B-1109 [une 1971 POPULATION DYIVAJIHCY OF THE BOLL WEE VZL AND MODIFIED COTTON TYPES Implication: for Pert Management TEXAS AéM UNIVERSITY ' TEXAS AGRICULTURAL EXPERIMENT STATION H. O. Kzmkel, Acting Director, College Station, Texa: CONTENTS Summary . . . . . . . . . . . . . . .. Introduction ____ .. Methods ............................ .. Population Dynamics of the First Generation .... .. Population Dynamics of the Second Generation. Results First Generation Studies Second Generation Studies Implication of Population Study Findings .......... .. Plant Breeding and Its Role in Pest Management Acknowledgment Literature Cited 2 5 5 5 7 8 l0 l3 14 SUZMMAR Y The population dynamics of the v ~ l cotton was investigated near College Stati“? to 1963 and from 1965 to 1968. Findings the time of weevil generations in cotton able. Rates of increase of first generation _ small numbers of overwintered weevils as thirtyfold. When large populations of tered pests infested cotton, a reduction in efficiency occurred. Rates of increase of fold were recorded. Economic threshold Q that overwintered populations must be k about 22 females per acre in order not - damage from the first generation. t» overwintered females per acre produced generation weevils to inflict heavy da - ‘l Lankart Sel. 57 cotton was used, it was a” the major threat of boll weevil damage from the first generation. _ That is, if ~ r1 damage from this generation, the crop mature to experience damage from the 7 eration, regardless of the size of the second!’ Concepts gained from this study dr n . _ portance of early maturing cottons in Q weevil damage and in reducing winter _ diapausing individuals. Certain new k strains of cotton, when planted in high d t», seem to escape weevil damage and reduce ' over. ’ ‘i l‘ -= m THE UNITED STATES HAVE CREATED )1» impact equal to that which resulted I r w ations of the boll weevil, Anthonomus an, as the pest moved across the rain- ;-- ucing area of the United States in ‘i ’s. Within a few years, common pro- ods became impractical; and, at least for 1'1 atives were slow to develop. Before the 4;. invasion, growers farmed cotton in an "I vu that did not contain a single pest b, potential of the weevil for yearly repeti- ‘ There were outbreaks of bollworrns, _' Boddie, especially in Texas and Okla- cotton leafworrns, Alabama argillacea 1- e not uncommon. But because of vari- 5 and ecological reasons, these insects ‘ - pread universal pests of cotton. f? weevil was not subjected to the environ- tions imposed on the bollworm and I .1 The weevil is essentially a one-host »- ins on cotton during the entire grow- f; rom moderate numbers of overwintered v may develop into yield-damaging 'thin the span of a single generation. a parasitism by other arthropods do not I‘ - ol the boll weevil. Also, in nearly all p r the pest infests cotton during the _ a ilcanoverwinter. Any insect species _ ~ attributes has the potential of being <._economic pest. The boll weevil, of - en to be one of the most destructive _ ~ uced into the United States. in a ial cotton varieties grown before the l; were slow to fruit and, consequently, vulnerable to the insect. It became chers that earliness in cotton varie- iost effective and immediate way to from the weevil (l). It became clear 7‘ - " to continue being grown profitably, ‘° . tion as possible must be made early season before weevil populations de- w numbers. Breeders at a number "tiated programs to select cottons that fruiting characteristics. These efforts early varieties were developed, and POPULA TION DYNAMICS‘ 0F THE BOLL WEEVIL AND 1140191111512 c01tr01v TYPES Implications for Pest Management ]. K. Walker, ]r. and G. A. Nilefl‘ growers incorporated them into their production pro- grams. Cotton production in the rainbelt area sur- vived (2). For all practical purposes, the substitution of early producing cottons was the only means used by growers that allowed farmers to produce cotton successfully in spite of the weevil. An effective insecti- cide was found in calcium arsenate dust in 1918, but for various reasons many planters did not use the material In addition to the use of early fruiting plant types to lessen weevil damage, early entomologists recognized that cotton plants should be destroyed as soon as possible after harvest in the fall (4). These scientists were aware that something was different about many of the boll weevils in the fall generations, and somehow this difference allowed the insects to _ overwinter successfully (5). Today it is known that the overwintering ability of the boll weevil is due to diapause, a physiological adaptation occurring primarily in the fall that permits the insect to over- winter in cold climates (6). Stalk destruction immediately after harvest was thought to lessen the overwintering potential of boll weevil populations as a result of the removal of cotton as a food source. In a period of time when cotton was harvested by hand over a period of several months, it is doubtful that stalk destruction could ever have been carried out early enough in the season to produce a great reduction in potential overwintering weevil population. Nevertheless, the concept was sound, and in recent years it has been amplified in the fall control of diapausing boll weevils on the High Plains of Texas (7). In this program organophosphate insecti- cides have been directed toward boll weevils that have the potential for diapause. In effect, this accom- plishes the same goal as the old recommendation for early stalk destruction. Despite the benefits that might have resulted from stalk destruction practices in the first years after the boll weevil invaded the United States, there was abundant winter survival of the pest. Infestation intensity varied with the season and location. The ‘Respectively, associate professor, Department of Entomology and associate professor, Department of Soils and Crop Sciences, Texas A8cM University. 