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Leaves 101-104 are misnumbered. Bibliography: leaves 155-215. In this study thirteen populations of P. xylostella from crucifer growing areas of Queensland, Victoria, Tasmania, South Australia and Western Australia were surveyed for resistance to Bt (Bacillus thuringiensis) toxins using a leaf-dip bioassay method.

The floating aquatic weeds common salvinia (Salvinia minima Baker) and giant salvinia (Salvinia molesta Mitchell) degrade aquatic systems through fast, mat forming growth. The Salvinia specialist weevil Cyrtobagous salviniae Calder and Sands has been used to reduce the severity of giant salvinia infestations and associated with reduced severity of common salvinia infestations. Genetically, morphologically and biologically distinct strains of C. salviniae exist, but their relative potential for success as biological control agents of Salvinia species has not been evaluated. This thesis (1) describes a recirculating water system designed for conducting such studies and (2) reports the results of C. salviniae strain comparisons. A recirculating water system with a high degree of replication and minimal variation in water flow, temperature and light intensity was used for laboratory experiments using sixty-day temperature profiles averaging 31.4, 26.5 and 8.0ºC derived from surface water temperatures measured at lakes in expected range of Salvinia species in the North America. Larval and adult population numbers of two C. salviniae strains (Australia and Florida) were determined for each temperature profile along with feeding induced plant necrosis on both Salvinia species. Australia C. salviniae had lower survivorship rates to adulthood on common salvinia than did Florida C. salviniae at the 31.4 and 26.5ºC temperature profiles. Neither strain reproduced, and no significant between-strain differences in plant necrosis were detected at the 8.0ºC temperature profile. At 31.4ºC there were no significant differences in adult counts, larval counts or plant damage between the two strains on giant salvinia. At 26.5ºC, however, significantly fewer larvae were collected from initially released adults and significantly less plant necrosis was associated with weevil feeding by Florida strain compared to Australia strain weevils. These results may have arisen from comparing Australia weevils from a growing colony to Florida weevils from a declining colony. Overall, the results indicate that only Florida C. salviniae should be released against common salvinia. Florida C. salviniae may be equally suitable to Australia C. salviniae for releases against giant salvinia, but further study is needed to fully assess the potential for using Florida C. salviniae against giant salvinia.

Indigenous natural enemies occur within field grown crops at varying densities dependent upon a variety of other biotic and abiotic parameters. This natural control often does not provide adequate suppression, which results in the application of other remedial pest management solutions including augmentative biological control. When releasing mass-reared natural enemies into a backdrop of indigenous natural enemy populations, competitive interactions are likely to occur. To assess the influence of these interspecific interactions on the outcome of such biological control practices, studies were conducted both in a laboratory and in a simulated, field grown, cut chrysanthemum (Asteraceae: Dendranthema grandiflorum) production system. Competitive interactions of two commercially available parasitoids were studied both in terms of parasitoid-host population dynamics and the impact of interspecific interactions on crop quality at harvest in this type of system. The parasitoids Diglyphus isaea and Dacnusa sibirica attacking the leafminer Liriomyza langei were used as the model insect system. Both parasitoids are cosmopolitan and are known to occur in many ornamental production areas. Conclusions drawn from laboratory experiments were that D. sibirica produces more offspring that D. isaea over approximately the same number of days. Treatment comparisons in the field included single species releases with complimentary releases of both species either simultaneously or with two-week time lags, as well as a no release control to measure the background effects of natural mortality. Conclusions drawn from results of population-level studies replicated within and among years were that levels of interspecific competition among parasitoid species were undetectable at leafminer densities typical of field-grown ornamental crops; thus, the efficacy of one species released into a backdrop of potentially competing parasitoids did not negatively affect the outcome of the augmentative biological control. The two species were able to coexist inside field cages for the duration of the crop. Most of the release treatments suppressed host densities lower than the control cages where no parasitoids were released, and there were no treatment effects on host suppression. Even though parasitoid release combination did affect the amount of damage visible at harvest, there was no influence on the number of flowers produced (yield).

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The parasitoid Anagyrus kamali Moursi [Hymenoptera: Encyrtidae] has been recently introduced into the Caribbean as a biological control agent against the Hibiscus Mealybug (HMB), Maconellicoccus hirsutus Green [Homoptera: Pseudococcidae]. Information on this parasitoid is scarce and investigations of its biology and behaviour were conducted to optimize its mass-production, and improve our understanding of the A. kamali/M. hirsutus system. Host selection experiments showed that, of nine species tested, HMB was the only suitable mealybug species for A. kamali development. Third nymphal instar was the optimal stage for wasp mass-production since A. kamali progeny from this stage had a female biased sex ratio and it had a weaker immune response as evidenced by lower encapsulation rate than adult female HMB. Parasitoid functional response was of type III in variable-time conditions, ensuring the preservation of HMB population at low density, and of type II--III in fixed-time conditions, leading to a better use of HMB population in mass-rearing. Temperature and photoperiod had a profound impact on parasitoid fecundity, 26°C and LD 0:24 being the optimal condition to maximize A. kamali oviposition. Parasitoid body size was positively correlated to its fitness. Large parasitoids lived significantly longer, had a higher fecundity, and progeny emergence with a lower sex ratio than small ones. Studies on mating showed that A. kamali is arrhenotokous and that multiple mating is required to optimize progeny sex ratio. Progeny production by mated females was also higher than that of virgin females. Female parasitoid fecundity was negatively correlated to their density due to mutual interference. Under mass-rearing conditions, 75 female A. kamali per cage was the optimum. Finally, under stored condition, food supply and low temperature (20°C) appeared essential to sustain parasitoid longevity. However, storage periods up to 14 days did not affect parasitoid lifetime fec