malathion ‘- the diapause control program. The fields which had not been treated durini summer harbored more than 6,000 immature W per acre on September 3, 1965. Egg productif these fields wasstabilized by the first malathion i, ments made during the 5-day period begi September 7. Unfortunately, widespread and h‘_ rains occurred during the period of the second a O ‘I ‘o _ P- : ‘o, O i ‘w’ '5 so .. .' u .' g ’ ‘l I F‘ 1 s 1 ' ‘a i _ ’ g I igure . easona mci n, .|b n) diapause in field-collected, 60 _ *___ FIELD COLLECTED '4__ 5:2 REARED l/ boll weevils compared to 1 g | I \ square- and boll-reared -~ __ o‘ | i U Dates indicate days on v 's,~| . field adults were collected 40 _ | ABOLL REARED on which square- and boll- I \ ‘I I - adults emerged. Field-co , _ O '| -\| . adults were examined on | 5 / of collection, while square-i _ | o Z‘ boll-reared adults were fed 2° D ~ _D bolls for 20 days before f g "9 examined for diapause; i .. .§ . f ?' 0 - o | 1 I L J | a l | l I 1 | | I 1 15 1 15 1 15 1 15 1 15 15 1 15 1 15 APRIL MAY JUNE JULY AUG SEPT OCT NOV 16 l!» Figure 2. Estimated numbers of immature boll weevils per acre in fields treated during the growing season compared to those in untreated fields, Dickens County, Texas, I965. All fields were treated with malathion during the diapause control pro- gram in the fall of 1965. ESTIMATED NUPEER IPMATURE WEEVILS PER ACRE, THOUSANDS —— UNTREATED DURING SUIWIER ',-— TREATED DURING ', smarma - \ ', o \ during mid-September, and egg production in fields soared, reaching a peak of almost 15,000 acre on September 15. h - 2 show that these rains destroyed the effec- ess of the second malathion application and jly reduced the effectiveness of the Phase 1 pro- iFields treated by producers during the summer Imany times fewer immature boll weevils per acre j did untreated fields. For example, on September Population trends in . 28 8 12 18 OCT 3, the immature population in these fields averaged slightly more than 2,000 immature weevils per acre. This compares to more than 6,000 per acre in the untreated fields. The first malathion application reduced egg production in these fields (Figure 2). As indicated by the record made September l0, egg pro- duction in the treated fields, as in the untreated fields, soared during the rainy period of mid-September. This increase, however, was not nearly so great as in the untreated fields as peak numbers of approximately LE 5. ESTIMATED PERCENTAGE REDUCTION IN THE POTENTIAL OVERWINTERING POPULATION OF ADULT i WEEVILS IN THE HIGH PLAINS OF TEXAS PRODUCED BY THE FALL APPLICATIONS OF MALATHION, 1965 Treated acreage Untreated control Estimated Estimated Estimated Estimated number number of number number of Estimated of adults Percent hibernating of adults Percent hibernating percent per acre diapause adults per acre diapause adults reduction l0 2,350 15 519 14.6 76 6,650 20 1,302 12.5 163 14,550 ' 2s s93 23.7 212 6,950 8 478 8.0 38 11,000 50.0 ' 5,500 99.3 12 7,050 61.0 4,301 18 567 ,__ , 53.6 304 15,550 60.0 9,330 96.7 2s 334i; " 37.5 ~ 125 11,650 40.0 4,660 97.3 ember 1 204 I 75.0 153 12,200 58.0 7,076 97.8 5 8 176 50.0 88 6,750 75.0 5,063 98.3 16 209 0.0 0 5,150 75.0‘ 3,863 100.0 21 211 23.2 49 6,350 7 5.0‘ 4,763 99.0 Mean 489 29.8 121 8,850 61.7 5,570 98.3 ircentages of diapausing weevils for these two dates were estimated as being the same as in the collection of November 8. 5,000 immature weevils per acre were reached on September 20. This was considerably less than the 15,000 immature weevils per acre reported for the untreated fields. These data show the great impor- tance of the regular season control efforts made by producers during August. The third and subsequent malathion treatments eventually reduced egg production in all fields to extremely small levels by mid-October. However, the adults which developed from eggs laid in mid- September presented a threat to the success of the program in November. Effects of the Phase 1 and 2 treatments on the adult populations are shown in Table 5. The average numbers of weevils per acre in the monitored fields of the control zone are compared to a nearby untreated acreage. The untreated acreage was located in Stone- wall County adjacent to the control zone. These data show that at time of the last record (November 21) made just before the first killing frost there were 99 percent fewer potential diapausing adult boll weevils in the