THE EFFECTS OF SPHAERALCEA SPP. ON OVERWINTER SURVIVAL AND REPRODUCTIVITY OF BOLL WEEVILS, ANTHONOMOUS GRANDIS BOHEMAN (OVIPOSITION, LONGEVITY, ATTRACTANTS).
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University Micrcxilms International 300 N. Zeeb Road Ann Arbor, Ml 48106
1327053
Palumbo, John Charles
THE EFFECTS OF SPHAERALCEA SPP. ON OVERWINTER SURVIVAL AND REPRODUCTIVE OF BOLL WEEVILS, ANTHONOMOUS GRANDIS BOHEMAN
The University of Arizona M.S. 1985
University Microfilms International 300 N. Zeeb Road, Ann Arbor, Ml 48106
THE EFFECTS OF SPHAERALCEA SPP.
ON OVERWINTER SURVIVAL AND REPRODUCTIVITY
OF BOLL WEEVILS, ANTHONOMOUS GRANDIS BOHEMAN
by
John Charles Palumbo
A Thesis Submitted to the Faculty of the
DEPARTMENT OF ENTOMOLOGY
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 8 5 STATEMENT BY AUTHOR
This thesis 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 thesis are allowable without special permission, provided that accurate acknowledgement of 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 must be obtained from the author.
SIGNED
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
Theo F. Watson Date Professor of Entomology ACKNOWLEDGEMENTS
I would like to express my most sincere gratitude to Dr. Theo
Watson, for his advice and guidance throughout the duration of this research. I wish to thank Dr. Leon Moore, Dr. Irene Terry, and Dr. Don
Tuttle for their valuable suggestions while reviewing the manuscript.
I would like to thank Todd Hannan and Clay Mullis, Yuma Valley
Agricultural Center, for the assistance and support they provided throughout the project.
Special thanks go to my parents, Joseph and Joan Palumbo for their constant encouragement, support, and assistance in preparation of the manuscript. My fiance K. C. Faber, with her love and under standing, provided the emotional and spiritual support necessary for the completion of this project.
iii TABLE OF CONTENTS
Page
LIST OF TABLES V
LIST OF ILLUSTRATIONS vii
ABSTRACT viii
INTRODUCTION 1
LITERATURE REVIEW 4
Overwinter Survival 4 Feeding and Oviposition 8 Reproduction on Alternate Hosts 11 Overwinter Reproductivity 14
METHODS AND MATERIALS 17
Overwinter Survival 17 Oviposition 18 Preoviposition 20 Overwinter Reproductivity 22
RESULTS 23
Overwinter Survival 23 Oviposition 28 Preoviposition Development 32 Overwinter Reproductivity 36
DISCUSSION 42
LITERATURE CITED 54
iv LIST OF TABLES
Page
1. Average survival and maximum longevity of overwintering boll weevils emerging from bolls in January and March and provided various conditions in the insectary, 1984 24
2. Average number of weeks adult boll weevils survived in the insectary after removal from dry bolls and kept without food or provided globemallow or cotton squares, 1984 26
3. Summary of average heat unit accumulation in the insectary for boll weevils which were maintained under dry conditions or with globemallow after emerging from dry bolls in January and March, 1984 .... 30
4. Total number of eggs oviposited by gravid female boll weevils provided with cotton squares, and two species of globemallow buds in a one week period in the laboratory, 1984 31
5. Total number of eggs oviposited by gravid females caged on cotton and globemallow plants in the greenhouse in a one week period, 1984 31
6. Total number of eggs oviposited by reproductive female boll weevils on cotton and globemallow treated with aqueous extracts in the laboratory in a 24-hour period 33
7. Average number of feeding punctures by reproductive female boll weevils in cotton squares and globe mallow buds, alone or treated with aqueous extracts ... 34
8. Average number of days required for newly-emerged females to oviposit when feeding on various food sources at a constant temperature of 30° C with a 14-hour photophase, 1985 35
v LIST OF TABLES - CONTINUED
Page
9. Preovipositional status of newly-emerged female boll weevils provided with globemallow for 0, 5, 10 and 15 days prior to placement on squares 37
10. Number and percentage of male boll weevils which were reproductive (R) or nonreproductive (NR) after feeding on cotton squares or globemallow buds in simulated winter and spring environments 38
11. Number and percentage of female boll weevils which were reproductive (R) or nonreproductive (NR) after feeding on cotton squares or globemallow buds in simulated winter and spring environments 39
12. Total number of heat units accumulated at 15-day intervals in simulated environments in the laboratory 41
vi LIST OF ILLUSTRATIONS
Page
1. Total average percentage of boll weevils surviving at 15, 30, 45, 60, 75 and 90 days held without food (DRY) or provided globemallow or cotton squares in the insectary 25
2. Percentages of boll weevil adults surviving in the insectary for 7, 15, 21, 28 and 35 days provided dry conditions after emerging from dry bolls in January and March, 1984 ..... 27
3. Percentages of boll weevil adults surviving in the insectary provided with globemallow after emerging from dry bolls in January and March, 1984 .... 29
vii ABSTRACT
The overwinter survival and reproduction of boll weevils,
Anthonomous grandis Boheman, on globemallow, Sphaeralcea spp., in
Arizona was studied. In addition, the effect of aqueous extracts of cotton and globemallow on oviposition was compared.
More boll weevils survived for 90 days when provided with cotton squares (69%) or globemallow (18%) than weevils held without food or water (0%). Weevils emerging from infested bolls in January survived significantly longer (2.4 weeks) than weevils emerging in
March. More female boll weevils which had fed on globemallow in a simulated spring environment attained reproductive status (52%) than similar females held in simulated winter conditions (12%). Gravid females consistently failed to oviposit into buds of globemallow in the greenhouse. When buds were treated with an aqueous cotton extract, oviposition was observed. Oviposition was reduced 54% in cotton squares treated with globemallow extract.
viii INTRODUCTION
The boll weevil, Anthonomous grandis Boheman, has recently become a serious pest in cultivated cotton throughout central and western Arizona. Economic infestations were first observed in 1962 when
"stubbing" cotton was a common practice in Pinal and Yuma Counties (Fye
1968). Stub cotton, i.e., cotton cultivated as a perennial, provided an
ideal overwintering habitat for boll weevils by allowing stalks and bolls
to remain in the fields throughout the winter. Mandatory plowdown and
adjusted planting dates imposed in 1965 subsequently reduced boll weevil
infestations to a noneconomic status (Beatty 1977).
Regulations banning stub cotton were temporarily relaxed from
1978-1982 with approximately 40,000 acres initially cultivated (Taylor
and Hathorn 1979). By 1981, boll weevil infestations were again wide
spread in both stub and planted cotton growing in Maricopa and eastern
Yuma Counties (Bergman et al. 1982). Stub cotton cultivation was again
prohibited after the 1982 growing season in an effort to reduce boll
weevil populations to noneconomic levels. However, boll weevil popula
tions continued to spread west in 1983, damaging previously uninfested
cotton fields near the Colorado River (Borth 1984). Due to heavy in
festations in most of Yuma and La Paz Counties in 1984 and the emergence
of high numbers of overwintering weevils this past spring, boll weevils
now pose a serious threat to the future of cotton production in Arizona
and southern California (Watson 1985).
1 2
It has generally been accepted that stub cotton production was responsible for the current establishment of boll weevil populations in
Arizona. Small undetectable boll weevil populations, probably of Mexican origin (Burke 1968), were able to increase when continual host material was made available. The failure to shred and plow under harvested plants has contributed to the overwintering survival by allowing hibernating adults to remain undisturbed in their developmental cells within mature bolls (Fye and Parencia 1972). Regrowth of cotton terminals through the winter produced squares approximately 6 weeks earlier than annual-grown cotton, providing boll weevils emerging in the spring with an immediate food source (Bergman et a. 1981).
The present 45-day host-free period has failed to significantly reduce boll weevil populations infesting cotton in the spring. With the elimination of cotton plants providing food and shelter in the winter by adequate cultural practices, boll weevils are now successfully bridging overwintering periods as free-living adults in desert habitats. Leggett
(1968) showed that boll weevils freed from dry bolls and placed in cotton trash under winter conditions survived long enough to reinfest planted cotton. However, exactly how the adults survive in nature has not been determined.
