Population dynamics of selected pests (Panonychus ulmi, Aculus schlechtendali, Aphis citricola, Dysaphis plantaginea spp.) in Virginia apple orchards and predators (Leptothrips mali, Haplothrips subtilissimus, Orius insidiosus, Stethorus punctum, Dereacoris nebulosus, Chrysopa spp.) were monitored during 1977-78 under 3 reduced pesticide programs. The pesticide program with phosalone and Dikarᴿ as its principal components allowed the largest number of predators to remain in the orchard and controlled most pests. L. mali and H. subtilissimus were the most abundant predators and appeared to respond numerically to densities of A. schlechtendali. O. insidiosus and D. nebulosus usually increased late in the season and S. punctum responded to densities of P. ulmi inconsistently but together with thrips may have had an important role in reducing P. ulmi populations. Chrysopa spp. remained at consistently low levels throughout the study. Laboratory studies indicated that phosalone and Dikar were the least toxic to L. mali among the pesticides tested. Benomyl can probably be substituted for Dikar in order to lessen mortality of A. schlechtendali in the field. L. mali was studied in the laboratory to determine aspects of its development, biology and prey relationships. Mean development time (days) for each stage at 23.9°C was: egg, 7.5; Ist larva, 5.7; 2nd larva, 5.4; prepupa, 1.0; pupa I, 1.5; pupa II, 4.0 and total (eggadult), 25.6. The preoviposition period ranged 5-7 days and the mean no. eggs/lab-reared (LR) and field collected (FC) females were: mated - LR, 13.0; FC, 28.0 and unmated - LR, 11.7; FC, 45.1. Mean longevity (days) of unmated females (LR, 50.1 and FC, 54.2, respectively) was greater than that for males and mated females. L. mali completed development on Golden Delicious apple pollen in 23 days (1st stage larva - adult). This thrips fed on the following orchard pests: A. schlechtendali, Tetranychus urticae, Lecanium corni, and on the eggs of Laspeyresia pomonella and Platynota flavedana. No feeding was observed on S. punctum, but L. mali fed on the phytoseiid mite, Proprioseius oudemansi. The functional response of all feeding stages of L. mali to densities of P. ulmi was determined at 18.3, 23.9, and 29.4°C and the numerical response of adult female L. mali to this mite species was investigated. The greatest effect of temperature on the functional response curve was observed with field collected adult female L mali. The numerical response of L. mali reached a maximum of 0.70 eggs/ female/48 h. The individual or joint potential impact of L. mali with S. punctum or O. insidiosus on P. ulmi was evaluated in the laboratory. At a mite density of 45/arena, L. mali with S. punctum killed significantly more P. ulmi than L. mali or S. punctum alone. In 75% of the replicates where L. mali was combined with O. insidiosus, the latter killed and consumed the thrips. A simple, non-destructive, but inefficient visual sampling method for L. mali on apple foliage was compared to a destructive, time-consuming, efficient limb-tapping sampling technique. With this comparison the usefulness of the visual sampling method was improved, thus increasing the potential of this sampling technique. / Ph. D.

The effects of pheromone trap placement on male moth catches of both species were studied. For P. flavedana, traps hung at 2.1 and 3.0 meters captured the greatest number of moths. Trap heights of 1.2, 2.1, and 3.0 meters caught the greatest number of P. idaeusalis moths. The outside-the-canopy trap position captured more P. flavedana moths, while the within-canopy trap location caught the greatest number of P. idaeusalis moths. Traps placed in the west portion of the tree captured the greatest number of P. flavedana moths. P. idaeusalis moth catches were not influenced by compass quadrants. Trap design and pheromone dispenser and rate influenced trap catches of P. flavedana. Development of P. flavedana and P. idaeusalis on a meridic diet was observed at constant temperatures in the laboratory. Lower developmental threshold values for egg, larval, and pupal stages of P. flavedana were: 10.6, 8.6, 9.0°C, respectively. Lower developmental threshold values of 9.7, 7.0, and 8.5°C were estimated for P. idaeusalis egg, larval, and pupal stages, respectively. An average of 101.5 °D_10.6’, 379.6 °D_8.6’, and 126.0 °D_9.0’ were required for development of egg, larval, and pupal stages of P. flavedana, respectively. P. idaeusalis required 104.7 °D_9.7’, 442.7 °D_7.0’, and 132.2 °D_8.5’ to complete development in the egg, larval, and pupal stages, respectively. Differences in rate of development were observed between food sources for both species. Within-tree spatial distribution of egg masses and fruit damage resulting from larval feeding for both species was investigated. P. flavedana egg masses were mostly found in the southern portion of the tree below 1.8 meters. Egg masses of P. idaeusalis were observed in greatest numbers in the southern and eastern quadrants of the tree below 2.8 meters. Fruit damage caused by larvae of both species was greatest in the lower portion of the tree. Wind dispersal of first-instar larvae between trees is believed to have influenced fruit damage distribution. The seasonal activity of P. flavedana and P. idaeusalis was monitored. Degree-day accumulations for first moth catch, first and peak egg deposition, and first and peak egg hatch of both generations are presented. / Ph. D.

