Although parasitoid wasps have shown promise as model systems for studying life history evolution, empirical studies of certain traits in these small insects have proven difficult. In this dissertation, two "black boxes" in the life histories of female parasitoids are examined: (1) oosorption, and (2) dispersal by flight.I first demonstrate that a short-lived species with high early reproductive investment (Eretmocerus eremicus) resorbs eggs, which runs counter to the notion that the time costs of oosorption are prohibitive to such wasps. Instead, it appears that the resorption mechanism in E. eremicus is capable of both decreasing costs and increasing nutritional benefits of oosorption relative to that of other parasitoid species. In addition, a literature review reveals four functional hypotheses for parasitoid oosorption: (1) age-related egg apoptosis, (2) conservation of ovarian capacity, and (3) nutrient allocation to either longevity or future oogenesis. As none of these can be rejected, I propose several avenues of future research: 1) refinement of physiological techniques to measure nutrient traffic into and out of eggs, 2) morphological phylogenetic studies of oosorption mechanisms, 3) development of lifetime nutrient budgets for parasitoids with different reproductive life histories, 4) examination of decay rates of oocytes with different yolk types, and 5) increased study of ovarian dynamics in pro-ovigenic parasitoids.Next, I describe results from a vertical flight chamber study designed to test hypotheses regarding the correlation between pre-oviposition dispersal and reproductive effort in parasitoid wasps. This experiment was conducted on 1-d-old female whitefly parasitoids from five species in two genera. The two Eretmocerus spp. showed a higher flight propensity than the three Encarsia spp. This may be, in part, due to a more time limited life history in the former. Within species, egg load did not correlate well with flight propensity for all species examined. Finally, among individuals of Er. eremicus, the relationship between effective flight distance and egg load appears to be context dependent, as data consistent with both positive and negative correlations were collected. Correlational changes between flight distance and egg load may be due to variation in biotic (female longevity) or abiotic (temperature, relative humidity) factors.

Juvenile hormone (JH) is the central hormonal regulator of life-history trade-offs in many insects. In Aedes aegypti, JH regulates reproductive development after emergence. Little is known about JH’s physiological functions after reproductive development is complete or JH’s role in mediating life-history trade-offs. By examining the effect of hormones, nutrition, and mating on ovarian physiology during the previtellogenic resting stage, critical roles were determined for these factors in mediating life-history trade-offs and reproductive output. The extent of follicular resorption during the previtellogenic resting stage is dependent on nutritional quality. Feeding females a low quality diet during the resting stage causes the rate of follicular resorption to increase and reproductive output to decrease. Conversely, feeding females a high quality diet causes resorption to remain low. The extent of resorption can be increased by separating the ovaries from a source of JH or decreased by exogenous application of methoprene. Active caspases were localized to resorbing follicles indicating that an apoptosis-like mechanism participates in follicular resorption. Accumulations of neutral lipids and the accumulation of mRNA’s integral to endocytosis and oocyte development such as the vitellogenin receptor (AaVgR), lipophorin receptor (AaLpRov), heavy-chain clathrin (AaCHC), and ribosomal protein L32 (rpL32) were also examined under various nutritional and hormonal conditions. The abundance of mRNA's and neutral lipid content increased within the previtellogenic ovary as mosquitoes were offered increasing sucrose concentrations or were treated with methoprene. These same nutritional and hormonal manipulations altered the extent of resorption after a blood meal indicating that the fate of follicles and overall fecundity depends, in part, on nutritional and hormonal status during the previtellogenic resting stage. Mating female mosquitoes also altered follicle quality and resorption similarly to nutrition or hormonal application and demonstrates that male accessory gland substances such as JH III passed to the female during copulation have a strong effect on ovarian physiology during the previtellogenic resting stage and can influence reproductive output. Taken together these results demonstrate that the previtellogenic resting stage is not an inactive period but is instead a period marked by extensive life-history and fitness trade-offs in response to nutrition, hormones and mating stimuli.

The trade-off between gametes and soma is central to life-history evolution. Oosorption has been proposed as a mechanism that can mediate this trade-off. When conditions are not conducive to successful reproduction, females are expected to be able to recoup nutrients from unfertilized oocytes and reinvest them into the somatic processes that promote survival and hence future reproduction. Although positive correlations between oocyte degradation and lifespan have been documented in oviparous insects, the adaptive significance of this process in species with more complex reproductive biology has not been explored. Oocyte degradation via apoptosis (programmed cell death) occurs in response to enforced virginity in females of the ovoviviparous cockroach, Nauphoeta cinerea. Observed apoptosis may represent oosorption, however, an alternative but not mutually exclusive argument is that oocyte apoptosis may represent oocyte ageing and clearance in order to maintain reproductive synchrony. The aim of this thesis was to test the hypothesis that the function of oocyte apoptosis is oosorption in N. cinerea. I found that in addition to enforced virginity, starvation induces oocyte apoptosis. However, the life history outcome following one form of stress is the opposite of the other. Hence, the functional role of oocyte apoptosis appears to be different depending on whether apoptosis is induced through starvation or age. Following a period of starvation-induced apoptosis females exhibit the increase in survival and future reproduction predicted by oosorption. Whereas, following a period of age-induced apoptosis females suffer fecundity and longevity cuts. However, age-induced apoptosis does not appear to simply be cellular ageing and clearance. In conjugation with age-induced apoptosis, ovariole number declines whilst the size of surviving oocytes increases. Hence, it appears that resources from sacrificed oocytes are being recycled into the survivors, and that this reinvestment in current reproduction trade-offs with future reproductive capacity. My thesis shows the importance of studying proximal mechanisms alongside more traditional measures of life history, as the relationship between isolated biological levels is not always clear.