Physiological status of overwintering boll weevils, Anthonomus grandis Boheman, in Arizona.

Item Type text; Dissertation-Reproduction (electronic)

Authors Sivasupramaniam, Sakuntala.

Publisher The University of Arizona.

Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Download date 03/10/2021 22:46:19

Link to Item http://hdl.handle.net/10150/185143 INFORMATION TO USERS

The most advanced technology has been used to photograph and reproduce this manuscript from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation.copies are in typewriter face, while others may be from any type of computer printer.

The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed through, substandard margins, and improper alignment can adversely affect reproduction.

In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.

Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book.

Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order.

U-M-I University Microfilms International A Bell & Howell Information Company 300 North Zeeb Road. Ann Arbor. M148106-1346 USA 313/761-4700 800/521-0600

Order Number 9100560

Physiological status of overwintering boll weevils, Anthonomus granda's Boheman, in Arizona

Sivasupramaniam, Sakuntala, Ph.D. The University of Arizona, 1990

U·M·I 300 N. Zeeb Rd. Ann Arbor, MI 48106

PHYSIOLOGICAL STATUS OF OVERWINTERING BOLL WEEVILS,

Anthonomus grandis Boheman, IN ARIZONA

by Sakuntala Sivasupramaniam

A Dissertation Submitted to the Faculty of the DEPARTMENT OF ENTOMOLOGY In partial Fulfillment of the requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate college THE UNIVERSITY OF ARIZONA

199 0 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE

As members of the Final Examination Committee, we certify that we have read

the dissertation prepared by ____S_a_k_u_n_t_a_1_a __ S_i_va_s_u~p_r_a_m_a_n_i_a_m ______

entitled Physiological Status of Overwintering Boll Weevils, Anthonomus grandis Boheman. in_A_r_i_z_o_n_a ______

and recommend that it be accepted as fulfilling the dissertation requirement

for the Degree of ______~D~o~ct~o~r~o~f~P~h~i~l~o~s~o~ph~y~ ______

Date

D

Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.

~~Dissertation Director ? 2

STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University' of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of the source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgement the proposed use of the material is in the interests of scholarship. In all other instances, however, permission may be obtained from the author. 3

ACKNOWLEGEMENT

It is with great pleasure that I express my sincere gratitude to Professor Theo F. watson for being my Graduate Director and advisor. The cooperation, continued support, and the extremely congenial and friendly working atmosphere provided by him rendered the program very pleasant and enjoyable. The least I could say is that I feel privileged to have had Dr. watson as my supervisor. I also wish to extend my thanks to Drs. Leon Moore, Irene Terry, Paul G. Bartels and Dennis Ray, for serving on my commi ttee, reviewing my manuscript, and for their helpful suggestions. I am also deeply indebted to Dr. Patricia Jones and Mr. Rick Axelson for their invaluable advice and assistance with graphics and statistical analysis. My very sincere thanks and gratitude are due to Dr. Abdelgadir Osman, for the continuous support and ever willing help given throughout the period. I wish to also thank Ms. Justine Collins for typing the manuscript and assisting with many other tasks. This research was supported by a grant provided by Cotton Research and Protection Council (Project No. 977522), which is gratefully acknowleged. Finally, it gives me great pleasure to thank all Professors, Staff, Secretaries and students of the Department of Entomology, for the support and friendship extended to me during my stay here. I wish each and everyone of you good luck and happiness. 4

TABLE OF CONTENTS Page

LIST OF ILLUSTRATIONS • 7

LIST OF TABLES 9 ABSTRACT · ...... 11 INTRODUCTION · ...... 13 LITERATURE REVIEW • . · ...... 18 Taxonomy . • . • • • • . . • • • • • • 18 Allozyme variation among populations of boll weevils in Arizona and Mexico ..• 20 Origin and Dispersal • . • • • . • . • . . • . 21

Biology •.....•.• . . • . • . 22 Life History • • • • • . • • • • . . . . . 22 Developmental Period ...... • . 24 Preoviposition Period, Fecundity and Oviposition ••••..•..•••... 26 Longevity of Adult Weevils . • • . • . 29

Damage and Control · ...... 30 Damage . . • • . . . 30 Economic Impact 31 Control .•• 31 Chemical Control 31 Cultural Control ...... 32 Host Plant Resistance .•.....•.•..•...••....• 34 Pheromone Traps ••• · ...... 34 Eradication ••...... 35

Alternate Hosts 37

Diapause 39 Diapause Mediated Dormancy, Seasonal Migration and Seasonal Polyphenism • • . • .• ••. 45 Dormancy ••.•..•...••••••• 45 Seasonal Migration ...••••••• 56 5

TABLE OF CONTENTS Page Seasonal Polyphenism .•. 47 Diapaus~ng Stage • 48 Diapause Induction • • . 49 Diapause Syndrome ••• 51 Prediapause • • • • • . 51 Diapause Intensification •••.••••• 52 Diapause Completion • . • . . . . 53 1. Diapause Duration • . . . 55 2. Diapause Maintenance .•.... 56 3. Diapause Termination ••• . .. 57 Incidence of Diapause in the Boll Weevil . • • 59 Survival of Overwintering Weevils ••.. 63 Emergence Profile of Overwintered Weevils 66

MATERIALS AND METHODS . • • • • ...... 69 Diet and Rearing Conditions 69 Bioclimatic Chambers • • • ...... 71 Sex Separation • • • • 71 Diapause Determinations ...... 71

1987/1988 Collections 72 Hibernation Cage Studies • .. ...•.• 73 1. Role of Moisture •. ..•••... 74 2. Survival . • • . . .. .•....• 75 3. Emergence Pattern • • • . . . • 75 Laboratory Studies • • • . . • . . •. 75 1. Sex Ratio •....• .••..•. 76 2. Diapause Determinations . . . • .• 76 3. Photoperiod and Temperature on Diapause Development ....••.•. ••• 76 a. Reproductivity •... ••.. 76 b. Survival and Longevity •...•• 78 1988 Collections 78 Sex Ratio ..•.•.•••.•..••. 79 Diapause Determinations . . • • • • • 80 Photoperiod, Temperature and Food on Diapause Development . • . . . • • • • 80 Photoperiod and Temperature on Survival and Longevity ...... 81 Moisture Content • . . . . • • . • . . . . •. 81 6

TABLE OF CONTENTS

Page Lipid Determinations • . . . . • . 81 1. Total Lipids • • • • • . • • • . . .~ • . 81 2. Separation of Lipid Classes 82 Late Season Infestation and Survival • . • • • 84 spring 1989 85 Analyses of Data ...... 86 RESULTS AND DISCUSSION 87 1987/1988 Collections from Laveen ...... 87 Trap Collections . . • • • • . • • . . • . 87 Sex Ratio •••...••.. 90 Emergence in Hibernation Cages . •. ..• 93 Survival in Cages .••.•....•.... 96 Diapause Status ...... • 102 Reproductive Behavior of Weevils at Three Temperature/Photoperiod Regimes •...• 107 Transfer to Activating Conditions •••• 115 Longevity at Three Temperature/Photoperiod Reg imes •••••••••.•••••••.• 118

Marana Collections - 1988 •••.•.••.••. 124 1. Non-Feeding Quiescent Weevils . • . . . . . 124 2. Sex Ratio • . • • • • • . • •. •.•. 126 3. Diapause Status • • • . • . . • • . 126 4. Effect of Photoperiod, Temperature and Food on Diapause Development and Completion of Post-Diapause Morphogenesis • . • . . • . . 126 5. Longevity of Fed and Unfed Weevils ...• 133 6. Moisture and Lipid Content .....••. 134

Effect of Plant Phenology on the Physiological Condition of the Weevils •...•..••. 139 Late-Season Infestations • . • • • • . . . • . 143 spring 1989 ...... 146 CONCLUSION ...... 147 LITERATURE CITED ...... 153 7

LIST OF ILLUSTRATIONS

Number Page 1 A: Pheromone trap counts of boll weevils; B: Mean monthly temperatures (Laveen, 1987/1988) ••..••..•.•.. 88

2 Percentages of male boll weevils in trap and field collections (Laveen 1987/1988) ••••.••• 91 3 Percentage cumulative emergence of boll weevils in hibernation cages : dry and moist regimes (Laveen, 1987/1988) ••.••.•••••.•••.•••• 94

4 Seasonal survival of boll weevils collected from traps and field (dry and moist regimes), when placed in hibernation cages (Laveen, 1987/1988) •.• 99 S Seasonal incidence of diapause in boll weevils. A: Trap collected weevils. B: weevils dissected from dry bolls. C: weevils emerging from dry bolls (Laveen, 1987/1988) ...... 104

6 Progress of diapause development in boll weevils collected from traps (1) and bolls (2), evidenced by differences in ovipositional delay in samples transferred to two temperature/photoperiod regimes. A: 2SoC, 14L:10D. B: 20°C, 12L:12D (Laveen, 1987/1988) .. 110

7 Progress of diapause development in boll weevils collected from traps (1) and bolls (2), evidenced by differences in egg-lay in samples transferred to two temperature/photoperiod regimes. A: 2SoC, 14L:10D. B: 20°C, 12L:12D (Laveen, 1987/1988) •.••....•.•...... 111

8 Longevity of boll weevils (fed on artificial diet) collected from traps (1) and bolls (2), when subjected to three temperature/photoperiod regimes. A: 2SoC, 14L:10D. B: 20°C, 12L:12D. C: lSoC, 10L:14D (Laveen, 1987/1988) ...••.•••••.•• ••..••••..• 121 9 Longevity of boll weevils (unfed) collected from traps (1) and bolls (2), when subjected to three temperature/photoperiod regimes. A: 2SoC, 14L:10D. B: 20°, 12L:12D. C: lSoC, 10L:14D (Laveen, 1987/1988) .•. 122 8 LiST OF ILLUSTRATIONS Number Page

11 Progress of diapause development in boll weevils collected from two fields, evidenced by differences in preoviposition period in samples transferred to diapause-averting temperature/photoperiod (25°C, 14L:10D), and fed on cotton squares, blooms, bolls, or artificial diet. A: October collections. B: November collections (Marana, 1988) . . . • • . . • 131 12 Progress of diapause development in boll weevils collected from two fields, evidenced by differences in egg lay in samples transferred to diapause-averting temperature/photoperiod (25°C, 14L:10D), and fed on cotton squares, blooms or bolls, or on artificial diet. A: October collections. B: November collections (Marana, 1988) • • • • . • • . 132 9

LIST OF TABLES Number Page 1 Seasonal survival of trap and feild-collected boll weevils in emergence cages (Laveen, 1987/1988) •..•.• 98 2 Mean percentages of boll weevils in reproductive (R), intermediate (I) or diapausing (D) categories (Laveen, 1987/1988) • • . • • • • • • . . . . • . • 103 3 Observations on preoviposition period of boll weevil females subjected to two temperature/ photoperiod regimes (Laveen, 1987/1988) ...... 108

4 Observations on fecundity of boll weevil females subjected to two temperature/photo­ period regimes (Laveen, 1987/1988) ...• 109

5 Effect of temperature and photoperiod on diapause development and completion in boll weevils, measured by increase in egg-lay after transfer to activating conditions (Laveen, 1987/1988) •...•••••.••...••. 116

6 Longevity of boll weevils subjected to three temperature/photoperiod regimes (Laveen, 1987/1988) •..••••...•...• 119 7 Longevity of unfed boll weevils subjected t.o three temperature/photoperiod regimes (Laveen, 1987/1988) •..••..•...•..•.•• 120 8 Assessments on reproductive condition of inactive boll weevils using the 'paper towel method' of separation (Marana, 1988) ...... • • . • . . . 125 9 Mean percentages of boll weevils in reproductive (R), intermediate (I) or diapausing (D) categories (Marana, 1988) ..••.•.•...•.••. 127 10 Observations on preoviposition period of female boll weevils fed on different diets (Marana, 1988) 128 11 Observations on fecundity of female boll weevils fed on different diets (Marana, 1988) • • • • . • • 129 10

LIST OF TABLES Number Page

12 Observations on mean longevity of boll weevils subjected to. two temperatures (Marana, 1988) 133 13 Average weights and lipid content of boll weevils (Marana, 1988/1989) ...... 135 14 Lipid composition of boll weevils (Marana 1988/1989) ...... 136 15 Observations on late season infestation of cotton bolls and seasonal survival of boll weevil life stages (Marana 1988/1989) • • . • • • • • . . . . . 144 11

ABSTRACT The overwintering physiology of boll weevils was evaluated using collections from a field in Laveen and 2 fields in Marana, Arizona, during the 1987-1988 winter and spring, and the 1988 non-cotton season, respectively. The objectives of the study were to determine if the strain of boll weevils, Anthonomus grandis Boheman, in Arizona enter true diapause, when diapause occurs, proportion of population entering diapause, and factors inducing diapause. Comparative studies were performed on 1987-1988 collections from both pheromone traps and bolls, to assess sex ratio, survival, reproductive behavior and adult longevity. Large numbers of weevils were caught in traps from September 1987 through April 1988, and there was no evidence of correlation of trap catches with prevailing temperatures. Hibernation cage studies also showed the absence of a sustained period of inactivity, and emergence was completed before the availability of squaring cotton. significantly higher survival was observed among boll-enclosed weevils relative to the trap collected weevils, when placed in cages. Furthermore, moderate moisture was found to have a positive influence on survival. Studies on diapause and reproductive behavior revealed that a significant number of weevils in the trap collections was reproductive, whereas, a higher proportion of weevils 12 collected from bolls seemed to be in a non-reproductive or diapausing condition. Subjecting weevil samples to three telilperature/photoperiod regimes (2SoC, 14L: 100; 20°C, 12L: 120; and lSoC, 10L: 140) showed that higher temperature/longer light cycle was more conducive to diapause completion and post diapause development. But, on transferring sub-samples to altered temperature/photoperiod regimes, temperature was determined to be the more important factor inducing diapause termination. Evaluations on longevity showed that 20°C 12L: 120 photoperiod was optimal for survival of both fed and unfed weevils. Studies on weevil-samples collected from the two fields in Marana to evaluate the influence of plant phenology on overwintering status showed that the two populations were significnatly different with respect to diapause status, reproductive behavior, egg lay, preoviposition period, moisture and fat content, and lipid composition. Higher proportions of weevils collected from the field with mature cotton bolls (Field 2) were found to be in a state of firm diapause, whereas those from a field with all stages of fruiting cotton (Field 1) were predominantly reproductive or intermediate. 13

INTRODOCTION The boll weevil, Anthonomus grandis Boheman, continues to threaten cotton production in the New World. The presence of the Mexican boll weevil, Anthonomus grandis, in western Mexico and Arizona, north of its original range has been the result of dispersal and adaptation to both wild and cultivated forms of Gossypium (Burke et al. 1986). Although the boll weevil was first found attacking cultivated cotton in Arizona in 1920 (Morrill 1921), only sporadic infestations were observed until the 1960's (Bottger 1965). The recent establishment and spread of boll weevil populations in Arizona in the late 1970's has generally been attributed to stub cotton production, providing continuous accessibility to host material throughout the noncotton season (Bergman et al. 1982). As mentioned by Fye and Parencia (1972), the failure to shred and plow under the harvested crop has led to the increased survival of hibernating adults, since they could be harbored undisturbed in their developmental cells within mature bolls. Moreover, regrowth of cotton terminals through the winter, provide the adult weevils emerging in the spring with an immediate source of food (Bergman et al. 1981). Bottger et al. (1964) reported that infestations in 14 Sonora, Mexico posed a threat to cotton production in previously uninfested areas in Arizona and California. They suggested the establishment of a treated buffer zone between the infested area and Arizona cotton, and the implementation of a thorough stalk-destruction program soon after harvest, to reduce overwintering populations. The culture of stub cotton in the early 1960's resulted in widespread infestations of boll weevils in cultivated cotton in Arizona in 1964 and 1965 (Fye, 1968). He recommended that early stalk destruction and sanitation were essential for the cultural control of the boll weevil. The adoption and enforcement of mandatory plow­ down regulations in 1965 by the state proved to be effective and the boll weevil ceased to be a problem in Arizona cotton (Fye and Parencia, 1972). In 1978, the Arizona Commission of Agriculture and Horticulture relaxed the regulations pertaining to plow down and permitted the growing of stub cotton for a five-year period. Bariola (1983) reported that about 40,000 acres of stub cotton were grown in 1978. Gillespie et al. (1979), Bergman et al. (1981) and Bergman et al. (1982), reported on the subsequent buildup and spread of infestations from 1978 through 1982. The Arizona Commission of Agriculture and Horticulture reimposed the ban on production of stub cotton during the 1983 growing season.

However, infestations were continuously found in many cotton- 15 growing areas -in Arizona and southern California (Henneberry et al. 1988), indicating that widespread infestations had become established and continued to exist even in the absence of stub cotton. Subsequently, a unified eradication effort was launched by state, federal and Mexican officials to eradicate the weevils along the Colorado River in Arizona, California and Northern Mexico (Watson et al. 1986). They also reported, that although populations were drastically reduced after the initial phase of this program in 1985, severe boll weevil infestations were found in central Arizona, concurrent with the eradication efforts in western Arizona. The accumulation of knowledge on the weevil populations and the elucidation of their population dynamics in the Southwest would greatly facilitate the development of effective management practices and eradication programs. Concern regarding the increased severity of the boll weevil problem in Arizona, and the imminent threat it posed to cotton production in southwestern and western Arizona, prompted the initiation of research efforts during the last decade, in an effort to elucidate the ecology and physiology of this pest (Bariola et al. 1984, Bergman et al. 1983, Watson et al. 1986) • Chemical control of the boll weevil is impractical and costly and hence it has been suggested that information 16 concerning th~ incidence of diapause in specific populations is necessary in order to design programs to reduce the vulnerable overwintering populations (Lloyd et al. 1964, Rummel and Frisbie 1978). Although the overwintering physiology of the boll weevil has been extensively studied since the beginning of this century (Sanderson 1905, Brazzel and Newsom 1959, Carter and Phillips 1973, Guerra et al. 1982), the manner in which A. grandis ensures its survival during the winter months has been difficult to elucidate (Guerra et al. 1982). Undoubtedly, resolving the ecological and physiological behavior of the various populations forming the boll weevil complex, and understanding all aspects of diapause such as development, survival, etc., could ensure that suppressive efforts would be more cost-effective. Guerra et al. (1982) and Guerra and Garcia (1982), reported that overwintering weevils from a subtropical area near Brownsville, Texas do not exhibit classical diapause, and remained physiologically active and reproductive throughout fall and winter. According to Fye et al. (1970), most overwintering weevils in Arizona did not meet the criteria of full diapause. Based on limited studies, watson (unpublished) considered that boll weevils in the South~lest were reproductively active throughout winter and early spring during periods of warm weather. But, the situation had not 17 been unequivocally resolved. The study reported herein was initiated in the Fall of 1986. The objectives of this study were: 1. To determine if the strain of boll weevil in Arizona is capable of entering true diapause. 2. To determine when diapause occurs, proportion of population entering diapause, and factors inducing diapause. 18

LITERATURE REVIEW TAXONOMY The boll weevil Anthonomus grandis Boheman, was first described by Boheman (1843) using specimens from Veracruz, Mexico. In 1913 Pierce collected specimens from the wild cotton, Gossypium thurberi Todaro from Santa Rita Mountains, Arizona and described it as Anthonomus grandis var. thurberiae. Pierce (1913) presented morphological criteria for separating the adults and recommended that this new form should be considered a new species. Werner (1960) and others considered the variety thurberiae to be a subspecies. Warner (1966) reports that in the years since thurberiae was described, taxonomists attempting to separate it from grandis using the characteristics outlined by Pierce met with little success, although the problem was mostly academic since the distribution of the two forms was not known to overlap except for occasional attacks by thurberiae on cuI tivated cotton in Arizona. But in 1963, a population of weevils attacked cotton in the Santa Cruz and Gila River Valleys in Arizona, and the possibility that the irrigated cotton in Arizona might be subjected to severe economic damage by a "boll weevil" caused great concern. Thus, the proper identification of the weevils became necessary, and Warner 19 (1966) undertook an intensive study of more than 4000 specimens representative of the two named subspecies of grandis. She used three characteristics in distinguishing the two species, namely, the curvature of the setae of the pronotum, sculpture of the metepisternum and the shape and sculpture of the scutellum. When she used these characters to define the limits of distribution of thurberiae and grandis, not only was the distribution of the two weevils revealed, but

some populations appeared to differ from the typical forms of both. Based on these three characters, it was possible to name the boll weevil of the southeastern united states, Anthonomus grandis grand is; the thurberia weevil, Anthonomus grandis thurberiae; and the intermediate form, wherein the holotype of grandis falls was termed the "intermediate". But Burke

(1968) reviewing the available evidence considered that the variations in these populations were host induced, and using eight characters, proposed that subspecific nomenclature should be discontinued and that A. grandis be divided into three host races: the Southeastern boll weevil found in Texas and Southeastern U. S., the Thurberia boll weevil found in wild cotton in Arizona and occasionally in llaarby cultivated cotton, and the Mexican boll weevil found in the cultivated cotton of Arizona and Mexico. 20 Allozyme variation among populations of boll weevils in Arizona and Mexico: Electrophoretic techniques enable the determination of genetic differences among individual insects and among populations of insects in a relatively simple manner (Bartlett, 1981). These techniques have also been useful tools in the taxonomic differentiation of closely related species (Sluss et al., 1978). The confusion prevalent in boll weevil taxonomy has created an uncertainty in assessment of the potential for damage by the boll weevil to commercial cotton production in Arizona (Bartlett et al., 1983). Fye and Parencia (1972) discussed these complications and called the weevils in Arizona "complex". Hence, Bartlett (1981) mentioned that although the weevils from Arizona have been the subject of extensive morphological studies, very little is known regarding the population genetics of members of the "complex". He considered that information on gene-flow between populations of weevils in Arizona could help clarify some of the questions raised by Warner (1966) and Burke (1968) on the relationships of the various forms. Bartlett (1981) reported on genetic variation measured in isozyme systems of boll weevil and thurberia weevil populations collected in Arizona. He used electrophoretic 21 techniques to' study isozyme gene frequency differences in samples of three populations of weevils: thurberia weevils, Anthonomus grandis thurberiae Pierce, from bolls of a wild cotton, Gossypium thurberi Todaro; boll weevils, A. grandis grandis Boheman, from bolls of Pima cotton, ~. barbadense L.; and boll weevils from pheromone traps located around a field of short staple stub cotton, ~. hirsutum L. The three sites of collection were only separated by 50 to 210 krn. Based on the results of his study, Bartlett (1981) concluded that, the three collections of weevils were not from the same random mating population, the differences in genotypic frequency were significant between populations, the collections appear to represent three different gene pools with little gene flow between them and hence the three populations may be existing as host' races of A. grandis. He reported that although these results are not surprising when one considers the geographic distances separating the populations, cotton is more or less continuous across these distances and the weevils can very likely cover such distances.