The anthocorid, Orius insidiosus (Say) is a common polyphagous predator in Virginia apple orchards, particularly in orchards under reduced pesticide programs. The purpose of this research was to contribute to the basic knowledge of the biology and ecology of O. insidiosus in Virginia orchards and to evaluate the potential for its incorporation into IPM programs currently being developed. Egg and nymphal development of O. insidiosus was studied at 17°, 23°, 29°, and 35°C. Nymphs were supplied with an excess of the European red mite, Panonychus ulmi (Koch). There was a linear relationship between development rate (l/Days) of O. insidiosus and temperature. Developmental threshold temperatures were calculated as 10.2°C for the eggs; 8.9°, 7.5°, 10.7°, 12.5°, and 9.9°C for nymphal instars 1-5 respectively; and 10.0°C for total nymphal development. Mean degree-days (DD) requirements were 75.8 for eggs; 45.0, 38.0, 27.8, 28.8, and 64.9 for instars 1-5 respectively: 201.7 DD were required for total nymphal development. Nymphal development was also studied using aphids and pollen as food sources. Mean time (days ± S.E.) for total nymphal development at 23°C was 19.0 ± 0.0 with aphids and 20.0 ± 0.5 with pollen. As already mentioned, O. insidiosus is a polyphagous predator. Extensive laboratory and field observations established a number of small, soft-bodied insects and mites as well as the eggs of several lepidoptera are acceptable as prey. O. insidiosus also feeds on other beneficial species including predaceous thrips and mites. O. insidiosus falls prey to a number of other general orchard predators, particularly spiders, chrysopids, and other predaceous Heteroptera. During 1977-1978, the population dynamics of O. insidiosus along with a complex of predators and pests in orchards under three different pesticide programs was studied. O. insidiosus underwent 2-3 generations per year in Virginia orchards, depending on the availability of prey. Adults overwintered in the orchard, but most migrated into the orchard during May-early June from other areas. O. insidiosus first responded to aphid populations, but as this prey became scarce in late June, O. insidiosus fed on the European red mite whose populations were usually building up at that time. This study indicated that O. insidiosus responded numerically to increasing mite densities. Numerous weeds and crops serve as alternate sites for 0. insidiosus populations. Corn and alfalfa are often adjacent to orchards in Virginia and apparently serve as a reservoir for O. insidiosus throughout the season. Thistle (Carduus spp.) harbors large numbers of O. insidiosus which prey on thrips. These natural and cultivated alternate sites may be important to the management of O. insidiosus populations. Since pesticides are an important component of an IPM program for apples, the relative toxicity of 14 compounds (2 rates of each) to adult O. insidiosus was evaluated. Common cover-spray materials, aphicides, miticides, new materials such as synthetic pyrethroids, and fungicides were tested. Generally, O. insidiosus tolerated many of the compounds being considered for use in our developing IPM programs--especially at the lower rates. The functional response of O. insidiosus to densities of the European red mite was studied at 18.3°, 23.9°, 29.4°, and 35.0°C. Prey densities ranged from 5-80 mites/ cage. Mite consumption was recorded during five, three-hour intervals during the day. O. insidiosus did exhibit a functional response and increasing temperatures resulted in increased feeding at most prey densities. The data provided a good fit to both the type-2 and type-3 functional response models. The interspecific interactions of 5th instar O. Insidiosus and 2nd instar larvae of another mite predator, Leptothrips mali (Fitch) was studied in the laboratory. L. mali is a potential prey for O. insidiosus, but has a defensive anal secretion which repels predator attacks. Most contacts between well fed O. insidiosus and L. mali resulted in mutual avoidance. Most attacks by O. insidiosus were unsuccessful, especially if the approach was from the rear. Contact with the thrips' anal secretion resulted in immediate repelling of O. insidiosus with subsequent cleaning activity lasting 1-3 minutes. This study supports earlier work that indicated these two predators were compatible, especially in the presence of another food source such as the European red mite. / Ph. D.

Methomyl at seven concentrations, 0.051 to 0.204 kg ai/378.5 l water, was evaluated against eggs of pest and beneficial insects and mites associated with apples. The pest eggs studied were: Laspeyresia pomonella, Panonychus ulmi, Platynota spp., aphids, and Argyrotaenia velutinana. For A. velutinana, five rates of methomyl ranging from 0.013 to 0.204 kg ai/378.5 l water were used. Platynota spp., aphid, and A. velutinana eggs were highly susceptible to the material. P. ulmi eggs were not susceptible. Eggs of beneficial syrphid flies, Aphidoletes aphidimyza, Leptothrips mali, and Stethorus punctum were highly susceptible to methomyl. Eggs of Orius insidiosus were moderately susceptible. Chrysopa spp. eggs appeared to be unaffected by the material. LC₅₀ values for methomyl on eggs of Platynota spp. L. pomonella, O. insidiosus, Chrysopa spp., and S. punctum were generated. LC₅₀ values for P. ulmi eggs were unobtainable. Three rates of methomyl, used as an ovicide, were evaluated in the field for control of the Platynota spp. complex on apples compared to two formulations of FMC 45806, permethrin, and Bacillus thuringiensis. Methomyl provided the best control. Seasonal activity of P. flavedana and P. idaeusalis were monitored in reference to degree-day accumulations. Regression equations for male moth flights and egg deposition of the species are presented. Seasonal activity and prospects for development of a phenology model to predict seasonal activity of the species is discussed. / Master of Science