Alternate hosts play important roles in the survival of many pests during unfavorable periods. For example, Heliothis spp. are able to utilize various wild hosts when their cultivated hosts are not avail able (Knipling 1979). Although boll weevils are primarily monophagous insects, they have been reported to utilize some species of the Malvaceae family when cotton is unavailable (Cross 1973). Globemallow, Sphaeralcea 3 spp., a perennial malvaceous shrub, is found in all cotton growing areas throughout Arizona. Stoner (1968) reported boll weevil adults feeding on blooms and fruiting buds of globemallow in March and April. Thus, it may be possible that boll weevils are able to survive the cotton-free period by overwintering in globemallow until cotton is available. Al though reproduction in globemallow is not likely, this possibility has not been thoroughly investigated. Therefore, the present studies were initiated to investigate the ability of boll weevils to utilize globe mallow during overwintering periods. The objectives of these studies were to determine: (1) the survival of adult boll weevils in over wintering habitats with respect to globemallow; (2) the ovipositional capacity of boll weevils on globemallow; and (3) the reproductive potential of overwintering boll weevils feeding on globemallow in simulated winter environments. LITERATURE REVIEW
Overwinter Survival
Boll weevil adults overwinter primarily in ground trash near previously infested cotton fields (Beckman 1957). In the southeastern
United States, leaves accumulated under trees in woods serve as an ideal overwintering habitat. Fye et al. (1958) reported that approximately
50% of weevils entering leaf litter in woods survived to emerge the following spring. Adults collected from South Carolina woods trash and reinstalled in several different trash environments survived best in moist litter 8-cm deep (Taft and Hopkins 1966).
Weevils have been shown to overwinter in a variety of habitats in Texas. Davis et al. (1975) reported an average of 35% overwinter survival by weevils in the ground trash of deciduous trees in central
Texas over a 10-year period. Overwintering in shinnery oak mottes, a thicket of hybrid oak trees intermingled with shinnery bush, was shown to enhance boll weevil survival and delay spring emergence (Slosser et al. 1984). In the Lower Rio Grande Valley of Texas, boll weevils were found to successfully survive the winter in desert grasses and ground cover of salt cedar, Tamarix pentandra Pall., mesquite, Prospis spp., and palo verde, Cercidium spp. trees (Graham 1978).
In Arizona, boll weevils have primarily been observed over wintering in dry bolls where stub cotton was grown. Cassidy (1926) observed adult boll weevils surviving the winter in their developmental cells within bolls left on stalks of an abandoned cotton field. Studies
4 5 later confirmed that boll weevils found in stub cotton almost always overwintered in unharvested bolls, unless the bolls were destroyed
(Bottger et al. 1964). Bergman et al. (1982) reported that approxi mately 33% of dry bolls collected from cotton stalks in stub cotton fields in March contained live boll weevils. Furthermore, Watson et al.
(1984) reported that infested bolls collected in mid-November and placed in a shaded breezeway during the winter contained live weevils until early June.
Adult weevils have also been shown to overwinter in Arizona in ground trash near previously infested fields. Leggett and Fye (1969) demonstrated that free-living adults were capable of surviving the winter in simulated ground trash when adequate moisture was available.
Live adults have been collected from leafy ground trash of ironwood tree,
Olyneva tesota Gray, palo verde tree, and creosote bush, Larrea tridentata (DC.) Coville, during January and February (Fye et al. 1970).
However, these same authors reported that similar trash examinations in late March and April yielded no adults. Fye and Parencia (1972) re ported that approximately 30% of the adults placed in cages with sudangrass in January survived to emerge between March 29 and May 18.
Overwinter survival is greater for boll weevils entering habitats late and subsequently emerging from them later in the spring
(Bondy and Rainwater 1942). Overwinter emergence in the Southeast and central Texas is initiated in early May, influenced by warmer tempera tures and a longer photophase (Fye et al. 1958; Hummel and Carrol 1983).
Similarly, overwintering boll weevil adults are first captured in pheromone traps in the Southeast in early May (Roach and Ray 1972). 6
In the Lower Rio Grande Valley of Texas, boll weevils start emerging from overwintering habitats in January and are continually caught in pheromone traps through mid-April (Graham et al. 1978;
Wolfenbarger et al. 1976). Recent studies by Guerra and Garcia (1982) found that boll weevils can be caught in pheromone traps throughout the entire cotton-free period.
The pattern of emergence during the winter in Arizona is similar to that occurring in the subtropical areas of Texas. Emergence from hard bolls was shown to occur from January through May, influenced by temperature and precipitation (Watson, unpublished data). Fye et al.
(1970) maintain that no period of sustained overwinter inactivity is apparent, suggesting that emergence from overwintering habitats occurs when the physiological threshold (13° C) is exceeded. Pheromone trap- catch data indicates that the majority of the overwintering population emerges from January through mid-April (Bariola et al. 1984).
Perhaps the most critical period of overwintering survival is the duration from the time weevils emerge until the time cotton begins to square. Overwintered boll weevils do not enter cotton fields until squares are available in the summer (Ridgeway et al. 1971). In the
Southeast, cotton seedlings are generally available in mid-May, but cotton does not begin to square until mid-June (Roach et al. 1971).
Therefore, weevils must survive a one-month period without food in order to reinfest cotton. Hunter and Hinds (1905) estimated that weevils could survive approximately 58 days after emergence from an overwinter habitat. However, Fye et al. (1958) reported an average longevity of
22 days in field cage studies in South Carolina. 7
Planting dates in Arizona vary throughout the state, which determine when cotton is available for overwintering boll weevils.
Squaring in southwestern Yuma County begins as early as May (Don
Howell, personal communication). Since boll weevils are active all winter in Arizona, adults may have to survive for long periods when no cotton is available. Fye and Parencia (1972) reported that the mean longevity of boll weevils emerging in Arizona in March was 12.5 days when no sustenance was provided. More recently, Bariola (1984) found that weevils caught in pheromone traps lived an average of less than
10 days when placed in an insectary with no food or water.
Boll weevils in the Southwest may search for alternate hosts during favorable conditions when cotton is not available. The pollens of many malvaceous plants are known to be utilized by boll weevils as alternate food hosts, most of which occur in areas where weevils are active throughout the winter (Cross et al. 1975). Adults, indigenous to tropical areas of Mexico, rely on Hibiscus tiliaceus L. as a food source to bridge the dry season from February to May (Guerra et al.
1984). In west Texas, yellow woollywhite, Hymenopappus flavescens Gray is available as a food host as boll weevils emerge from nearby habitats
(Rummel et al. 1978). Overwintered weevils caged on H. flavescens survived significantly longer than weevils provided with free moisture only (Rummel and Carroll 1984). Globemallows, Sphaeralcea spp., are utilized by boll weevils in Arizona as alternate food hosts. At least five native perennial species bloom throughout the winter in cotton- growing areas (Kearny 1964). Longevity of adults on fruiting tips of globemallow ranged from 13 to 53 days in April (Stoner, 1968). Boll 8 weevils taken from pheromone traps in January survived a maximum of 42 days when caged on flowering globemallow plants in an outdoor insectary
(Bariola, 1984).
Feeding and Oviposition
Cultivated upland cotton, Gossypium hirsutum L. (Family
Malvaceae) is considered the primary host of the boll weevil in the
United States. Cotton production occupies up to 600,000 acres in the desert valleys of Arizona, where the growing season may extend from
February through November (Anonymous 1985). A wild species of cotton
Gossypium thurberi Todaro, is found in the mountain ranges of southern
Arizona at elevations above 3,000 ft. (Kearney et al. 1964). An endemic race of Anthonomous grandis, var. thurberiae, the thurberia boll weevil, breeds in the capsules of the thurberia boll. However, this weevil form is not believed to be the same weevil attacking cultivated cotton, which is of Mexican parentage (Burke 1968).
Boll weevils utilize the squares (floral buds) and bolls
(seed-producing fruit) for adult feeding and oviposition as well as developmental sites of the immature stages. Adult weevils prefer squares for oviposition and feeding in the Southeast (Hunter and Hinds 1905).