ORIGIN AND DISPERSAL Burke et ale (1986) attempted to develop a reasonable interpretation of the origin and dispersal of the boll weevil based on its taxonomy, biology, host relationships and 22 available historical data. They are of the opinion that A. grandis originated in Meso-America on plants of the malvaceous genus Hampea, and the original populations are morphologically similar to the weevils prevalent in southern Mexico today (i.e., the Mexican boll weevil). The presence of the Mexican boll weevil in western Mexico and Arizona north of its original range on Hampea is considered to be due to the dispersal brought on by adaptation to both wild and cultivated forms of Gossypium. Burke et ale (1986) assume that a fairly long period of isolation of populations of A.grandis must have occurred in northeastern Mexico to give rise to the more or less morphologically distinct southeastern boll weevil, which was first reported in Texas in 1892, and quickly spread throughout the southeastern united states in the early part of this century. They also feel that the increase in cotton production in both western and eastern Mexico resulted in the significant local expansion of the populations already found on wild hosts. The establishment of the weevil on cultivated cotton is considered to be an important factor in the adaptation of the weevil to nontropical and cooler conditions. 23

BIOLOGY

Life History:

Most of the information available concerning the life history of the boll weevil is derived from work performed in the early part of this century (Parrot et al., 1970). According to Cushman (1911), the life history of the weevil may be divided into three phases; the developmental, preoviposition and oviposition periods. He further divided the developmental period into the egg or incubation stage, larval, pupal and postpupal or teneral adult stages. He clarified that the teneral adult stage is the period following the casting of the pupal skin, during which the weevil remains in the pupal cell. In 1912, Hunter and Pierce compiled all previous studies on the biology of the boll weevil into a large bulletin and summarized available information on the life history. The female weevil deposits the egg in a cavity formed by eating into a cotton square or boll. In a few days, the egg hatches into a legless grub which begins to feed making a larger space for itself as it grows. During the course of larval growth, the skin is shed at least thrice, the last being at the time of pupation. After a few days the pupa sheds its skin, completing the transformation into the adult stage. Parrot et ale (1970) mentioned that Hunter and Pierce (1912) either failed to mention the number of larval instars, 24 or were uncertain of the fact. Parrot et ale (1970), using head capsule measurements demonstrated that Anthonomus grandis Boheman molted twice during larval development and had three well defined i~stars.

Developmental period: Many studies have been conducted to date on the developmental biology of the boll weevil, embracing a wide range of time and conditions of humidity, temperature, rainfall, altitude, soil, etc. including all extremes found in the cotton belt. As mentioned by Fye et ale (1969), knowledge about the developmental period of the boll weevil is essential for three reasons: 1) to determine the most efficient temperature for purposes of mass rearing weevils on artificial diet to be used in research and control programs, 2) the test insects should have a comparable rearing background if physiological and ecological comparisons are to be made in the laboratory, and 3) the effects of heat flux on the population should be determined for analysis of the development and dynamics of populations under field conditions. Hunter and Pierce (1912) reported that the immature stages, on the average, require about two to three weeks, and a further period of feeding of about one-third the preceding 25 developmental -time is necessary to complete sexual maturity in order for reproduction to begin. Furthermore, records tabulated by Hunter and Pierce (1912) showed that the length of the developmental period varied with the period of time for which the infested squares hung on the cotton plant after egg puncture. smith (1921) reported on studies performed in Madison, Florida, in the year 1918, and he mentioned that the results of this study are fully in agreement with the findings reported by Hunter and Pierce (1912). smith (1921) showed that development under insectary conditions was much more rapid than under the most favorable outdoor conditions. He mentioned that the development of the weevil was retarded on the plant, more so on the ground, and accelerated in the insectary. He determined that the developmental period averaged ca. 22 days in the field and showed a 6.8 to 7.4 day acceleration in developmental rate in the insectary, when reared on both upland and sea island cotton. Roach (1973) studied developmental changes using time-lapse photography technique.

He found that when held at 26.6°C, the duration of the stages was: 2-3 days for the egg, 1-2 days for the first larval instar, 1-1.5 days for the second instar, 4-7 days for the third instar including the prepupa and 4 days for the pupa.

Fye et al. (1969) studied the developmental period of five strains of the boll weevil at several fluctuating and 26 constant temperatures. They determined that the developmental period ranged from 88 days at 15°C to 17 days at 30°C, while the period increased to 17.5 days at a temperature of 35°C. They partly attributed the absence of boll weevil populations in Arizona in mid summer to the deleterious effect of temperatures between 30 and 35°C. Further, rearing at fluctuating temperatures did not increase the developmental time over the time required at constant temperatures as long as the heat input was similar and the temperatures were below 30°C. watson et ale (1986) determined the developmental time of the immature stage of the boll weevil from egg to adult at four constant and 2 fluctuating temperature regimes, and found that it ranged from 38.3 days at 20°C to 16.0 days at 30 and 35°C, and 39°C was near the upper developmental threshold. They observed that developmental time at the lower fluctuating temperature treatment (21-34°C), was intermediate between that found at 25° and 30°C, which conformed to the expected pattern since the mean temperature was intermediate. Furthermore, the developmental time was also affected by the type of cotton fruit in which the larvae developed, the shortest time occurring in cotton squares, and the longest in bolls (Watson et al., 1986). 27 Preoviposition period, fecundity and oviposition:

Fenton and Dunnam (1929), based on laboratory studies in South Carolina from 1924 to 1926, reported that the boll weevil had a maximum of four generations per season. Studying the life history in field cages in two successive years, Hopkins et al. (1969) determined that five generations of the boll weevil developed, although in the second year the fifth generation adults did not lay eggs because they emerged after a frost. According to Hunter and Pierce (1912), the preoviposition period, the time taken for the adult to oviposit after emergence, ranges from four to 14 days during the breeding season. smith (1921) reported that female weevils reared in the outdoor insectary required on the average, 8.9 days to begin ovipositing, and the period varied from six to 20 days. He further mentioned that boll weevils reared under normal field conditions appeared to have more vitality compared to those bred in the insectary, and gave an average preoviposition period of 7.07 days. In a two year study, Hopkins et al. (1969) found that the preoviposition period averaged four days during the first and 5.2 days during the second year, and exhibited no large differences among generations. As determined by Hopkins et al. (1969), the oviposition 28 period could vary between years and among generations. Cushman (1911) mentioned that the average daily oviposition per female was 4.78 eggs, the maximum number of eggs deposited by anyone weevil during one day was 12, and the average total

oviposition was 221.75 eggs. Since the period of reproductive activity of the boll weevil is very long, the rate of egg

deposition is a question requiring much time for its

determination. Hunter and Pierce (1912) reported that the rate of oviposition is influenced by variations in temperature, relative humidity, and by the abundance of clean squares that the weevil can find. They mentioned that female weevils frequently oviposit until the last day of their lives, but usually a period of a few days intervenes between the

cessation of oviposition and death. Hunter and Pierce (1912)

stated that the known maximum number of eggs laid by a single individual weevil which lived for 275 days was 304, and the eggs were deposited at the rate of 7.6 eggs per day for 41

days. The maximum period of oviposition recorded was 135 days.

Smith (1921) determined that under insectary conditions, the

first and second generation boll weevils deposited eggs for

periods of 39. 7 and 35. 2 days , respectively. They further reported that stUdies on fecundity showed that the average number of eggs per female on upland cotton was 166.1 and the

average number of eggs per day was 4.92, whereas on sea island 29 cotton, the corresponding figures were 113.5 eggs per female and 3.8 eggs per day. Fye (1969) determined that the fecundity of the weevils was highly variable, and the potential was very drastically reduced in the field. He also found that oviposition was erratic but often peaked between the fourth and twelfth week after emergence of the females, with the maximum rate of oviposition varying appreciably from 12 to 41 eggs per week. oviposition of weevils from cultivated cotton was completed between 20 and 30 weeks after emergence and was closely associated with longevity.

Longevity of adult weevils: In considering the duration of adult weevils, many factors should be considered including, the nature of the food supply, seasonal conditions, the sex of the individual and the time of entrance into and emergence from hibernation. Lambremont and Earle (1961), studied the longevity of boll weevils from Mexico and Louisiana under controlled laboratory conditions. Survival data plotted for the colonies approached the typical sigmoid curve characteristic of an animal population demonstrating senescence. They determined that longevity was variable and was a function of sex, culture, and holding conditions and the male weevils from Mexico demonstrated greater longevity with a mean of 121.5 days and 30

a maximum of 199 days. They mentioned that in general, the lifespan obtained in this study exceeded that obtained when weevils were held in the insectary or field cages, and it is to be expected that rearing at lower temperatures could prolong the lifespan even further. On the other hand, Fye (1969) worked on adult weevils collected from cultivated cotton in Arizona and determined that they lived an average of six months in the laboratory and a few lived as long as 11 months in the field.

DAMAGE AND CONTROL

Damaqe: cotton is the only major host plant of the boll weevil. The floral buds or squares are preferred as food and oviposition sites, although bolls are used as alternate ovipostion sites, and bolls and leaves are used as food sources when squares become scarce (Jones et al., 1975). Hunter and Pierce (1912) reported that the destructive power of the female weevil is at least five times as great as that of the male even though the females make only twice as many punctures, due to its habit of distributing its ovipositional punctures among a great number of squares. They mentioned that this great capacity for destruction has been one of the most evident points in the history of the spread of the boll 31 weevil. Prior to ovipositional maturity, females act similarly to male weevils, and both sexes feed continually. The attack of the weevil on the squares results in the formation of an abscission-layer, which causes it to ultimately separate entirely from the plant (Hunter and Pierce, 1912). They also reported that it is usual to find under 10 percent infestation in a given cotton field when the squares have just begun to form, but generally increases rapidly through the season until it is almost impossible to find an uninfested square.

Economic J:mpact: According to Head (1982), cotton producers spend nearly $250 million annually to reduce boll weevil damage, but still lose one to three percent of their crop. Coker (1976), estimated that $12 billion have been spent on this insect since it entered the United states in 1892. Yet, this $12 billion dollar estimate represents only direct costs and is conservative since there are SUbstantial indirect costs attributable to boll weevil infestations.

Control: Chemical control: More insecticides have been applied for boll weevil control than any other crop pest. The U.S. Department of Agriculture estimates that one-third of all 32 insecticides used in the U.S. have been to counter the boll weevil problem. Moreover, the efforts to control the boll weevil have created other costly insect problems, resulting in the rise of secondary pests such as Heliothis spp. to primary status. Within 10 years of the use of DDT on cotton, there were many reports of resistance to DDT in the boll weevil (Roussel and Clower, 1955~ Walker et al., 1956~ Fye et al., 1957). Following these reports, the growers switched to using organophosphorus insecticides, along with many combinations such as toxaphene-DDT (Brazzel and Lindquist, 1960). Although organophosphates have been in use since 1956, and no resistance to them has been documented in the boll weevil, laboratory studies have shown that there is a threat that it could develop (Graves et al., 1967 ~ Urrelo and Chambers, 1978). Studies conducted by Bariola and Bergman (1982), testing several organophosphates and pyrethroid insecticides, showed that the poor control reported by Arizona growers was not attributable to resistance, but to the behavioral traits of the weevil. Considering the monetary and environmental impacts of insecticide-use in boll weevil control, it appears that it is necessary to incorporate other methods of control.

Cul tural Control: Cultural control practices for the boll 33 weevil fall into three major areas: short-season cotton production, trap cropping and fall stalk destruction. Short­ season cotton production is based on the principal that weevils are much more injurious to squares than bolls, and the objective is to have a rapid fruit set before weevil populations build up to injurious levels, thereby reducing weevil damage (Parker et al., 1980). Walker and Niles (1971) deduced that at the time of second generation weevil emergence, about half of the bolls from a rapid-fruiting cotton strain would mature enough to avoid damage while only about one third of the bolls from a slow-fruiting variety would be protected, thereby giving as high a yield of cotton in a compressed fruiting season. Trap cropping for control of boll weevils involves managing a small portion of the cotton field to provide a preferred environment to which the insect will be attracted and can thus be more readily controlled (Gilliland et al., 1976). Although the most advocated method of trap cropping is early planting of a small portion of the field (Gilliland, 1974; Moore, 1983), there has been unwillingness on the part of the farmers to split plant their field (Weaver, 1980). Stalk destruction prevents immatures from reaching the adult stage and eliminates the principal resting site for overwintering weevils (Hunter, 1914). According to Niles et 34 ale (1978), early stalk destruction has been the most consistently and strongly advocated practice for controlling the boll weevil.

Host Plant Resistance: The search for cotton varieties resistant to the boll weevil was initiated around the turn of this century, and one of the first characteristics found to confer resistance to the weevil was okra leaf cotton (Cook, 1906). Hunter and Pierce (1912) reported resistance in red leaf cotton varieties. with the advent of synthetic insecticides in the 1940's, host plant resistance, as a means of insect control in cotton, was shelved for a time (Maxwell, 1980), but in the late 1950's and early 1960's interest in this field was again rejuvenated. Plant characteristics such as pubescence (Wannamaker, 1957), frego bract, red plant color, okra leaf, and other genetic characteristics from primitive cotton lines were found to offer some form of resistance (Buford et al., 1967). During the last two decades, further improvements have been made on existing characteristics and new ones developed. Male sterile cotton (Glover et al., 1975), early abscission of infested squares (Coakley et al., 1969) and nectariless cotton (Niles, 1976) have shown some promise in controlling the weevil. 35 Pheromone traps: Grandlure, the synthetic sex and aggregation pheromone of the boll weevil, elicits behavioral response identical to that produced by male boll weevils (Hardee et al., 1972). The seasonal response pattern includes attraction of male and female weevils (aggregation) of the early overwintering and late dispersing generations (Hardee et al., 1969: Wolfenbarger et al., 1976): and attraction of the females (sex) in mid­ season (Mitchell and Hardee, 1974). Different trap designs have been used for purposes of survey, detection, management and suppression studies on the boll weevil. Leggett and in-field traps have been determined to be more competitive in capturing boll weevils when compared to other traps (Leggett, 1980). During early and late-season, traps should be placed around the field and hibernating sites: whereas in the mid-season, traps should be located in the cotton fields (Witz et al., 1981). They also mention that the ratio of grandlure components, seasonal trap placement, population fluctuations, seasonal response of the weevils and capturing efficiency of traps are some of the factors influencing trap catches.

Eradication: The pilot Boll Weevil Eradication Experiment in southern 36

Mississippi, conducted from 1971 to 1973 was designed based on a number of newly developed suppression techniques (Boyd, 1974). This proj ect was in fact a small scale effort with successive applications of control tactics with emphasis on a massive release of sterile males (Lloyd et al., 1974). Al though boll weevil populations were largely suppressed (NAS, 1975), data available at the termination of the experiment indicated that eradication had not been successful (Annonymous, 1973). Next, the Trial Boll Weevil Eradication Experiment, a three year effort (1978-1980) was conducted on a large scale in North Carolina and Virginia; employing intensive pheromone trapping, reproductive-diapause treatments, growth regulators, and sterile male releases (Ganyard et al., 1981). Although they believe that the weevils had been eliminated from the eradication zone, the National Academy of Sciences was unsure as to whether eradication or suppression had been accomplished (Mussman, 1982). According to Perkins (1980), there is controversy within the entomological community regarding the feasibility of a beltwide eradication program. Although past trials have shown technical feasibility, and there are environmental benefits associated with eradication (Annonymous, 1981); according to ESA (Annonymous, 1978), accomplishing an all out boll weevil eradication effort of such magnitude is felt to be 37 biologically and operationally improbable.

ATERNATE HOSTS

Originally and for some time, the boll weevil was considered to be a monophagous insect restricted to develop only on plants of the genus Gossypium (Cross et al., 1975). Ahmad and Burke (1972) reported that the boll weevils belong to a genus in which the species develop on host plants of narrow taxonomic ranges; and that there were no known instances where they cross family lines in their choice of host plants.

More recently, other plant genera have been added to the host range of the boll weevil (Cross et al., 1975). According to Lukefahr and Martin (1962), the genus Cienfuegosia has a wide distribution in both North and South America, and three species of this genus have been reported to serve as hosts of the boll weevil. They suggested that the weevil may have attacked Cienfuegosia before it was recorded as a pest of cotton in 1885. In their review on the host plants of the boll weevil, Cross et al. (1975), reported that as far as is known, boll weevils can only successfully develop on plants of several genera wi thin the tribe Gossypieae of the family

Malvaceae, and that oviposition and development can occur in the flower buds and/or capsules, dependent on the "biotype" 38 of the weevil ·and the host species involved. They considered that host plants of the boll weevil other than cultivated cotton were relatively unimportant in the united states. They also recorded that in nature, marginal reproduction may occur in Cienfuegosia heterophylla (vent.) Garcke, Hibiscus syriacus L., Pseudabutilon lozani (Rose), and Sphaeralcea angustifolia (cav.) Don., and that although the most important alternate host in the united states may be Cienfuegosia drummondii, it is restricted in its distribution to a narrow strip along the Texas lower Gulf Coast.

stone~ (1968) compiled a list of malvaceous plants which are considered to be hosts of the boll weevil, and divided them according to their use for food or for food and oviposition. The genus Spheralcea is commonly found in Arizona and is found in all areas of the state. He determined that boll weevils fed readily on the fruit, buds and flowers of

~.ernoryi, but failed to reproduce on it. He therefore concluded that these plants can at least provide food in the interim when the weevils emerge from hibernation, prior to the availability of cotton. Moreover, he speculated that boll weevils in Arizona can and do move in and out of hibernation on warm days in winter and then feed on Sphaeralcea. Palumbo (1985) studied the effects of Sphaeralcea spp. on the overwinter survival and reproductivity of boll weevils in 39 Arizona, and -determined that gravid females consistently failed to oviposit on globemallow buds under greenhouse conditions. He also reported that oviposition declined by 54% in cotton squares treated with globemallow extract whereas when buds were treated with aqueous cotton extract, oviposition was observed.

DIAPAUSB Seasonal changes are characteristically cyclic, persistent and geographically widespread. In many parts of the world, environmental conditions suitable for development, growth and reproduction are usually prevalent only during particular seasons (Tauber and Tauber, 1976). Short or longterm, cyclic or acyclic, severe or mild, and widespread or localized changes in the biotic and abiotic factors are characteristic of all environments on earth, whether terrestrial or aquatic (Tauber et al., 1986). Synchronization of growth, development and reproduction with appropriate seasonal conditions is characteristic of all animal life cycles. A unique set of ecophysiological responses regulate seasonal cycles in conjunction with biotic and abiotic seasonal changes in the habitat of every species (Tauber et al., 1983). Hence, the great diversity and variability of seasonal adaptations prevalent within and among 40 species is an· essential feature of phenology. According to Tauber et ale (1986), most seasonal adaptations are less responsive to the immediate conditions of the environment, unlike the features animals have evolved in order to adapt to acyclic phenomena. Hence, seasonal responses are directed at harmonizing the entire life cycle with seasonal environmental changes. The pervasiveness of environmental alterations has ensured that these changes have acted as a major selecting force influencing the evolution of diverse groups of flora and fauna. As a result, a state of dormancy is commonly found in many species, so that they could synchronize their functions during favorable periods while enhancing survival during unfavorable times (Tauber and Tauber, 1986). On considering insect and acarine life cycles, they exhibit striking physiological and behavioral adaptations to the seasonally changing environments (Tauber and Tauber, 1986). Most insects show seasonality in their life cycles. Since the beginning of agriculture, farmers carefully observed the life cycle of insect pests, and silkworm growers tended to retain hibernating eggs in good condition for the following season (Masaki, 1983). The special physiological nature of the diapausing state was recognized for the first time in the latter part of the last century, but the other side of the 41 seasonal regul!!tion system, the photoperiodic timing mechanism was studied nearly half a century later (from Tauber et al., 1986). Since these pioneering works, there has been an exponential rate of growth in research activity up to the 1980's (Masaki, 1983). Through the years, several, at times somewhat conflicting definitions of diapause have been made stemming from the numerous research approaches on the subject. The term diapause was first coined by Wheeler (1893) to describe a resting morphogenetic stage in the embryonic development of the grasshopper, Xiphidium. Andrewartha (1952) mentioned that unfortunately, unnecessary confusion was created in the early years of this century because ecologists used the term loosely in describing any state of arrested development. Shelford (1929) recognized that diapause was a phenomenon quite distinct from the simple inhibition of development by unfavorable environmental conditions, and suggested the use of the term only in instances where development is arrested spontaneously and does not immediately respond to any ordinary amelioration of the external environment. He maintained that the term 'quiescence' should be used to describe temporary inhibition of development by unfavorable environmental conditions, with the resumption of development once the hindrance is removed. Hence Shelford (1929) drew a clear distinction between diapause and 42 'quiescence', although it is difficult to distinguish between these two. Andrewartha (1952) cites many examples to demonstrate that diapause is not always a phenomenon which is clearly recognizable. Subsequently, the term was sometimes used to refer to suppressed growth, development or reproduction at any stage in the development of insects (Lees, 1956). In 1952, Andrewartha published the first comprehensive review on diapause. In this review, he summarized previous research, showed how essential diapause was to the survival of insects in seasonally inhospitable environments, placed diapause within an ecological setting, defined and clarified terms, and also provided a comprehensive perspective for the analysis and interpretation of data (Tauber et al., 1986). According to Andrewartha (1952), in considering diapause, it is useful to think of development in terms of 'morphogenesis' and 'physiogenesis', the morphological and physiological aspects, respectively. He defined it as a stage during morphogenesis of some animals during which growth and development are suspended or greatly reduced. He further stated that physiogenesis may also be suspended under conditions usually conducive to growth and development but under some conditions, such as relatively low temperatures, may be resumed and progress to a stage enabl ing growth to 43 proceed in response to stimuli suoh aD warmth and moisture. For ecological purposes he oonsidors diapauoQ as a stage in physiogenesis which needs to be oompleted bofore morphogenesis can be resumed. The 'diapause stago' io a otage in the life cycle when morphogenesis is almost at a otandstill, and 'diapause development' to mean physiogonQsio, whioh proceeds during the diapause stage, in preparation for aotive morphogenesis, indicating the oomplotion of the diapause stage. He further elaborated that oloar-out distinction between diapause and non-diapauso stago in tho life oyole are unusual in nature and at loast slight morphologioal ohanges can be witnessed during diapause whilo physiologioal prooesses constituting diapause development may not bQ restrioted to the diapause stage. Lee's (1956) monograph on the physiology of diapauae in arthropods was the next major oornorotono on diapause in insects, in which he analyzed diapaufJo from both physiologioal and ecological angles. The definition of diapauso was later expanded by de Wilde (1962) to inoludo an array of physiological and behavioral ohangos oonatituting tho diapause syndrome. In 1976, Tauber and Tauber roportQd that diapause is a 'widespread form of dormanoy' soon among inseot and acarine species and that its initiation, maintenanoe and termination, postdiapause development, and finally growth, 44 development and reproduction represent well defined phenological events in the life history of insect species. They considered that the successful adaptation of organisms to the cyclic seasonal changes in their environment would be determined by the precise timing of the above mentioned events. In their treatise, Tauber et ale (1986) attributed the difficulties encountered in defining diapause as a specific physiological phenomenon to its great variability between species, polyphyletic origin, and function as a timing device for various phenological adaptations, including many cases of dormancy, seasonal migration and polyphenism. They stressed the concept that the physiological stability of the insects change with the progression of diapause; the full expression of which follows a predictable course, hence refering to the dynamic stage of diapause with multifaceted symptoms thus recognizing it from a broader angle. Tauber et ale (1986) further states that diapause serves to maintain insect life cycles in phase with the changing seasons, and define diapause as tI ••• a neurohormonally mediated, dynamic stage of low metabolic activity. Associated with this are reduced morphogenesis, increased response to environmental extremes, and altered or reduced behavioral activity. Diapause occurs during a genetically determined stage(s) of metamorphosis and 45

full expression develops in a species-specific manner, usually in response to a number of environmental stimuli that precede unfavorable conditions. Once diapause has begun, metabolic activity is suspended even if conditions favorable for development prevail. II They further explained that many insects undergo specific physiological, behavioral and morphological modifications enabling them to meet the oncoming adverse seasonal extingencies due to their ability to perceive environmental cues signalling these oncoming events, thus emphasizing the primary controlling influence of diapause­ inducing token stimUli or other environmental factors preceding the seasonal change. They termed the modifications which occur in a species-species sequence the \ diapause syndrome' •