control zone than in un- treated acreage. The seasonal averages of all records made during the control period indicate a 98.3 percent overall reduction in the population. Thus, it might be concluded that the new two-phase diapause control program was as efficient as the hypothetical model of Knipling’s (1963) which predicted a 99 percent reduction. A comparison is made in Table 6 of the estimated average number of adult boll weevils per acre in Dickens County during the 1964 and 1965 diapause control programs. These records show that there were 92 percent fewer adult weevils per acre in Dickens County at the end of the 1965 program than at a similar time following the 1964 program. It was calculated that the two-phase diapause control pro- gram should be approximately 90 percent more effec- TABLE e. A COMPARISON or THE ADULT BOLL WEE- vu. POPULATIONS IN DICKENS COUNTY IN 1964 AND 1965 snowmo THE IMPROVED EFFICIENCY or THE TWO-PHASE PROGRAM. OF 1965 1965 1964 Estimated number Estimated number Percent Date of adults of adults reduction per acre per acre Oct. 12 578 3,280 82 18 339 2,208 85 28 358 4,277 92 Nov. 1 242 594 59 6 22 6,178 99+ 16 154 2,323 93 21 158 Mean 264 3,143 92 10 tive than the 1964 program. Again, field perf , confirmed the hypothesis. j Examinations were made for adult boll in January 1966 in leaf litter from known hibe- sites across the control zone (Table T - examinations were made only at locations in? boll weevils had been found during similar made in January 1965. These "results indicat an average of 48 potential over-wintering boll 4 per acre of hibernation site had survived th diapause control program. This number rep ' an average reduction of 98.2 percent in th population when compared to 1964. The per reduction of weevils in hibernation sites was exactly the same as obtained in the field reported in Table 5. These records provide almost conclusive“ that the two-phase program of 1965, which co v control of the last reproductive generation wi 1 of the diapausing broods, was considerably effective than the 1964 program. The latter p , had as its objective the killing of the potentiaj wintering adults during the feeding period afte emerge from infested squares or bolls but befo *- leave cotton fields in search of suitable overwin sites. ’ CONCLUSIONS The population trends presented in Table Figure 2 show the advantage of initiating insecticidal treatments of the diapause control: gram in the first week of September. The boll population increased approximately 10-fold fro tember 3 to 20. This increase occurred even t j the population was subjected to three malathion ments between September 6 and 20. There is ..; to estimate the size the 1965 population might reached in September if the malathion treatmen ..; been delayed to September 16, or later, as they i in 1964. There is no doubt that the popu increase in September, 1965 would have been I- greater if there had been no treatment, and per the population may have even increased to the K proportions as was present in the uncontrolled i lation in September, 1964 before the diapause c l’ program was initiated. ’ One other factor favoring the earlier treat, date of 1965 is the pattern of migration of the weevil populations in the High and Rolling Pi The first evidence of migration from field tofieli the control zone was detected during early Septe The first 1965 malathion treatment made during‘ 5-day period of September 7 to 12 apparently coin with the beginning of migration. The first malathion treatments made in September undoub A‘ COMPARATIVE EFFECTIVENESS OF THE 1964 AND 1965 DIAPAUSE CONTROL PROGRAMS IN REDUCING ’ OF THE POTENTIAL OVERWINTERING BOLL WEEVIL POPULATIONS Treated acreage Untreated acreage Estimated Estimated Estimated Estimated number Average number of number Average number of of adults percent in hibernating adults of adults percent in hibernating adults percent per acre diapause per acre per acre diapause per acre reduction 2,323 25 363 6,600 48 3,168 89 211 23 49 6,350 75 4,763 99 w a relatively great and serious migration j». weevil t0 uninfested acreage to the west. iuld have increased the size of the control g2 siderably. e combined results produced by the 1964 and i grams are compared in Table 7. These data ‘it at the overwintering population was reduced 7 ximately 90 percent in 1964 and 99 percent . In population suppression programs, the efiwhich survive are