Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) is the most important insect pest for greenhouse flower crops. Thripinema nicklewoodi Siddiqi (Tylenchida: Allantonematidae) is an entomoparasitic nematode attacking and sterilizing the thrips. Methods to propagate and study T. nicklewoodi were developed. I observed an excretion rate of 21.4 nematodes per day by parasitized female thrips. The sex ratio of the excreted nematodes was 6:1 (female:male). After exposing 50 healthy first instars to four parasitized female thrips in a rolled bean leaf, I obtained a 75.3% mean parasitization rate in the adult stage of the thrips. In contrast to previous reports, male thrips were found to be parasitized as readily as females. Parasitism reduced the longevity of both adult female and male thrips by 26% and 61%, respectively. T. nicklewoodi when presented with various thrips life stages achieved the highest attack rate in first and second instars and prepupa. Free-living nematodes were found to escape from hosts through the anus and penetrate new host thrips through the intersegmental membranes of the thorax and abdomen. While nematode parasitization affected tospovirus propagation, it did not reduce transmission of impatiens necrotic spot virus even though parasitism reduced feeding activity of adult female thrips by 81% on leaves, 38% on pollen, and 22% on honey. However, despite lowered total feeding, probing by parasitized thrips (in honey) was not reduced, and this may explain why lowered feeding does not result in lowered virus transmission. In a study of the population dynamics on caged impatiens in greenhouse, nematode transmission persisted for seven host generations and populations of normal (i.e., not parasitized) female thrips declined by 39–79% in the nematode treatment compared to the control. However, no significant reductions were found in numbers of larval thrips between nematode treatments and the control. A higher proportion of male thrips occurred in populations with nematodes in which adult female thrips declined significantly compared to the control population. T. nicklewoodi released seven times on caged impatiens in a greenhouse did not provide preventative control of thrips, though the population growth of second instar, adult female, and male thrips was suppressed by 44, 68, and 49%, respectively.

The cranberry fruitworm, Acrobasis vaccinii Riley (Lepidoptera: Pyralidae), is a serious pest of cranberry (Vaccinium macrocarpon Ait.). Reported hosts also include highbush blueberry ( Vaccinium corymbosum L.), lowbush sweet blueberry (Vaccinium augustifolium Ait.), and black huckleberry [(Gaylussacia baccata (Wang.) K. Koch], all of which grow in the woodlands (called uplands) surrounding Massachusetts bogs. Since a thorough understanding of movement patterns of a pest species within and between host habitats is crucial for the implementation of a successful management program, moth movement was studied in time and space through trapping of wild and mark-released moths. The results, reported in Chapters I and II, demonstrate that the moth is very mobile and that large flights occur in both cultivated bogs and their surrounding uplands. Trap studies also showed a significant effect of trap height on the number of moths captured. Moths were active later at night in the upland, and males, in particular, were active in the trees, which suggested adoption of a “hilltopping” strategy to enhance their chances of mate finding. In field and lab studies reported in Chapter III, the periodicities of emergence, mating, and oviposition were recorded, and the data suggest that it is advantageous for females to delay mating when conditions are favorable for oviposition. Females were polyandrous, and assessment of spermatophore age in females suggested that mating may occur more frequently in the upland compared to the bog. Studies reported in Chapter IV showed that moth activity and infestation occurred earlier in both blueberry plantings and in the uplands than cranberry. The large numbers of moths captured in the uplands did not appear to originate from larvae developing in the uplands, since infestation of wild berries could not be corroborated. A study of host preference and performance in four different hosts (cultivated cranberry and blueberry, wild blueberry and huckleberry) is reported in Chapter V. Huckleberry was the least preferred for oviposition, and both of the cultivated berries were more suitable for larval development when compared to the wild hosts. The relationship between preference ranking and performance was positive. Implications of these findings are discussed.