Diapause-Mediated Dormancy, Seasonal Migration and Seasonal polyphenism: Diapause can have several ecological manifestations which are interrelated: dormancy, seasonal migration and seasonal polyphenism~ and diapause is usually, but not always, the pivotal adaptation of all three and may involve a delay in reproduction. Tauber et al. (1986) discussed these three major ecological expressions of diapause in detail and analyzed their relationship to diapause in order to illustrate their 46 roles as compQnents of seasonal cycles.

Dormancy: overwintering in insects usually involves some form of dormancy and dormancy is often designated as either quiescence or diapause (Lees, 1956). Gehrken (1985) states that simple quiescence leads to the suppression of developmental processes, is directly imposed by adverse environmental conditions, and recovery resumes soon after the conditions improve; whereas, diapause is a genetically controlled suppression of development which typically begins prior to the onset of the adverse physical conditions and may not be terminated until long after the improvement of the conditions. According to Tauber et al. (1986), the majority of cases of dormancy in insects are diapause mediated. Hence, it occurs in response to specific seasonal cues or token stimuli, to which the insect responds by embarking on a series of neurohormonally mediated physiological and behavioral changes, thus preparing itself for the unfavorable conditions in advance. In such instances, diapause prevents the premature termination of dormancy which could lead to untimely growth and reproduction.

seasonal Migration: Insects undergoing diapause-mediated migration perceive seasonal cues far in advance of the 47 seasonal change, and in response undergo an endocrinologically mediated state of reduced metabolism and lowered responses to vegetative and reproductive stimuli. These migrations are timed to occur during a very specific period in the course of diapause, and hence these migrations to and from the diapausing sites are an outcome of interaction between the physiological state of the insect and the seasonal factors that preceded the environmental change, and are not influenced by the conditions of the immediate environment (Tauber et al., 1986). They also clarify that although nearly all insects show some migration or movement to the shelter-sites during diapause, its relation to dormancy and the degree to which it is expressed varies considerably.

Seasonal polyphenism: Many insects show annually repeating changes in color and/or the structure of their bodies and wings in adaptation to seasonally recurring factors in the environment. Diapause mediated seasonal polyphenism are changes which are induced and expressed at specific times during the course of diapause and may have a protective function (Hazel and West, 1983). According to Tauber et ale (1986) they may also be of use in the efficient allocation of energy between wing development and seasonal migration, and growth and reproduction, and may also contribute to pre- or 48 post-diapause· development during periods of seasonal transition. Lees (1961) reported on the endocrinological link between seasonal polyphenism and diapause, while Hazel and west (1983) showed that it is influenced by token stimuli influencing diapause. Based on these data, Tauber et ale (1986) concluded that these phenotypic changes occur as a part or in association with the diapause syndrome although their relationship seems to differ among species.

Diapausing stage: Insects express high inter- and intra-specific variability in their characteristic diapausing stage, but diapausing stages are species specific. While some are mainly a function of the genetic makeup of the relevant species, others are connected to differences in environmental conditions before or during diapause. In general, diapause occurs in only one stage and this stage is central to synchronizing the life cycle with the seasonal environmental changes both before and after dormancy (Tauber et al., 1986). Andrewartha (1952) recorded that diapause may be obligate or facultative. He mentioned that when it is obligate, it is inherent and seems to occur independent of environmental variation, and every individual in every generation experiences diapause, the life cycle being termed uni-voltine. 49

On the other hand, facultative diapause arises in response to an appropriate environmental stimulus and is usually associated with a multi-voltine life cycle. As mentioned by Masaki (1983), it is important to keep in mind that in the course of evolution, intricate interactions between different stages within each life cycle and also between those of different species may be possible, and the diapausing stage affects the seasonal arrangement of the whole life cycle, and as a result, the environmental pressures brought on other active stages is dependent on the diapausing stage. Thus, clearly, the fitness of the whole life cycle is an important consideration in the selection of an optimal seasonal strategy.

Diapause Induction: The primary feature of diapause is its anticipatory nature. Insects could perceive token stimuli signalling future deterioration of the environment far in advance of the diapausing stage and store the information for later translation into neuroendocrine functions in the form of diapause induction. Biochemical, physiological and genetic mechanisms are involved in information storage and translation. Tauber et al. (1986) therefore mention that the sensitive stage has a vital function in the life cycle since 50 it determines whether development proceeds in a diapause- or reproduction-destined course, and is involved in the perception of environmental cues and information storage for later translation into neuroendocrinal function. Diapause-inducing stimuli, like diapause, are perceived only during specific genetically determined stages, and while in some species, the sensitive stages and the diapausing stage may be widely separated, in others, especially in those diapausing as adults they overlap (de Wilde et ale 1959: Tauber and Tauber, 1970). Kono (1982) reported that environmental factors such as the type and quantity of food can influence the sensitive stage. According to Tauber et ale (1986), the position and extent of the sensitive period in the life cycle, and the relative sensitivity throughout the sensitive period are all determined by both intrinsic and environmental factors. Taylor (1980) mentions that in nature, the proportion of a population entering into diapause and the depth of diapause are determined by the degree of coincidence of the sensitive stages and the diapause-inducing stimuli, the effectiveness of these stimuli, the age-class structure and the growth rate of the population. Hence, he considers that in the field, all conditions affecting population parameters interact with the token stimuli and the genetic characteristics of the 51 population to-have a profound effect on the percentage and depth of diapause at any given time. Diapause syndrome: The neuro-endocrinal, metabolic, behavioral and morphological changes occurring following the perception of the diapause-inducing stimuli, constitute the diapause syndrome. According to Tauber et al. (1986), the diapausing organism characteristically undergoes a sequence of events within each of these categories, which could very often be represented by a U-shaped curve, consisting of the prediapause, diapause induction and intensification, diapause maintenance and termination and the postdiapause transition period. They further elaborated that in all cases the diapause syndrome takes on a species-specific pattern, although some aspects such as reduced metabolism are shared by all animals, while others such as suppression of reproductive function is restricted to adult diapuase.

prediapause: As mentioned before, the ability of the insect to reach the sensitive stage at the appropriate time of the year would determine its successful entry into dormancy. Reaching this stage too late or too soon could both be disastrous, especially in instances where the insect has a relatively long generation time. Tauber et al. (1986) 52 emphasize the -importance of the behavioral and morphological changes preceding diapause to the diapause syndrome. These changes occur during a particular phase of the life cycle in response to seasonal cues, and are vital to, the successful induction of diapause at the correct time, reaching a suitable site in which to undergo diapause, and hence to survival itself. Three essential features associated with prediapause are: the regulation of growth and reproduction ensuring that the diapausing stage is reached before seasonal changes occur, buildup of metabolic reserves required for survival during dormancy and the development of behavioral and morphological changes aiding in the movement to the diapausing site and protection during dormancy. According to Kono (1980), these stages may demonstrate increased feeding activity during the prediapause stage, and the energy derived from it is often used in the buildup of reserves for diapause.

Diapause intensification: Early during diapause initiation, a noticeable reduction in feeding and growth rates could be observed. Related to these external manifestations, many measurable internal changes could be seen to occur in regular sequence as diapause commences and intensifies (Tauber et al., 1986). They note that the depression in oxygen 53 consumption is often measured, indicating the reduction in metabolic activity, typical of diapause; and hence is a good indicator of diapause depth. Further, intensification of diapause could be illustrated by several other factors, including, decrease in RNA synthesis, decrease in muscular response to electrical stimulation, altered sensitivity to applied or injected hormones, intensification of diapause color, etc., and environmental conditions often have a profound effect on the successful induction and intensification of diapause.

Diapause Completion: Diapause induction and intensification are followed by a phase of diapause maintenance during which time all or most of the diapause symptoms specific to the species could be seen (Tauber et al., 1986). Moreover, it is a time during which the organisms are sensitive to token stimuli and thermal reactions are altered from the nondiapause pattern such that growth and development are prevented even if environmental conditions are favorable. As reported by Hodek (1983), recent observations especially with diapausing adults and larvae do not conform with the traditional concepts of diapause. It has been demonstrated that diapausing animals concurrently undergo changes necessary for the timely completion of diapause, and these changes 54 constitute 'd·iapause development'. Tauber et ale (1986) considers that since the knowledge on the ecological and physiological processes occurring during diapause is very limited to enable us to apply specific terms to events during diapause, the term 'diapause development' is consistent with the fact that diapause involves numerous simultaneous and/or serial processes which eventually leads to its completion. Two types of interlocking processes, diapause development and activation, have been considered to lead to the termination of diapause. Hodek (1983) distinguished between these two processes by using two neutral terms. Horotelic completion of diapause meaning evolving at the standard rate, for diapause development; and tachytelic completion of diapause or evolving at a rate faster than the standard rate, to describe activation. The use of these terms emphasizes the dynamic aspect of diapause and helps avoid the criticism over the ambiguous term, 'diapause development'. Furthermore, although diapause could be completed by either horotelic or tachytelic processes, activation early in diapause leads to a longer tachytelic completion since the horotelic processes are not far advanced than if activation occurs when the horotelic processes are nearing completion, when a relatively weaker stimulus could lead to the completion of diapause after a shorter activation delay (Hodek, 1983). 55 As mentioned by Andrewartha (1952) the prerequisites for both diapause development as well as activation are normally met with under natural conditions. Hodek (1983) considered that diapause development can proceed in autumn and winter during periods of low temperatures and short photoperiods, and is followed by vernal activation which coincides with increase in temperature, light intensity, and day length, the appearance of essential food, and the beginning of the rainy season. He therefore noted that laboratory studies should take into consideration the stimulating effect of environmental change during transfer from outdoors to the laboratory. The importance of photoperiod and temperature as major factors in the environmental regulation of insect diapause has been extensively reviewed by Lees (1956) and Tauber and Tauber (1976); although most of the information available relates to winter diapause (Hodek, 1983).

1. Diapause-Duration: Diapause-duration is a species­ specific and/or strain-specific character and can range in nature from several weeks to several years, and during this time, the depth of diapause as well as the insect-response to environmental factors change during fall, winter and spring in a species- or strain-specific pattern (Tauber et al., 1986). They report that in nature, the length of diapause 56 ultimately depends on the interaction between genetic characteristics of the species, strain, or individual, environmental factors influencing diapause depth, the sensitive stages perceiving the stimuli, and the environmental condi tions determining rate of diapause development. According to Tauber et ale (1986), "insects mayor may not rely heavily on predetermined conditions to determine diapause duration. Nevertheless, it has been well demonstrated that environmental factors during diapause strongly influence the course and duration of diapause."

2. Diapause Maintenance: As mentioned by Hodek (1983) even though there is considerable agreement on the gradual progress of diapause development, there is a diversity of hypothesis on the underlying mechanisms. Yet, in nature, sensitivity to day length and altered thermal thresholds are the most common factors (Tauber et al., 1986). Very often, there is a gradual change in response to diapause-maintaining stimuli with the progress of diapause (Tauber and Tauber, 1976). It has been reported that insects usually undergo a gradual reduction of sensitivity to day lengths during photoperiodically maintained diapause, and similar alterations occur in insects' responses to temperature (Ando, 1983; Tauber et al., 1983). 57 In species where more than one factor maintains diapause, the diapausing organism may exhibit simultaneously, both sensitivity to photoperiod as well as a lowered thermal range for diapause development (Tauber et al., 1986). Moreover, they report that different levels of the same diapause-maintaining factor may function during different phases of diapause. For instance, according to Tauber and Tauber (1973) in the Mohave strain of the green lacewing, Chrysopa carnea, the autumnal phase of diapause is maintained by day length, whereas the hibernal-early vernal phase is maintained by the absence of prey. Hence, even though the abiotic factors may be favorable for breeding, diapause is maintained until prey becomes available. Similarly, a two-phase diapause is witnessed in the european corn borer, in which photoperiod maintains the first phase of diapause, while water intake is required for the termination of the second phase (Beck, 1967).

3. Diapause Termination: The manifestation of diapause completion involves endocrinological changes associated with maturation of gonads, mating and oviposition, but, the causes of diapause completion still remains obscure. Hodek (1983) considered that although the concept of diapause development has been almost generally accepted, the phenomenon of activation remains rather vague. In 1952, Andrewartha's theory 58 of diapause completion stressed on the 'horotellic' process of diapause completion. Moreover, in spite of the warning given by Norris (1964), of the capacity of diapausing adult insects to respond to environmental activation other than photoperiod, it is this process which has been given considerable attention. According to Hodek (1983), it may be due to the possibility of "unambiguous interpretation" of this mode of activation. In many instances, it has been found that the rate of diapause development is higher at warmer temperatures (Tauber and Tauber, 1976), and that diapause completion has two optima, one at low, and another at higher temperatures (from Hodek, 1983). Hodek (1983) mentions that probably the activating role of temperature and photoperiod are qualitatively different, and moreover, although the activation by photoperiod and temperature was not needed in many instances, the promotion of tachytelic processes by 'warming', improvement of food medium, injury, or increase in light intensity had been ignored. Furthermore, Hodek (1983) states that:

" ••• under irregular c1 imatic conditions, a strategy invo1 ving many mechanisms of diapause completion may have greater survival value, and both mechanisms needn't work concurrently in the same area. A trait may have been conserved from the past, or may have been brought in by 59 immigrants from regions with different climates. An absolute distinction between diapause development and

diapause development and diapause activation cannot always be made and the processes leading to diapause completion still represent a black box."

It is therefore evident that diapause is a dynamic state characterized by physiological changes; and these changes could even occur if the animals are held under constant conditions

(Tauber et al., 1986). They consider "that the physiological changes within the diapausing organisms, the innate characteristics of the species or strain, as well as the seasonal environmental changes contribute to the dynamism of the diapausing state.

Incidence of Diapause in the Boll Weevil:

Early workers believed that the adult boll weevils were forced into hibernation by a lack of food prior to or following frost in the fall or when the mean temperature fell between 55° and 60°F (Hunter and Hinds, 1904; Newell et al., 1926). In 1959, Brazzel and Newson demonstrated that the boll weevil adult enters reproductive diapause prior to seeking hibernation sites in late summer and fall. They characterized the diapausing state in this insect to be associated with cessation of gametogenesis and atrophy of gonads, increased fat content, decreased water content, and a decreased 60 respiration rate. Based on their studies conducted in Louisiana, they reported that diapause occurred in some individuals as early as June 30th and movement to winter quarters by August 16th during 1957. Diapausing weevils were found in ground trash during all months of the year except for June and July, and males resumed spermatogenesis prior to departure from their winter quarters whereas females had to feed on seedling cotton before oogenesis could begin. Many workers categorize overwintering boll weevils based on their reproductive status and fat content in the abdomen as being in 'intermediate' or 'firm' diapause (Walker and Brazzel, 1959; Lambremont, 1961). Only those individuals having poorly developed reproductive organs and sufficient fat to obscure the tracheae and other internal organs when viewed through the abdominal terga, i.e., 'in firm' diapause, are considered to be capable of surviving the winter (Walker and Brazzel, 1959). Yet, Lambremont (1961), found the 'intermediate' weevils in ground trash in January in Louisiana. Mitchell and Taft (1966) demonstrated that it is illogical to assume that 'fat' weevils are capable of surviving the winter and that weevils need very little fat to survive the winter. They considered that the atrophied condition of the reproductive organs is a much better criterion of diapause in the late season weevil than the fat content. They further explained the presence of large amounts of fat in diapausing weevils as being incidental 61 to the occurrence ~f diapause and that it is probably due to the fact that weevils continue to feed at a time when their metabolic rate and food requirements are considerably reduced. Studies conducted in the subtropical areas of Texas during 1978-1980 revealed that the boll weevils collected during the non­ cotton season remained physiologically active and could remain reproductive throughout winter, provided proper nourishment was available from cotton regrowths or seedling plants in unattended or abandoned fields. Bergman et ale (1983), and Bariola (1984), reported similar findings in Arizona where they determined that reproductive boll weevils were found to occur during winter months as long as cotton bolls or squares were available as food. Lloyd and Merkl (1961), and Mitchell and Mistric (1965) mentioned that the initiation of diapause in the field was closely associated with the onset of maturity of the cotton plants. Lloyd and Merkl (1961) found that in Mississippi, diapausing segments of the weevil populations moved to their overwintering quarters well in advance of the first killing frost. It is interesting to note that Mangum et ale (1968), determined that diapause could be induced in adult boll weevils by exposing eggs to 11-hour periods of whi te I ight daily and subsequent stages in darkness. They reported that adults responded to different photoperiods only if the immature stages were held in darkness. Various environmental factors have been shown to influence 62 the induction of diapause in insects. Cobb and Bass (1968) found that when newly emerged boll weevils collected from squares during mid-June to mid-August were subjected to various combinations of food, temperature and photoperiod; diapause was found to occur in certain combinations of these variables, but not when they were individually exposed to each of these factors. In general, highest diapause incidence and fat accumulation occurred in the groups subjected to a 80°F, 10-hour photoperiod, a 50°F, 14-hour dark period, and fed square or bolls. Diapause in males seemed to exceed that seen in females and less fat accumulation was witnessed in those fed on the laboratory diet. As mentioned by Carter and Phillips (1973), boll weevils diapause in the tropics with only minimal changes in photoperiod and temperature, and hence it is logical to assume that these weevils could respond to host plant maturity and initiate diapause as a means of circumventing the oncoming dry season. They conducted research on the effects of cotton plant maturity, abscisic acid, and an anti-auxin on diapause response in the boll weevil. Their results showed that the female boll weevils are very sensitive to the physiological condition of the cotton plant, whereas the males are relatively less sensitive to the plant and more sensitive to photoperiod. They also found that the addition of abscisic acid to the synthetic medium affects the fecundity and diapause response and spraying anti-auxin on the cotton plant promotes diapause in 63 the weevil. In earlier investigations conducted by Sterling (1972), to determine whether differences exist in the ability of boll weevils to survive the winter when larvae were raised on different kinds of food, greatest survival was obtained from boll-reared weevils (l-S%), relative to field-collected adults (O-S%) and those reared from squares (0-5%). He considered that the intermediate survival seen among the field-collected adults was because they had presumably fed on both bolls as well as squares. There has been much interest concerning the accumulation of foodstuffs, particularly lipids in relation to diapause in the boll weevil. Lambremont et al. (1964) reported that the type of fat deposited in the diapausing adults was a function of adult diet. They also considered body fat buildup to be correlated wi th diapause induction. Nettles and Betz (1965) mentioned that bolls contain 5-S fold higher sugar content than squares and Betz and Lambremont (1967) observed that glycogen was a much more labile storage component and is used up early during the overwintering period. Increased sucrose in the adult diet with a concomitant decrease in protein was found by Tingle et al. (1971) to promote diapause. survival of overwinterinq weevils: survival of the adult boll weevil during the hibernation period depends on the ability of the weevil to seek suitable 64 hibernation sites or microenvironments offering maximum protection which in turn would determine the subsequent early cotton season population (Taft and Hopkins, 1966). Hence, hibernation and winter survival of the boll weevil has been investigated by entomologists for many years. Boll weevils have been found to hibernate in surface ground trash in wooded areas adjacent to infested cotton fields, weed and grass growth on ditch banks, farm buildings, straw piles, spanish moss, under bark of trees, and in late-maturing cotton bolls (Cowan et al., 1963). They also reported that a high percent carryover of boll weevils from one crop year to the next occurs in surface ground trash adjacent to infested cotton fields. Taft and Hopkins (1966) determined that in South Carolina, survival was greater in wood trash three inches deep with no moisture than in the treatments at other depths and receiving normal rainfall of 14.6 inches. But, laboratory studies conducted by Leggett and Fye (1969) in Arizona indicated that survival and longevity after emergence increased when moisture levels in the bolls and in the simulated trash in which the weevils were hibernating were above 0.5 and 0.044g of water /g of boll and trash respectively. In 1942, Bondy and Rainwater had found that only a small percentage of weevils survived even the mildest winters and that temperature was the most important factor affecting survival. They determined that during a four year period when the minimum temperature was below 15°F, the average survival was 0.21 per cent as compared with 5.67 65 percent obtained for the five years when the minimum temperature was 19°F or above. They also showed that a relatively large number of weevils hibernated in spanish moss when it was found adjacent to cotton fields in South Carolina. Fye et al. (1959) conducted experiments in South Carolina and determined that high populations of weevils were found in trash half to three inches deep, and more weevils were found in deciduous leaf trash than in pine straw, and greater numbers existed in slightly moist trash than in exceedingly dry or wet material. They were also able to show that 90% of the weevils move a distance of about 180 feet from the cotton field to hibernate. Bottrell et al. (1972) reported that in the rolling plains of Texas, the primary overwintering habitats were sand shinney oak, Quercus havardii Rydb., chinaberry, and poplar; and dense rangeland stands of mesquite, prosopis glandulosa Torr. They mentioned that hibernating populations were largely concentrated in the proximity of cotton fields, and only a small proportion of the cotton fields situated in open terrain became infested with weevils. Their results are in agreement with the findings of Rummel and Adkisson (1970), who stated that the distribution of infested cotton fields is primarily determined by the presence of favorable overwintering sites within the cotton growing area, and infestations were most often detected only in fields situated less than half a mile from the overwintering habitats. They too noted that more than 50% of 66 the infested fields were located in the vicinity of heavy shinney oak or mesquite stands. Bottger et ale (1964) mentioned that the thurberia weevil occurring in Arizona on wild cotton could only survive the winter as adults in pupal cells within old bolls in cotton fields and in surface trash. In Central Texas, Cowan et ale (1963) determined that boll weevils can survive the intercrop period in bolls on standing stalks within the cotton fields and that they could also overwinter in bolls on soil surface, even during relatively severe winters.

