Parasitism of tomato fruitworm larvae in process tomatoes at Pukekohe

A process tomato trial was undertaken at Pukekohe to investigate the interactions between tomato fruitworm, Helicoverpa armigera, and its larval parasitoids - the accidentally introduced generalist, Meteorus pulchricornis, and the introduced specialists, Cotesia kazak and Microplitis croceipes. Total mortality of larvae caused by parasitism was 75%, with M. pulchricornis, the dominant parasitoid, reared from 54% of parasitised larvae, and C. kazak and M. croceipes reared from 33% and 13% respectively. Cotesia kazak attacked smaller larvae than the other two species and was able to survive in the presence of the entomopathogenic fungus Zoophthora radicans late in the crop. These results contrast with those for corresponding parasitism in Hawke's Bay where C. kazak is very dominant. It is concluded that the availability of alternative hosts in areas like Pukekohe is causing the displacement of C. kazak there but that this is having little impact on biocontrol of this pest in tomatoes.