Effects of water extracts of frass from three locust species and various plants on oviposition and embryonic development in the desert locust, Schistocerca gregaria

Abstract

The water extract of desert locust, Schistocerca gregaria, frass collected in the wild had an oviposition inhibitory (OI) effect when mixed with sand and presented to adults. Likewise, the leaves of six plant species, as well as frass produced by desert locusts fed with these plants, exerted OI effects when compared with the control sand wetted with water alone. In general, frass extracts had a greater OI effect than the extracts of leaves. The OI effect was also observed when adult desert locusts were exposed to extracts of frass produced by two other locusts, the Bombay locust, Nomadacris succincta, and the migratory locust, Locusta migratoria, fed with rescue grass, Bromus catharticus. Among the three species of locust, desert locust and migratory locust frass exerted a greater OI effect than Bombay locust frass. Frass samples extracted with hot and cool water produced similarly high OI effects, indicating that bacterial involvement during extraction is unlikely. Hatching rates of desert locusts were significantly reduced by extracts of all of the above mentioned frass when the extracts were mixed with sand and used to incubate the eggs. In contrast, the lethal effects of leaf extracts on the hatching rates varied depending on the plant species. The embryos became deformed within four days when three-day-old eggs were incubated in sand containing frass extracts from desert locusts fed with rescue grass, whereas no apparent morphological changes were observed when seven-day-old eggs were similarly tested, although their hatching rate was significantly reduced.