Emergence Profile of Overwintered Weevils: The emergence profile of boll weevils from overwintering habitats is an aspect of boll weevil biology which has evoked much interest, since an understanding of this phenomenon is important in the development of effective control strategies. According to White and Rummel (1978), although hibernation cages have been often used in the study of boll weevil emergence from overwintering quarters, it is difficult to correlate the emergence profile obtained from cage studies with the weevil populations found in presquaring cotton. They determined that pheromone traps provide a relatively accurate index of population size and activity and that ca. the last 10% of the weevils emerging from overwintering sites contributed to the major portion of the population infesting 67 cotton. Mitchell and Hardee (1974) found that weevils in advanced diapause tended not to respond to traps and that it is the females that respond to the traps while searching for more favorable cotton for oviposition. They also reported that weevils in firm diapause remained in the trash during winter months, and hence, it is during the months April to June that trap captures are representative of the total population. Leggett et al. (1988) reported that the emergence profile of boll weevils from their overwintering habitats was variable among years and even among fields within a year, and that the use of heat units was no more accurate than the use of Julian dates in predicting emergence. Moreover, an accurate model cannot be developed unless the factors regulating trap efficiency are known. Leggett and Moore (1982) found that the diet or nutritional history of the weevils is one of the factors affecting weevil response to traps. Segers et al. (1987) reported that in the lower Gulf coast of Texas, diapausing individuals were found in trap catches most months of the year, highest proportions occurring from July through February, while reproductive weevils were caught all year. They also determined that the numbers caught in traps and their state of reproductive diapause appeared to be determined by the availability of fruiting cotton rather than the weather. In Arizona Bariola et al. (1984) determined that trap catches were close to zero during the summer months, June-August, and began to increase 68 in the fall, reaching maximum numbers in January and February. They further reported that relatively large numbers of weevils were being caught during the host-free period suggesting that emergence from the bolls was occurring throughout this period and hence these weevils were in an active state during winter months, in search of hosts or mates. 69

MATERIALS AND METHODS The investigations reported herein were conducted at the Department of Entomology Laboratory, Campus Agricultural Center, Tucson, Arizona. Meteorological records were obtained from the Arizona Meteorological Center.

DIET AND REARING CONDITIONS

The artificial diet used in these studies was basically similar to that described by Hilliard and Keeley (1984). However, reduced amounts of microbial inhibitors were incorporated into the diet mixture in order to facilitate oviposition. Adult weevils were provided pellets of about 0.7 ml diet coated with a 1:1 mixture of bees wax and paraffin wax. Although it was impossible to maintain aseptic-operation conditions in the laboratory, many sanitation practices were adapted to reduce microbial contamination. Special care was taken to eliminate microbial contamination of eggs, by using proper sterilization methods, and by autoclaving the petri dishes and filter papers used for implantation of eggs. Cotton plants of the variety DPL 61 were grown in greenhouses to provide squares and bolls when necessary. 70

SIOCLIMATIC CHAMBERS Modified freezers with temperature control capacity (Partlow temperature control, Model RFC 52) and programmable timers (York Time Switch) to regulate photoperiod were used as bioclimatic chambers in the experiments. The fluorescent light source used during the illumination phase of these experiments was furnished by 3, 20-watt daylight (General Electric) fluorescent lamps. The relative humidity in these chambers was maintained at 70 ± 7%.

SEX SEPARATION Sexes were separated using the rostrum characteristics described by Pierce (1913).

DIAPAUSB DETERMINATIONS Diapause determinations were made by dissecting weevils under water in wax-bottomed petri dishes. Newly-emerged immature (teneral) adults with soft exoskeletons were not included in these determinations. Body fat and gonadal examinations were made using a standard dissecting microscope at lOx magnification. Body fat in live weevils was observed by removal of elytra and hind wings prior to dissection. The amount of lipid tissue was easily discernible under the transparent dorsal cuticle. Upon 71 dissection, the weevils were classified as diapausing and non­ reproductive, intermediate, or active and reproductive (Table 1). Weevils were considered to be in firm diapause when the gonads (ovaries and testes) were atrophied, with no indication of oogenesis in females, and the weevils had some visible fat. Weevils were categorized as active when the gonads were well developed, showing active oogenesis in the females, and usually the weevils had little or no fat. Weevils classified between these categories were judged to be intermediate. Hence, the presence of a large fat body alone was insufficient evidence of diapause, and the reproductive status was considered to be of greater importance in placing individuals into the firm diapause category.

1987/1988 COLLECTIONS Investigations on the survival, reproductivity and seasonal occurrence of diapause were conducted during the 1987-1988 non-cotton season using collections from a cotton field exhibiting a very high boll weevil infestation and low productivity. The field was about 8 ha in area and was located in the Laveen area in Maricopa County, Arizona. Weevils from two sources, pheromone trap catches and field collected bolls were used as representative of overwintering populations. Pheromone trap collections were made using Leggett traps 72 (Leggett and Cross, 1971). Twenty traps, each containing a dispenser treated with 3 mg of grandlure, were positioned peripherally on all sides of the cotton field beginning September 1987 and continuing through May 1988. Lures were replaced every two weeks. The traps were inspected twice a week during periods of high trap catches, but only once a week when the population declined. Immediately after collection, the weevils were counted, dead and injured weevils discarded, and the remaining weevils taken to the laboratory maintained at 28°C and 50-60% relative humidity. The healthy, active weevils were selected for testing. In addition, more than 4,000 dry infested cotton bolls were hand picked directly from the standing stalks during the first week of November 1987. These bolls were returned to the laboratory for further studies. An initial sample of 200 bolls was dissected to estimate the number and percent survival of the boll weevil forms (larvae, pupae, adults and empty developmental cells) found in the collections. The rest of the bolls were placed in hibernation cages.

Hibernation Cage studies: Two large saran screen walk-in cages exposed to ambient weather conditions were installed near the Entomology Laboratory at the University of Arizona Campus Agricultural 73 center in November 1987. The cages used were 3.4 by 1.7 by 1.7 m in dimension and had metal frames covered with drop-over saran screen cage tops. A zip-lock door on one end permitted installation and removal of hibernation material. During the first week of November, about 2,000 trap­ collected weevils were brought to the laboratory and confined in 230 ml paper ice cream cups (25 weevils and a paper towel in each) with mesh-covered lids. These cups with their enclosed weevils were buried in bermuda grass to a depth of about 10 to 12 cm on the floor of the cages. Seventy-five to one-hundred of the field-collected bolls of cotton harboring boll weevils were placed in each of 46 plastic boxes (40 by 27 by 9 cm). These boxes were installed in each of the two hibernation cages on elevated boards 0.8- 1.4 m above the soil surface.

1. Role of Moisture: These prel iminary studies were conducted to determine the effect of moisture on survival, and the emergence pattern of the weevils contained within bolls. The samples placed in one of the hibernation cages were subj ected to the moist regime whereas those in the other cage were kept dry. The dry weight of the bolls was unknown, but the level of moisture in each box was maintained by weighing the box once a week and 74 adding enough water to maintain the bolls at a predetermined weight.

2. Survival: Three cartons holding pheromone-caught weevils, embedded in a 2 cm layer of bermuda grass, were sampled weekly to determine percent survival. survival of the different boll weevil stages in the dry bolls was determined by dissecting 60 bolls (three replicates of 20) weekly from each cage.

3. Emergence Pattern: The two cages were checked for emerging weevils daily. Observations on emergence were commenced immediately after installation and continued through May 1988. These weevils were also used in further tests.

Laboratory Studies: Throughout the period, bi-weekly or monthly samples of 1) trap catches and 2) weevils emerging from bolls were used in the following studies and the data compared. Since large numbers of weevils were caught in traps, larger samples could be used in all studies. However, smaller and variable numbers of weevils from the field collected bolls were available for testing. 75

1. Sex Ratio: Sexes were separated as described previously and the sex ratio determined weekly in the pheromone trap catches (samples

of 100 weevils) and those emerging from bolls (20-60 weevils).

2. Diapause Determination: Weevils from the trap and field collections (pheromone caught, dissected from bolls, and emerging from bolls) were dissected monthly and placed in the appropriate category according to the criteria outlined previously. Again, newly emerged weevils were not used in the determinations.

3. Photoperiod and Temperature on Diapause Development: In an attempt to determine if photoperiod and temperature were diapause-inducing or -terminating factors, cohorts were reared in each of a series of photoperiod/temperature regimes: long photoperiod of 14:100 (long day) and 2SoC, intermediate photoperiod of 12L: 120 and 20°C, and short photoperiod of 10L:14D (short day) and lSoC.

a. Reproductivity: At monthly intervals, samples of weevils from the two popUlations were fed for 2 days, sexed, and the experimental 76 females (10 to 20 per treatment) were individually confined with a male in 28.4 ml plastic cups f.~.tted with cardboard covers. The cups were placed on wire racks and held in the programed bioclimatic chambers, in the regime peculiar to the specific cohort. Each pair of weevils was supplied every 1 to 3 days (as needed) with artificial diet pellets during the light phase. The old pellets were removed and examined for eggs. The effect of the experimental conditions was evaluated by studying ovipositional delay (preoviposition period), incidence of oviposition, egg viability and fecundity during the period of study. Egg viability was determined by mechanically removing the eggs from the diet using a pointer, sterilizing the eggs using 2% formaldehyde for 30 minutes and plating on moist filter paper in petri dishes. The dishes were held at 28-30oC and egg-hatch was observed for up to a 5-day period during which time the emerging first instars were removed daily. In mid-February 1988, sub-samples from the intermediate and short photoperiod regimes were transferred to: 1) photoperiod of 14L:I0D and 25°C, and 2) photoperiod of 6L:18D and 25 C. Observations were continued to ascertain whether the change in temperature and photoperiod would result in activation of diapause development. Tests extended over a 30- 60-day period. 77

b. survival and longevity: Longevity studies were performed on samples of fed and unfed weevils. The weevils were held in the 230 ml ice cream cups described previously. Monthly samples of three replicates of 10-25 unsexed weevils per replicate were subjected to a single unit of test conditions. The three temperature­ photoperiod regimes used in the reproductivity studies were used. All cartons were examined at 2-3 day intervals, new diet added when necessary, and dead weevils sexed, counted, and removed. Observations were continued until all weevils were dead.

1988 COLLECTIONS As a result of an area-wide boll weevil eradication program, weevil-infested fields were found until the latter part of the cotton season. In early September, two fields were located in Avra Valley (Pima county, Arizona), both of which were very heavily infested with weevils and appeared to yield little, if any, harvestable cotton. These two sites were about 10 km apart. The crop in Field 1 (planting date: AprilS 1988, irrigation termination date: September 16 1988) had a high proportion of squares and flowers until its termination in late October (plowed down on December 15, 1988) whereas, the 78 crop in Field. 2 (planting date: April 23 1988, irrigation termination date: September 1 1988) almost wholly consisted of nonpickable bolls at the time of initiation of these studies in early September. The latter field was available for collection (bolls on standing stalks) until it was plowed down on January 15 1989. Random samples of adult weevils were hand­ picked from squares, blooms, bolls and vegetative parts of the plants from Field 1, while in Field 2, the dry bolls were cracked open in order to obtain the weevils. Collections were made twice weekly from the respective fields, beginning in early September and continuing until stalk-destruction. Entry into diapause may be related to the changing physiological condition and fruiting (phenology) of the cotton plant (Carter and Phillip 1973). Hence these two test-fields could provide us with weevils for comparing the effect of plant phenology on diapause induction. The procedures followed in the undermentioned studies are as described for the 1987/1988 collections, unless specified otherwise.

Sex Ratio: Assessments were made weekly on samples from the two fields. 79 Diapausa .Determinations: Bi-weekly samples of weevils collected from the two test fields were retained in plastic boxes lined with paper towels and the weevils fed on diet pellets for three days. At the end of this period, each collection was separated into two subsets using the criteria described by Walker and Brazzel (1959) as follows: 1) inactive, non-feeding weevils found under the paper towels and 2) actively feeding weevils. Samples from the inactive weevils were dissected periodically to assess diapause status. Also, weevils collected in october and November were dissected periodically and the weevils categorized according to their reproductive status.

Photoperiod, Temperature and Food OD Diapause Development: weevils from the two sources were sexed, paired, and fed on fresh, unpunctured squares, blooms, small bolls and artificial diet pellets (twenty pairs of weevils per treatment). The weevils from the two populations were held under two photoperiod-temperature regimes: 1) photoperiod of 14L:10D and 25°C and 2) photoperiod of 10L:14D and 20°C. The diet was replaced every 1-2 days and preoviposition period, fecundity and egg viability assessed over a 30-day period. 80 Photoperiod and Temperature on survival and Lonqevity: weevils from the September and October collections were fed on diet pellets, and placed in the 230 ml ice cream cups (25 per cup, three replicates) and subjected to the two temperature-photoperiod regimes given above. Similarly, samples of unfed weevils were subjected to the same conditions. Survival and longevity were ascertained as previously outlined and observations made on oviposition.

Moisture content: Every two weeks, two, 25-weevil samples from each population were used in moisture determinations. Fresh samples of weevils were weighed and later oven dried at 70°C for 24 h to constant weight for determination of lean dry-sample weight.

Lipid Determinations: Biweekly samples of three replicates of 20 weevils from each population were used in lipid determination studies. Freshly collected weevils were stored in sealed 4 ml vials protected from light under nitrogen at -20°C.

1. Total Lipids: Lipids were extracted from the weevil samples by 81 modification of the procedure described by Bligh and Dyer (1959). The weevils were first weighed and the tissue homogenized in 1.6 ml distilled water using a motor-driven all glass homogenizer. The tissue residue was discarded, and 1 ml 100% methanol, two ml chloroform and 1 to 2 crystals of Butylated hydroxytoluene (BHT) were added to the extract. Pursuant to centrifugation, 2 ml each of chloroform and water were added to 2 ml of the extract to separate the solvents into a two phase system. Next the lipid-rich lower chloroform layer was carefully pipetted out and retained while the upper methanol/water layer was discarded. Anhydrous sodium sulphate was added to the lipid containing chloroform extract to remove traces of water. After 1 hr, the solution was carefully transferred to 4 ml vials, the solvent evaporated under a stream of nitrogen, and the vials capped tightly and stored at -20°C until ready for weighing. Lipid weights were obtained by resuspending the lipids in 1 ml of hexane and transferring the solution with great care into preweighed aluminum pans. The solvent was next evaporated using a gentle stream of nitrogen and the pans reweighed. In all instances, a blank sample was also run to detect any impurities.

2. separation of Lipid Classes: Lipids were extracted from samples by the procedure 82 outlined above, and then separated into five fractions using thin-layer chromatography (TLC). Prescored, channeled TLC plates (Baker SI 250F (4C) 5 by 20 cm) precoated with silica gel were used in these studies, using hexane: ether: acetic acid (60:40:1) solvent system. Initially, phosphotidylcholine-dipentadecanoyl, dipentadecanoin, tripentadecanoin, pentadecanoic acid and cholesterol standards (> 99% purity, u.s. Biochemicals) were separated in order to ascertain the Rf values of the different classes to aid in identification. Lipid samples were dissolved in small amounts of hexane and spotted using a 10 ul syringe and the chromatography was carried out in 21 by 20 by 8 cm glass tanks. The plates were air-dried for 1 minute and then enclosed in a glass jar with a few crystals of iodine. Lipid spots became brown against a yellow background, but the color would gradually fade once the plates were removed from iodine. Hence, the lipid fraction areas were quickly marked out. The five lipid fractions identified in this study by Rf values were, phospholipids, cholesterol, diglycerides, free fatty acids and triglycerides. Hydrocarbon fractions were not considered in these estimations. The fractions were next scraped off the plates, and filtered through glass wool using 10 ml diethyl ether. Trace 83 amounts of BHT.were incorporated, and the samples dried under nitrogen, vials capped tightly and stored at -20°C until ready for estimation. Fractions from the different samples were quantified spectrophotometrically (Model 240) using the vanillin reaction: 1) to the dry sample 200 ml of concentrated sulfuric acid was added, heated for 10 min at 100°C and cooled; and 2) 1 ml vanillin reagent was added to 80 ul of sample, the sample was vortexed and allowed to stand for 30 min. The absorbance was read at 530 nm against a blank. Estimations were made using a standard curve developed using the cholesterol standard.

Late Season Infestation and Survival: In late November/early December, on the standing stalks in two areas of Field 2 were found: 1) very dry bolls, only infested with adult weevils and 2) dry as well as "green bolls", infested mostly with larvae and a small proportion of pupae representing the progeny of a very late generation of reproductive weevil population. The development of immature stages to adults in these late-season bolls, and the percent survival of the different forms was studied by separately collecting 500-700 infested bolls from each of the two areas. The bo~ls were taken to the laboratory and subsamples were first examined for live and 84 dead larvae, pupae and adults as well as empty developmental cells. The remaining bolls were held in plastic boxes in two bioclimatic chambers set at 15-and 20°C and with a photoperiod setting of 12L: 120. Fifty to a hundred bolls were sampled periodically to ascertain percent survival of the various stages.

SPRING 1989 In an attempt to determine the reinfestation potential of the 1989 cotton crop by overwintering populations in and around the two test-fields in Avra Valley, the following studies were conducted.

1. Pheromone traps were placed in the vicinity of the test-fields in February 1989.

2. At the time that pre-squaring cotton was found in the two fields, 6 potted fruiting plants/week/field (raised in greenhouses) were placed in and near the fields. These plants were watered regularly and inspected for weevil infestations 2 to 3 times a week until squaring was initiated in the field-planted cotton, at which time the study was terminated. 85

ANALYSES OF DATA The analysis of variance procedure was used in the analysis and interpretaton of data. When the treatment variances were determined to be significant using the F test, least significant differences (Probability=O.05) were computed to compare means. The SAS GLM program was used in the analysis. 86

RESULTS AND DISCUSSION

1987/1988 COLLECTIONS FROM LAVEEN

Trap Colleotions: From Fig. 1 it can be seen that boll weevils were captured in high numbers in September through April, and peak captures were obtained in November 1987 and February 1988. By May, the numbers caught had declined drastically and only 15 weevils were caught in the traps. It has been reported by many workers that peak captures of weevils occur following cotton defoliation, harvest, and stalk destruction (Ridgway et al. 1971, Merkl and McCoy 1978, Segers et al. 1987). Lopez (1980) found extremely high numbers in traps in Burleson Co. Texas during November and December, which he attributed to the presence of fruiting cotton. In the field under study, unproductive cotton was left in the field until the end of January, when shredding operations were begun. By this time, most farms in the Laveen area had completed the defoliation, harvesting, shredding and plowing operations. Thus, it could be inferred that the large numbers of weevils captured in the traps could be attributed to the management practices followed in the area. 87 Fiq. 1

A

17500

OT-----~----~------~----~----~----~------~--~ Sep Nov Jan Feb Mar Months

~~----~------~----~----~------~----~----~ Sep Oct Nov Jan Feb Mar May Months 88 The emergence pattern does not seem to be related to the temperature data. Walker and Bottrell (1970) determined that peak trap catches were not related to rainfall nor to ground litter temperature. Wade and Rummel (1978) and Rummel and Carroll (1983) determined that the variation in the emergence pattern among years may be attributed partly to plant phenology and climatic conditions at the time the weevils were entering diapause. Based on trapping studies performed in Arizona from 1981 through June 1984, Bariola (1983) reported that trap catches declined during April and were zero from June through August, were low in September and early October, but rose to high numbers in November and December. He also mentioned that trap catches varied greatly among different traps and from week to week. This variability in emergence, and lack of predictability in time and temperature data is also stressed by Leggett et ale (1988). Furthermore, Leggett et ale (1988) reported that using heat units to predict emergence was no more accurate than the use of Julian dates. The average temperature data for the Laveen area during the period of study (Fig. 1) shows that trap catches were not related to the weather data. More than 4,000 weevils were captured during December and January when the mean and minimum temperatures were very low. Leggett et ale (1988) mentioned that the variability 89 associated with the prediction of emergence for anyone field would be greater than predicting mean emergence for a group of fields: and each state or cotton growing area will have a different emergence profile. Thus, although the data obtained in this study is representative of the field under study for the 1987-88 noncotton season, it only represents the conditions in the field and the surrounding area during that season. Also, it has been reported that the overwintered population was active several weeks before the planting of cotton (White and Rummel 1978), and trap catches declined to very low levels in May and June when blooming cotton was found to be more attractive to boll weevils than pheromone traps (Lopez 1980, Rummel and Bottrell 1976). Although Fig. 1 indicates higher levels of weevil activity during the months of February and April 1988, due to the area-wide eradication program carried out in central Arizona during the 1987/1988 cotton season, it was not possible to relate the trap capture index to the infestation of cotton.

