Selectivity of pesticides used on cotton (Gossypium hirsutum) to Trichogramma pretiosum reared on two laboratory-reared hosts.

The side-effects of pesticides (insecticides, fungicides, herbicides and plant growth regulators) used on cotton were tested on adults and pupae of Trichogramma pretiosum Riley reared in the laboratory on two different hosts, the Angoumois grain moth (Sitotroga cerealella Olivier) and the Mediterranean flour moth (Ephestia kuehniella (Zeller)). The eggs of the host enclosing the parasitoid pupae received direct pesticide sprays, while the adults of the parasitoid were exposed to the pesticides through contact with residues on sprayed eggs offered to parasitism. Alpha-cypermethrin, carbosulfan, deltamethrin, endosulfan, profenofos and zeta-cypermethrin were highly noxious to the parasitoid, significantly reducing the percentage of emergence and parasitism of T. pretiosum developing in E. kuehniella or S. cerealella eggs. However, the pupal stage of the parasitoid developing in S. cerealella eggs was less susceptible to alpha-cypermethrin and deltamethrin. Lufenuron and metamidophos greatly reduced the percentage of adult emergence from eggs of both hosts, while novaluron only interfered on this variable when the wasps were developing in E. kuehniella eggs. However, lufenuron and monocrotophos had no effect on the parasitoid pupae of T. pretiosum developing in E. kuehniella eggs. Chlorfluazuron, diafenthiuron, diflubenzuron, fentin hydroxide, mepiquat chloride, novaluron, thiacloprid and triflumuron did not affect T. pretiosum emergence when eggs of S. cerealella enclosing pupae of the wasps were surface treated. The pesticides azoxystrobin, carbendazin + thiram, mepiquat chloride and novaluron had no effect on the ability of the wasps to parasitise E. kuehniella eggs. However, only mepiquat chloride did not affect the percentage of F1 wasps emerging from E. kuehniella eggs. The remaining pesticides moderately reduced the percentage of emergence and parasitism of the wasps when they had contact with the chemicals during their pupal or adult stage. Thus there were differences in pesticide toxicity according to the host used for parasitoid development. These differences were hypothesised to occur because of differences in egg morphology and parasitoid performance.