3 early fruiting cottons allowed growers to continue production, but the effective production period was limited in general to the first few weeks of fruiting. After that time boll weevil populations often would explode into great numbers and eliminate further fruit set by the crop. Consequently, the high yields produced by present production methods were im- possible. This situation continued until the appearance of the chlorinated hydrocarbon insecticides in the first years after World War II. These broad spectrum compounds were dramatically effective and at the time appeared to offer great promise for insect-free cotton production. Control was spectacular, and yields greatly increased. It became profitable to grow indeterminate cotton varieties that continued to fruit throughout the growing season. Successful insect con- trol fostered irrigation and fertilizer practices, thus increasing the demand for longer fruiting and high- yielding relatively indeterminate varieties of cotton. Production hinged on the duration of the growing season in an area, not on how much time the crop had to set fruit before boll weevils attained large populations. The prolonged fruiting patterns of the indeterm- inate cottons, although increasing yield potential, served to provide ample food for weevils developing diapause in the fall after insecticidal treatments had been halted. This situation ran counter to the old stalk destruction concept; however, this actually made ' little difference. The boll weevil could be controlled easily with the new insecticides during the growing season despite the survival of great numbers during the winter. It became apparent to many entomologists, and later was shown experimentally, that applications of the broad-spectrum organic insecticides directed toward the boll weevil resulted in almost total destruc- tion of the beneficial arthropod population in cotton (8, 9). This unfortunate result eliminated insect predation and parasitism and led to outbreaks of the bollworm-tobacco budworm complex in the cotton field. The damage inflicted by these pests often equals that of the boll weevil’s presence which initiated the insecticidal treatment. The boll weevil came to be known as a “key” insect. That is, control programs had to be initiated for the weevil; but following the first insecticidal treat- ments, secondary pests, that is, the bollworm and tobacco budworm, often would increase because of the decimation of the beneficial arthropods that normally control them. However, the bollworm- tobacco budworm did not present a serious problem to producers for many years because these insects could be effectively and economically controlled with DDT. In summary, the new organic insecticides were so effective that earliness of production and prompt stalk destruction were no longer considered essential 4 to boll weevil control. Most phases of lated to cotton production, entomological wise, came to be based on the pomise of wf continued insecticidal pest control. Therei concern that the certain insects had devel ance to DDT a few years after the insecti ' used in the 1940's. * By the mid-l950’s, the: long term c insecticides came under close scrutiny v weevil developed resistance to certain ~i hydrocarbon insecticides in Louisiana (ll next few years most of the rainbelt cotton..- states experienced the same problem, and ' t» chlorinated hydrocarbon resistance began fl in bollworm-tobacco budworm popula Growers solved the chlorinated hydrocar - problem by switching to organo-phos cides. Recently, however, high levels of Q the organo-phosphate insecticides have in field populations of the tobacco bud _ laboratory cultures of the ‘bollworm growers continue to treat with o ;. t." materials, these two pests will develop , levels of resistance. 1' The implications for the future are c ~;_ insects will have to be controlled or if techniques that place less emphasis on i insecticides. There are no alternate in i -, able for use, and there is small likelihood l‘ being developed in the near future. Alte .17“ for solving cotton insect pest problems '_ be devised if the crop is to be profitab‘ the rainbelt area. New approaches to cotton insect ably will be built around the pest cept. The aim of this method is to use a a of techniques that collectively hold a below the economic threshold of damage same time produce a minimum of dc effects in the agro-eco system. Eradica levels of control are not sought in pest i instead, the goal is economic containm t -I__' The diapause boll weevil control i has been successfully followed on the ~¥ Rollings Plains may be considered a u management. Three practices condu w gram combine to reduce the winter c weevils. These are 1) insecticidal con y reproductive generation of weevils; control to kill potential diapausing " fall months; and 3) defoliation and s - to remove the cotton food source that is,‘ the development of overwintering wee l‘- insecticides are used