Isley (1928) reported that early-season squares are essential for re production and establishment of the F^ generation, since weevils which fed on terminal foliage deposited no eggs. In Arizona, Fye and Parencia
(1972) indicated that females showed a slight preference for bolls for ovipositing, although squares were preferred at certain times. However, 9 the percentage of infestation in these sites varies with the season and condition of the plants (Burke 1976).
Boll weevil development can be very rapid, depending on tem peratures and site of development. Adults were reared from squares in a much shorter time than from bolls in the Southeast where an average of
5 generations per year are observed (Hopkins et al. 1969). Sterling and Adkisson (1971) reported that the development of boll weevils in field cages varied from 11 days in squares compared to 31 days in bolls late in the growing season in Texas. In Arizona, approximately 390 heat units are required for completion of immature development in squares, compared to approximately 507 heat units in bolls (Huber 1984). There may be as many as eight generations in a year where full-season cotton is grown (Moore 1983).
Female adults emerging from developmental sites during the growing season pass through a preovipositional period of approximately
4 to 5 days, varying slightly with temperatures and diet (Lincoln 1976).
Diapausing boll weevils taken from South Carolina woods trash in
January and brought into the greenhouse began ovipositing in squares after feeding an average of 17.9 days (Roach 1979). However, weevils from pheromone traps in Texas and Arizona collected during the winter oviposited as early as 6 days after feeding on squares in the labora tory (Beriola 1984; Guerra et al. 1982).
Boll weevils oviposit in squares by making a hole in the plant tissue during feeding. After deposition of a single egg, the puncture is usually sealed with a secretion of frass forming a wartlike cap
(Mitchell and Cross 1969). Hunter and Pierce (1912) reported that 10 squares of intermediate size were preferred for oviposition. In a com parison study, Fenton and Dunham (1929) observed that females usually oviposited in squares from 6 days old until 3 days prior to blooming.
Evert and Earle (1963) found that females preferred cotton squares weighing about 319 mg for oviposition.
The size or texture of squares may not be a critical factor in initiating a feeding puncture, as long as the proper feeding stimulant is present. Keller et al. (1962) reported the presence of water soluble substances from cotton squares which arrested boll weevil behavior and stimulated feeding on treated unnatural substrates such as agar plugs and bean pods. Jenkins et al. (1963) found that okra, Hibiscus esculentus L., and cucumber, Cucumis sativus L., seedlings which are normally unacceptable as food hosts to the boll weevil, were readily fed upon after being sprayed with an aqueous square extract. Although all parts of the cotton plant contain boll weevil arrestants and feeding stimulants, the calyx surrounding the square contains the highest concentrations (Maxwell et al. 1963).
Factors which influence the selection of host feeding sites or initiate feeding may also influence egg deposition. Richardson (1925) concluded that the prerequisites for oviposition were suitable surface, odor and chemical stimuli. Cotton squares and bolls possess the chemi cal qualities that contribute to the acceptability of cotton as a substrate for egg deposition (Evert and Ray 1962). The presence of resin glands on squares is considered an important factor in stimu lating oviposition (Stephens 1959). Vanderzant and Davitch (1958) found that eggs were deposited in artificial diets containing ether or 11 ethanol extracts of cotton pollen, but not in diets lacking the extract.
Evert and Earle (1964) reported that cotton anthers contain a water soluble component capable of stimulating gravid females to deposit eggs in agar plugs coated with wax.
Reproduction on Alternate Hosts
The boll weevil is usually considered host specific to cotton but certain alternate hosts have been observed. Presently, boll weevils are known to develop only on plants within several genera of the tribe
Gossypiae (Family Malvaceae) (Burke 1976). Fryxell (1968) reported that of the 8 genera in the tribe, at least some species in 4 genera
(Gossypium, Cienfugosa, Thespesia and Hampea), are significant as repro ductive hosts. A few other malvaceous genera not included in the above tribe (Hibiscus, Sphaeralcea and Pseudobutilon), may act as marginal hosts (Cross et al. 1975). That is, limited natural reproduction has been observed once or on very few occasions.
Boll weevils are believed to have infested cultivated cotton
(G. hirsutum) as early as A.D. 900 in Oaxaca, Mexico (Warner and Smith
1968). The weevil was first reported on cultivated cotton in Monclova,
Mexico (Jones 1962) and later observed in Texas near Brownsville in 1893
(Howard 1984). The boll weevil has subsequently spread to all cotton- growing areas in the United States, with the exception of areas of
California (Beasley and Henneberry 1985).
The first record of boll weevils feeding on a host other than
Gossypium in nature was reported by Coad (1914). He observed the emer gence of a single adult from Hibiscus syriacus L., at Victoria, Texas, growing near a weevil-infested cotton field. Gaines (1933) confined weevils on H. syriacus and reported larval development on flower buds of the plants. Bondy and Rainwater (1935) found mature larvae developing in H. syriacus in South Carolina and observed limited adult emergence from infested buds. Wormser (1944) reported boll weevil feeding and oviposition on young okra pods, Hibiscus esculentus L., but immature development did not occur. Parrot et al. (1966) concluded that limited natural reproduction occurs in Hibiscus spp. only when the plant is growing near heavily infested cotton and is therefore not an important alternate host.
Within the general range of the boll weevil, six species of the genus Cienfugosia grow throughout the year. Two of the species,
C. drummondi (Gray) and C. rosei Fryxwell are known to be reproductive hosts of boll weevils in south Texas (Lukefahr and Martin 1962). Burke and Clark (1976) reported that plants at approximately one-third of the localities known for Cienfugosia spp. had been found to be infested with boll weevils. Cross et al. (1975) suggested that boll weevils may be able to maintain small populations on C^. drummundj in south Texas in the absence of cotton.
Another plant genus which boll weevils sometimes utilize in nature is Thespesia. Lukefahr (1956) reported finding boll weevil larvae in the floral buds and seed pods of Thespesia populnea (L.) plants growing near heavily infested cotton fields near Brownsville,
Texas. Later, Lukefahr and Martin (1965) successfully reared several generations of boll weevils on Thespesia lampas (Cav.) in field cages in south Texas. 13
The most recent discovery concerning possible alternate hosts of boll weevils was made by Fryxell and Lukefahr (1967) who observed immature weevils developing in flower buds of Hampea rovirosae Sandl., in Veracruz, Mexico. The weevil populations attacking the Hampea trees in Veracruz were felt to be endemic, since the closest cultivated or wild cotton was approximately 100 miles away. Maxwell et al. (1969) observed that although oviposition occurred in all fruiting bodies of this dioecious species (H. rovirosae), immature development did not occur in the female trees. A mechanism of resistence (non-preference) in the female buds discourages selection by adult female boll weevils and bud substrates prevented development (antibiosis) of boll weevil larvae (Lukefahr and Maxwell 1969).
None of the above malvaceous genera discussed has been ob served growing wild in Arizona. However, Sphaeralcea spp. is commonly
found growing throughout the state. As reported earlier, Sphaeralcea is a food source for boll weevils during the winter when cotton is not growing. Stoner (1968) reported collecting teneral boll weevils from
fruiting buds 7 days after placing them in emergence boxes. The author
theorized that the weevils did not develop on the plants but rather,
were feeding on the buds at the time of the collection. Although Coad
(1914) was unsuccessful in rearing boll weevils on Sphaeralcea
lindhiemeri (Cav.), Cross et al. (1975) reported the emergence of a
teneral adult from a flower bud of this species at Presidio, Texas. 14
Overwinter Reproductivity
Overwintering adult boll weevils spend the winter in a physio logical state of diapause in the southeastern United States. Early researchers felt that during the winter, boll weevils became inactive as a response to low temperatures and unavailability of suitable hosts
(Hinds and Yothers 1909). However, Brazzel and Newsom (1959) reported that portions of boll weevil populations in Louisiana entered a true diapause characterized by the termination of reproductive activity, cessation of gametogenesis, gonadal atrophy and increased lipid accumulation.
