This thesis examines the effects of malathion, chlorpyrifos, fipronil and spinosad mixed in fruit fly protein bait on attraction, feeding and mortality of the Queensland fruit fly, Bactrocera tryoni (Froggatt). The effects of weathering of the protein bait-insecticide mixtures on the mortality of B. tryoni were also measured along with attraction, feeding response and toxicity of the protein bait sprays on important arthropod natural enemies particularly the red scale parasitic wasps, Aphytis lingnanensis (Compere) and Comperiella bifasciata (Howard), the green lace wing, Chrysoperla carnea (Stephens) and the mealy bug predator, Cryptolaemus montrouzieri (Mulsant).

In field cage experiments, protein-starved male B. tryoni showed the same level of attraction to protein baits mixed with malathion, chlorpyrifos, fipronil, spinosad and protein alone used as the control. However, protein-starved females elicited a difference in attraction with protein baits containing chlorpyrifos and spinosad. Traps with spinosad bait mixtures captured significantly more females compared to traps containing chlorpyrifos bait mixtures. Laboratory feeding experiments on protein-starved female flies demonstrated that baits containing malathion and chlorpyrifos deterred flies from feeding on them. In contrast, no such deterrence was detected with baits containing spinosad, fipronil and protein alone. These results demonstrated that the type of toxicant mixed with protein bait sprays can influence the attraction and feeding responses of B. tryoni. Therefore the process of screening toxicants for use in protein bait mixtures is important and should entail field and laboratory tests.

In terms of toxicity, protein baits mixed with malathion and chlorpyrifos caused significantly higher fly mortality and demonstrated a more rapid fly knock down than did spinosad, fipronil and protein alone as the control. Spinosad however was a slow acting toxicant, causing a gradual increase in fly mortality over time.

Fly mortality obtained with protein bait mixtures containing malathion, chlorpyrifos and fipronil, applied on citrus leaves, and weathered out doors for up to 6 days did not vary significantly from freshly applied baits. However, the residual effectiveness of bait mixed with spinosad waned significantly after 3 days of out door weathering. Fly mortality caused by 3 day aged spinosad bait mixture was significantly lower than fresh bait mixtures, suggesting a rapid break down of spinosad under field conditions.

The parasitism rates of the two most important parasitoids of red scales, A. lingnanensis and C. bifasciata, measured before and after commencement of fruit fly bait spraying in two commercial citrus orchards, did not show any significant negative trend. Aphytis were not attracted to Pinnacle protein, the most commonly used fruit fly protein lure in Australia. A significantly higher number of Aphytis were attracted to honey solution and protein bait mixed with 20% sugar, compared to protein bait alone. A no-choice test further confirmed this result, demonstrating no difference in attraction between protein and water.

Protein bait containing malathion, chlorpyrifos, fipronil, and spinosad, fresh and weathered for up to 12 days, caused high mortality in Aphytis. In contrast protein bait mixed with spinosad caused a lower Aphytis mortality after 12 days out door weathering, compared to chlorpyrifos bait mixture. However, for other weathering periods, no such differences in mortality between the treatments were observed. In addition, the parasitizing capacity of Aphytis, after being exposed to these weathered residues, was reduced. Except for the control, aged bait mixtures significantly reduced the fecundity of Aphytis. Therefore, while integrating chemical based field control along with bio-control agents, appropriate measures should be in place to reduce the negative impacts of toxic residues.

Overall, the findings from this study indicate that spinosad is a suitable alternative to the older toxicants, for incorporation into fruit fly protein baits. Moreover, fruit fly protein baits in the field are less likely to disrupt the activites of important natural enemies. However, chemical-based control of insect pests in a cropping system should be designed carefully with the objective to prevent potential harm to susceptible biological control agents such as Aphytis.