Development of a trap to contaminate variegated grasshoppers (Zonocerus variegatus L.) (Orthoptera: Pyrgomorphidae) with Metarrhizium flavo-viride Gams & Rozsypal in the field

English

Locusts and grasshoppers are important pests of agriculture in West Africa. Application of chemical insecticides is the major control mechanism. However, concerns arising from human health problems and environmental' hazards have put forward a strong case for biological control. A simple trap incorporating an attractant and a biological control agent, Metarrhizium flavo-viride, to contaminate the cassava pest, Zonocerus variegatus. is described. The attractant, an extract of the Siam weed, Chromolaena odorata, attracted significantly more adults and 5th 16th instars in the field than plant parts of C. odorata and cassava leaves presented whole or crushed in distilled water. At a mean Z. variegatus field population density of 1.1m", the mean trap catch wlls 27.2 trap" day·l. All insects trapped on the first day died from fungal infection within 10 days (LTso = 6.1 days), with the need to replace the pathogen with a freshly prepared one after 7 days in the field. Trapped insects, infected or uninfected, showed a bimodal pattern of exit from the traps with peaks at 09.00 and 17.00 h. The pattern of spread of infected and uninfected insects after exiting from traps were similar. The farthest group mean displacements from traps were 34.2 and 36.3 m in 5 days for infected and uninfected insects, respectively, leading to a suggested trap density of 2 ha·l.

Adu-Mensah, J.