Several environmental stimuli are apparently responsible for inducing diapause in the boll weevil. Field and laboratory studies have demonstrated that the reproductive status of weevils during winter can be changed with alterations of food, temperature and photoperiod
(Phillips 1976). Earle and Newsom (1964) found that reproductive in activity could be induced by short (11-hour) photophases and suppressed
by long (13-hour) photophases and increased temperatures. Lloyd et al.
(1967) reported that various environmental stimuli induced diapause characteristics in the boll weevil. These included: exposure to an
11-hour photophase in larval and pupal stages; exposure to night tem
peratures of 10° C as an adult; and boll feeding in the larval and
adult stages.
Boll weevils in the southeastern United States and central Texas
first exhibit diapause characteristics in early August when night tem
peratures decrease and very few squares are available for feeding
(Mitchell and Mistrict Jr. 1965). Cole and Adkisson (1983) found that 15 the greatest percentage of boll weevils in central Texas entered diapause in early October and remained in this state until late spring.
Mitchell and Hardee (1974) reported that boll weevils in diapause tend not to respond to pheromone traps but remain in overwintering habitats during warm periods.
A true diapause does not appear to occur in boll weevil populations found infesting cotton in the subtropical areas of Texas and Mexico. Initial studies by Graham et al. (1979) indicated that boll weevil adults examined in the fall began exhibiting diapause charac teristics about the time cotton fields were defoliated in July and
August. Wolfenbarger et al. (1976) found that weevils caught in pheromone traps during the winter were nonreproductive. However, recent studies by Guerra et al. (1982) indicated that boll weevils overwinter ing near Brownsville, Texas accumulated fat but remained reproductive and physiologically active all winter. The authors maintain that a quiescent or "resting" state more accurately defines the overwintering physiological condition that boll weevils exhibit during the mild sub tropical winters. Guerra et al. (1984) attributed this quiescent overwintering behavior as a survival mechanism to avoid starvation during cotton-free periods.
Most overwintering boll weevils in Arizona do not meet the criteria of a true diapause associated with weevils in the southeastern
United States. Fye et al. (1970) considered 75% of boll weevils col lected from desert ground litter in January as reproductive. Bergman et al. (1983) reported that the majority of adults captured in pheromone traps through the winter did not exhibit true diapause characteristics. Bariola (1984) found that some female boll weevils caught in traps in March were capable of oviposition after feeding on
squares of cotton for 3 days. METHODS AND MATERIALS
Overwinter Survival
Boll weevil survival, as influenced by the availability of globemallow, was studied during the winter and spring of 1984 in an outdoor insectary in Tucson, Arizona. The insectary was modified to simulate, as closely as possible, actual winter and spring temperatures occurring in Yuma County. Daily maximum and minimum temperatures were recorded with a hygrothermograph (B.I.C. Model 7410). Cotton squares used in the study were collected from plants (Deltapine 62) reared in a greenhouse. Globemallow terminal branches with flower buds were collected twice weekly from plants in Pima and Yuma Counties. The collections belonged predominantly to three species: Sphaeralcea emoryi
Torrey, _S. coulteri (Watson) Gray and £>. ambigua Gray.
Adult boll weevils were collected from dry bolls remaining on stalks in an unplowed cotton field in the North Gila Valley (Yuma
County) on January 10, 1984. The following day, fifty unsexed adult boll weevils were placed in each of 3 plastic containers with screened plastic tops. In two containers, boll weevils were provided with the following: (1) 15-20 terminal branches of globemallow providing an abundance of flower buds; and (2) 15 cotton squares and 5 cotton bolls.
In the third container the weevils were kept without plant material or water (DRY). A double-layered paper towel was placed in the bottom of the dry containers to provide shelter. Squares and globemallow
17 were replaced twice weekly when the number of surviving boll weevils was recorded.
A similar study was initiated on March 17, 1984. Adults were collected from dry bolls which had been collected on January 10, 1984, and placed in the insectary until the beginning of this study. The boll weevils were provided with food sources identical to the earlier study.
Male and female boll weevils removed from dry bolls collected in Yuma County on January 10, 1984, were paired and placed in 1 oz clear plastic containers. Each pair was provided a cotton square on which to feed and oviposit. The boll weevil pairs were placed in tem perature cabinets equipped with temperature controls (Partlow Control
Model RFC32) and programmable light switches (York Time Switch Model
72207). The cabinets were set at a constant temperature of 30° C with a 14 L : 10 D photoperiod. The squares were replaced every 2 days and examined for egg deposition for approximately 4 weeks. After this period nonreproductive pairs were discarded. Thirty reproductive pairs were then placed in fresh 1 oz clear plastic containers provided with either: (1) 2 cotton squares; (2) 5 £>. emoryi buds, or (3) 5 £5. coulteri buds. The containers were then replaced in the controlled temperature cabinets. The squares and buds were removed and dissected daily over a 7 day period to determine if oviposition had occurred.
Eggs which were placed within a puncture were classified as internally 19 oviposited and those either deposited on the fruit or on the con tainer were classified as external.
Additionally, similar pairs of reproductive adults were placed on either cotton or globemallow plants which were enclosed in 90 x 90 x
60 cm screened cages and placed in a greenhouse set at a mean tempera ture of 26° C on March 3, 1984. Ten reproductive pairs were placed on
DPL 62 plants growing in 2-gallon containers. Fifteen pairs were placed on Sphaeralcea spp. plants growing in 3-gallon containers. Individual plants were removed and replaced daily, and all fruiting structures were dissected for determining presence of eggs. The study was terminated after 7 days.
Effects of aqueous extracts of cotton and globemallow on boll weevil ovipositional and feeding behavior were studied in the labora tory. Adult weevils used in this study were collected from infested squares and bolls in a cotton field at the Yuma Valley Agricultural
Center on October 4, 1984. Adults were paired and allowed to become reproductive following the same procedure as in the previous oviposi tional studies.
A cotton square extract was prepared similar to that described by Maxwell et al. (1965). A 15-gram fresh-weight sample of squares approximately 12 days old was blanched in 200 ml of boiling distilled water for 5 minutes. These squares were then ground to a fine paste with a small amount (30 ml) of distilled water and centrifuged in an
I.C. clinical centrifuge (Model CL) at #4 speed for 30 minutes. After centrifugation, approximately 18 ml of water extract was poured off and placed in a test tube. 20
A globemallow water extract was prepared similar to the square extract. Fifteen grams of SL emoryi flower buds were blanched in 150 ml of distilled water for 5 minutes. Buds were quickly frozen for 10 days at -5° C. The buds were then ground to a paste with 30 ml of distilled water and centrifuged at #4 speed for 1 hour. Centrifugation took longer than the cotton extract due to difficulty in separating the aqueous layer from the gummy plant material. Approximately 20 ml of basic extract were poured off and placed in a test tube.
Reproductive females were placed in petri dishes with #6 Watman filter paper and provided with either: (1) 15 globemallow buds soaked in distilled H20 for 5 minutes; (2) 15 globemallow buds soaked in cotton extract for 5 minutes; (3) 5 cotton squares soaked in globemallow extract for 5 minutes, or (4) 5 cotton squares soaked in distilled water for 5 minutes. Each petri dish contained 5 females and treatments were repli cated 4 times for a total of 20 reproductive females exposed to each treatment. The petri dishes were then placed in a controlled environment of 30° C and 14 L : 10 D photoperiod.
The treatments were removed after 12 hours, replaced with freshly treated material which was again removed after another 12 hours of exposure. The treated buds and squares were examined at both inter vals and the number of feeding punctures and eggs deposited, externally or internally, was recorded.
Preoviposition
Preoviposition studies of overwintering female boll weevils were
conducted in the laboratory in a constant 30° C temperature and a 14 L : 10 D photoperiod. Adult boll weevils were collected from dry bolls at the Yuma Valley Agricultural center on October 4, 1984. Forty-five pairs of newly emerged adults were separated into three equal groups.
Within each group, 15 individual pairs were placed into 1 oz containers.
