Synergistic manipulations of plant and insect defences.

BACKGROUND: It has been demonstrated previously that cis-jasmone acts as an elicitor of plant defence mechanism(s) by inducing secondary metabolism. It has also been demonstrated that temporal synergism can result in hypersensitive insect pests due to the inhibition of metabolic enzymes. RESULTS: Laboratory bioassays demonstrated that pre-exposure of insects by piperonyl butoxide followed by cis-jasmone treatment of crops, reduced Aphis gossypii on cotton by 80% and Myzus persicae on sweet pepper by 90%. By microencapsulating the cis-jasmone and combining with piperonyl butoxide, Bemisia tabaci on tomatoes was reduced by 99%. A field trial with microencapsulated cis-jasmone combined with piperonyl butoxide resulted in a comparable reduction of whitefly egg numbers to that given by the registered rate of imidacloprid, with efficacy of 89% and 93%, respectively. CONCLUSIONS: If insect defence enzymes are compromised by piperonyl butoxide whilst plant defence is primed by cis-jasmone, there are possibilities of an insecticide-free method of controlling insect pests. The success seems largely dependent upon the toxicity of the plants' secondary chemistry.

Comparative biological activities of a plaque-purified variant and a Turkish native isolate of SpliNPV-B against Spodoptera littoralis (Lepidoptera: Noctuidae).

The noctuid moth Spodoptera littoralis (Boisduval) is an important pest of many cultivated plants worldwide and five different geographical Nucleopolyhedrovirus (NPV) strains of this pest have been isolated to date. Two of these, a plaque-purified variant of the S. littoralis NPV from Morocco (SpliNPV-M2) and a SpliNPV isolated from field-infected S. littoralis larvae found in Turkey (SpliNPV-TR1), were compared biologically in terms of infectiveness (median lethal dose, LD50) for third instars and in terms of virulence (median lethal time, LT50) for neonates and third-instar S. littoralis larvae. The LD50 values of SpliNPV-TR1 and SpliNPV-M2 were 20.73 and 185.21 occlusion bodies (OBs)/larva, respectively, with non-overlapping confidence limits indicating they were significantly different. Thus, SpliNPV-M2 was found to be significantly less infective (about nine times higher LD50) than SpliNPV-TR1. The LT50 values of neonates for SpliNPV-M2 and SpliNPV-TR1 were 37 and 43.9 h at a concentration of 10(6) OBs ml(-1), respectively. For these same isolates, the LT50 values at a concentration of 3 x 10(6) OBs ml(-1) were calculated as 35.6 and 41.7 h, respectively. The LT(50) values of third instars for SpliNPV-M2 and SpliNPV-TR1 were 147.4 and 160.5 h, respectively, at a dose of 3000 OBs/larva and 145.4 and 152.4 h, respectively, for the same isolates at a dose of 20,000 OBs/larva. On the other hand, Helicoverpa armigera (Hübner) and Agrotis ipsilon (Hufnagel) revealed a lack of lethality of the SpliNPV-TR1 isolate.