Sex Ratio: The percentage of males found in trap collections and those dissected from bolls are represented in Fig. 2. It could be seen that there is a slight variation in the sex ratio of Fig- 2 100

90

80

70 .A...... ' ...... 18 " .... al60 •A...... /S...... A ...... ~ •••••••• •••••••• ••••...• -6,"--' '" CD 6,... "'l::i-'-""" fs

'SOCD ~40 a..CD 30

20

10

O~TI--~--~--~~--~--~--~--~~--~--~--~~--~--~--~ 9/6 9/23 10/6 10/23 11/6 11/23 12/6 12/23 1/6 1/23 2/6 2/23 3/6 3/23 4/6 4/23 5/6 Beginning Date -----.- traps "'--"'---6 field \0 o 91 weevils obtained from the two samples, the females outnumbering the males in trap collections during September through December when compared with the field collections at this time. The average sex ratio for trap collections was 1:1 (1,500 weevils sexed), while a 1.2: 1 (723 weevils sexed), male: female ratio was obtained for the field-collected weevils. In general, a 1:1 ratio was maintained. The results obtained in these studies are similar to those obtained by Mitchell and Hardee (1974). Mitchell and Hardee (1974) maintained that the males predominate in field collections in mid-summer and fall, since the females migrate in search of oviposition sites, while in the spring the ratios are similar in weevils from traps and the field. In 1905, Hunter and Hinds reported a 1:1 ratio except for a higher percentage of males among hibernating weevils. similarly, Brazzel and Newsom (1959) found that weevils obtained from ground trash throughout the year had a sex ratio of 1.5 male: 1 female, whereas that of reproducing weevils was 1:1. But, Brazzel and

Hightower (1960) found a higher percent of males in traps during most of the year except in May and June. Guerra and Garcia (1982) reported higher proportions of males in pheromone trap collections. Hence, as mentioned by Mitchell and Hardee (1974), the sex ratio of the weevils captured in traps is not always representative of field populations. 92

Emerqenoe Zn Hibernation Caqes: A total of 697 weevils emerged at irregular intervals from the bolls held in the cages from November 7, 1987 through April 28, 1988. These, and an additional 157 weevils which emerged from extra bolls collected at the same time were used in the various studies. The cumulative emergence patterns in the two cages are given in Fig. 3. No sustained period of inactivity is apparent, although the average temperatures from the end of November through the first week of February ranged from about -5 to 15°C. Based on studies performed in Arizona, Fye et al. (1969) reported that the lower physiological developmental threshold of the boll weevils was about 13°C. The mean temperature and accumulative heat input were determined to be inaccurate bases upon which to estimate activity (Fye et al. 1970). Therefore, it is not surprising that weevils continued to emerge throughout the period in the test cages. During this period, the daily high temperatures ranged from about 8 to 25°C. Hence, as mentioned by Fye et al. (1970), provided other conditions are suitable, the weevils emerged any time the temperature exceeded the physiological threshold. The highest number of weevils emerged during January and February, although temperatures remained low. By February 6, Fiq. 3 100 _____ ------6 lJ.------­ 90 ,,--';~ --- 1>_'---"-'''/ 80 .Ii 70 i:/ : g / CD ~60 :ii: G) : an /: ~50 :f:' :::J // e40 j./ (3 ..•..••.. 30 ... "", ... _ .. __K···········/l 20

10

O~~I----~--~--~----~--~----~--~--~----~--~----~--~ 11/6 11/23 12/6 12/23 1/6 1/23 2/6 2/23 3/6 3/23 4/6 4/23 5/6 Beginning Date

-6---6-·-6 1.0 ~ MOist Dry W 94 nearly 60% of.the weevils had emerged, and by March 6 more than 84% had emerged. This is in contrast to the results obtained by Bergman et ale (1983), where higher numbers emerged during periods of increased daily maximum temperatures. In our studies, the rate of emergence was decidedly more gradual and seemingly unrelated to temperature fluctuations, since relatively high temperatures prevailed during the months of March and April. Also, about 10% more weevils emerged from the moist regime, probably because the moisture increased survival and/or permitted the escape of the weevils by rendering the bolls softer. Hibernation cages have been used by many workers to study boll weevil emergence pattern from overwintering sites (Hunter and Pierce 1912, Reinhard 1943, Fye et ale 1958), and as mentioned by White and Rummel (1978), the emergence profile of the weevils from overwintering habitats is of great interest in the development of effective control procedures. However, the results presented herein show that the time of peak weevil emergence in cages cannot be related to infestation of presquaring cotton. The same is confirmed from reports from Fenton and Dunnam (1929) and White and Rummel (1978). Bondy and Rainwater (1942) deduced that emergence in cages and those in the open field occurred considerably earlier than emergence from natural hibrnation quarters. Fye 95

et al. (1958). performed studies on weevils collected from several areas in the Carolinas and Virgina. Based on their resul ts they deduced that the timing of emergence of the weevils is related to an ecological adaptation prior to entry into hibernation, leading to the emergence of weevils in spring under conditions of plant growth which would ensure their survival and procreation. cotton in the Laveen area is planted by April, and it starts to develop squares only 5-6 weeks after planting. The weevils cannot reproduce until this time and hence have to feed on leaves, tender stems and leaf buds. One hundred percent of the weevils had emerged by early April in our studies. However, Leggett and Fye (1969) indicated that the early emerged weevils can survive provided they have proper moisture, and according to stoner (1968), Sphaeralcia spp. may provide food for the emerging weevils until the time of cotton squaring. survival in cages: Inspection of the bolls, before placing them in the cages, revealed that there were no live immature stages in the bolls. Initial counts indicated there were 100±15 adult weevils, or about 1 adult per boll, that had been placed in each cage. At the time of placing the bolls in the cages on 96 November 6, 19.87, about 5% of the developmental cells in the dry bolls were empty, showing that about 5% of the weevils had already exited. The results obtained in these studies are presented in Table 1 and Fig. 4. It could be seen that the trap-collected weevils have little chance of surviving the winter until a food source is available in spring. Hence, as reported by Mitchell et al. (1966), weevils emerging from boll and hibernation quarters during winter after all food sources have been eliminated have a very poor chance of surviving to serve as precursors for the spring generations. When these trap­ caught weevils were placed in hibernation material without having been fed, mortality was very high; only 22.7% and 9.3% were surviving by December 6th and January 6th, respectively. As found in the results, weevil survival was significantly higher in the bolls, and more than 10% of the boll weevils survived until the beginning of April 1988. Moreover, significantly higher proportions survived in the moist regime. Based on their studies on the boll weevil complex in Arizona, Leggett and Fye (1969), concluded that low levels of moisture enhance survival and emergence, but reported that a breaking point existed in the moisture­ survival relationships, and higher levels were not necessarily associated with increased survival. Furthermore, the moisture regime(s) tested in these studies cannot be directly extrapolated to the conditions in field habitats. 97 Table 1. Seasonal survival of trap and field-collected boll weevils in emergence cages (Laveen, 1987/1988)'

Percent Survival

Month Field-Collections Trap

Collections Moist Regime Normal (Dry)

11/7 - 11/22/87 68.0 100.0 100.0 11/23 - 12/6 22.7 98.3 98.7 12/7 - 12/22 16.0 85.0 80.3 12/23 - 1/6/88 9.3 51.0 42.0 1/7 - 1/22 4.0 36.7 31.7 1/23 - 2/6 1.3 32.7 27.7 2/7 - 2/22 2.7 23.0 21.7 2/23 - 3/6 0.0 25.7 18.3 3/7 - 3/22 1.3 22.3 14.0

3/23 - 4/6 0.0 12.7 11.7

4/7 - 4/22 0.0 14.7 8.0

4/23 - 5/6 0.0 4.0 3.0 5/7 - 5/22 0.0 2.7 0.0 5/23 - 6/6 0.0 0.0 0.0

'Placed in emergence cages in Tucson on 11/7/87. Fig ... 100 a---tli '\< "~" 90 \~'" \~~ 80 ~\ \\ \ " \\ \ \ 70 \ \ \ \ \ " \ \ \ " \ \ J60 \ \ .~ \ '. \ \ ::J \ \ cn50 \ A. \ " . ... \ .... c \ ". m"", '...... CD~40 a.. " , 8-''' '" '6- "'6... 30 ----..... •••••• --6.-"" ""'...... '--. ---- '-'-"'A ...... ~ - ' . 20 ...... - -'. -----e__ '-" __" .__ -__ -A __...... ~ .'A---- ._ ~.----t!J_ 10 ...... _ ..... -I!)...... •.

...... :n""t!7 ..___ ···-··-··· _ u 0 ----+----.- 11/6 11/23 12/6 12123 1/6 1/23 216 2123 3/6 3/23 4/6 4/23 5/6 5/23 Beginning Date ..-.--.. Traps A'-"'--'" Moist .. ~..... Dry \0 00 99 Based on a 4-year study in South Carolina, Bondy and Rainwater (1942) concluded that only a small percentage of weevils survived even the mildest winters and that temperature was the most important factor affecting survival. They also found that different dates of installation of the bolls in cages, resulted in different survival rates, the highest survival being obtained for the November 15 installation relative to the October 15 and November 1 installations. Earlier installation would force the weevils early into hibernation in a weakened condition, thus showing the practical value of early stalk destruction. The winter temperatures in Arizona during 1987/1988 were relatively low, wi th minimum temperatures of below OoC on some days in December and January. Hence, the mortality rates, and emergence patterns obtained during this season, would very likely be different from those obtained in other years. Moreover, the bolls collected for this study had matured by September, and were left in the field until early November, and at the time of collection were very dry. Therefore, the weevils found within had not been forced into hibernation due to the experimental prodcedure. The results revealed that a small proportion of the weevils found in unproductive bolls can survive in Arizona until February or March when a ready food source (Sphaeralcia spp.) was available. Hence, the weevils emerging throughout spring could be hazardous to the crop of the subsequent season. Yet, as mentioned by Leggett 100 and Fye (1969), additional variables such as prehibernation and developmental nutrition would have to be incorporated into studies in order to arrive at any firm conclusions. The much higher survival rates of weevils within bolls is to be expected, since the trap-collected weevils would move about actively during periods of warmer temperatures, leading to waste of metabolic energy compared to the inactive weevils within the bolls. Thus, it is natural to conclude that weevils overwintering within the bolls play a major role in maintaining populations compared to those overwintering outside the bolls (Fye and Leggett 1969). Cowan et ale (1963) showed that in central Texas, boll weevils can survive from one crop year to the next in bolls on standing stalks, even during unusually severe winters. Their results also indicated that weevils can even survive in fields where stalks were destroyed and plowed down in early winter, although mortality was much higher in bolls buried under the soil surface. These findings were confirmed by Bergman et ale (1983) who showed that it is difficult to predict whether more weevils surived in field cages or in protected shelters, since the results obtained over a period of several years was very variable. Therefore it would be difficult to predict whether more weevils survive in shredded bolls, bolls on standing stalks, or in other overwintering shelters. It is natural that weevils overwintering in the cooler regions of the united states have been selected to survive 101 under more severe winter conditions than that found in Arizona. The higher survival of weevils enclosed in bolls may be due to a high proportion of these weevils being in a physiological state suitable for withstanding the winter months in an unfed condition.

Diapause status: The reproductive/diapause status of weevils in the three categories tested: trap collections, weevils dissected from bolls and those emerging in cages, are given in Table 2 and Fig. 5. Boll weevils were found in all three reproductive states during the period of study. It could be seen that significantly higher percentages of reproductive and intermediate individuals and very low proportions of those in firm diapause were found in the trap collections, relative to the samples from the other two categories. It is only during November through January, that the numbers in the diapausing category tended to increase. In contrast, of those dissected from the bolls, a very high percentage of the weevils was found to be either intermediate or in firm diapause. Moreover, except for those sampled in september, october and February, a large proportion of the boll weevils was in firm diapause. The same was true of the weevils emerging from bolls, except for the fact that there was a decline in numbers of diapausing weevils during February and March. The proportion of weevils in firm diapause was higher among weevils dissected from bolls 102 Tabla 2. Mean percentages of boll weevils in reproductive (R),

intermediate (I) or diapausing (D) categories (Laveen, 1987/1988)

Traps' Bolls-12 Bolls-23

Sample R I D R I D R I D

Sept. 43.3 51.1 5.5 12.0 72.0 16.0 Oct. 36.7 53.3 10.0 8.0 68.0 24.0 Nov. 36.7 40.0 23.3 12.0 24.0 64.0 0.0 26.7 73.3 Dec. 16.7 52.7 20.0 0.0 32.0 68.0 6.7 26.6 66.7 Jan. 16.7 63.3 20.0 2.2 44.7 53.3 6.7 40.0 53.3 Feb. 13.3 80.0 6.7 6.7 60.0 33.3 13.3 53.3 33.3 Mar. 26.7 60.0 13.3 4.7 35.6 60.0 13.3 46.7 40.0 Apr. 20.0 70.0 10.0

'Collected from traps.

2Dissected from dry cotton bolls. 3Emerging from bolls. 103

Fig. s 100 110 A 110

70

110 eo I 40 :10

110

10

0 ~uou_ Slatua ~ MGn1h

100 110 B 110

70

110

110 I 40 :10

110

10

0 A I .. A I .. IllaproclucU_ 8latua ... Cal NGw Deo .-n M.- MGn1h

100

110 C

70

-110 I 40 :10

Il1O

10

0 ....,rocIuoUv. 8latull 1104..., 104 relative to those that emerged from bolls. Bergman et ale (1983) reported that although some of the adult weevils emerging from bolls at the beginning of December exhibit at least intermediate diapause, the weevils in Arizona remain physiologically active throughout winter. These findings confirmed the reports of Guerra et ale (1982) in subtropical areas of Rio Grande Valley in Texas. Bergman et ale (1983) also mentioned that the incidence of diapause increased dramatically in February following emergence from dry bolls. They hence concluded that the weevils produced in late-season bolls overwinter successfully, and the specimens caught in grandlure-baited traps may not be representative of the total pouplation. Based on results obtained in our study also, the data obtained on trap-collected weevils are drastically different from those obtained in those emerging from and found in late season bolls. Mitchell and Hardee (1974) also determined that the percentage of diapausing individuals found in traps during the fall was lower than that found in the field. Fye et ale (1970), determined that the boll weevils in Arizona do not diapause in the classic sense and did not meet the criteria of firm diapause as seen in southeastern boll weevils. They based their deductions .on the fact that the weevils initiated reproductive activities any time stubbed cotton was available, and the fact that weevils were virtually absent in trash in late March, indicating that the weevils 105 were active throughout the year. But, as reported by Segers et ale (1987), the presence of diapausing weevils may be more closely related to the availability of fruiting cotton than the weather, and the incidence of weevils in firm diapause in this current study rose sharply following harvest and stalk destruction. Previous studies by Sterling and Adkisson (1966) in the TLGC also showed that the termination of cotton fruiting resulted in a high percentage of firmly-diapausing weevils in trap collectins, even though the temperatures and day lengths were appropriate for nondiapausing reproductive weevils. Hence, based on the results of these studies, we could deduce that the weevils captured in traps are not representative of the physiological and behavioral state of the entire population. As mentioned by Mitchell and Hardee (1974), the weevils in advanced diapause may not respond to the traps, while the reproducing weevils tend to be caught while in search of new feeding and oviposition sites. They also stated that traps were most representative of the population during the months of April, May and June. Since their work was performed in Mississippi, the timing would be very different among the weevils found in Arizona. Moreover, the presence of Sphaeraelcia spp. as alternate hosts early in the year, would ensure the survival of emerging weevils even though they do not reproduce on this host (Palumbo, 1985). Hence, during the winter months, squaring stubb cotton is the 106 only host on which oviposition is possible. It is therefore very relevant that the high numbers of weevils in the dry bolls exhibited firm diapause, although the condition could vary from field to field, depending on the fruiting condition of cotton during the previous season and the management practices followed therein.

Reproductive Behavior of weevils at Three Temperature/Photoperiod Regimes Assessments on the preoviposition period and egg lay of trap- and field-collected weevils at two of the temperature/photoperiod regimes (2SoC 14L: 100 and 20°C 12L: 120) tested are presented in Tables 3 and 4 and Figs. 6 and 7. There were significant differences in both the preoviposition period and the total egg lay between the two collections, as well as between the two temperature/photoperiod treatments. The weevils emerging from the bolls had longer preoviposition periods, and laid fewer eggs throughout the season. As anticipated, the 2SoC, 14L:100 treatment gave significantly higher egg-lay and shorter preoviposition periods than the 20°C, 12L: 120 treatment. At lSoC 10L: 140, only two of the trap­ caught weevils laid eggs (one each) during the 60-day observational period. Moreover, significant differences in egg-lay were observed between the samples from different months. Fertility was reduced during Oecember and the proportion of weevils laying eggs was lower in the field 107 Table 3. Observations on preoviposition period of boll weevil females subjected to two temperature/photoperiod regimes (Laveen, 1987/1988)'

25°C 14L:I0D 20°C 12L: 120 sample Traps2 Field3 Traps Field Mean Range Mean Range Mean Range Mean Range sept. 5.6 4-8 7.6 5-9 oct. 7.9 5-11 8.6 6-11 Nov. 12.2 8-15 14.2 6-20 16.7 9-21 32.5 25-40 Dec. 16.0 8-18 28.0 14-52 1:5.3 14-17 50.7 47-52 Jan. 13.3 6-18 28.7 12-58 17.0 15-18 33.0 16-50 Feb. 7.7 5-14 25.3 13-47 18.0 15-21 28.4 13-47 Mar. 9.3 4-16 16.1 11-23 10.0 5-16 26.8 16-29 Apr. 5.8 3-15 14.1 11-17

'preoviposition period given in days. 2Collected from traps. 3Emerging from bolls in cages. Table 4. Observations on fecundity of boll weevil females subjected to two temperature/photoperiod regimes (Laveen, 1987/1988)

25°C 14L: 100 20°C 12L: 120

Traps' Field2 Traps Field

Sample % eggs/ % eggs/ % eggs/ . % eggs/ laying feme laying feme laying feme laying feme

September 85.0 103.4 35.0 20.2

October 90.0 83.4 40.0 17.5

November 60.0 54.6 40.0 27.3 35.0 17.1 13.3 10.0

December 45.0 29.6 26.7 12.5 15.0 7.4 20.0 5.7

January 65.0 61.4 20.0 18.7 20.0 12.3 13.3 6.0

February 75.0 59.6 26.7 24.0 25.0 13.2 33.3 11.0

March 70.0 89.1 46.7 25.1 15.0 10.3 26.7 7.5

April 80.0 104.8 35.0 9.9

'Collected from traps.

2Emerging from bolls in cages.

I-' a 00 109

Fiq. 6

80~------~ A

10

o 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 Colleetlon sep Oct Nov Dec Jan Feb Mar Apr Month

80~------~ B 50

10

o 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 Colleetlon Sep Oct Nov Dec Jan Feb Mar Apr Month 110

Fiq. 7 150r------~ A 125

1 2 1 2 2 1 2 1 2 1 2 1 2 1 2 CoII~on sap Oct Nov Dec Jan Feb Mar Apr Month

150r------~ B 125

25

o 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 Collection - Oct Nell Dec Jan Feb Mar Apr Month 111 collected weevils, relative to those caught in traps. At 20°C, reduction in percentage of egg-laying females was more evident in both collections. Observations on egg-fertility revealed that the % egg-hatch was not related to the observed differences in reproductive pattern. Egg-fertility ranged from 45-95%. Negative criteria such as suppressed developmental and metabolic rates are usually used to identify insects in diapause (Gehrken 1985). Beck (1980) mentioned that the pre- diapause reproductive system of newly emerged adults is usually at an early stage of development and remains relatively undeveloped throughout the diapausing period. Therefore, mauturation of germ cells after diapause termination may require much time. Walker (1967) reported that diapause in boll weevils is not the rigid state that typifies this physiological condition in other insects. He mentioned that certain weather conditions or the phenology of cotton plants in a particular field may influence diapause reversion in the fall, and that this premature breaking of diapause may significantly affect population buildup in the fall. Data obtained in the studies reported herein show that diapause-termination and post­ diapause morphogenesis are related to the temperature/photoperiod conditions, and collection time. Harris et al. (1966) determined that the average mean length and range of preoviposition periods were variable according 112 to the collection time; the weevils collected earlier in the season, eg., in september, began ovipositing earlier than those collected in october. However, they found that some females had a preoviposition period shorter than one week until night temperatures had dropped to less than 50°F. Studies on diapause-inducing and diapause-suppressing photoperiods have indicated that photoperiods of about 12 hours or less induce diapause while longer photoperiods suppress diapause (Earle and Newsom 1964, Mangum et al. 1968). Moreover, Mangum et al. (1968) deduced that adults responded to different photoperiods only if the immature stages were held in darkness. It is therefore clear that the prerequisites for diapause development and activation are usually fulfilled in nature (Andrewartha 1952). Diapause development proceeds in fall and winter during periods of short day lengths and low temperature, followed by activation during spring coincident with increases in photoperiod and temperature, availability of food and arrival of rain (Hodek 1983). In the interpretation of the results of these studies, it is important to note that diapause can be completed by both horotellic and tachytellic processes. Yet, as mentioned by Hodek (1983), it is difficult to clearly distinguish between diapause development and activation. He further states that activation early in diapause when horotellic processes are not far advanced, would result in tachytellic completion lasting longer, than if activation occurs when horotellic 113 processes are further advanced, or almost completed. In the latter instance, a weaker activation stimulus would be sufficient to produce the same response in a shorter activation delay, and the threshold for reproduction is exceeded when the two mechanisms are mutually complementary. Hence, it is not surprising that weevils collected in early fall and spring had shorter preoviposition periods and laid more eggs than those collected in late fall/winter. Results obtained by watson et ale (Unpublished) showed that weevils collected from pheromone traps during winter had a mean oviposition delay of 13.6 days at 30°C compared to the short period of 3-5 days found in newly-emerged adults. They found that both the duration of oviposition and the number of eggs produced were considerably lower in the weevils collected from traps in winter. Therefore, these findings are in agreement with the results reported here. Guerra et ale (1982) determined that weevils collected from traps during the fall, winter and spring in the Rio Grande Valley, Texas, oviposited within 2-5 days in the laboratory, and fecundity was never reduced. But, it is interesting that no fertile eggs were obtained in the weevils caught by them during December to February, and egg fertility was only restored after feeding the weevils for 10 to 20 days on cotton squares. They related the infertility to a 'nutritional deficiency' and felt that it may not be caused by a diapausing condition, and that the recovery of the insects on the removal of the \ adverse 114 conditions' is characteristic of quiescence. However, it may be that food or climatic conditions were necessary stimuli aiding in the completion of processes associated with diapause completion and post-diapause development.