Brachymeria intermedia is an introduced endoparasitoid of the gypsy moth, Lymantria dispar. To gain understanding of the basic mechanisms by which B. intermedia influence population densities of the gypsy moth, the oviposition behavior of this parasitoid was studied. Both the physiological state and the informational state of the animal at a certain point in time may influence the development of the behavior. Factors of the physiological state here investigated are egg load and age of the female parasitoid. Factors of the informational state here investigated are the number of hosts previously encountered, the host species encountered and characteristics of the sites where pupae previously were encountered. Chapter 1 contains the introduction and outline of the study. Chapter 2 shows that experience is an important factor influencing the rate of acceptance of hosts by the parasitoid. The sequence of behaviors before ovipositor insertion does not change with experience. Chapter 3 shows that parasitoids, deprived of hosts from emergence, accumulate eggs up to a certain level, but have a low rate of acceptance. Early exposure to pupae increases the rate of acceptance. B. intermedia adjust their egg production to host availability. Chapter 4 shows that the rate of acceptance for an alternate host increased with age in parasitoids, deprived of hosts from emergence. Rearing the parasitoids on an alternate host and/or oviposition experience on an alternate host did not influence the rate of acceptance of the alternate host. After oviposition experience on the alternate host contaminated with kairomone, uncontaminated hosts were accepted at the same rate as gypsy moth. Chapter 4 shows that B. intermedia is able to use learned visual cues, thereby restricting their searching area to a microhabitat previously found to be profitable. Under laboratory conditions and under semi-natural conditions, parasitoids could be trained to search for pupae either on the ground or on a tree model. Subsequent training to the other microhabitat reversed this effect. The studies show that both the physiological state and the informational state of the parasitoid influence oviposition behavior. Questions are raised and discussed as to the extent of polyphagy of B. intermedia in North America.

The life history and behavioral ecology of Myiopharus doryphorae (Riley) and Myiopharus aberrans (Townsend), important parasitoids of the Colorado potato beetle (CPB) Leptinotarsa decemlineata (Say), were investigated through a series of field and laboratory studies. The recruitment-recruitment method of determining percentage parasitism was compared with traditional methods in assessing population dynamics of the CPB and Myiopharus. Over the three-year period of the study, percentage parasitism calculated from traditional foliage sampling showed an erratic pattern. Revised estimates employing the recruitment method revealed a consistent 30-50% mortality of CPB larvae due to parasitism even when the CPB prepupal population density reached 80 per square meter per generation, showing that Myiopharus spp. can cause high levels of mortality to CPB larvae at higher host densities than has been reported in most previous field studies. Field sampling demonstrated that M. doryphorae and M. aberrans overwinter as first-instar larvae within adult diapausing CPB and complete their development the following spring after the emergence of the parasitized beetles. Growth-chamber studies were conducted to quantify development of summer-generation M. doryphorae at different life stages. During the first four days after being larviposited, these M. doryphorae remain as first-instar larvae but grow an average of 0.45 $\pm$ 0.03 mm prior to the prepupal stage of their hosts, in which the parasitoids complete development. During this latter period, development rates of M. doryphorae were found to track closely those of the CPB itself when modeled as a nonlinear function of temperature assuming cessation of growth outside the approximate range of 4-34$\sp\circ$C. The model appears to require additional adjustment at temperatures below 10$\sp\circ$C. Laboratory studies showed that M. doryphorae do not discriminate between CPB larvae fed sublethal doses of B. thuringiensis and larvae not fed with B. thuringiensis. M. doryphorae appear more sensitive to CPB larval movement than to the presence or absence of B. thuringiensis. Through field studies a series of behaviors was identified and their frequency and duration were quantified for the two Myiopharus spp., which appeared not to vary their allocation of time in response to each other's presence in the same field. A significant difference was found between the frequencies of larviposition by the two Myiopharus species across ranges of temperature and time of day. Behavioral studies led to the discovery that larvipositing M. doryphorae and M. aberrans females discriminate between parasitized and non-parasitized host larvae, rejecting the former on contact and failing to larviposit in them when other potential hosts are available. This discrimination breaks down to some extent late in the growing season when CPB larvae of appropriate stages are rare; breakdown of host discrimination is accompanied, however, by the defense of recently parasitized hosts by females of both Myiopharus species, and is followed by the switch of larvipositing M. aberrans from larval hosts to adult CPB which are more common at this time of year.