Natural enemies of tropical locusts and grasshoppers: their impact and potential as biological control agents.
The main groups of natural enemies of Acrididae, including predators, parasitoids, entomophilic nematodes and pathogens, are discussed in relation to their value as mortality factors and their potential as biological control agents with particular reference to tropical Asia and Africa. In-depth studies relating to Schistocerca gregaria, Zonocerus variegatus, Oedaleus senegalensis and Chortoicetes terminifera are outlined. The conclusions of population dynamic studies on the impact of natural enemies are summarized and it is shown that there is a consensus that natural enemies are unable to prevent locust outbreaks but can provide a useful constraint on the rate of population increase and may hasten the collapse of plagues. The possibilities for biological control are discussed and it is concluded that there is little prospect for classical biological control of mobile locusts but that there may be some opportunities for introduction of insect predators for suppressing static grasshopper populations. Augmentative release programmes are not considered to be feasible. However, the most promising approach to biological control appears to be the development of pathogens, particularly those fungi which can be cultured in vitro, as biological pesticides.