in this program, i, are applied after the production period,” when the crop is no longer susceptible bollworm-tobacco budworm infestati . Recent findings appear to offer new g for the management of boll weevil pop 'ders the population dynamics of the boll Q how these phenomena might relate to ' determinate rapid-fruiting cottons. __ Methods Dynamics of the First Generation purpose of the study was to determine the creases of first generation boll weevils in - ed with various numbers of overwintered ~ to ascertain how the overwintered and tions related to the phenology of the cotton (e experiments, during the 4-year period, ." e conducted in a 1 /22-acre plot of cotton 9,100 feet) planted near Easterwood Airport ‘Station, Texas. The site was in a small bottom surrounded by dense woods, iiut 2 miles from the Brazos River Valley a acreages of cotton are grown. Beginning ; l-just before squaring—the cotton in the mined two to three times per week, and J were obtained. Records were made of * of overwintered boll weevils, square pro- M numbers of squares punctured. tered weevils were allowed to oviposit p days after appearance of the first one-third 7 s (squares first acceptable for oviposition if weevils). Subsequently, the insects were w , and an application of methyl parathion jto kill any weevils that might have been p’ thereby, preventing further egg deposition 'ntered brood. Any weevils found after ‘ assumed to be of the first generation. intered weevils were removed from the a manner that a population of 500 adults acre could be maintained. During the ,2 generation emergence data were noted at intervals of l or 2 days following the (‘t- of overwintered weevil infestation. tion sampling continued until about 45 “vuaring began. All weevils found were l» u the plot and destroyed. Dynamics of the Second Generation periment was conducted from 1965 to _ same location and plot as the previous l The study was designed to measure the ~ generation populations of boll weevils i» v d from varying numbers of overwin- Also, the relationships of the over- ‘f. I! and the first and second generation g logy of the cotton plant were examined. ue in this experiment differed from that first generation study in that all over- “ ils encountered in sampling were sexed gwith small spots of lacquer on the elytra. f! re-identification and permitted careful f; the numbers of female weevils infesting Since one of the objectives of the study was to measure the total number of second generation weevils produced, the application of methyl parathion was not made until the conclusion of first generation weevil emergence or about 39 to 44 days after the first one-third grown squares appeared on the cotton plants. Thus, the overwintered and first generation individuals were allowed to oviposit unmolested. Individuals emerging after 39 to 44 days of squaring were assumed to be members of the second generation; these were removed and destroyed. _ Results First Generation Studies 1960—The first one-third grown squares appeared June l0, and an extremely large number of over- wintered weevils (Figure 1) punctured a great per- centage of these and later forming squares (Figure 2). The population averaged 2,693 overwintered indi- viduals per acre during the first 17 days of the squaring period. The total number (13,354 per acre) of first generation weevils represents about a five-fold rate of increase from the overwintered population (Figure 1). 1961—Again, large numbers of overwintered weevils (Figure l) infested the plot and punctured a great percentage of the squares during the first 18 days of fruiting (Figure l and 2). The rate of increase of the first generation (6,050 weevils) over the average of the parent brood (2,728 weevils) was about twofold. 1962—The results differed markedly from the previous two seasons. From an average overwintered population of 314 per acre during the first 18 days of fruiting, a first generation of 10,274 individuals per acre developed (Figure 1). The rate of increase was about 33-fold. This large difference in rate of increase between 1962 and the first 2 years of the experiment is explained in Figure 2. The graphic representations of square production in 1960 and 1961 are relatively flat lines; this is unlike the normal fruiting sequence of cotton and contrasts sharply with the rapid rates of squaring recorded in 1962 and 1963. The feeding and oviposition activities of the enor- mous populations of 1960 and 1961 actually limited square production and consequently the number of oviposition sites. The occurrence of multiple feeding and egg punctures in individual squares, especially where the crowded weevils were forced on to very small squares, caused the fruits to be shed early, almost as rapidly as they appeared on the plant. This re- stricted the development of normal numbers of squares optimum in size for oviposition. The first generation weevils in 1960 and 1961 were the victims of the density of their parents. There was such competition for young square-s for feeding by the parents that few suitable squares were left for oviposition and develop- ment of the larvae. Thus, a high density population has a built-in mechanism for controlling its numbers. 5 4000 _ Avg. overwintered Total first gene- A veevll population raflon populaflon per acre per acre i- 1960 2,693 |3,354 2,728 6,050 314 10,274 352 14,058 é 5 NUMBER 0F BOLL UEEVILS PER ACRE .'