Each group was provided either: (1) a cotton square; (2) an artificial diet pellet (Hilliard and Keely 1984), or (3) 5 globemallow buds. The food sources were removed and dissected daily until oviposition was observed. The number of days after emergence until the first egg was deposited was recorded. Females which were fed on globemallow were classified as ovipositing when eggs were first observed either exter nally or internally deposited. Eggs oviposited on the first day were transferred to an artificial diet in 1.5 oz plastic containers and examined daily for emerging larvae. If eggs failed to hatch after 8 days, they were considered nonviable.
An additional preoviposition study was undertaken to determine the influence of feeding on globemallow prior to oviposition in cotton squares. Eighty pairs of newly emerged boll weevils were separated into 4 groups. Within each group, individual pairs were placed in 1 oz plastic containers. Each group was provided one of the following con ditions: (1) squares; (2) globemallow buds for 5 days, replaced by squares on day 6; (3) globemallow buds for 10 days, replaced by squares on day 11, or (4) globemallow buds for 15 days, replaced by squares on day 16. Only squares were dissected daily for presence of egg deposi tion. The number of days that females fed on squares prior to initiation of oviposition was recorded. Eggs deposited in squares on 22 the first day were transferred to artificial diet and observed for larval emergence.
Overwinter Reproductivity
Adult boll weevils were obtained from infested bolls in a field near Roll, Arizona (Yuma County) on November 4, 1984. The following day 25 newly emerged adult pairs were placed in each of 8 waxed cardboard containers with screened tops and provided with 5 cotton squares. Additionally, 25 pairs of newly-emerged adults were placed in each of 8 containers and provided with 10-12 globemallow fruiting branches. Half of the containers of boll weevil pairs pro vided with globemallow and cotton were placed in temperature cabinets with temperatures fluctuating from 6.1° to 22.8° C with a 10 L : 14 D photoperiod simulating winter conditions. The remaining containers (4 globemallow and 4 cotton) were placed in temperature cabinets with tem perature fluctuating from 12.7° to 31.1° C and a 12 L : 12 D photo- period approximating springtime conditions. Boll weevils in one container from both temperature regimes and host food source were dissected at 15-day intervals thereafter. The dissected boll weevils were examined for fat accumulation and reproductivity using criteria similar to that of Brazzel and Newsom (1959). Female boll weevils with oocytes in their ovaries and males with enlarged testes or seminal vesicles distended with sperm were considered reproductive. Individual weevils whose tracheae and internal organs were at least partially ob scured by yellow adipose tissue and showed no evidence of gametogenesis were classified nonreproductive/fat. RESULTS
Overwinter Survival
Significant differences were found among the survival means of boll weevils obtained from bolls when provided nothing (dry), globe- mallow buds, and cotton squares (Table 1). Longevity of boll weevils provided with globemallow was approximately 4 times greater than weevils without globemallow. The means for survival at 45 days were 95, 86, and
4% respectively, when boll weevils were provided with cotton squares, globemallow or nothing (Figure 1). At 90 days, mean survival was 60% for those weevils provided with cotton squares compared to only 18% for those provided with globemallow.
Mean survival of boll weevil adults that emerged from bolls in
January when provided nothing (dry) and globemallow was significantly greater than the mean survival of adults that emerged in March (Table
2). However, no significant difference was found between survival means of adults when provided with cotton squares for food.
Figure 2 shows the mean percentage of survival of boll weevils that emerged during January and March and then maintained without food
(dry). After 15 days, mean survival was 72 and 14% for weevils that had emerged in January and March, respectively. After 35 days, weevils emerging in March were dead, but 10% of weevils emerging in January were still surviving.
For boll weevils provided with globemallow after emergence, survival amounted to 65 and 53% at 60 days for weevils emerging in March
23 Table 1. Average survival and maximum longevity of overwintering boll weevils emerging from bolls in January and March and provided various conditions in the insectary, 1984.
Conditions Average Maximum Provided No. Weeks Weeks
Dry 2.2 + 0.9 & 5.9
Globemallow 8.9 + 3.1 b 19.7
Cotton Squares 15.5 + 5.8 c 24.8
1/ standard deviation and means in each column followed by a different letter are significantly different as indicated by analysis of variance and mean separation using Newman-Keuls Sequential Studentized Range (p=.05). •I COTTON EBB GLOBEMALLOW
DAYS AFTER EMERGENCE FROM BOLLS
Figure 1. Total average percentage of boll weevils surviving at 15, 30, 45, 60, 75, and 90 days held without food (dry) or provided globemallow and cotton squares in the insectary. 26
Table 2. Average number of weeks adult boll weevils survived in the insectary after removal from dry bolls and kept without food or provided globemallow or cotton squares, 1984.
- Food Source Date of .. Emergence— None Globemallow Cotton
10 January 3.0 a—^ 9.6 a 16.8 a +1.2 +3.9 +5.2
17 March 1.3 b 7.2 b 15.7 a +0.5 +2.6 +6.3
— Date when adults were removed from infested bolls and placed in the insectary with or without a food source.
2/ — standard deviation (n=50) and means in each column followed by by a different letter are significantly different as indicated by analysis of variance and mean separation using Newman-Keuls Sequential Studentized Range (p=.05). JANUARY
MARCH
15 21 28 35
DAYS AFTER EMERGENCE FROM BOLLS
Figure 2. Percentage of boll weevil adults surviving in the insectary 7, 15, 21, 28 and 35 days provided dry conditions after emerging from dry bolls in January and March, 1984. 28 and January, respectively (Figure 3). However, after 90 days, survival of January-emerged weevils was 32% as compared to 5% for those which emerged in March.
The total and daily average heat units accumulated by boll weevils when provided with globemallow or nothing (dry) in the insec- tary are shown in Table 3. Although weevils emerging in January under dry conditions accumulated more average total heat units, adults emerg ing in March accumulated almost twice as many heat units per day. Boll weevils which emerged in March accumulated more daily and total heat units when provided with globemallow.
Oviposition
Reproductive female boll weevils, which had fed on cotton squares for 28 days after adult ecdysis, failed to oviposit in globemallow buds under optimal conditions in the laboratory. However, a few eggs were deposited externally on or near the buds in the containers (Table 4).
Similar reproductive females oviposited normally into cotton squares during the same time interval.
Ovipositional results of reproductive females, caged on plants is presented in Table 5. Females failed to oviposit either on or in the buds or blooms of Sphaeralcea plants in the greenhouse. Although numerous eggs were deposited in squares on caged cotton plants these females laid approximately 1 egg per day less than those on squares in the laboratory.
Limited oviposition by reproductive females occurred in globe mallow buds that were coated with an aqueous extract of cotton squares JANUARY
100 MARCH
80 \
60 \
40
20
'•'iii 15 30 45 60 75 90
DAYS AFTER EMERGENCE FROM HARD BOLLS
Figure 3. Percentages of boll weevil adults surviving in the insectary provided with globemallow after emerging from dry bolls in January and March, 1984. 30
Table 3. Summary of average heat unit accumulation in the insectary for boll weevils which were maintained under dry conditions or with globemallow after emerging from dry bolls in January and March, 1984.
Overwintering Fahrenheit Heat Units Conditions Maintained Cumulative (Daily) Range
Dry January 168.0 53 - 364 (7.8) (7.7 - 8.6)
March 129.8 59 - 263 (12.1) (11.5 - 12.4)
Globemallow January 640.4 83 - 1606 (9.2) (6.9 - 12.6)
March 976.2 154 - 1710 (15.9) (12.8 - 18.1) Table 4. Total number of eggs oviposited by gravid female boll weevils provided with cotton squares, and two species of globemallow buds in a one week period in the laboratory, 1984.
Host Provided 1/ Internal External 2/
Cotton Squares 453 19
Sphaeralcea emoryi 0 10
Sphaeralcea coulteri 0 8
1/ o — Females were placed in temperature cabinets set at 30 C and a 14-hour photophase. 2/t — Eggs were deposited on the outer surface of the calyx and corolla of squares and buds or on the surface of the containers.
Table 5. Total number of eggs oviposited by gravid females caged on cotton and globemallow plants in the greenhouse in a one week period, 1984.
Host Provided Internal External
Cotton Plants 239 0
Sphaeralcea spp. plants 0 0 32
(Table 6). When buds were dissected after 12 hours of exposure to females, 3 eggs had been deposited internally among the anthers of 2 separate buds. After the second 12-hour exposure no eggs were found.
