Content area
Full Text
ABSTRACT: The desert plant, Lotus corniculatus (Fabaceae), inhabits the Saudi Arabian Sahara Desert. In these areas the desert locust, Schistocerca gregaria (Orthoptera, Acrididae), feeds on L. corniculatus containing the plant allelochemical linamarin; a cyanogenic glucoside that is usually toxic to polyphagous insects. Under laboratory conditions this plant was fed to S. gregaria. Haemolymph proteins and allelochemicals detoxification in S. gregaria, fed on L. corniculatus were assessed. Female 5th instar nymphs were reared on L. corniculatus or on wheat seedlings, Triticum aestivum, as control. In insects, glutathione-S-transferase is one of the most important detoxifying enzymes. The activity of glutathione-S-transferase (in units/gram) in the mid-gut tissues of 5th instar nymph females fed on L. corniculatus was significantly higher than in those fed on T. aestivum. The quantity of haemolymph proteins (in mg 100µl^sup -1^) in adult locust females resulting from nymphs fed on L. corniculatus was significantly less than it was in females fed on T. aestivum. Decreasing protein synthesis in the adult females of S. gregaria might be related to detoxifying toxic compounds in L. corniculatus.
KEY WORDS: S. gregaria, Lotus corniculatus, haemolymph, proteins, glutathione-S-transferase, linamarin, detoxification
INTRODUCTION
The objective of this study was to investigate the ability of the desert locust, S. gregaria, to resist the toxicity of linamarin allelochemical in the desert plant, L. corniculatus, and the relation to the amount of protein synthesis in the haemolymph of locust adults fed as 5th instar nymphs on the desert plant L. corniculatus. The desert locust, S. gregaria, is a major insect pest in the Middle East and Northern Africa. It has a long history of devastating crops and contributing to famines in many African countries. Desert locusts have the ability to detoxify many of the toxic materials in their host plants that prevail in their preferred habitat and this allows a considerable food diversity for locusts. Ozenda (1977) mentioned that S. gregaria do not prefer L. corniculatus as food. According to Berenbaum (1986) generation of cyanide from linamarin is usually enzymatic and occurs if linamarin is exposed to linamarase. Herbivorous insects can tolerate toxic compounds because they have evolved various physiological mechanisms to avoid the harmful effects of toxins. Most herbivorous insects rely heavily on enzymatic degradation for the neutralization of ingested allelochemicals. Polysubstrate...