more important than those f" killed. There were nine times fewer insects g the two-phase program of 1965 than the "tional program of 1964. This means that for S, boll weevils which might have survived the if there had been no diapause control program, w ived the conventional program of 1964, but ne survived the two-phase program of 1965. l. will be extremely difficult, if not impossible, ce a boll weevil population by present diapause l: procedures to such a small size that insecticidal 1 measures may be abandoned completely. It more likely that insecticidal control will have i continued until other non-insecticidal control res are developed for eliminating the last 1 per- f the population. ' ACKNOWLEDGMENTS Ais research was conducted in cooperation with the Ento- i- Research Division, USDA, under a memorandum of ‘ent 12-14-100-5607 (33). The aerial spraying operation nducted under the supervision of the Plant Pest Control in, USDA, with assistance from the Texas Department of flture. Assistance of numerous personnel from these latter ncies in obtaining insect records during the spraying tion and examination of hibernation sites also is gratefully ledged. Special thanks is due Bruce Hewlett and co- ‘rs, Plant Pest ContfpliDivision, USDA, who furnished p: tion records for the untreated acreage reported in 5. iThe diapause control program over the eight-county area jorganized and financially supported by the cotton producers ’e area as represented by the Plains Cotton Growers, l’ orated, Lubbock. e combined results obtained to date indicate u LITERATURE CITED Adkisson, P. L., J. W. Davis, W. L. Owen and D. R. Rummela 1965. Evaluation of the 1964 diapause boll weevil control program on the High Plains of Texas. Tex. Agr. Exp. Sta. Dept. of Entomol. Tech. Rpt. No. 1. Brazzel, J. R. 1959. The effect of late-season applications of insecticides on diapausing boll weevils. J. Econ. Entomol. 52:1042-1045. Brazzel, J. R. 1961. Destruction of diapause boll weevils as a means of boll weevil control. Tex. Agr. Exp. Sta. Misc. Publ. 511. Brazzel, J. R., T. B. Davich and L. D. Harris. 1961. A new approach to boll weevil control. J. Econ. Entomol. 54:723- 730. Brazzel, J. R. and B. G. Hightower. 1960. A seasonal study of diapause, reproductive activity, and seasonal tolerance to insecticides in the boll weevil. J. Econ. Entomol. 53:41-46. Brazzel, J. R. and L. D. Newsom. 1959. Diapause in Anthono- mus grandis Boh. J. Econ. Entomol. 50:603-611. Cleveland, T. C. and G. L. Smith. 1964. Effects of post-season applications of insecticides, defoliants and desiccants on diapausing boll weevils. J. Econ. Entomol. 57:527-529. Duclaux, M. E. 1869. De Yinfluence du froid de l’hiver sur le developpement de 1’embroyon du ver a’ soil, et sur l’eclosion de la graine. C. R. Acad. Sci., Paris, 6921021. Earle, N. W., and L. D. Newsom. 1964. Initiation of diapause in the boll weevil. J. Ins. Physiol. 10131-129. Knipling, E. F. 1963. An appraisal of the relative merits of insecticidal control directed against reproducing versus dia- pausing boll weevils in e"forts to develop eradication pro- cedures. A letter dated January 28, 1963, addressed to members of the Cotton Insects Research Branch, Ent. Res. Div., Agr. Res. Ser., U. S. Dept. Agr. Lloyd, E. P., M. L. Laster and M. E. Merkyl. 1964. A field study of diapause, diapause control, and population dynamics of the boll weevil. J. Econ. Entomol. 57:433-436. Malley, F. W. 1901. The Mexican cotton boll weevil. U. S. Dept. Agr. Farmer’s Bull. 130. Mitchell, E. R., and W. J. Mistric, Jr. 1965. Seasonal occurrence of diapause and hibernation of the boll weevil in North Carolina. J. Econ. Entomol. 58:309-312. Smith, G. L., T. C. Cleveland and J. C. Clark. 1965. Field tests for control of overwintered boll weevils. J. Econ. Entomol. 58:360-361. Sterling, W. L. and P. L. Adkisson. 1966. Differences in the diapause response of boll weevils from the High Plains and Central Texas and the significance {of} this phenomenon in revising present fall insecticidal control programs. Tex. Agr. Exp. Sta. Bull. 1047. Townsend, C. H. T. 1895. Report on the Mexican cotton boll weevil in Texas. Insect Life 7(4) :295-309. ll Texas 161M University Texas Agricultural Experiment Station College Station, Texas 77840 fiflww Director ‘Publication-Annual Report or Bulletin or Report of Progress Permit i105 OFFICIAL BUSINESS £1. ‘ 4f- Penalty ior private ~i payment ot po