During the 24-hour period, 19 eggs were deposited externally, 15 of these were near punctures on the corollas of the buds. Females that were provided with globemallow buds treated with distilled water did not oviposit. Cotton squares treated with an aqueous extract of globe- mallow buds contained approximately one-half as many eggs as the squares treated with distilled water.
Cotton squares treated with globemallow extract contained sig nificantly fewer feeding punctures than untreated squares after both 12 and 24 hours of exposure (Table 7). No significant difference in mean number of feeding punctures by boll weevils between treated squares and treated buds was found after either 12-hour exposure period. Globemallow buds treated with cotton extract were fed on to a greater extent than were untreated buds after 12 hours, but no statistical differences were observed at 24 hours.
Preoviposition Development
The average first day of oviposition was significantly different between newly-emerged females provided with cotton squares, artificial diet, or globemallow buds (Table 8). Females provided with globemallow buds fed for an average of 10 days longer than did those provided with cotton squares before oviposition was initiated. Although females that fed on globemallow only deposited eggs externally, 16% of the eggs yielded viable immature boll weevils. The percent of females which 33
Table 6. Total number of eggs oviposited by reproductive female boll weevils on cotton and globemallow treated with aqueous ex tracts in the laboratory in a 24-hour period.
Eggs Deposited Treatment—^ Internal External—^
SQS 141 4
SQS/GM Extract 76 1
GM/SQS Extract 3 19
GM 0 0
— Treatment Legend: SQS = cotton squares; SQS/GM Extract = cotton squares treated with globemallow extract; GM/SQS Extract = globe- mallow buds treated with cotton square extract; GM = globemallow buds.
2/ — Eggs deposited on the outer surface of the calyx and corolla of squares and buds, or on the surface of the container. 34
Table 7. Average number of feeding punctures by reproductive female boll weevils in cotton squares and globemallow buds, alone or treated with aqueous extracts.
Treatment— 12 Hours 24 Hours
SQS 12.0 +4.2 a—^ 11.2 +4.6 a
SQS/GM Extract 7.2 +3.1 b 6.0 +2.6 b
GM/SQS Extract 7.0 +2.8 b 5.5 +1.7 b
GM 2.4 +1.4 c 2.3 +1.8 b
— Treatment Legend: SQS = cotton squares; SQS/GM Extract = cotton squares treated with globemallow extract; GM/SQS Extract = globe- mallow buds treated with cotton square extract; GM = globemallow buds.
2/ — + standard deviation (n = 20) and means in each column followed by a different letter are significantly different as indicated by analysis of variance and mean separation using Newman-Keuls Sequential Studentized Range (p = .05). 35
Table 8. Average number of days required for newly-emerged females to oviposit when feeding on various food sources at a constant temperature of 30° C with a 14-hour photophase, 1985.
2/ • Average Day First- Percent—^ Food Source Egg Oviposited Egg Viability
Cotton squares 5.7 +1.4 a 72 a
Artificial diet 8.1 +1.2 b 65 a
Globemallow buds^ 15.8 +3.9 c 16 b
—^Females were considered ovipositing when eggs were observed oviposited externally; no eggs were oviposited internally in the globemallow buds.
2/ — +_ standard deviation (n = 20) and averages in column followed by a different letter are significantly different as indicated by analysis of variance and mean separation using Newman-Keuls Sequential Studentized Range (p = .05).
—^Percent of first eggs oviposited in which a viable immature boll weevil emerged. 36 produced viable eggs was significantly higher when allowed to feed on cotton squares and artificial diet.
Placement of females on globemallow buds prior to their place ment on cotton squares significantly reduced the amount of time to first oviposition. Females that fed on globemallow buds for 15 days before placement on squares, produced eggs 4 times earlier after feeding on squares than did females which were provided only squares upon emergence (Table 9). When females were fed on globemallow buds for 5 days, oviposition occurred twice as early as females fed on cotton squares. The percent egg viability was higher for females that fed on cotton squares only; however, that by females feeding on globemallow was more than 50% in all cases.
Overwinter Reproductivity
Boll weevils provided cotton squares, in two simulated over wintering environments were more reproductive than weevils which were provided with globemallow buds (Tables 10 and 11). Male boll weevils tended to be more reproductive and accumulate less fat than did females regardless of host provided or simulated environment to which they were exposed. The mean percent of female boll weevils attaining reproductive status when provided globemallow for 60 days was 12% and 52%, respec tively, when placed in simulated winter and spring environments. The total percentage of female boll weevils accumulating fat after 60 days of "feeding on globemallow in simulated winter and spring environments was 44% and 29% respectively. 37
Table 9. Preovipositional status of newly-emerged female boll weevils provided with globemallow for 0, 5, 10 and 15 days prior to placement on squares.
. NO. DAYS PROVIDED GLOBEMALLOW Reproductive — Averages — 0 5 10 15 2/ Day First Egg— Ovip. in Square 5.7 a 2.6 b 1.8 be 1.5 c +1.4 +1.5 +1.3 +0.7
Percent Egg Viability 72 52 55 59
H.U. Accum.—^ On Squares 165 75 52 43
—^Females provided with squares only.
2/ — Average number of days females fed on squares before oviposition was observed following globemallow feeding periods. + standard deviation (n = 20) and means in row followed by a different letter are signifi cantly different as indicated by analysis of variance and mean separation using Newman-Keuls Sequential Studentized Range (p = .05).
3/ — Average number of heat units accumulated until oviposition was observed after placement on squares on constant 30° C. 38
Table 10. Number and percentage of male boll weevils which were reproductive (R).or nonreproductive (NR) after feeding on cotton squares or globemallow buds in simulated winter and spring environments.
_ 1/ „ . 2/ Winter— Spring—
NR NR 3/ 4/ Days Fed R— Lean Fat— R Lean Fat
COTTON
15 5 9 11 15 6 4 30 10 6 9 18 2 5 45 11 3 11 21 1 3 60 13 3 9 22 0 15
Total % 39 21 40 76 9 15
GLOBEMALLOW
15 3 12 10 12 5 8 30 7 10 8 16 1 8 45 9 8 7 18 0 7 60 10 8 7 18 1 6
Total % 29 38 33 64 7 29
— Males were placed in temperature cabinets set at a variable temperature of 6-22° C with a 10 L : 14 D photoperiod, simulating winter con ditions (December-February) in western Arizona.
2/ — Males were placed in temperature cabinets set at a variable tempera ture of 13-32° C with a 12 L : 12 D photoperiod, simulating spring conditions (March-April) in western Arizona.
—^Males with enlarged testes and seminal vesicles which were distended with sperm were classified as reproductive.
4/ — Males with yellow adipose tissue at least partially obscuring trachaea and alimentary canal were classified as nonreproductive. 39
Table 11. Number and percentage of female boll weevils which were reproductive (R) or nonreproductive (NR) after feeding on cotton squares or globemallow buds in simulated winter and spring environments.
1/ 2/ Winter— Spring—
NR NR 3/ 4/ Days Fed R— Lean Fat— R Lean Fat
COTTON
15 4 7 14 15 4 6 30 6 7 12 17 2 6 45 7 5 13 20 0 5 60 10 4 11 20 0 5
Total % 27 23 50 72 6 24
GLOBEMALLOW
15 1 11 13 10 7 8 30 3 11 11 12 6 7 45 3 12 10 14 4 7 60 5 10 10 16 2 7
Total % 12 44 44 52 19 29
— Females were placed in temperature cabinets set at a variable tem perature of 6-22° C with a 10 L : 14 D photoperiod, simulating winter conditions (December-February) in western Arizona.
2/ — Females were placed in temperature cabinets set at a variable tem perature of 13-32° C with a 12 L s 12 D photoperiod, simulating spring conditions (March-April) in western Arizona.
—^Females with oocytes in their ovaries were classified as reproductive.
4/ — Females with yellow adipose tissue at least partially obscuring trachaea and alimentary canal were classified as nonreproductive. 40
Total heat unit accumulation for each dissection period, 15-day intervals, is shown in Table 12. Significantly more heat units were accumulated at each dissection interval by adult boll weevils placed in simulated spring environments. The total average heat units accumulated
by adults was 237 and 612, respectively, for adults placed in simulated winter and spring environments. 41
Table 12. Total number of heat units accumulated at 15-day intervals in simulated environments in the laboratory.
