The Control of Chafer Grubs (Schizonycha Sp., Coleoptera, Melolonthinae) in the Sudan

Abstract

Schizonycha larvae, of a species that cannot yet be named with certainty, are a serious pest of “lubia” (Dolichos lablab) and “dura” (Sorghum vulgare) in the Sudan Gezira. Damage from these grubs has seriously reduced lubia yields at the Gezira Research Farm during the 1946–52 seasons. Soil application of BHC, at rates between 10 and 40 gm. γ isomer per feddan (1·038 acre) give excellent control of this pest on lubia. Application with the seed at the time of sowing (in effect, by drilling) is, in general, more effective than broadcasting or applying the insecticide along the ridges. Seed dressings appear to be ineffective for control, with lubia.Population estimates show that γ BHC does not kill Schizonycha larvae but repels them or prevents feeding. The larvae occur in the soil to a maximum depth of 60 cm., and are concentrated around the plant roots. The mean depth varies with time of year, and probably with type of plant, between 15 and 30 cm. The mean depth of the pupa is 15 cm.; this does not appear to be influenced by BHC.Larvae are widely distributed in the Gezira but are most abundant in the South and Centre Groups of the Scheme. There is evidence that, where chafer larvae and termites are associated with groundnuts, the chafer larvae are responsible for initiating damage while the termites are secondary invaders. The beneficial effect of a good lubia crop (resulting from BHC application) is reflected in the cotton crop two years later.