§' Methyl parathion "____app Zzed r’ '0' \ <7 Jpnmn \ ""101; u,‘ 0.. “ha” 7 ¢‘£."l|¢q|o0601100003000nnnunuunla D_QQ§" Figure 1. I g first generati vils from v.1‘; lations of i_ weevil parents, acre plot of M 63. The ove sects were q posit in each ‘ for about 20.; they were -~?_ methyl para i»; recorded after cation were i?" tion insects =6‘; moved when 0 ' - 5 l0 15 20 DAYS AFTER APPEARANCE 0F FIRST 1/3 GROHN SQUARES It increases at a much lower rate than a low density ' population because of intro-specific competition. 1963—As in 1960 and 1961, large numbers of overwintered weevils infested the plot. In order to maintain a smaller weevil population, the cotton was examined three times a week during the first 19 days of fruiting, and sufficient overwintered weevils were hand-removed to maintain fewer than 500 individuals per acre. A total of 1,760 weevils per acre was re- moved. The remaining population averaged 352 per acre during the first 19 days of squaring (Figure 1). The rate of increase of the F1, first generation, population (14,058) over the average overwintered population (352) was fortyfold (Figure 1). However, it is likely that this rate was somewhat inflated since weevils were removed from the plot at frequent intervals to establish an average population of 352. Undoubtedly, the weevils which were removed had deposited some eggs; therefore, the oviposition which occurred probably was somewhat greater than would have been accomplished by an average population of 352 overwintered weevils. The percentage of squares punctured by the over- wintered weevils was greater than the year before (Figure 2), but apparently no interference with fruit- ing occurred. As in 1962, very rapid square produc- tion took place during the first 19 days of squaring, and the population of overwintered weevils should have had ample oviposition sites. As in 1962 these 6 i s .. “i. results strikingly contrast with the data u ~ 1960 and 1961. The concept of density seems to have an important bearing on rate of increase of the boll wevil. Reprod a ciency is favored when cotton is infested, numbers of overwintered weevils. ‘i 125 I | l | ¢———-— I960 “has: u-I |9s| '-' c: J u- |9s2 aor-"I: < m0 -___- |953 ‘I n: e‘ I u: ,' ,1 o. g‘ I 50 A i ; w w 7s - [L] n ‘x Q 61' 1 C ,- :> c: ‘If c‘: v-l - I’ i u- I c: n: c-unu-n-Ja Lu m z Z z | 0 5 10 15 20 ‘y . DAYS AFTER APPEARANCE 01 FIRST l/3 GROWN SQUARES Figure 2. Squaring curves of cotton exposed, population levels of overwintered boll weevils in a of cotton, 1960-63. ‘ | T I I I | OVERHINTERED HEEV I LS ‘i - rmsr GENERATION wwoammnm g p-J 1 lL 3 A Methyl. paruthion i "'\ flfmales per “P? e _- ' s m "f" ‘o days _ x Total second k “WW9 ll’ \\__ __ generation per acre: \__ " a ‘l’ 1 -_~' | I 5mm | | 1 l0 20 I 40 5O 60 70 nus AFTER APPEARANCE or FIRST 1/3 snowu- sou/ants I. »' opment of boll weevil generations in a 1/ 22-acre "A 1965. The overwintered and first generation L"! wed to oviposit for 39 days; then the weevils with methyl parathion. Weevils recorded after qere second generation insects and were removed ntial for tremendous population expan- ‘weevil may be seen from these 4 years of ,2 is apparent that overwhelming numbers f‘ will result from several hundred over- weevils per acre. Where these levels of w brood occur, a grower would have "production period of about 30 days after '_‘_ third grown squares appeared. After - accumulation of several thousand first individuals per acre would drastically 73- fruit set. Previous studies in the area have shown that severe damage ‘tton when boll weevil numbers reach acre (l4). l ion Studies t several years, population studies were measure the size of the second genera- i» relationship to overwintered and first " 'l numbers and to determine how to the phenology of the cotton plant. * were considerably smaller than those “in the first generation studies. This was ‘A it allowed a critical examination of 5the second generation individuals that from relatively small numbers in the generation; ,--~ overwintered female boll weevil popu- n the plot was equivalent to 22 females A - 3). These occurred during the first one-third grown squares first appeared. females were not found in the plot after n“ A of overwintered weevils naturally infest-- this time. From this infestation of 22 females, which oviposited during the first l0 days of squaring, a peak number of approximately 300 first generation weevils per acre were counted. The overwintered male and female population combined generally punctured less than 1 percent (Figure 4) of the squares during the first 18 days of squaring. The percentage of squares punctured by first generation weevils gradually in- creased, and by 40 days after squaring, 18 percent were punctured. This population level of first gen- eration weevils was well below the economic threshold. Second generation weevil emergence began 45 days after the first eggs of the season were laid in the first one-third grown squares (Figure 3). A total population of 5,100 individuals per acre was recorded. These resulted from an initial population of only 22 overwintered females per acre. Figures 5 and 6 show how the squaring and flowering curve for 1965 might be partitioned into those portions exposed to each of the generations. Under the present study conditions, the greatest threat to cotton production would be realized from the first generation of boll weevils. The second generation, although large, began emergence at a time when there was a rapid cessation of fruiting as the crop neared maturity. Consequently, the damage potential of the second generation appears to have been small. This premise is supported by results of studies conducted in North Carolina to determine the length of time that applications of insecticides for boll weevils should continue with respect to the squaring curve of cotton NUMBER 0F SQUARES PER ACRE (l.000's) 0 l0 20 30 40 50 60 70 DAYS AFTER APPEARANCE 0F FIRST’ I 1/3 GROWN SQUARES Figure 4. Seasonal squaring curves in a 1/22-acre plot of cotton exposed to different population levels of boll weevils, 1965-68. 