The qualitative and quantitative aspects of mating behavior, the stimulus for locating and mating, and the effects of varying temperatures on mating behavior and oviposition were studied in the laboratory. Postdiapausing weevils, collected in April, and nondiapausing weevils, reared in the laboratory, were utilized. In both groups, the males aggressively mounted the females from any angle or position with little or no indication of prior courtship. In petri dishes at 75 ± 3° F, both groups spent about 59% of their total time in mating behavior. Mounted time spent in actual copulation (aedeagus inserted) was 47% for nondiapausing pairs and 74% for postdiapausing pairs. This difference in behavior was probably caused by the younger, nondiapausing females which often prevented copulation by tucking the genital opening under the elytra. Males, when given a choice between virgin and non-virgin females, mated with non~virgins in a ratio of 7:1. Nondiapausing pairs mounted fewer times .for longer durations per mounting than the postdiapausing. Crowding by other weevils appeared to reduce mating efficiency, but not mating initiation. Sight was found to play a role in attracting weevils to each other over distances of.a few inches. No evidence of sound production was discovered, nor was there found to be a pheromone serving as a sex attractant. Since males mounted other males as well as other species of curculionids, there is apparently rto mechanism for recognition of sex or species. Higher temperatures resulted in a greater number of mountings of shorter duration. At lower temperatures, pairs mounted fewer times and riot infrequently copulated for as long as 12 hours. The number of ovipositing females and the average number of eggs per female increased with the temperature. / Master of Science

Call number: LD2668 .T4 1979 C54 / Master of Science

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The purpose of this investigation was to test three insecticides on all the life stages of the alfalfa weevil. The objectives were to obtain information on the toxicity of certain insecticides on the alfalfa weevil in the laboratory, to establish standard susceptibility curves of the life stages of the alfalfa weevil to the insecticides tested, to establish a basis for insect resistance, to compare the speed of action of certain classes of insecticides and to observe the effects of certain insecticides on molting, feeding and other processes that may be affected. Dibrom, heptachlor epoxide, and Indian were tested against various life stages of the alfalfa weevil. These three insecticides were chosen because of the differences in their chemistry and activity. Dibrom, a volatile organophosphate, could be expected to act fast but have relatively limited residual life.Heptachlor epoxide as a cyclodiene compound should have exhibited the characteristic latent period of from two to six hours before symptoms of its activity appeared. The residual activity should be great. Indian, a more stable organophosphate than Dibrom, would be expected to be somewhat intermediate between the other two in speed of action and residual activity. Each insecticide was impregnated in filter paper at the dosage of 100 micrograms per square centimeter of filter paper surface. The insects were introduced on to the filter paper for continuous exposure to the insecticide residue. Mortality and certain other effects were recorded according to time of exposure. In general, responses of the alfalfa weevil to the three insecticides were comparable. One insecticide may have been quicker acting than the other two against a particular life stage, but the differences in the effects of the insecticides were not great. In every case, the three insecticides inhibited feeding, molting, or maturation to another life stage. / Master of Science

Virginia is a natural laboratory for studying overwintering habits of the alfalfa weevi1. At higher elevations, winters are relatively harsh and weevil pressure on the alfalfa crop is usually light. Much heavier pressure is the rule at lower elevations where winters are milder. The goal of this study was to examine the effects of fall and winter temperatures, parasites, and fall regrowth management on population dynamics of overwintering stages of this insect. Sixteen commercial alfalfa fields in Montgomery Co. (elevation 610 m) and Bedford Co. (elevation 300 m) were used in the study. Approximately half the fields each year were either harvested or grazed to remove fall regrowth. In the other fields, fall regrowth was left standing through the winter. Six different pitfall trap designs were compared for collection efficiency, installation and servicing effort, and cost. Barrier traps outperformed the other trap designs and were inexpensive and easy to install and service. Sweepnet samples were used to monitor weevil adults during their fall migration. A newly designed sampling device which removes all plant material, litter, and approximately 2 cm of soil from a 1/20 m² area, was used to measure absolute densities during fall and winter. Based on these absolute density samples fewer adults overwintered within fields in which fall regrowth was removed. Dissections revealed the presence of three parasites: Hyalomyodes trianqulifer (Loew), Microctonus aetheopoides Loan, and M. colesi Drea. Total parasitization rates were low. The highest measured rate was 16.1% in Bedford Co. in 1984-85. Female reproductive development also was determined through dissection. Females reach sexual maturity shortly after returning to alfalfa fields in the fall. Most contain full-size eggs in their oviducts from late fall through the winter. Egg densities as measured by laboratory incubation of field collected plant material indicated no differences related to elevation in early February, but significantly more viable eggs were present by late March at the low elevation site. In 1984, Bedford Co. samples indicated significantly more eggs in fields receiving no fall regrowth management. A simulation model called OAWSIM (Overwintering Alfalfa Weevil Simulation) was developed to examine the influence of factors which affect overwintering life stages. Model predictions indicate fall and winter temperatures, and fall regrowth management are major influences on the population dynamics of this insect. / Ph. D.

Three sampling methods for estimating abundance of alfalfa weevil (AW) larvae (Hypera postica Gyllenhal) were evaluated for both accuracy and precision. Calibration equations were developed to convert intensity estimates of AW larvae among sampling methods. Greenhouse experiments evaluating the interaction of moisture stress and defoliation by AW larvae indicated that yield response of alfalfa to AW feeding is dependent on moisture stress levels. Field studies on the influence of AW feeding on alfalfa confirmed the importance of moisture stress in alfalfa tolerance to weevil feeding. Quadratic regression models are presented to predict yield loss and changes in stem density as a function of weevil intensity. A sequential sampling plan was developed and validated for use in pest management decision making. Validation of the plan indicated an average error rate of 1.8%, with the number of samples needed reduced by 55% in 1980, 53% in 1981, and 28% in 1982. A net benefit analysis the Virginia Alfalfa IPM program indicated that growers participating in the program during 1981-84 realized an estimated average increase in net revenue of $8.80 per hectare from the alfalfa weevil scouting program, and $28.13 per hectare from the potato leafhopper scouting program. / Ph. D. / incomplete_metadata