Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Selecting parasites for biological control of lepidopterous stalk borers in summer grain crops in South Africa.

Abstract

The noctuid Busseola fusca and the pyralid Chilo partellus are the most important pests of summer grain crops (maize and sorghum) in South Africa. Owing to the behaviour of these lepidopterans and the high production costs for summer grain crops, chemical control of these pests is often unsatisfactory. Altogether, 2 egg parasitoids (Trichogramma chilonis and T. ostriniae), 4 larval parasitoids (the braconids Cotesia flavipes and Allorhogas pyralophagus, the ichneumonid Mallochia pyralidis and the tachinid Paratheresia claripalpis) and 2 pupal parasitoids (the ichneumonid Xanthopimpla stemmator and the eulophid Tetrastichus howardi) were recently introduced into South Africa to control B. fusca and Chilo partellus on summer grain crops. Laboratory studies, however, showed that T. howardi was a facultative hyperparasitoid, and field releases were stopped until further information was available on its biology. In laboratory studies the eulophid was found to have a wide host range; it was reared as a primary parasitoid from Lepidoptera, Coleoptera and Hymenoptera and as a hyperparasitoid from the tachinids P. claripalpis and Palexorista laxa, the ichneumonids M. pyralidis and X. stemmator and the braconid Cotesia kazak. However, preference tests showed that females of T. howardi preferred to parasitize phytophagous insects, hosts they had been reared from and hosts which they had previously been exposed to. On the basis of these results and the risk that T. howardi may have an adverse effect on other parasitoid guilds in the summer grain crops, it was decided to defer releases of this species.