7 (15). Results of this research indicated that increased production was not obtained by continuing applica- tions past the time that cotton squaring had dimin- ished to about 13,000 squares per acre (one square per row foot). Figure 4 indicates that the second generation weevils in the present study did not start emerging until squaring had decreased to about 13,000 squares per acre. The results of the 1965 study suggest that if populations of overwintered female boll weevils occur at levels no greater than l0 to 20 per acre, there would be a period about 45 days after the first one~third grown squares appear before damage would be suffi- cient to reduce yields. In the dryland experiment utilizing the Lankart Sel. 57 variety of cotton, 45 days was a sufficient production period for maximum fruit set (yields). In irrigated culture using indetenninate varieties, 45 days probably would not be an adequate amount of production time. In this situation it is probable that the second weevil generation might cause considerable economic damage. 1966-68—In each of these three seasons, the over- wintered female populations were great enough to produce a sufficient number of first generation weevils (Figures 7, 8 and 9) to cause considerable crop damage. The smallest first generation peak recorded was about 1,000 individuals per acre in 1968, and 55 percent of the squares were attacked (Figure 4). In each of the 3 years, the first weevil generation hindered boll set; 60 1 | _| | x I | ,_ ._ OVERVIINTERED HEEVIL _ INFESTATIGI 140 _ ' ‘i FIRST csusmnou " __ msassnce "' _.. l w 12° sscouo emzmrgon “"- == EMERGENCE k) c: —- - X nu 100 ' l l\ l0 U) ~ r- m o CK @ u: c: N Z o O -| g; \J -_ u. o 60 Z u] L1 m a: = 40 z 20 0 0 l0 20 30 40 50 60 70 DAYS AFTEflR APPEARANCE or FIRST 1/3 GROWN SQUARES Figure 5. The relationship of seasonal squaring in a l/22-acre plot of cotton to several generations of the boll weevil, 1965. The shaded and unshaded areas in the figure indicate the portions of the squaring curve exposed to each generation. and as a result of poor boll retention, a U squaring curve was re-initiated after 50 da I 4). Ample squares were consequently pro a third generation. It seems that when overwintered bo l. populations are of sufficient size to produ aging first generation, the resultant failure “boll load” cause-s the cotton to re-initiate» late in the season. This fosters the devel v later weevil generations. As the incidence of f rapidly increases in the later generations, the : fruiting curve becomes important to the d of great numbers of potential overwinteri ;‘ During the 1966-68 studies, the small overwintered weevil population averaged per acre, and yet these were sufficient to V first generation population that punctured ~ of the squares. In 1965, a population of 4?. per acre did not give rise to an economif aging first generation. Therefore, the f threshold of overwintered weevils that are v5 a damaging first generation apparently is of 22 females per acre. t Implications of Population Study Findings The significant point that emerges g population studies of the boll weevil is 1,1 predictability of the time during the fruitfl of cotton when damaging numbers of W T develop from various numbers of overwint i_ insects. The fruiting sequence of cotton, reproductive characteristics of the pest '_ produce an orderly emergence phenomen weevil generation that should help in pl u_ management programs. The data suggest“ much of the production of Texas dryland; primary goal of boll weevil control sho '1 reduce overwintered populations to l0 to l; per acre. If this could be accomplished, if in cotton by the overwintered and first gen weevils should not affect yields. The 10 to“ l per-acre population level might be achif applications of an organo-phosphate in -§ plied at squaring and at intervals thereafter} such an approach, the beneficial arthro, tions would be destroyed, and dangerous and tobacco budworm infestations may de’; the other hand, the use of the fall diapa * program to reduce overwintered boll w " I fewer of the hazards associated with i ’ ment. Results ob-tained on the High Pl ' indicate that overwintered populations can V with this program to much less than the: female-per-acre threshold. Control of the diapausing generation, together with app -" foliation and desiccation, could remove the a threat from the dryland areas. Inseason 1 the pest, and all of the attendant secon (If problems that develop because of the ' Whlfe blooms durlng___ second generation emergence Figure 6. The relationship of the flow~ ering in a 1/22-acre plot of cotton to the emergence period of second generation boll weevils, 1965. l l I Aw 30- 4o 2o so DAYS AFTE_R APPEARANCE OF FIRST 1/3 GROWN SQUARES 30m I | | I if“ key pest, would be substantially elimi- i: --- ovwlwwvwgvlw ' ' I ’ ' ' _ ._, ----.