Response of pests of brassicae and their parasitoids to synthetic and natural feeding deterrents
Antifeedants and growth regulators have potential as alternatives to conventional methods of insect pest control. As with conventional chemicals it is important to consider their effects on natural enemies of the pests. The aim of this project was to determine whether the bitter-tasting synthetic chemical denatonium benzoate as an antifeedant and compare with neem derivatives. Other aims were to investigate their effect on parasitoids and the field infestation of cabbage pests. Denatonium benzoate is systemic and had no contact effect but acted as an antifeedant on a generalist sap feeder Myzus persicae and reduced the survival, fecundity, and lifespan. Neem derivatives, Azatin EC and Pestistat R were more effective of which Azatin EC was the most effective. Antifeedants further reduced the fecundity and survival when parasitized with its parasitoid, Aphidius matricariae and neem derivatives had adverse effects on both aphid and the parasitoid. Denatonium benzoate and Pestistat R with a specialist leaf feeder, Pieris brassicae and all antifeedants with Plutella xylostella (generalist leaf feeder) and Chrysodeixis eriosoma (specialist brassica leaf feeder) reduced the leaf area consumed and it was inversely proportional to the concentration. The highest leaf area consumption was in denatonium benzoate and the lowest in Pestistat R. Higher azadirachtin concentrations were detrimental but denatonium benzoate was safer to the larval parasitoid, Cotesia plutellae. Denatonium benzoate and Azatin EC reduced field infestation of M. persicae, P. xylostella and C. eriosoma in Peradeniya, Sri Lanka and Azatin EC was the most effective. Denatonium benzoate acts as an antifeedant against cabbage pests and safer towards parasitoids hence can be used in integrated pest management programmes. Neem derivatives are comparatively more effective on pests but harmful to parasitoids. Denatonium benzoate and Azatin EC effectively reduced the pest infestation under field conditions.