Destruction of eggs as an alternative to chemical control of the grasshopper pest Zonocerus variegatus (L.) (Orthoptera: Pyrgomorphidae) in Nigeria

Abstract

Zonocerus variegatus (L.) is a chronic but relatively minor pest of crops in West Africa, and expensive control measures are not generally warranted. Egg pods, which take approximately six months to develop, are deposited in highly aggregated sites found scattered throughout cultivated areas. To test the feasibility of reducing populations in large areas by digging up the egg pods, two areas, of 18·5 and 20 ha, were selected near Ibadan, Nigeria, for investigation. Egg-laying sites were identified by observation and the egg pods subsequently dug up. There were on average one or two sites, 5·7 m² in area, per hectare. Counting the following season's hatching populations in the two areas showed that the potential hatches had been reduced by 83 and 91%, respectively. Control by community self-help is suggested, where individual farmers identify and dig up laying sites on their own land, exposing the egg pods to desiccation on the soil surface. If this was carried out by all the farmers in an area, populations of Zonocerus could be reduced and crop damage minimised. Such control can be carried out at little or no cost and with very little labour.