Simulated Overwinter Environment^ Days Winter Spring
15 96 245 30 192 490 45 279 734 60 384 980
Total Average 237.8 612.3
— Temperature cabinets in the laboratory set to simulate environmental conditions during the winter and spring (December-April) in western Arizona. DISCUSSION
Overwintering adult boll weevils which were provided globe- mallow to feed on in the insectary, survived significantly longer than did weevils held under dry conditions. The optimum survival occurred where boll weevils were allowed to feed on cotton squares, but this was expected since cotton is considered the primary host (Cross et al.
1975).
As discussed previously, boll weevils are known to feed exclusively on various genera within the family Malvaceae, of which globemallow is included. All boll weevils that were placed on ter minal branches of globemallow in this study fed readily upon the pollen in buds, greatly extending their survival. According to Cate and Skinner (1978) boll weevils are primarily pollen-feeding insects.
The extent to which globemallow pollen was metabolized and physio logically utilized by the boll weevil was not determined in this study. However, since weevils which fed on globemallow survived approximately 4 times longer than did weevils held under dry con ditions, it is presumed that pollen provided some nourishment or at least metabolic water. Without food or water available to replenish water lost through transpiration, dehydration will quickly result in dea-th (Edney 1977), which ultimately occurred with the weevils which were provided with no food and held under dry conditions.
The time period at which boll weevils emerge from over wintering habitats and begin to actively search for a food source
42 appears to influence their longevity. Boll weevils which were re
leased from dry bolls during early winter lived for longer periods than
did weevils that emerged in spring. Considering the three host con
ditions that weevils were provided, adults which emerged in January
survived an average of 25 days longer than did weevils which emerged
in March. This is primarily attributed to differences in temperature
(daily heat accumulation), which was greater in the insectary in the spring. However, before being removed from infested bolls, weevils emerging in March had remained enclosed in bolls in the insectary during January and February, exposed to similar temperatures that free-living adults were experiencing. Thus, March emerged weevils actually survived for 2 months within bolls in the insectary before becoming free-living adults.
Since boll weevils are poikiolthermic, metabolism and physio logical activities are regulated by the temperatures they encounter.
Insect longevity is usually greatest at the lowest temperature at which an insect can normally feed with a minimum expenditure of ener gy (Chapman 1982). Boll weevils actively overwintering in the insectary, beginning in January, were exposed to shorter days and accumulated fewer heat units per day. Adults which were provided with no food or water and held under dry conditions depended on fat re serves accumulated during immature development to maintain metabolic activity. The adults emerging in March probably experienced a greater depletion of their fat reserve on a daily basis as well as previous expenditures of energy while encapsulated in dry bolls. Therefore, these adults exhibited a more rapid increase in mortality. This 44
conclusion is consistent with Fye et al. (1958) who showed that over
wintering boll weevils which maintained the most crude lipids lived the
longest. Similarly, boll weevils feeding on globemallow during periods
of lower daily heat accumulation could maintain a better balance be
tween the utilization of nutrients and metabolism of any fat reserves.
Boll weevils subjected to cooler temperatures would also be able to
better conserve their water balance as a result of feeding on globe-
mallow pollen. Furthermore, the relative humidity in the insectary
was greater in January and February than at any other time during the
study. Since the loss of metabolic water is greatest under low humi
dity (Ramsay 1935), weevils which emerged in March probably experienced
greater dehydration than did those that emerged in January.
The capability of boll weevils to utilize globemallow pollen
to extend overwinter survival is important. To successfully reinfest
cotton the following season, overwintering boll weevils must survive
a cotton-free period of approximately 4 months during the winter and
spring. Overwintering weevils actively search for hosts when daytime
temperatures exceed their physiological threshold (Fye et al. 1970).
Evidence of this activity (locomotion and feeding) was observed in the
insectary, except during periods of cool (less than 10° C) daytime temperatures. In cotton-growing areas of Yuma County, globemallow
produces buds from December through April depending on amounts and time of rainfall. Therefore, it may be possible that overwintering
boll weevils actively seek out globemallow on warmer days and could
potentially remain on the plants until cotton becomes available. 45
Cotton can be planted in Yuma County as early as February 15,
but on the average, planting is done during March. Plants begin pro
ducing squares after accumulating approximately 700 50 heat units
after seed germination (Huber 1981). Temperatures in the insectary
were converted to heat units and the approximate dates when cotton
squares would be available to boll weevils were estimated using a heat
unit approximation computer program developed by Dr. Roger Huber,
Department of Entomology, University of Arizona. Cotton planted on
February 15 and April 1 would start producing squares in approximately
71+5 and 52+2 days, respectively.
Bariola (1984) contends that although globemallow significant ly extended the overwinter longevity of boll weevils, its influence may not be great enough to enable the weevils to survive until fruit ing cotton is available. However, based on the maximal longevity of boll weevils feeding on globemallow in the insectary and the estimated dates of square availability, approximately 17% of those which emerged in January survived long enough to potentially infest cotton planted on February 15. Approximately 25% of the boll weevils that emerged in
March were alive when squares were estimated to be produced by cotton planted as late as April 1. This is quite significant considering that none of the boll weevils that were provided dry conditions at either emergence date survived long enough to reinfest even the earliest planted cotton. Additionally, environmental conditions which promote globemallow growth (mild winter temperatures and adequate moisture) are also important for optimal boll weevil survival (Leggett and Fye 1969).
Thus, in cotton-growing areas where globemallow flourishes, the present 46 cotton-free periods may not be adequate to prevent boll weevils from reinfesting cotton.
No development of boll weevils in the fruiting buds of globe- mallow was observed during the course of these studies. Gravid females consistently failed to oviposit in buds of two species of globemallow.
It was presumed, since S. coulteri fruiting buds were comparable in size to cotton squares, females might have shown an ovipositional pre ference for them rather than for the smaller buds of £. emoryi. Females that were provided with cotton squares, however, deposited approximately
4.2 and 3.4 eggs/female/day in the laboratory and greenhouse respec tively. Fye (1969) reported similar averages by reproductive females caged on cotton plants at comparable temperature regimes.
A few eggs were deposited externally near feeding punctures on the corolla of globemallow buds by females in the laboratory. On the buds where this behavior was observed, the females had made multiple feeding punctures and extensive feeding was evident. Gaines (1933) observed similar external oviposition by female boll weevils on
Hibiscus militarius Cav., and attributed this behavior to the fact that the females had developed to sexual maturity on cotton. Because this behavior was not observed in either cotton or globemallow plants in the greenhouse, external oviposition in the laboratory may have been an unnatural reaction to the simulated environment.
Coad (1914) attributed lack of oviposition in the buds of
Sphaeralcea lindhiermi Gray, to the heavy, woolly calyx which would render egg deposition extremely difficult. Similarly, the calyx on both species of globemallow which was provided to gravid females in 47
the laboratory, is covered with hairy, hooklike trichomes. The calyx
of £. emoryi is described as being more conspicuously pubescent than
the herbage (Kearney et al. 1964). The females provided with globe-
mallow, preferred to feed through the corolla, but feeding punctures
were observed in the calyx of these buds also. Stephens (1949) showed
that female boll weevils preferred to oviposit in squares which were
considered to possess a glabrous calyx. It seems likely that the
pubescence of the globemallow bud may act as a morphological barrier
to oviposition. Conversely, eggs could be deposited easily through
the relatively smooth corolla, as occurs in cotton squares.
The effect that chemical stimuli has on a female may greatly
influence ovipositional behavior. Dethier (1954) noted that olfactory
stimuli received from the host are very important in eliciting ovi
position. For example, boll weevil oviposition was highly deterred in
the flower buds of Hibiscus syriacus until the calyxes were removed
(Parrott et al. 1966). Although the calyxes were not a morphological
barrier, they contained a water soluble substance that discouraged
weevil feeding and oviposition.