Transfer to Activating Conditions: Fecundity data on weevils transferred from 20°C, 12L:12D (November and December collections) and lSoC, 10L:14D (January collection) to 2SoC at 14L: 100 and 8L: 160 are presented in Table S. comparisons on changes in fecundity were related to weevil samples retained under the conditions prior to transfer. The results indicated that weevils transferred from all three treatments mentioned above were in a condition, where reproduction could be stimulated at higher temperatures. Significant differences in egg-lay were obtained after transferring to 2SoC. The 8L: 16D diapause-stimulating photoperiod, did not cause a reduction in egg lay compared to the 14L: 10D, diapause-inhibiting photoperiod. The mean egg lay for weevils held under the previous exposures was S.3/female, whereas an egg lay of 27.2- and 23.6/female was obtained for weevils held at 2SoC, 14L:10D and 8L:160 photoperiod, respectively. The fertility obtained at the two photoperiods was not found to differ significantly. Thus, it is likely that once diapause development is completed, higher temperatures may be more important than photoperiod in termination of diapause and post-diapause development. Weevils that had been 115 Table 5. Effect of temperature and photoperiod on diapause development and completion in boll weevils, measured by increase in egg-lay after transfer to activating conditions (Laveen, 1987/1988)

Sample Previous until Control2 25° Exposure (14L: 100) (6L: 180)

11/87 20°C 12L: 120 2/16/88 10.7 44.0 24.3 12/87 20°C 12L: 120 2/16/88 5.3 26.7 34.3 1/88 15°C 10L: 140 2/16/88 0.0 11.0 12.3

'12 pairs per replicate, 3 replicates measured over a 30-day period. 2control: Previous exposureto the other samples which had been collected 1-2 months earlier. 116 previously held at 15°C, 10L:14D photoperiod laid significantly fewer eggs compared to the weevils exposed to 20°C, 12L:12D photoperiod before transfer. This may be related to the fact that the weevils from the former treatment had been collected in January, and therefore diapause development could not have proceeded far enough in these weevils relative

An interesting study was performed by Hodek and Hodkova (1986) on diapause completion and post-diapause morphogenesis in Pyrrhocoris apterus. They exposed 3-9-week-old diapausing adults for 1-10 weeks to combinations of temperature (26°C, 15°C) and photoperiod (18L:6D, 12L:12D) under starvation conditions, followed by measuring the incidence of oviposition and duration of oviposition delay after a switch to 18L:6D, 26°C and feeding conditions. The use of starving females in their studies prevented vitellogenesis, and hence they were able to reliably separate diapause completion from post­ diapause morphogenesis. They found that high temperature was essential to the tachytellic process of photoperiodic activation, but it did not require feeding, and at 15°C, 18L: 6D; only horotellic completion of diapause (diapause development) was possible but at a slower rate than at 26°C. Moreover, tachytellic processes were even stimulated by starvation. Findings of Hodek (1968) showed a resumption of

oviposition after a transfer of ~. apterus from short to long days and 26°C. Since starved weevils could not be used in our studies, it is not possible to separate post-diapause 117 development from post-diapause morphogenesis. However the data suggest that temperature is an important factor stimulating vitellogenesis and egg lay.

Lonqevity at Three Temperature/Photoperiod Reqimes: Data obtained from these investigations are shown in Tables 6 and 7 and Figs. 8 and 9. Both trap- and field­ collected weevils lived longer at 20°C, 10L:14D photoperiod and, longevity was greatly reduced at lSoC, 10L: 14D photoperiod. Observations on feeding activities revealed that weevils held at lSoC showed very low levels of feeding. Hence, the reduced longevity of these weevils may also be related to partial starvation. Unfed weevils at the different regimes showed a similar trend to their fed counterparts. Significant differences in longevities were also found between collections made during different months, but these differences were not consistent in all treatments. In trap collections, the prevailing environmental conditions such as low temperatures and host-free period, could have caused the active weevils to have exhausted their reserves and thus be in a weakened condition at the time of collection. Although the weevils emerging from bolls lived for relatively longer periods, by February and March, their reserves too could have been used up to some extent at 2Soc. Lambremont and Earle (1961) determined that longevity of boll weevils was variable, and was related to sex, culture 118 Tabla 6. Longevity of boll weevils subjected to three temperature/photoperiod regimes (Laveen, 1987/1988)'

Sample Traps2 Field3 Traps Field Traps Field

Sept. 102.3 158.3 35.0

Oct. 88.7 131. 7 32.3 Nov. 155.7 133.5 169.3 260.7 45.7 70.0

Dec. 108.7 158.7 142.7 209.3 16.3 49.7 Jan. 64.7 153.7 153.7 179.0 19.3 39.7 Feb. 70.3 73.7 93.7 164.7 18.0 50.0 Mar. 100.7 62.7 163.7 106.0 21.3 31.3

Apr. 146.0 189.3 24.0

'Fed on artificial diet pellets. 2Collected from traps. 3Emerging from bolls. 119 Tabla 7. Longevity of unfed boll weevils subjected to three temperature/photoperiod regimes (Laveen, 1987/1988)

Sample Traps' Field2 Traps Field Traps Field

Sept. 8.7 15.0 11.0 Oct. 10.0 18.3 10.3 Nov. 8.0 11.5 17.0 25.3 8.7 11.7 Dec. 5.0 11.7 8.0 23.0 4.7 7.3 Jan. 3.3 8.7 9.7 18.3 5.0 6.7 Feb. 6.0 8.7 9.0 19.3 4.3 7.0 Mar. 7.3 7.0 14.0 11.3 6.3 5.7 Apr. 6.7 21.0 6.3

'Collected from traps. 2Emerging from bolls. 120 - Fiq. 8 - A - J- I'· -• 0 Collection Month

.. ~------~ - -

o Collection Montn .. - C J- I'· - 0 1 1 Collection IMP 000 ..an Mer Monlh 121

Fiq.9

~,------, A

, II , II , II , II , II , II COIlec:tlon &eo 0cX New Dea .Jan ,..0 Month

eo~------, 8

COllectIon Man,,,

.. ,------, c

,.

• COIlec1lon Month 122 and holding conditions. Plots of survival data for the three cultures approached the typical sigmoid curve characteristic of an animal population having senescence. In their early work in Texas, Hunter and Hinds (1904) determined that winter survivors had an average life span of 80 days for males and 70 days for females in spring, when held under the seemingly ideal conditions of a laboratory. They also found that the average life span of first generation weevils was 58 days for males and 56 days for females. Field­ cage studies to determine the longevity of weevils emerging from hibernation have revealed that weevils lived for a much shorter period on non-squaring as well as squaring cotton (Fenton and Dunnam 1929, Fye et ale 1959), compared to the results obtained from laboratory studies. Fye (1969) reported that weevils collected from cultivated cotton in Arizona lived an average of six months in the laboratory, and a few lived as long as 11 months. Thus he too mentioned that longevity was abbreviated in the field. Studies on longevity of trap-caught overwintered weevils in Arizona by Bariola (1984) indicated that the weevils lived 69 days on cotton bolls, 44 days on squares, 22 days on sphaeralcia spp. terminals, and 9 days when unfed. Hence the longevity of weevils seems to be highly variable, depending on the climatic conditions, availability and source of food, and the physiological condition of the weevils. Thus, it is to be expected that results obtained in our studies should differ from those obtained by other 123 workers. The significant differences observed due to interaction of temperature/photoperiod, collection time and source, and availability of food, could all be related to differences in metabolic and physiological state of the weevils concerned.

MARANA COLLECTIONS - 1988 The results from these investigations showed interesting differences related to the reproductive physiology of the two populations collected from the two fields.

1. Non-Feedinq Quiescent weevils: Dissections of the non-feeding quiescent weevils from the two fields using the paper towel method showed that more than 90% of the weevils sampled from Field 2 were in either intermediate or firm diapause. variable numbers of weevils from Field 1 (56-70%) fell into the intermediate and firm diapause category (Table 8). These findings may indicate that the method of separation is more appropriate when a higher proportion of weevils in the sample were diapausing. Furthermore, it could be that some of those sampled from Field 1 may be undergoing a process of egg resorption before entry into diapause, and hence may not really be categorized as 'reproductive'. 124 Tabla 8. Assessments on reproductive condition of inactive boll weevils using the 'paper towel method' of separation (Marana, 1988)'

Field - 12 Field - 23

Non­ Non- Sample Reproductive Reproductive Reproductive Reproductive

(R) (I+D)4 (R) (I+D)

9/7 34 81 1 93

9/24 48 62 o 98

10/5 54 73 2 84

10/27 38 69 o 65

'using the method outlined by Walker and Brazzel 1959.

2Field with cotton in all stages of fruiting.

3Field with nonproductive cotton bolls.

4I : Intermediate, D: Diapausing weevils. 125 2. Sex Ratio: The sex ratio of the two populations was not very different. The percentage of males to females in both populations ranged from 1:1 to 1.5:1 (500 weevils sampled per field).

3. Diapause status: Significant differences in the diapausing status were noted on dissecting individuals from the two fields (Table 9). Higher proportions of weevils from Field 1 were in the reproductive and intermediate category than the diapausing category during october, but in November, the percentage of weevils in firm diapause showed an increase. In contrast to these results, hardly any of the boll weevils obtained from Field-2 were found to be reproductive. Significnatly higher number of weevils from Field 2 were found to exhibit firm diapause (means: Field 1 = 26.7%, Field 2 = 56.7%); whereas significantly higher proportions of Field 1 weevils were determined to be reproductive (means: Field 1 = 30.0%, Field

2 = 1.7%). 4. Effect of Photoperiod, Temperature and Food on Diapause Development and Completion and Post-Diapause Morphogenesis: Tables 10 and 11 and Figs. 10 and 11 show the differences in preoviposition period and egg lay of the weevils at two temperature and photoperiod regimes when fed on squares, blooms, small bolls and artificial diet pellets. 126

Table 9. Mean percentages of boll weevils in reproductive (R), intermediate (I) or diapausing (D) categories (Marana, 1988)

Field - l' Field - 22

Sample R I D R I D

10/1/88 31.7 56.7 11.7 1.7 60.0 38.3 10/16/88 41.7 43.3 15.0 3.3 43.3 53.3 11/1/88 31.7 30.0 38.3 0.0 25.0 75.0 11/16/88 15.0 43.3 41.7 1.7 40.0 60.0

'Field with all stages of fruiting cotton.

2Field with unproductive cotton bolls. 127 Table 10. Observations on preoviposition period of female boll weevils fed on different diets (Marana, 1988)1

Field 12 Field 23

Diet Sample 14 Sample 25 Sample 1 Sample 26

Mean Range Mean Range Mean Range

Squares 7.7 5-23 22.5 12-42 20.3 10-32 Blooms 11.3 7-15 17.7 8-32 26.5 24-29 Bolls 12.5 6-23 24.0 6-45 26.0 15-35 Diet 18.8 12-23 16.5 11-22 23.3 16-32 pellets

1Ma intained at 25°C 12L:12D; preoviposition period in days. 2Field with all stages of fruiting cotton.

3Field with unproductive cotton bolls. 4october collection. 5November collection.

~ovember collections from Field 2 did not lay eggs for 30 days. 128

Table 11. Observations on fecundity of female boll weevils fed on different diets (Marana, 1988)'

Field - 12 Field - 23

Diet sample-14 sample-25 Sample-1 sample-26

% % % laying eggs/f laying eggs/f laying eggs/f

Squares 45 18.0 20 10.5 20 5.0 Blooms 15 3.3 15 7.7 10 2.5 Bolls 60 23.4 20 6.5 15 6.3 Diet 20 10.5 10 3.5 15· 3.6 Pells.

1Ma intained at 25°C 12L:12D. 2Field with all stages of fruiting cotton.

3Field with unproductive cotton balls. 40ctober collections.

5November collections.

~ovember collections from Field 2 did not lay eggs for 30 days. 129

Piq. 10 ~~------~ A

10

o 1 2 1 2 1 2 1 2 Field Squatal BloOms Bolli DIet Food

~~------~ B

I I

1 1 1 Field SqUMII BIoOmIJ Bolli Dlot Food 130

Fiq. 11 ~r------~ A

10

0 1212 1 2 1 2 FIeld Squar. 8Iooma E!oIIa DIet Food

~~------~ 8

10

0 11 1 1 FIeld Sq..... BIoom8 Bolli Dfet Food 131

Table 12. Observations on mean longevity of boll weevils subjected to two temperatures (Marana, 1988)

On Diet Pellets Unfed

Sample

Field 13 96.7 122.0 8.3 13.3 11/88 Field 24 116.0 144.7 10.3 21.7 11/88

1,2Soth treatments at 12L: 120 photoperiod.

3Field with all stages of fruiting.

4Field with unproductive bolls. 132 Again, significant differences in both preoviposition period and egg lay were observed in the weevils collected from the two fields, but the preoviposition period was not determined by the diet nor the time of collection. The preoviposition period was longer, egg lay considerably reduced, and a lower proportion of egg-laying females was found in weevils collected from Field 2 relative to those collected from Field 1. None of the weevils held at 20°C, 12L:12D photoperiod laid any eggs. In the October collections from Field 1, a higher proportion of weevils oviposited, and laid the most number of eggs in bolls, followed by squares, less on blooms, and least on diet pellets at 25°C. Furthermore in the samples from Field 1, there was a decline in egg lay in the November collection compared to the October collections.

5. Longevity of Ped and Unfed weevils As seen in Table 12, weevil collections from Field 2 survived longer at 25°C and 20°C in both the fed and unfed treatments (mean longevity: Field 1 = 60.1 days, Field 2 = 73.2 days). Twelve weevils from Field 2 survived over 35 days at 20°C in the absence of food. Also, the mean survival of 75.4 days at 20°C was significantly higher than the mean of 57.8 days obtained at 25°C. Since there was no evidence of cotton regrowth in Field 2 as early as September, it is very possible that most of the weevils collected from this field had fed exclusively on bolls. The survival of these weevils 133 for longer periods indicates that it is very likely that they had sufficient time to feed before entering into diapause.

6. Moisture and Lipid content:

The mean we~ and dry weights of weevils from Field 2 were greater than those of weevils from Field 1 (Tables 13 and 14). Moreover, the proportion of dry weight to fresh weight was higher in the collections from Field 2 when compared to those from Field 1 indicating that weevils from Field 2 had a lower moisture content. Lloyd and Merkl (1961) determined that reproducing boll weevils have an average dry weight of 30-36%. studying trap collected weevils in Mississippi, Thompson and Leggett (1978) observed that dry weights of both males and females ranged from 22 to 43% with an average of 37%. In our studies, the dry weight of the Field 1 weevils ranged from 29 to 34%, while those from Field 2 ranged from 38 to 44%. Similar findings were reported by Gaston and Fischer (1985), on dormant and non-dormant larvae of Chironomus plumosus. They found that dormant males and females were 60% and 40% heavier, respectively, than their non-dormant counterparts. Their study also indicated that the proportion of dry weight to fresh weight increases with the increase in fresh weight of the larvae , and that the dry weight was higher in the females compared to males. The total fat content of boll weevils comprised up to

14.7% (range = 6.9-14.7%) in samples from Field 2 while, the Table 13. Average weights and lipid content of boll weevils (Marana, 1988)1

Field 12 Field 23

Sample Wet wt. Dry wt. Lipids wet wt. Dry wt. Lipids

(mg) (mg) (% WW) (mg) (mg) (% WW)

9/12 10.53 4.63 4.8+0.5 19.35 9.24 11. 6±1. 6

9/27 11.14 4.85 3. 9±1. 3 19.48 10.21 9.7±1.0

10/10 10.18 5.11 4.7±1.4 20.98 11.12 12.3+1. 3

10/25 12.75 5.78 4.9±2.0 19.89 8.92 10.4±1.8

11/7 10.89 4.63 4.9±2.3 19.47 11.46 11.5±3.2

11/20 12.41 5.49 5.3±0.8 18.37 11.98 9.9±2.8

12/8 18.87 10.69 8. 3±1. 2

12/25 19.25 10.81 8.9±1.4

'Average weight of 25 insects.

2Field with cotton in all stages of fruiting.

1Jnproductive cotton field.

I-' W .j:- Table 14. Lipid composition of boll weevils (Marana, 1988)1

Field 12 Field 23

6 1 Sample PL4 Chol5 FFA DG TG8 PL Chol FFA Da TG

9/12 44.2 2.5 21.1 18.3 14.9 32.3 1.8 26.9 13.8 25.2

9/27 40.7 4.2 18.9 16.8 19.4 28.7 2.6 25.8 12.3 31.6

10/10 37.9 2.9 20.7 16.9 21.6 30.3 2.9 26.1 13.8 26.9

10/25 25.3 1.3 29.3 24.2 19.9 27.3 3.2 20.7 16.7 32.1

11/7 33.4 2.5 16.8 19.7 27.6 31.3 4.1 22.5 12.7 29.4

11/20 28.4 3.1 21.4 24.3 22.8 26.2 3.4 28.3 15.3 26.8

Means: 35.0 2.8 21.3 20.0 21.0 29.4 3.0 25.0 14.1 28.7

1 Mean of two determinations.

2 Field with all stages of fruiting cotton.

3 Unproductive cotton in field.

4 Phospholipids

5 Cholesterol

...... 6,7,8 Free fatty acids, Diglycerides and Triglycerides w U1 136 maximum fat content in weevils from Field 1 was only 6.7%, and ranged from 2.3-6.7%. Findings of Labremont et ale (1964) show that body fat of boll weevil adults comprised up to 25% in the initial stage of diapause but later decreased to 3% over a period of seven months. The higher fat content of weevils sampled from Field 2 may indicate the overwintering status of these weevils. Although a detailed lipid analysis was not performed, thin layer chromatography of the lipid mixture revealed that the major classes of lipids in both collections were phospholipids, free fatty acids, diglycerides and triglycerides. Cholesterol was found in very small quanti ties in both samples. In general, the percentage of phospholipids was the highest followed by triglyceride and free fatty acid content. Phospholipids and triglycerides constituted more than 50% of the lipids, while SUbstantial amounts of diglycerides and free fatty acids were also found. It could be seen from the results that the diglyceride content of samples from Field 1 was higher than that in Field 2 samples. The relative amounts of free fatty acids and triglycerides were different in samples obtained from the two fields, higher amounts of free fatty acids being found in samples from Field 2. No major differences in lipid composition were found among samples from Field 2, but the phospholipid content was lower, and relative proportions of free fatty acids, di- and tri-glycerides higher in the last three samples obtained from Field 1. 137 Mitchell et al. (1973) found that the early-diapausing boll weevils, i.e., at boll maturity can sustain this physiological status for an extended period of time due to the availability of good food supply, enabling the insect to deposit sufficient lipids for overwintering. The data support the results reported herein. Most investigations on lipid content of boll weevils have been performed on the fatty acid composition. According to Cookman et al. (1984), fatty acid composition of larvae of many species of insects varies with that of the diet. Their observations on the velvetbean caterpillar showed that the fatty acid composition of larvae reared on different diets was significantly different. They also stated that the fatty acid composition of the larvae was precisely reflected in the adul ts. Thus, it is to be expected that adults collected from the two fields, feeding mainly on squares in Field 1 and bolls in Field 2 should reflect their dietary differences in the composition of fatty acids. Mitchell and Cross (1969) reported on the reduction in the level of total fatty acids in both sexes of the boll weevils with the progress of the season, and deduced that it may represent some deterioration of cell membranes and consequently decreased egg products, diminished rate of feeding and shorter mean time of oviposition. Many workers (Grau and Terriere 1971, Takata and Harwood 1964, Moore 1980, and Bridges and Phillips 1972) studied different factors such as rearing temperature, adult feeding, sex, age, and extent 138 of activity which may further affect adult fatty acid composition. Lambremont (1965) mentioned that in diapausing weevils, neutral lipids can act as a source of fatty acids for phospholipids which are essential for adequate membrane structure. But, according to him, since the boll weevils lack the capacity to dehydrogenate saturated fatty acids to polyunsaturated acids, all di- and tri-unsaturated fatty acids must be obtained from the diet.