- FIRST GENERATION Cztrsazvtrsgizrsta:‘zzzrzgpi; += -~--~ - season in the dryland production areas. Z , wflmthm f‘ w Had ted cotton and the current relatively m?‘ ‘ varieties, the problem is more difficult. 3‘ r1‘ ,1‘ / l’ f. uction period is utilized to produce x m“ i ‘V’ = _ jthe second generation of weevils presents g ' 0," I l f uction. Weevils emerging after the s" f | l J- squaring, while not constituting much 3 ‘°°°- ,1 i f - Ediyland production, would be a serious 3 I - irrigated, relatively indeterminate g m“ Avgrageipf 66lfemales per '1' i _ ,this cotton to escape damage by the Z f“ YSHQZJTIQ“ ‘M’ I m: second Mme“ f; _ _ h“ 21 - ‘I _ per acre: l2,474 L- on, 1t would be necessary for a fall i . ~ u to reduce overwintered numbers ° ' ' J ' ' ' ' ' 4 . ,._. _ t. _ _ o 1o 2o so 4o so . so 1o 3 DAYS AFlTlEsR GARPOPHENA RSA NUCAER 08F FIRST :7 . Q E “i011 Period f0!‘ ifligated COUCH 3X’ Figure 7. Development of boll weevil generations in a l/22-acre ‘ time of season when ingidenge of plot of cotton, 1966. The overwintered and first generation a: ' the. timing and number of insectp insects were allowed to oviposit for 41 days; ‘then the weevils needed to reduce diapausing weevil were destroyed with methyl parathion. Weevils recorded after . _ _ the application were second generation insects and were removed V, ld be much more critical. whm ¢ount¢d_ 9 I | | | | I OVERUXNTERED IEEVILS ---- "" FIRST GENERATIO! "an". PARATmm ‘Iv-I'- SECGID GENERATIM Ii‘ k APPLIED HERE / 1w I :' I I i 1500- . / .. 1' 2500'- 2000- / NUMBER 0F BOLL HEEVILS PER ACRE ‘I000 - - Tota‘! second generation per acre: / 11.990 Average of 79 females per 5w _ acre during first 19 days of squaring ' Jmc 7 o, o | l 1"’ I I I _ o 1o 2o so 4o so so‘ 7o DAYS AFTER APPEARANCE 0F FIRST‘ l/3 GROHN SQUARES Figure 8. Development of boll weevil generations in a 1/ 22-acre plot of cotton, 1967. The overwintered and first generation insects were allowed to oviposit for 41 days; then the weevils were destroyed with methyl parathion. Weevils recorded after the application were second generation insects and were removed when counted. Despite the greater difficulty of utilizing the pest management principle of diapause control in areas producing cotton over long production periods, results obtained in Texas indicate that populations of over- wintered weevils may be reduced to very low levels. Injurious levels have not developed until late in the subsequent season, if at all. This system of pest management could be tailored to the various cotton production and variety situations in Texas. It also might be used to eliminate a great amount of inseason chemical control for the boll weevil. Although the pest management approach for reducing diapausing boll weevil populations seems tenable for both the dryland and irrigated areas of Texas, recent developments by breeders at Texas A8cM University offer the means for greatly improving this technique. Certain genetic stocks of cotton have been selected that mature remarkably early. This earliness does not result in a loss in yield if the cotton is grown in high density culture. Such cottons may provide a significant breakthrough in pest manage- ment schemes aimed at reducing boll weevil popu- lations. Plant Breeding and Its Role in Pest Management Cotton breeders in the Department of Soil and Crop Sciences at Texas A8cM University have de- veloped a series of experimental strains which, com- pared to predominant commercial varieties, are earlier in the initiation of flowering and set fruit more rapidly. In some of these strains, the boll maturation period also has been shortening. These modifications in fruiting habit produce an acceleration of the over- all fruiting period, hasten crop maturity and advance ‘IO _ plot of cotton, 1968. The overwintered and u; ._—-—- OVERHINTEREO HEEVILS f‘, ---- -- rmsr stuemnou < 2500 I-I-v-i SEmND GENERMHW n: u: a. w —J 2000 0-4 > Lu Lu Z ‘I500 .4 .4 o m a» z Ila y pm-atMan u- ‘I000 ‘PPM’ ° p i ‘z I m ‘I \ 2 500 I ks =3 Average of 40 females per ‘ "‘ z acre during first 20 days | | of squaring ’I I Jun: .15 J! | n _t_./‘-—-—- """ l _ O l0 20 30 40 W DAYS AFTER APPEARANCE or Fl 11s crown SQUARES 1 Figure 9. Development of boll weevil generation! ' insects were allowed to oviposit for 44 days; --§ were destroyed with methyl parathion. Weevils , the application were second generation insects and when counted. 4 harvest by 10 to 25 days, depending on ‘A and cultural conditions. In some strains- markedly enhanced by increasing plant A number of experimental cotton X evaluated in detailed studies conducted; Station in 1967 and 1968. Data from l the growth and fruiting characteristics of types. Figure 10 shows the differences “I habit among three selected strains w a commercial variety planted in single n, 40 inches apart. Plants in the drill were 1 m0 1 1 | I 1 I I | nun-mi l x 4 - 21 l, .. -..._- | x 5 - 5b f" N ............. 5 - 19 ' f / so - ----- Deltaplne 1e '__,..---~" ' ,1 n,’ w‘ l’ _ f’ I 0 I I I I Q "l » 1 S‘ f 1’ 5 ’ ' "1 . .. ' I f l’ .- /’I f‘! 2P '" /, l CUMULATIVE BLOOHING, 8 z . I "_ .