Similarly, a water soluble substance extracted from globe-
mallow buds significantly discouraged the feeding and oviposition of
gravid females in treated cotton squares. The effects of this sub
stance reduced both feeding and oviposition by almost 50%. It is presumed that the biologically active material was extracted from the calyx or pollen, since the flower petals of the corolla consisted of a gummy substance, probably organic in nature, that was discarded
during centrifugation. As expected, females failed to deposit eggs. either externally or internally, into untreated globemallow buds. How
ever, the deterrent substance in the globemallow extract did not
totally inhibit oviposition in the extract-treated squares is it natu
rally does in globemallow buds. This may be due to the concentration
of the active substance in the extract. It may not have been concen
trated enough to completely mask ovipositional stimulants which are
present in cotton squares (Keller et al. 1962). Also, there may have
been additional organic deterrents in the calyx, pollen or corolla
which were not extracted from the buds through the simple procedures
utilized in this test.
A water soluble material extracted from cotton squares sig nificantly increased feeding in treated globemallow buds. The extract of the cotton squares apparently contained a feeding stimulant capable of eliciting more feeding punctures than normal. Because weevils will feed on untreated globemallow buds, it is likely that a similar sub stance is naturally present in globemallow that acts as a feeding stimulant. Furthermore, 2 gravid females oviposited into the anthers of extract-treated globemallow buds. Oviposition did not occur in untreated globemallow buds. Since the cotton extract was capable of inducing oviposition in globemallow, we can assume that cotton squares contain an ovipositional stimulant. However, only 10% of the females exposed to the extract-treated buds actually deposited eggs internally.
This might suggest that, like the concentrations of globemallow extract, the concentration of ovipositional stimulant in the cotton extract was not strong enough to completely mask ovipositional deter rents in the globemallow buds. The lack of organic substances in the 49 extract probably did not reduce the effects of the stimulant, because female boll weevils have deposited eggs into many unnatural hosts with similar water-extracts of cotton squares (Evert and Earle 1964). It is important to note that oviposition took place in the corolla of the extract-treated buds and eggs were deposited directly underneath, in the anthers.
Therefore, it is reasonable to assume that the nonpreference of globemallow buds as a reproductive host is due to an ovipositional deterrent present in the buds. Because feeding and induced oviposi tion was directed through the corolla of the buds, it seems likely that the calyx contains the highest concentration of the deterrent. Tri- chomes present on the calyx may to some extent hinder oviposition in the buds. Globemallow buds do seem to contain a moderate feeding stimulant, which is probably strongest in the corolla and pollen.
Although oviposition was not observed in globemallow, newly- emerged boll weevil adults were capable of reaching reproductive maturity while feeding exclusively on globemallow pollen. As in the ovipositional studies, females deposited eggs externally on the buds, which was an indication that sexual maturation had been attained. It appears that globemallow pollen provides nutrients which are necessary for vitellogenesis. However, since females provided with globemallow fed 3 times longer than did females on squares before oviposition occurred and only 16% of the externally deposited eggs were visible, it is probable that globemallow pollen is providing suboptimal quan tities and/or qualities of the yolk precursors necessary for egg production. Due to the lack of physiological and biochemical data 50 on the essential components available in globemallow pollen for boll weevil nutrition, it is difficult to draw any conclusions.
When female boll weevils were provided globemallow buds from
5 to 15 days prior to feeding on cotton squares, their preovipositional period on cotton was significantly shorter than for females that were provided squares or globemallow buds alone. Furthermore, more than 50% of the eggs deposited by all females in this study were fertile. Ap proximately 70% of the eggs oviposited by femaled provided with squares alone yielded viable larvae. These findings would further suggest that cotton pollen contains a greater quantity or quality of the nutrients necessary for egg production. Yolk production in insects is initiated primarily when sufficient proteins and fatty acids have been provided
(Chapman 1982). Earle et al. (1967) determined that without the addi tion of essential fatty acids, egg production in female boll weevils was suppressed. Thus, globemallow pollen may lack sufficient amounts of essential fatty acids and proteins necessary for normal egg develop ment in boll weevils.
Boll weevil adults, collected from cotton bolls in south western Arizona and provided with cotton squares and globemallow in simulated winter and spring environments, showed the capacity to attain reproductive maturation unlike boll weevils overwintering in the south eastern United States. However, a percentage of the adults during periods of cooler, shorter days (less than 50%) appears to enter a true diapause, characterized by gonadular atrophy and accumulation of adipose tissue. 51
Male and female boll weevils provided with cotton in both simulated overwintering environments attained a higher percentage of reproductivity than did similar adults when feeding on globemallow.
This can be expected since earlier tests indicated that under optimal conditions, weevils reached reproductive maturity sooner than did those on globemallow. However, it is important to note that weevils under suboptimal overwintering conditions, can attain either sexual maturity or accumulate a fat reserve while feeding exclusively on globemallow buds.
In the simulated winter environment, very few female boll weevils were considered reproductive. A larger percentage of females, however, showed reproductive maturation in the warm spring environ ment. It seems likely that this difference can be attributed to the temperature and photophase being more optimal in the spring that was encountered in the winter simulation. Earle and Newsom (1964) found that weevils failed to attain reproductive status when adults were ex posed to short (10 hour) photophases and low nightly temperatures.
Similarly, Lloyd et al. (1967) reported that none of the adults which fed on cotton in a 13-hour photophase and a mean temperature of 17.5° C entered into diapause.
It is important to consider the potential utilization of globe mallow by free-living adult boll weevils overwintering in southwestern
Arizona. As discussed previously, boll weevils are capable of utilizing globemallow to extend their survival, enabling them to potentially re- infest cotton. Furthermore, since a portion of boll weevils in the laboratory has shown a propensity to attain a firm reproductive status 52 during a cotton-free period, it is possible that weevils that over wintered on globemallow could enter cotton fields in May and June and immediately begin oviposition. Currently, early season insecticide treatments are aimed at killing overwintering boll weevils entering cotton as it begins to produce squares (Moore 1983). This is the period of the year in which boll weevil populations are the lowest and most vulnerable to control. It, therefore, seems likely that repro ductive weevils actively overwintering on globemallow, would be more difficult to kill as they entered into cotton than lean, nonreproductive weevils seeking food. Boll weevils caught in pheromone traps during the winter in Arizona had a lower tolerance to organophosphate insecticides than did boll weevils collected from bolls (Watson and Crowder 1983).
Development of immature boll weevils in globemallow buds has not yet been observed in nature or in the laboratory. Generally, in order to reproduce, adult boll weevils have the same dietary needs as do larvae which probably reflects the intimate association of this insect and its host (Vanderzant 1963). Since adult boll weevils are capable of utilizing globemallow pollen to attain reproductive matura tion, it appears likely that immature boll weevils could complete development in globemallow if provided sufficient amounts of pollen.
Stoner (1970) reported a related species of the boll weevil, Anthonomous sphaeralcea Fall, reproducing and developing in buds of all species of globemallow in Arizona. The larvae of A. sphaeralcea are much smaller than the average boll weevil larvae and usually consume the majority of the pollen within the bud during immature development. Because most globemallow buds are relatively small, as compared to cotton squares of 53 similar age, the amount of pollen available to an immature weevil may not be great enough to enable it to complete development. However, I have personally observed small boll weevil adults (slightly larger than
A. sphaeralcea) emerging from cotton squares that were no bigger than a typical globemallow bud. Boll weevil populations which utilize pollen of alternate hosts in south Texas and Mexico during cotton-free periods, have been established in these areas for many years (Cross et al. 1975).
It may be possible that the newly established boll weevil populations in Arizona, could in time, adapt a strain of weevil capable of over coming the ovipositional non-preference for globemallow and reproduce in this host when cotton is not available.
In summary, the survival of overwintering boll weevils in
Arizona may be enhanced by the utilization of globemallow pollen. Boll weevils overwintering in globemallow can successfully survive present cotton-free periods to reinfest cotton fields the following season.
Chemical deterrents contained in globemallow fruiting buds appear to inhibit female boll weevils from ovipositing in them. Although globe mallow cannot be considered a true reproductive host, it can provide a sufficient pollen source for boll weevils to attain reproductive maturation. LITERATURE CITED
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