Effect of Plant Phenology on the Physiological Condition of the Weevils: Brazzel and Hightower (1960) reported that the reproductive activity of the boll weevil is closely related to the phenology of the cotton plant, i.e., the reproductive activity of the boll weevil increases with the vigor, plant growth and fruiting, even as late as September. Investigations very similar to the studies reported herein were conducted by Mitchell and Mistric (1965) in North Carolina during 1961-1962. Their stUdies were performed in and near two cotton fields, one with a high productive level and effectively treated with insecticides and the other virtually untreated and with a low productive level. They determined that differences in rates of diapause in the fields were closely related to the onset of maturity in the cotton plants, and weevils began to hibernate in late August near the untreated field and late september near the treated field. It 139 is interesting to note that the number of weevils in hibernation gradually declined during October and November in the untreated field, whereas numbers steadily increased in the treated field during the same period. They concluded that many of the early-diapausing weevils in the untreated field died before the onset of winter. As early as 1928, Isely reported that although weevil larvae feed and develop in either squares or bolls of cotton, the adults prefer the squares as a source of food; and moreover, squares or very small bolls are essential for reproduction. He mentioned that oviposition would soon cease during the later part of the season if squaring is terminated, and hence there appeared to be a definite correlation between the availability of squares in a field, late during the season, and the carryover of overwintering females the following spring. since Isely (1928) reported his findings, similar reports on the relationship of entry into diapause and the maturity of the cotton plant have been made by Lloyd et ale (1964), Mitchell and Mistric (1965), Walker and Bottrell (1970), and Carter and Phillips (1973). until the late 1950' s diapause in boll weevils had been generally accepted to be a fall phenomenon. However Brazzel and Newsom (1959) found diapausing weevils in ground trash all year round with the exception of June and July. Hence, these findings were contradictory to the long-held belief that diapause in boll weevils was initiated by a short photoperiod, 140 cool temperatures, and mature host plants, characteristic of the fall environment. Lloyd et ale (1964) and Mitchell and Mistric (1965) identified two periods of boll weevil entry into diapause. Lloyd et ale (1967) studied the effect of photoperiod, temperature, and diet on the induction of diapause and determined that boll-feeding by adults induced diapause in field populations during the first period, whereas all the factors acted in concert later in the season during the second period of entry into diapause. Further to these studies, Carter and Phillips (1974) researched in Arkansas to elucidate the role of the host plant and plant growth substances in regulating the incidence of seasonal diapause in the boll weevil. They determined that diapause incidence in boll weevils increased as fruiting levels decreased. Based on their results, they deduced that in addition to responding to short photoperiods characteristic of the fall environment in the temperate zone, boll weevils may respond to physiological changes in the fruiting activity of the cotton plant throughout the season, and may utilize abscissic acid as a chemical messenger as an indicator of seasonal changes.

Thus, it is evident that as mentioned by Isely (1928), the availability of food essential for reproduction is as important for the survival of boll weevils in a given locality from season to season, as the availability of suitable hibernation quarters. Al though mid-season diapause is 141 generally considered inconsequential to the seasonal population dynamics of the boll weevil, as mentioned by Carter and Phillips (1973), it could provide a valuable tool in suppressing and managing populations by the use of early maturing, fast fruiting, determinate varieties of cotton. It is interesting to note that Leggett and Moore (1982) and Moore et al. (1986) found that adult diet determined the response of weevils to grandlure traps. The weevils emerging from squares or an artificial diet with 11% protein and 2% sucrose were more responsive than those fed on bolls or an artificial diet with 5% protein and 4% sucrose. Thus, they deduced that the boll-fed weevils may bypass the traps to enter hibernation areas. Our observations on trap catches in and around the two fields showed that large numbers were caught in traps placed near Field 1 in November, whereas very few weevils from Field 2 were responsive to traps. It therefore seems very likely that the physiological and reproductive status of the boll weevils is related to the physiological condition of the cotton plant. The weevils from the field where plant growth and fruiting was found during september/October, responded with a lower incidence of diapause, longer preoviposition period, lower egg lay, and reduced longevity as compared to the weevils from Field 2, where there was only unproductive cotton. Clearly, boll weevils probably possess an array of facilities to circumvent a wide range of unfavorable conditions (Carter and Phillips 142 1973) and plant maturity could be considered to be as or more important than photoperiod in predicting incidence of diapause in the boll weevil (sterling 1972). Considering the fact that many of these studies have been related to mid-summer diapause in the temperate regions, it may be considered that the stimulating influence of plant phenology may be an overriding factor in inducing late-season diapause in subtropical regions such as Arizona. In this respect, studies on the relationship of plant phenology to the reproductive status of the weevils would have greater implications in the formulation of effective control strategies in these regions.

Late-season Infestations: The results of these studies are presented in Table 15. The dry boll samples were found to be infested with adults only, whereas the green bolls contained larvae, pupae and adults. The presence of the green bolls at the eastern side of the same field (Field 2) in early December indicated cotton regrowth in that area in the latter part of the season. Hence, the last reproductive generation of the weevils must have oviposited on the fruiting forms in this area. In both instances, mortality was higher at 15°C, and by April, all weevil life stages were dead. The transformation of larvae to pupae and adults was relatively slow in the samples from green bolls, and mortality was higher at the larval stage. Thus, although there have been reports that survival was 143 Table 15. Observations on late season infestation of cotton bolls and seasonal survival of boll weevil life stages

(Marana, 1988) 1

Sample - 12

Sampling Temp.3 A-14 A-ds Exit % Survival Date Cells

12/7/88 Field6 32 7 12 82.1 1/9/89 20°C 26 8 15 76.5 15°C 8 27 13 22.9

2/6/89 20°C 12 21 19 36.4 15°C 1 29 14 3.3

3/16/89 20°C 3 20 24 13.0

Sample - 27

L-18 L-d9 P_110 p_d11 A-I A-d Exit % Cells Sur.

12/7/88 Field 20 3 6 0 3 0 2 90.6

1/9/89 20°C 10 7 10 0 4 0 8 57.1 15°C 2 11 0 2 2 8 2 16.0

2/6/89 20°C 3 8 2 4 3 7 7 29.6 15°C 0 8 0 4 1 5 4 5.6 3/16/89 20°C 1 9 1 5 2 8 9 16.4 144 1Collected from field with non-productive bolls on 12/7/88. 20ry bolls from the western side of the field.

3Held in environators at 15°C and 20°C. 4,5Adults-living(1) and dead(d). 6Sampled field collection before placement in environators.

70ld green bolls collected from eastern side of the field. 8,9larvae - living (1) and dead(d) • 10,11pupae - living (1) and dead (d).

120verall % survival of all life stages. 145 higher when weevils entered diapause late in the season, the infestation in the area under investigation had occurred too late in the season to enhance survival, at the prevailing environmental conditions.

SPR~NG 1989 These studies had to be terminated, due to the complete absence of any sign of boll weevil infestations in the vicinity of the two fields. 146

CONCLUSION

The boll weevil, Anthonomus grandis is a species which lives within a uniquely uniform habitat (cotton ecosystem) over a fairly wide geographical range. As mentioned by Southwood (1978), it is necessary to have better estimates of inter­ population variation as well as geogrphical variation in order to arrive at any firm conclusions regarding the geographical adaptation of life cycle strategies. Since diapause is one of the most important adaptive strategies evolved by insects not only permitting escape in time, but also interacting with developmental rates, determining patterns of voltinism, regulating seasonal phenologies and synchronizing life cycles (Dingle 1978), it is to be expected that diapause could play an important role in the adaptation of insects to geographical regions. Hence, since diapause is the primary seasonal adaptation of most insects (Waterhouse and Norris 1980), it is difficult to conceive that the boll weevil could have achieved its present wide distribution and abundance in its absence. Although many studies on colonizing species have demonstrated the responsiveness of diapause-mediated seasonal cycles to natural selection and illustrate the influence of local climatic condition on population structure, there have been no instances showing that diapause could evolve de novo 147 from completely nondiapuase tropical species (Tauber et ale 1986). Hence, they proposed a comprehensive model for the evolution of diapause in insects. They consider that tropical species which have expanded their geographical ranges with the introduction of their host plants into subtropical and temperate areas illustrate the point that the capacity to undergo diapause was already present in the original tropical homeland and formed the basis on which the life cycles adapted to the seasonal exigencies of the temperate zone. Therefore, it is difficult to conceive that although the boll weevil had a tropical ancestry, it could have evolved this feature in the southeastern strains from a nondiapause ancestor. The genetic and physiological plasticity permitting the action of natural selection and evolution of diapause must have been found in the original population. since the anticipatory aspect of diapause is its fundamental feature, it could follow that the origin of diapause could be related to the ability to perceive and respond to environmental cues which herald an approaching seasonal change (Levins 1968, Shapiro 1976, Tauber et ale 1986). comparative studies on intraspecific differences on incidence and duration of diapause in samples collected from different climatic areas have revealed that the variations are often clinical and well correlated with climatic gradients (Tauber et ale 1986). Furthermore, based on laboratory and field studies, they perceived that these variations undoubtedly represent the 148 responses of these species to climatic selection; and the high degree of evolutionary plasticity that insects possess allows them to respond to natural selection in the new areas within a relatively short period, even if the immigrant stock is small and is of limited genetic variability. Gradients in lifecycle phenomena have been observed with regard to photoperiod, temperature, food, and moisture in many insect species, from the tropics to the temperate regions (Riedl 1983, Brown 1983, Dingle and Bladwin 1983, Ando 1983, Masaki

1967). It has been proposed that boll weevils in the subtropical and tropical regions do not exhibit true diapause, but overwinter in a state of "quiescence" (Guerra et ale 1982). But, seasonal quiescence is associated with a high degree of responsiveness to the immediate conditions of the environment. The nondiapause migrations that such insects show would be followed by resumed growth, development and reproduction immediately after arrival at the new host or habitat, and does not precede prolonged periods of delayed growth, reproduction or development associated with diapause-mediated 'migrations' or movements (Tauber et ale 1986). Although the climatic factors in areas such as Arizona are less severe during winter than in the southeastern regions of the united states, the boll weevil has been found to reproduce only on cotton (Palumbo 1985). Tauber and Tauber (1973) determined that in the Mohave strain of Chrysopa carnea, the autumnal phase of 149 diapause is maintained by day length, while the hibernal-early vernal phase results from the absence of prey. Similarly, diapause in boll weevils too could be maintained in the subtropics until the host is available, although the climatic conditions may favor reproduction. It is also interesting that Tauber et al. (1986) mentioned that a period of "post-diapause quiescence" is a common phenomenon among some insects which enter diapause during late autumn or winter, but terminate diapause in late winter or early in spring. Futhermore, all the characteristics of diapause are maintained in these insects and development suppressed, but the insect has the capacity to respond immediately to growth- and reproduction­ promoting conditions. Hence, the results obtained in some of the investigations on boll weevils, in which reproduction was found to commence as soon as the food source was made available, may have been related to weevils which were in "post diapause quiescence". The differences in diapause status, diapause termination and post-diapause development obtained in the studies reported here between trap- and field-collected weevils, confirm suggestions made by Tauber et ale (1986). They believed that the use of light, food and pheromone traps may be adequate to monitor active, nondiapausing parts of the population but may overlook entirely or in part the diapausing individuals. Tauber et al. (1986) and Mitchell and Hardee (1974) reported that the trap-collected weevils do not represent the true 150 diapause status and the problem could be especially acute with respect to within-season variability. The studies reported herein showed that a proportion of weevils in Arizona do exhibit diapause symptoms, and it is related to the collection-source, and to plant phenology. Since diapause is a dynamic state, sampling throughout the overwintering period whenever possible, made it possible to establish the pattern of diapause maintenance and post-diapause development by nat~n:'ally occurring environmental factors. The boll weevil is a pest species which has become established in Arizona in recent years. Detailed longterm laboratory and field studies to elucidate factors that maintain diapause, timing and requirements for diapause termination, and the temperature and nutritional requirements for post-diapause development leading to reproduction is necessary to formulate effective pest management practices. Like many other economically important pests, most aspects of the biology and ecology of the boll weevil have been elucidated. But, many aspects of the overwintering biology of this species still remains to be clarified even with regard to the strains inhabiting the southern and southeastern areas of the united states. with regards to the populations inhabiting Arizona, these studies have shown that temperature, and food are important factors in diapause completion. Further work relating different photoperiodic conditions to diapause induction would be necessary to elucidate whether 151 photoperiodic cues early in the fall could increase the incidence of diapause. Based on these findings, we could confirm that iate planting of cotton, use of early maturing, determinate varieties of cotton, early termination, and area­ wide stalk destruction programs could help in reducing the overwintering/diapausing populations in Arizona. 152

LITERATURE CITED

Ahmad, H., H. R. Burke. 1972. Larvae of the weevil tribe Anthonomini. Misc. Publ. Entomol. Soc. Am. 8: 33-81. Ando, Y. 1983. Diapause and geographic variation in a leaf beetle. pp. 127-141. In V.K. Brown and I. Hodek [eds.], Diapause and life cycle strategies in insects. Junk, The Hague. Andrewartha, H. G. 1952. Diapause in relation to the ecology of insects. BioI. Rev. 27: 50-107. Annonymous. 1973. pilot eradication experiment: A report of the Entomological Society of America Review Committee. Bull. Entomol. Soc. Am. 19: 218-221. Annonymous. 1978. Eradication of plant pests - pros and cons. A report of the Entomological Society of America. Bull. Entomol. Soc. Am. 24: 35-54. Annonymous. 1981. Overall evaluation: beltwide boll weevil insect management programs. Economic Research Service Staff Report, No. AGESS 810721. pp. 3-12. Bariola, L. A. 1983. The boll weevil situation in the west. Proc. 1983 Western Cotton Prod. Conf. Las Cruces, NM. pp. 52-55. 153 Bariola, L.· A. 1984. Longevity and reproduction of overwintered boll weevils on cotton and alternate hosts. Southwest. Entomol. 9: 253-56. Bariola, L. A. and D. Bergman. 1982. Toxicity of selected insecticides to boll weevils in Arizona. Southwest. Entomol. 7: 142-145. Bariola, L. A., T. J. Henneberry and D. Bergman. 1984. Boll weevils (Coleoptera: Curculionidae): Emergence from bolls during the spring, and trapping of adults in Arizona. J. Econ. Entomol. 77: 1166-1170. Bartlett, A. e. 1981. Isozyme polymorph isms in boll weevils and thurberia weevils from Arizona. Ann. Entomol. Soc. Am. 74: 359-362. Bartlett, A. e., v. e. Randall and J. B. May. 1983. Allozyme variation among populations of boll weevils in Arizona and Mexico. Southwest. Entomol. 8: 118-130. Beck, S. D. 1967. water intake and the termination of diapause

in the European corn borer, ostrinia nubilal is. J. Insect. Physiol. 13: 739-750. Beck, S. D. 1980. Insect photoperiodism. 2nd edn. Academic Press, London. 154 Bergman, D., L. A. Bariola and T. J. Henneberry. 1981. 1980 Boll weevil infestations in Arizona cultivated cotton. Proc. 1981 Beltwide cotton Prod. and Res. Conf. pp. 70- 75.

Bergman, D. , T. J. Henneberry and L. A. Bariola. 1982. Distribution of the boll weevil in southwestern Arizona cotton from 1978-1981. Proc. 1982 Beltwide cotton Prod. and Res. Conf. pp. 204-207.

Bergman, D. , T. J. Henneberry and L. A. Bariola. 1983. Overwintering boll weevil populations in southwestern Arizona cultivated cotton. Proc. 1983 Beltwide cotton Prod. and Res. Conf. pp. 182-185. Betz, N. L. and E. N. Lambremont. 1967. Changes in stored glycogen and lipid associated with diapause of the adult boll weevil Anthonomus grandis (Coleoptera: Curculionidae). Ann. Entomol. Soc. Am. 60: 866-868. Bligh, E. G. and W. J. Dyer. 1959. A rapid method of total

lipid extraction and purification. Can. J. Biochem. Physiol. 37: 911-917. Boheman, C. H. 1843. Original description of Anthonomus grandis pp. 232-233. In C. J. Schoenherr [ed.], Genera et species Curculionidum. 7: 2. 155 Bondy, F. F.; and C. F. Rainwater. 1942. Boll weevil hibernation, survival and emergence under South Carolina conditions. J. Econ. Entomol. 35: 495-498. Bottger, G. T. 1965. stub cotton provides haven for western boll weevil. Prog. Agric. Arizona 17: 12-13. Bottger, G. T., W. H. Cross, W. E. Gunderson, and G. P. Wene. 1964. Recent research on the boll weevil in northern Sonora, Mexico, and the thurberia weevil in Arizona. J. Econ. Entomol. 57: 286-290. Bottrell, D. G., J. R. White, D. S. Moody and D. D. Hardee. 1972. Overwintering habitats of the boll weevil in the Rolling Plains of Texas. Environ. Entomol. 1: 634-638. Boyd, F. J. 1974. operational plan and execution of the pilot boll weevil eradication experiment. In Boll weevil suppression, management and elimination technology. USDA, ARS-S-71. pp. 62-70. 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 Anthonomous grandis Boh. J. Econ. Entomol. 52: 603-611. 156

Brazzel, J. R.- and D. A. Lindquist. 1960. The effectiveness of chlorinated hydrocarbon insecticides in Texas. J. Econ. Entomol. 53: 551-554. Bridges, J. R. and J. R. Phillips. 1972. Fatty acids of the

imago of Heliothis ~ (Lepidoptera: Noctuidae): an approach to determining larval hosts. In distribution, abundance and control of Heliothis species in cotton and other host plant. south. Coop. Sere Bull. 169. pp. 72- 79. Brown, V. K. 1983. Developmental strategies in British Dictyoptera: Seasonal variation. pp. 111-126. In V.K. Brown and I. Hodek [eds.], Diapause and Life Cycle Strategies in Insects. Junk, The Hague. Buford, W. T., J. N. Jenkins and F. G. Maxwell. 1967. A laboratory technique to evaluate boll weevil oviposition

preference among cotton lines. Crop Sci. 7: 579-581. Burke, B. R. 1968. Geographic variation and taxonomy of Anthonomous grandis Boheman. Texas A. & M. University Agric. Exp. Sta. Dept. Entomol. Tech. Report. 152 pp. Burke, B. R., W. E. Clark, J. R. cate, and P. A. Fryxe11. 1986. Origin and dispersal of the boll weevil. Bull.

Entomol. Soc. Am. 32: 228-238. 157 Carter, P. L. -and J. R. Phillips. 1973. Diapause in the boll weevil, Anthonomus grandis Boheman, as related to fruiting activity in the cotton plant. Arkansas Acad. Sci. Proceed. XXVII: 16-20. Carter, P. L. and J. R. Phillips. 1974. Factors influencing seasonal diapause in the boll weevil. Arkansas Farm Research XXIII: 2 coakley, J. M., P. G. Maxwell and J. N. Jenkins. 1969. Influence of feeding, oviposition and egg and larval development of the boll weevil on abscission of cotton squares. J. Econ. Entomol. 62: 244-245. Cobb, P. P. and M. H. Bass 1968. Some effects of photoperiod, temperature and food on the induction of diapause in the boll weevil. J. Econ. Entomol. 61: 624-625. Coker, R. R. 1976. Economic impact of the boll weevil. In Boll Weevil Suppress. Manaqment and elemination Tech. USDA,

ARS. S-71: 3-5. Cook, o. P. 1906. Evolution of weevil resistance in cotton. Science. 20: 666-670. Cookman, J. E., M. J. Angelo, P. slanksy and J. L. Nation. 1984. Lipid content and fatty acid composition of larvae and adults of the velvet bean caterpiller, Anticarsia gemmatalis as affected by larval diet. J. Insect.

Physiol. 30: 523-527. 158 Cowan, C. B; Jr., J. w. Davis and C. R. Parencia, Jr. 1963. winter survival of the boll weevil in cotton bolls in Central Texas. J. Econ. Entomol. 56: 494-496. Cross, W. B., M. J. Lukefahr, P. A. Fryxell and B. R. Burke. 1975. Host plants of the boll weevil. Environ. Entomol. 4: 19-26. Cushman, R. A. 1911. studies on the biology of boll weevil in the Mississippi delta region of Louisiana. J. Econ. Entomol. 4: 432-48. de wilde, J. 1962. Photoperiodism in insects and mites. A. Rev. Entomol. 7: 1-26. de wilde, J., C. S. Duintjer and L. Mook. 1959. Physiology of diapause in the adult Colorado beetle (Leptinotarsa decemlineata Say.) 1. The photoperiod as a controlling factor. J. Insect Physiol. 3: 75-85. Dingle, B. 1978. Migration and diapause in tropical, temperate and island milkweed bugs. pp. 254-276. .In H. Dingle [ed.], Evolution of Insect Migration and Diapause. Spring-Verlag, New York. Dingle, B. and B. D. Baldwin. 1983. Geographic variation in life histories: A comparison of tropical and temperate milkweed bugs (Oncopeltus) pp. 143-165 • .In V.K. Brown and I. Hodek [eds.], Diapause and Life Cycle Strategies in Insects. Junk, The Hague. 159 Earle, N. W., .and L. D. Newsom. 1964. Initiation of diapause in the boll weevil. J. Insect. Physiol. 10: 131-39. Penton, F. A. and B. W. Dunnam. 1929. Biology of the cotton boll weevil at Florence, S. C. USDA Agric. Tech. Bull. 112: 33-35. pye, R. B. 1968. Populations of boll weevils in selected fields in Arizona in 1965 and 1966. J. Econ. Entomol. 61: 377-380. Pye, R. B. 1969. Longevity and fecundity of the boll weevil complex in Arizona. J. Econ. Entomol. 62: 1408-1412. pye, R. B. and J. B. Leggett. 1969. Winter survival in Arizona of -thurberia weevils released from thurberia bolls. J. Econ. Entomol. 62: 467-470. Pye, R. B., and C. R. Parencia. 1972. The boll weevil complex in Arizona. USDA Production Research project 139. 23 pp. Pye, R. B., R. L. Walker and A. R •. Hopkins. 1957. Susceptibility of the boll weevil in South Carolina to several insecticides. J. Econ. Entomol. 50: 700-701. Pye, R. B., A. R. Hopkins, W. B. McMillian and R. L. Walker. 1958. Survival and emergence of boll weevils from several

areas under similar hibernating conditions. J. Econ. Entomol. 51: 745-746. 160 Fye, R. B., W.- B. McMillian, R. L. Walker and A. R. Hopkins. 1959. The distance into woods along a cotton field at which the boll weevil hibernates. J. Econ. Entomol. 52: 310-12. Fye, R. B., R. Patana and W. e. HcAda. 1969. Developmental periods for boll weevils reared at several constant and fluctuating temperatures. J. Econ. Entomol. 62: 1402- 1405. Fye, R. E., J. E. Leggett and e. D. Bonham. 1970. winter survival of the boll weevil complex in Arizona. J. Econ. Entomol. 52: 310-312. Ganyard, M. e., J. R. Brazzel and A. E. Hiller. 1981. Boll weevil eradication trial. Proc. Beltwide cotton Prod. Mech. Conf. pp. 38-40. Gaston, A. and J. Fischer. 1985. The oxygen consumption of non-dormant and dormant larvae of Chironomus plumosus (Diptera). J.Insect Physiol. 31: 762-772. Gehrken, K. 1985. Physiology of diapause in the adult bark beetle, Ips acuminatus Gyll., studied in relation to cold hardiness. J. Insect Physiol. 31: 909-916. Gillespie, J. H., T. F. Watson, T. J. Henneberry and L. A. Bariola. 1979. A comparison of 1978 insect population in stub and planted cotton in central Arizona. Proc. 1979 Beltwide cotton Prod. Conf. Phoenix, AZ. pp. 99-103. 161 Gilliland, P.·R., Jr. 1974. Traps and trap crops for boll weevil suppression. Proc. Beltwide cotton prod. Res. Conf. National cotton Council, Memphis, TN. pp. 128-130. Gilliland, P. R., Jr., W. R. Lambert and R. L. Davis. 1976. Evaluation of a trap crop system for boll weevil suppression. Proc. Conf., Boll Weevil Suppression, Management and Elimination Technology. USDA-ARS-S-71. Glover, D., D. P. Glover, and J. E. Jones. 1975. Boll weevil and bollworm damage as affected by upland cotton strains with different cytoplasms. Proc. Beltwide cotton Prod. Res. Conf. National cotton council, Memphis, Tenn. pp. 99-102 Grau, P. A. and L. C. Terriere. 1971. Fatty acid profile of the cabbage looper, Trichoplusia ni and the effect of

diet and rearing conditions. J. Insect Physiol. 17: 1637- 1649. Graves, J. B., J. S. Roussel, J. Gibbons and D. Patton. 1967. Laboratory studies on the development of resistance and cross-resistance in the boll weevil. J. Econ. Entomol. 60: 47-50. Guerra, A. A. and R. D. Garcia. 1982. Seasonal patterns of boll weevil response to grandlure-baited traps in the