-'/ 0, 1 | | I | 1 63 ' 79 95 ‘Ill 1Z7 “DAYS AFTER PLANTING Figure l0. Cumulative blooming percentages A mental strains and a commercial variety in con drill planting, 1968. I’ rvals. Each of the experimental strains c- 'ng earlier than the commercial variety. y» strains 1 x 6-56, the difference averaged ins 1 x 4-27 and 6-19, the differences Differences in rate of flowering are of Tl 'cance than the earliness of first flower. stupid-flowering entry, strain 6-19, 75 per- g- flower production was achieved 100 days The same level of flowering in the ariety, Deltapine 16, required lll days. t level of flowering in the other two termediate, averaging about 105 days. h‘ from the data represented by Figure 10 with an early April planting of the types, flowering might be 75 percent ,1‘ mid-July. A the production period of the experi- stocks is shortened when the modified 1' ted in conventional single row culture, plant densities are increased that really ‘leration in fruiting occurs. In the ' ent the same cottons also were y‘ ~ uble-drill pattern, with drills l0 inches (‘l beds and 5-inch plant spacing within J- e ll). In terms of plant population, ent to planting single drills on beds . In this planting arrangement the ‘began flowering at the same time as in system. However, the higher plant the double-drill planting had an é ect on the flowering rate of two strains. l, strain l x 6-56, the 75-percent point uction was achieved 98 days after plant- 11-6-19, this level was attained 94 days The other two entries, strain l x 4-27 A 16, showed no increase in flowering ted in the double-drill row. l 1 l | l I ,.- w’ - ,,,, " I I x 4 21 .- f’ l x s - ss ,__..--" ,1 - no" s a f‘ I l ‘I y I DoHaPlne v/ ,1 _ls / . , I . ., .- IXIBLE-UULL PUNTITB - 1 79 95 111 127 143 159 H DAYS AFTER PLANTING (ulative blooming percentages of three experi- P- a commercial variety in double drill plantings an ), I l I ' ' 7 l 1 F l I _.._._..._ l x 4 - 27 __ _ l >< s - 5s / _ n .............. .. s - I9 . ' _ 3Q ._ ---- -- Deltapine l6 _ __ >- I—- s-J F" T n: . a < 2 no n-t Lu > w >-— -—< '-' STNGLPIRILL PUNTING l»- < I ._l ' I’ " 2 I D 20 —- i _ — u - 0 ./ ‘l I l I I l l I l l T05 121 137 153 169 185 201 DAYS AFTER PLANTING Figure 12. Cumulative maturity percentages (percent open pickable bolls) of three experimental strains and a commercial variety in conventional single drill planting, I968. Differences in crop maturity among the various cottons are shown in Figures 12 and l3. The differ- ences among entries and between planting patterns generally parallel those previously described for flow- ering. In the single-drill plantings, the days from planting to 75 percent maturity, as measured by open pickable bolls, ranged from 148 days in the case of strain 1 x 6-56 to 160 for the Deltapine 16 variety. In the double-drill plantings, two of the four entries showed a substantial hastening of maturity, as com- pared to single-drill planting. The 7 5-percent matu- rity level of strain 1 x 6-56 was advanced by 5 days, and that of strain 6-19, by 18 days. For the other two entries, strain l x 4-27 and Deltapine 16, maturity was not affected by plant density. loo l I l l | l l l a’ I | | -——- I x 4 - 27 I: .. —-m-— l x 6 - 56 .. u ........ .. ... 6 - I9 f." -- / _ 80 - ----_ Delfaplne l6 ,1‘. ’ .._ > y l— _ . _ >4 _: Z If’ = so - ... l- z: __ / _ m INIBLPIZRILL PLANTING > 40 ._ ._. i l- € ~ .1 ..| Z § 20- _ u I 0 l 1 I l l l l I 105 121 137 153 169 185 201 DAYS AFTER PLANTING Figure l3. Cumulative maturity percentages (percent open pickable bolls) of three experimental strains and a commercial variety in double drill planting (two rows per bed), 1968. 1'l The potential value of the modified fruiting types such as strain 1 x 6-56 as an aid in pest management is attributable to two factors: 1. Precocity and rapidity of fruiting increases the probability for setting an acceptable fruit load before weevil infestations reach a level that will reduce yield. 2. Early and rapid crop maturity permits early dis- posal of crop residue, thereby reducing host plant support for diapausing weevils and contributing to a reduction in overwintering populations of the pest. The crop may be harvested and stalks destroyed before the environment forces the weevil into diapause. This would be disastrous to the boll weevil and might relegate the insect to the role of a minor pest. The importance of rapid fruiting and early ma- turity in combating the boll wevil can be seen in Figure l4. This is a hypothetical presentation. How- ever, the figure has been constructed from actual data obtained in independent studies of the boll weevil and of the fruiting performance of two geno- types of cotton. The flowering sequence of these genotypes is given in Figure l4 with the second generation emergence periods indicated during the riods of flowering. The flowering data were" re- corded in 1968 from irrigated plots of double-drilled Deltapine 16 and experimental strain 1 x 6-56. Yields in both genotypes were comparable. assumes that the second generation of the insect developed from an overwintered weevil population of 22 females or less per acre and that neither the over- wintered generation nor the first generation hindered fruit set. The graph - The population dynamics studies p - ~ 1, in this paper show that the first second f weevils began emergence 45 days after the, third grown squares appeared in the cot would be approximately 33 days after the of first flower. In cotton planted April ginning of the second generation emerg in strain 1 x 6-56 would be about July 5; in __ l6, about July 9. At these‘ times about -f_ bolls in the strain 1 x 6-56 would be l2 da v and consequently safe from boll weevil da u i’ pine 16, on the other hand, would have percent of its bolls past the critical -- v