The effects of apholate on diapausing and nondiapausing alfalfa weevil, Hypera postica (Gyllenhal), were studied. Different stages, sexes, and ages of the weevil were treated with aqueous-apholate solution. Adult topical application and larval and adult dipping methods were used in the experiment. Both showed the effectiveness of sterilization, and caused high mortality to the treated insects. Adult dipping was an acceptable method of treatment. The best age for treatment seemed to be reproductively mature virgin adults. Egg viability was similar to the check when only the females were treated with apholate. When only males or when both sexes were treated the egg viability was decreased depending on the apholate concentration used. The most effective apholate concentration for sterilizing male alfalfa weevils ranged from 0.5 to 1.0%. A gradual increase in egg viability occurred starting about the 3rd week after treatment. Dissection of the immature adults showed that gonadal development was delayed by apholate. The reproductive organs of apholate-treated mature adults were reduced in size. The treated males do not compete sexually on an equal basis with the normal males, although considerable mixing of sperm occurred during the mating of female weevils with the apholate-treated and -untreated males. / M.S.

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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

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