Rio Grande Valley of Texas. Southwest. Entomol. 67: 216- 220. 162 Guerra, A. A, R. D. Garcia and J. A. Tamayo. 1982. Physiological activity of the boll weevil during the fall and winter in subtropical areas of the Rio Grande Valley of Texas. J. Econ. Entomol. 65: 97-100. Hardee, D. D., W. H. cross, B. B. Mitchell, P. M. Huddleston, H. c. Mitchell, M. B. Merkl and T. B. Davich. 1969. Biological factors influencing responses of the female boll weevil to the male sex phermone in field and large­ cage tests. J. Econ. Entomol. 62: 161-165. Hardee, D. D., G. H. McKibben, R. C. Gueldner, B. B. Mitchell, J. H. Tumlinson and W. H. Cross. 1972. Boll weevils in nature respond to glandlure, a synthetic pheromone. J. Econ. Entomol. 65: 97-100. Harris, P. A., B. P. Lloyd and D. N. Baker. 1966. Effects of the fall environment on the boll weevil in northeast Mississippi. J. Econ. Entomol. 59: 1327-1330. Hazel, W. N. and D. A. west. 1983. The effect of larval photoperiod on pupal 'color on diapause in swallowtail butterflies. Ecol. Entomol. 8: 37-42. Head, R. B. 1982. Report of the cotton insect loss committee of the 35th annual conference on cotton insect research and control. Proc. 1982 Beltwide cotton Prod. Res. Conf. p. 182. 163 Henneberry, T. J., T. Heng and L. A. Bariola. 1988. Boll weevil: Grandlure trapping and early-season insecticide applications in relation to cotton infestations in Arizona. soutwest. Entomol. 13: 251-259. Hilliard, R. A. and L. L. Keeley. 1984. The effects of dietary nitrogen on reporductive development in the female boll weevil, Anthonomous grandis. Physiol. Entomol. 9: 165- 174. Hodek, X. 1968. Diapause in females of Pyrrhocoris apterus L. (Heteroptera). Acta. Ent. Biochem. 65: 422-435. Hodek, X. 1979. Intermittent character of adult diapause in Aelia acuminata (Heteroptera). J. Insect Physiol. 25: 867-871. Hodek, X. 1983. Role of environmental factors and endogenous mechanisms in the seasonality of reproduction in insects diapausing as adults. In V.K. Brown and I. Hodek [eds.], Diapause and Life Cycle strategies in Insects. Junk, The Hague. Hodek, X. and H. Hodkova. 1986. Diapause development and photoperiodic activation in starving females of Pyrrhocoris apterus (Heteroptera). J. Insect Physiol. 32: 615-621. 164

Hopkins, A. R~, H.M. Taft, and W. James. 1969. Life history of the boll weevil in field cages. J. Econ. Entomol. 62: 964-965. Hunter, W. D. 1914& The most important step in the cultural system of controlling the boll weevil. USDA Bull. Ent, 56. 7p. Hunter, W. D. and W. B. Hinds. 1904. The Mexican cotton boll weevil. U.s. Dept. Agric. Bur. Ent. Bull. 45. Hunter, W. D. and W. D. Pierce. 1912. The Mexican cotton boll weevil: A summary of the investigation of this insect up to December 31, 1911 Senate Doc. 305. Isely, D. 1928. The relation of leaf color and leaf size to boll weevil infestation. J. Econ. Entomol. 21: 553-559. Jones, J. w., H. D. Bowen, R. B. stinner, J. R. Bradley, Jr. R. s. Sowell and J. s. Bacheler. 1975. Female boll weevil oviposition and feeding processes: A simulation model. Environ. Entomol. 4: 815-821. Kono, Y. 1980. Endocrine activities and photoperiodic sensitivity during prediapause period in the phytphagous lady beetle, Epilachna vigintioctopunctata. App. Entomol. Zool. 15: 73-80. 165

Kono, Y. 1982~ Change of photoperiodic sensitivity with fat body development during prediapause period in the twenty­ eight-spotted lady beetle, Henosepilachna viqinoctopunctata Fabricius (Coleoptera: Coccinellidae). App. Entomol. Zool. 17: 92-101. Lambremont, B. N. 1951. Homogenate respiration of diapausing and nOlildiapausing boll weevils. Ann. Entomol. Soc. Am. 54: 313-316. Lambremont, B. H. 1965. Biosynthesis of fatty acids in aseptically reared insects. Compo Biochem. Physiol. 14: 419-424. Lambremont, B. H. and H. W. Earle. 1961. Longevity of the boll

weevil under laboratory conditions. J. Econ. Entomol. 54: 964-966. Lambremont, E. H., H. S. Blum and R. M. Sohrader. 1964. Storage and fatty acid composition of triglycerides during adult diapause of the boll weevil. Ann. Entomol. Soc. Am. 57: 526-532. Lees, A. D. 1956. The physiology and biochemistry of diapause in arthropods. Ann. Rev. Entomol. 1: 1-16. Lees, A. D. 1961. Clonal polymorphism in aphids. Symp. Royal Entomol. Soc. Lond. 1: 68-79. 166

Leggett, J. ~. 1980. Boll weevil: competitive and non­ competitive evaluation of factors affecting pheromone trap efficiency. Environ. Entomol. 9: 416-419. Leggett, J. B. and W. H. Cross. 1971. A new trap for capturing boll weevils. u.s. Cepe Agric. Coop. Econ. Insect Rep. 21: 773-774. Leggett, J. B. and R. B. Fye. 1969. The role of moisture in the winter survival of the boll weevil complex in Arizona. J. Econ. Entomol. 62: 147-149. Leggett, J. B. and R. P. Hoore. 1982. Influence of artificial and natural diets on boll weevil trap efficiency. Environ. Entomol. 11: 635-638. Leggett, J. B., W. A. Dickerson, K. P. Burnham, S. H. Roach, A. R. Hopkins and F. R. Planer. 1988. Boll weevil (Colepotera: Curculionidae): emergence profile of overwintered weevils measured by grandlure-baited traps and predicting total emergence. Environ. Entomol. 17: 903-910. Levins, R. 1968. Evolution in changing environment. Princeton University Press, Princeton, NJ. Lloyd, B. P. and H. B. Herkl. 1961. Seasonal occurrence of diapause in the boll weevil in Mississippi. J. Econ. Entomol. 54: 1214-1216. 167 Lloyd, B. P.,.H. L. Laster, and H. B. Herkl. 1964. A field study of diapause, diapause control and population dynamics of the boll weevil. J. Econ. Entomol. 57: 433- 436. Lloyd, B. P.# P. C. Tinqle and R. T. Gast. 1967. Environmental stimuli inducing diapause in the bollweevil. J. Econ. Entomol. 60: 99-102. Lloyd, B. P., J. R. HcCoy and J. W. Haynes. 1974. Release of sterile male boll weevils in pilot eradication experiment. In: Boll weevil suppression, management and elimination technology. USDA, ARS-S-71: 95-102. Lopez, J. D. Jr. 1980. Comparison of two types of boll weevil pheromone traps to monitor seasonal response. J. Econ.

Entomol. 73: 324-326. Lukefahr, H. J. and D. P. Martin. 1962. A native host plant

of the boll weevil and other cotton insects. J. Econ. Entomol. 55: 150-151. Mangum, C. L, N. W. Earle, and L. D. Newsom. 1968. Photoperiodic induction of diapause in the boll weevil, Anthonomus grandis. Ann. Entomol. Soc. Amer. 61: 1125- 1127. Masaki, S. 1967. Geographic variation and climatic adaptation in a field cricket (Orthoptera: Gryllidae). Evolution.

21: 725-741. 168

Masaki, s. 1~83. Climatic speciation in Japanese ground crickets. Geo. Journal 7: 483-490. Maxwell, P. G. 1980. Advances in breeding for resistance to cotton insects. Proc. 1980 Beltwide Cotton Prod. Res. Conf. National cotton Council, Memphis, TN. pp. 141-147. Merkl, M. B. and J. R. McCoy. 1978. Boll weevils: Seasonal response over five years to pheromone baited traps. J. Econ. Entomol. 71: 730-731. Mitchell, H. C. and W. H. Cross. 1969. oviposition by the boll weevil in the field. J. Econ. Entomol. 62: 604-605.

~itchell, B. B. and D. D. Hardee. 1974. Seasonal determination of sex ratios and condition of diapause of boll weevils in traps and in the field. Environ. Entomol. 3: 386-388. Mitchell, B. B. and W. J. Mistric, Jr. 1965. Seasonal occurrences of diapause and hibernation of the boll weevil in North Carolina. J. Econ. Entomol. 58: 309-312. Mitchell, B. B. and H. M. Taft. 1966. Starvation method for

obtaining diapausing boll weevils able to survive the

winter in hibernation. J. Econ. Entomol. 59: 55-57. Mitchell, B. B., P. M. Huddleson, N. H. Wilson and D. D. Hardee. 1973. Boll weevils relationship between time of entry into diapause and time of emergence from overwintering. J. Econ. Entomol. 66: 1230-1231. 169

Moore, L. 1983. Early season boll weevil control. University of Arizona cooperative Extension Service Bulletin, 8305. 2 pp.

Moore, R. P. 1980. The effect of varied amounts of starch, sucrose and lipids on the fatty acids of the boll weevil. Ent. Expt. App. 27: 246-254. Moore, R. P., S. H. Roach and J. E. Leggett. 1986. Seasonal variation in the respiration of migrant boll weevil (Coleoptera: Curculionidae) and the effects of food and environmental conditions on those captured in August­ September. J. Econ. Entomol. 79: 1206-1211. Morrill, A. W. 1921. Arizona wild cotton or thurberia and its insect enemies in relation to the cotton industry of the Southwest. J. Econ. Entomol. 14: 472-478. Kussman, H. C. 1982. Cotton boll weevil program: MSDA response to the national research council evaluation. Proc. 1982 Beltwide Cotton Production And Mechanization Conf. pp. 91-93.

National Academy of science. 1975. Pest Control: An assessment of present and alternative technologies. cotton Pest Control. Washington, D.C. 11: 75-85.

Nettles, W. C., Jr. and N. L. Betz. 1965. Glycogen in the boll weevil with respect to diapause, age, and diet. Ann.

Entomol. Soc. Ame~. 58: 721-726. 170 Newell, W., B •. P. Grossman and A. P. camp. 1926. The Mexican cotton boll weevil. Florida Agr. Exp. Sta. Bull. 180: 223-247. Niles, G. A. 1976. Nectariless cotton in host plant resistance. J. Econ. Entomol. 69: 627-675. Niles, G. A., L. H. Harvey and J. K. Walker. 1978. Cultural control of the boll weevil: Management strategies. Southern Coop. Sere Bull. 228.: 23-38. Norris, M. J. 1964. Environmental control of sexual maturation in insects. Symp. R. Ent. Soc. London. 2: 56-65. Palumbo, J. C. 1985. The effects of Sphaeralcea spp. on overwintering survival and reproductivity of boll weevils, Anthonomous grandis Boheman. Department of Entomoology. University of Arizona M.S. Thesis. pp. 61. Parker, R. D., J. K. Walker, G. A. Niles and J. R. Mulkey. 1980. The short season effect and escape from the boll weevil. Tex. Agric. Exp. Stn. Bull. 1350. 45 pp. Parrott, W. L., J. N. Jenkins and W. T. Buford. 1970. Instars and duration of stadia of boll weevil larvae. Ann. Entomol. Soc. Am. 63: 1265-1267. Perkins, J. B. 1980. Boll weevil eradication. Science. 207: 1044-1050. Pierce, W. D. 1913. The occurrence of a cotton boll weevil in Arizona. J. Agric. Res. 1: 89-98. 171 Reinhard, B. J. 1943. Hibernation of the boll weevil. Tx. Agric. Expt. Stn. Bull. 638. 23 pp. Ridgway, R. L., L. A. Bariola and D. D. Hardee. 1971. Seasonal movement of boll weevils near the High Plains of Texas. J. Econ. Entomol. 64: 14-19. Riedl, H. 1983. Analysis of codling moth phenology in relation to latitude, climate and food availability. pp. 233-252. In V.K. Brown and I. Hodek [eds.], Diapause and Life Cycle strategies in Insects. Junk, The Hague. Roach, S. H. 1973. Developmental changes in the boll weevil, Anthonomus grandis, studied with time-lapse photQgraphy. Ent. Soc. Amer. 66: 24-27. Roussel, J. S. and D. P. Clower. 1955. Resistance to the chlorinated hydrocarbon insecticides in the boll weevil (Anthonomous grandis Boh.) Louisiana Agric. Expt. sta. Cir. 41. Rummell, D. R. and P. L. Adkisson. 1970. Distribution of boll weevil infested cotton fields in relation to overwintering habitats in the high and rolling plains of Texas. J. Econ. Entomol. 67: 281-283. 172 Rummel, D. R. and D. G. Bottrell. 1976. Relationship of overwintered boll weevil response to phermone traps and natural entry into cotton in detection and management of the boll weevils with pheromone. TAMU/Tex. Agr. Exp. Sta. Research Monograph 8: 26-31. Rummel, D. R. and S. C. Carroll. 1983. winter survival and effective emergence of boll weevil cohorts entering winter habitat at different times. Southwest. Entomol. 8: 101-106. Rummel, D. R. and R. E. Frisbie. 1978. Suppression of potentially overwintering boll weevils as a pest management practice. pp. 39-49. l.n the boll weevil: Management strategies. Arkansas Agric. Exp. Stn. Southern Cooperative Service Bulletin. 228. Sanderson, E. D. 1905. Some observations on the cotton boll weevil. Proc. 17th Ann. Meeting Assoc. Econ. Ent. USDA Bur. Ent. Bull. 52: 29-42. Segers, J. C., T. C. Urban, D. M. George, J. H. Benedict, M. H. walmsley and E. P. pieters. 1987. Seasonal numbers, sex and diapause state of boll weevils captured in pheromone traps in the lower quI f coast of Texas. Southwest. Entomol. 12: 311-316. 173

Shapiro, A. H~ 1976. Seasonal polyphenism pp. 259-33. In M. K. Hecht, W. c. Steere and B. Wallace [eds.], Evolutionary Biology. Vol. 9, Plenum Press, New York. Shelford, V. B. "1929. Laboratory and Field Ecology. Williams and Wekins, Baltimore. Sluss, T. P., E. S. Sluss, H. H. Graham and X.DUBois. 1978.

Allozyme differences between Heliothis virescens and ~ zea. Ann. Entomol. Soc. Am. 71: 191-195. smith, G. D. 1921. Studies in the biology of the Mexican cotton boll weevil on short staple upland, long staple upland and Sea-island cottons. USDA Bull. No. 926. Southwood. T. R. E. 1978. The components of diversity pp. 19- 40. In L. A. Mound and N. Waloff [eds.], Diversity of Insect Faunas. Blackwell, Oxford - London - Edinburgh - Melbourne. sterlinq, W. 1972. Photoperiodic sensitivity in the ontogeny of the boll weevil. Environ. Entomol. 1: 568-571. sterlinq, 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. Texas Agri. Exp. Sta. B-1047, 7p. Stoner, A. 1968. Sphaeralcea spp. as hosts of the boll weevil in Arizona. J. Econ. Entomol. 61: 1100-1102. 174

Taft, H. K. ~d A. R. Hopkins. 1966. Effect of different hibernation environments on survival and movement of the boll weevil. J. Econ. Entomol. 59: 277-279. Takata, N. and R. P. Hardwood. 1964. Fatty acid composition during postembryonic development of mosquito Culex tarsalis Ann. Ent. Soc. Ann. 57: 749-753. Tauber, M.J. and C. A. Tauber. 1970. Adult diapause in Chrysopa carnea: Stages sensitive to photoperiodic induction. J. Insect Physiol. 16: 2075-2080. Tauber, H.J. and C. A. Tauber. 1973. Nutritional and photoperiodic control of the seasonal reproductive cycle in Chrysopa mohave (Neuroptera) J. Insect Physiol. 19: 729-736. Tauber, M. J. and C. A. Tauber. 1976. Insect seasonality: Diapause maintenance, termination and post diapause development. Ann. Rev. Entomol. 21: 81-107. Tauber, K. J., C. A. Tauber, J. R. Nechols and J. J. Obrycki. 1983. Seasonal activity of parasitoids: Control by external, internal and genetic factors. pp. 87-108. In V.K. Brown and I. Hodek [eds.], Diapause and Life Cycle Strategies in Insects. Junk, The Hague. 175 Tauber, X. J.,.c. A. Tauber, and S. Masaki. 1986. Seasonality, the evolution of life history and speciation. pp. 256- 286. In M. J. Tauber, C. A. Tauber and S. Masaki [eds.], Seasonal Adaptations of Insects. Oxford University Press, New York - Oxford. Taylor, P. 1980. Timing in the life histories of insects. Theor. populo BioI. 18: 112-124. Thompson, A. C. and J. E. Leggett. 1978. variation of lipid, protein and carbohydrate in overwintered boll weevils, Anthonomous grandis Boheman. Compo Bioch. Physiol. 60B: 201-203. Tingle, F. C., H. C. Lane, E. E. King and E. P. Lloyd. 1971. Influence of nutrients in the adult diet on diapause in the boll weevil. J. Econ. Entomol. 62: 596-599. Urrelo, R. and H. Chambers. 1978. synergism of anticholinesterase insecticide by non-insecticidal phosphorous esters in the boll weevil Anthonomous grand is Boheman. Turrialba 28: 71-76. Wade, L. J. and D. R. Rummel. 1978. Boll weevil immigration into winter habitat and subsequent spring and summer emergence. J. Econ. Entomol. 71:173-178. 176 Walker, J. K., Jr. 1967. Studies in the fall and winter of oviposition prior to diapause in the boll weevil with observations on reversion from diapause to reproduction. J. Econ. Entomol. 66: 798-802. Walker, J. K., Jr. and J. R. Brazzel. 1959. A method for collecting diapausing boll weevils for hibernation studies. J. Econ. Entomol. 52: 346-347. Walker, J. K., Jr. and D. G. Bottrell. 1970. Infestations of boll weevils in isolated plots of cotton in Texas, 1960- 1969. J. Econ. Entomol. 63: 1646-1650. Walker, J. K., Jr. and J. A. Niles. 1971. Population dynamics of the boll weevil and modified cotton types. Tex. Agric. Exp. Stn. Bull. pp. 1109-1114. Walker, J. K., B. G. Hightower, R. L. Hanna and D. P. Hartin. 1956. control of boll weevils resistant to chlorinated hydrocarbons. Texas Agric. Expt. Sta. Progr. Rept. 1902. Wannamaker, W. K. 1957. The effect of plant hairiness of cotton strains on boll weevil attack. J. Econ. Entomol. 70: 283-285. Warner, R. B. 1966. Taxonomy of the subspecies of Anthonomus grandis (Coloptera: Curculionidae). Ann. entomol. Soc. Am. 59: 1073-1088. 177

Waterhouse, D.- 'g. and K. R. Norris. 1980. Insects and insect physiology in the scheme of things. pp. 19-37. In M. Locke and D. S. Smi th [eds.], Insect Biology in the Future. Academic Press, New York. watson, T. 'g., D. Bergman and J. Palumbo. 1986. Effect of temperature and food on developmental time of the boll weevil in Arizona. southwest. Entomol. 11: 243-248. Weaver, J. B. 1980. Interspecific hybrid cotton as a trap crop for the boll weevil control. Proc. Beltwide cotton Prod. Res. Conf. National cotton Council. Memphis, Tenn. pp. 207-208. Werner, F. G. 1960. A new character for the identification of the boll weevil and the thurberia weevil (Coleoptera: curculionidae). Ann. Entomol. Soc. Amer. 53: 548-549. Wheeler, W. K. 1893. contribution to insect embryology. J. Morph. 8: 141-160. White, J. R. and D. R. Rummel. 1978. Emergence profile of overwintered boll weevil and entry into cotton. J. Econ. Entomol. 7: 7-13. witz, J. A., A. W. Hartstack, E. P. Lloyd. and E. B. Kitchell. 1981. Effect of infield trap spacing on potential catch of adult boll weevils entering cotton: a computer simUlation. Environ. Entomol. 10:454-457. 178 Wolfenbarger, .D. A., H. H. Graham, R. D. Parker and J. W. Davis. 1976. Boll weevil: Seasonal patterns of response to traps baited with glandlure in the lower Rio Grande Valley. Environ. Entomol. 5: 403-408.