stage. By August l0, approximately 60 V, the bolls should be open in strain l x defoliant could then be applied. In they 16, it would be about 18 to 20 days lat» defoliant application could be safely w] The accelerated production of strain l- allow significant early fruit set before _ f populations attain large numbers. And, of the latter, strain I x 6-56 might be harve; earlier than Deltapine 16 or other similar ' varieties. The early destruction of stal - 1 x 6-56 in turn would greatly reduce the ' over of the pest. -5 Perhaps, the earlier defoliation and p be sufficient to lower the population of o’ female weevils to less than l0 to 20 per acre‘, ing spring. This would prevent an early w up of great numbers of weevils, and the -i not suffer yield reducing infestation un 45 days after the initiation of squaring. B“ at least half of the yield should be safe from t, damage. A much greater degree of popular 40 .11- -—- ‘| x 5 - 55 Deltapine 16 A v white blooms during ,__ g second generation I \ 3 3o __ emergence I \ _ a. _ n: I \ Figure l4. Z I \ figure sh A Be ' second generat‘ mergence ‘n ' ' ' w _._;_ Deglfbpine Z6; 52% cidfiaetive bloom-ing, rapld fru1_ _, z: 2o \ "“' 30% of boZZs safe dguble-d .. o ._ _ _ » o I might red g’ damage and‘ m defoliation. , *- Zemflfiefiifii ‘ielefii?’ assum“ ' T 70% cianulatii» blooming, numbefg do , a: 49% of bolls safe . z = 1o __ __ nomic p0 the second _ ' 60% open boZZa riod. l1‘ ‘ Z s-56 b _ T 2:91.; w y so: a?» bazzzs W35 P101 ~ in De t ine ' ' Shy Augugl; so obtained in g o / ::.':::::::::::::::::... _ - " A A A A April 1 Hay 1 J1me 1 Sevt- 1 (planting) l2 _ 'ned if several organophosphate insecti- tions were made for reproducing and ~- ils between July 5 and the time of a application. This would assure max- ‘ tection and further reduce the potential over of the pest. 6-56 and similar genotypes are experi- 1s. They are not available to growers. i are needed in “tum out” and in fiber jthe mechanics of high density planting g ~ still being researched. Nevertheless, may hold considerable promise for the table yields might be achieved without production and harvesting periods late season when the environment forces diapause. This would greatly reduce of potential overwintering weevils. forcement to this management practice - from limited use of organo-phosphate 'ng the period of second generation weevil emergence and from areawide defoliation and desiccation. There are other advantages to be realized from these rapid fruiting plant types. These cottons mature so quickly that the period of susceptibility to the bollworm-tobacco budworm complex would be shorter in duration. Also, these new lines would allow harvesting during the hot, dry weather that generally prevails in South and Central Texas in August. This earliness also would provide some insurance against hurricanes and the heavy late sum- mer rains which frequently occur in late August and September. Acknowledgment This research was conducted in cooperation with the Entomology Research Division, ARS, USDA. The study was supported in part by Contract Grant 12-14- l00-8299(33) ARS, USDA. ‘l3 l4 Literature Cited ; Hunter, W. D. 1911. special reference to means of reducing damage. Farmers Bull. 344:25-26. Ware, J. O. 1937. Plant breeding and the cotton industry. USDA Yearbook:657-744. Ncwsom, L. D. and J. R. Brazzel. The boll weevil problem with USDA 1968. Pests and their control. In Advances in Production and Utilization of Quality. The Iowa State University Press, p. 567-405. Hunter, W. D. 1904. The most important step in the cultural system of controlling the boll weevil. USDA Bur. Ent. C. 56, 7p. Mally, F. W. Farmers Bull. 1901. The Mexican boll weevil. USDA 130, 29 p. Brazzel, J. R. and L. D. Newsom. 1959. Diapause in Anthonomus grandis, Boh. J. Econ. Entomol. 52(4):603- 611. Adkisson, Perry L., D. R. Rummel, W. L. Sterling and W. L. Owen, Jr. 1966. Diapause boll weevil control: A comparison of two methods. Bull. 1054, Tex. Agr. Expt. Sta., Texas A8cM Universtiy, 11 p. Ridgway, R. L., P. D. Lingren, J. W. Davis and C. B. Cowan, Jr. 1967. Populations of arthropod predators and Heliothis spp. after application of systemic insecticides to cotton. J. Econ. Entomol. 6(4):10l2-1016. 9. l0. ll. 12. 13. 14. .1 _- R Walker, J. K., Jr., Merle Shepard and W. L.‘ Effect of insecticide applications for the W‘, on beneficial insects and spiders. PR-2755, H Sta., Texas A8cM University, 11 p. " Roussel, J. S. and D. F. Clower. 1955. chlorinated hydrocarbon insecticides in __ (Anthonomus grandis Boh.)“ La. Agri. ' l‘ 9 P- '. Adkisson, P. L. and S. J. Nemec. ‘-“~‘1 effectiveness of certain insecticides for f and tobacco budwonns. Bull. 1048. Tex... Texas A8¢M University, 4 p. if‘ Nemec, s. J. and P. L. Adkisson. 1969. of insecticides for bollworm, tobacco bu weevil control. PR-2674. Tex. Agr. Expt. Universtiy, 5 p. v Carter, Frank L. and J. R. Phillips. thion resistance in a laboratory strain oily, J. Econ. Entomol. 61(6):1716-1718. Walker, J. K., Jr. and R. L. Hanna. ‘In, of populations of the boll weevil in various insecticides during 1959, 1960, and; Entomol. 56 (3):350-356. ‘i W. J. Mistric and B. M. Covington. 1969. ‘g as an economic indicator of approximatqpi‘ insecticidal treatments for boll weevil n»: Entomol. 62(1):35-36. [Blank Page in Griginal Bulletin] Texas Agricultural Experiment Station Texas A8¢M University College Station, Texas 77843 H. O. Kunkel, Acting Director-Publication ' Unmd Y