Is there a Relationship between the Level of Plant Metabolites in Cucumber and Globe Cucumber and the Degree of Insect Infestation?

Abstract

Cucumber plant was infested by three major insect pests, i.e., cotton aphid, white fly nymph and green bugs while globe cucumber, the wild cucumber species was kept healthy without any remarkable infestation. In addition, globe cucumber had higher ratios of T.S.S over T.N, T.S.S over T.C.A.A., T.S.S over T.F.A.A., higher content of cucurbitacins and phenolic compounds than cucumber in the two successive seasons. Lower values of these markers rendered cucumber susceptible to pests under study, not at all stages of growth but whenever these values were much lower through the growth stages. On the other hand, the major cucurbitacins were isolated and purified from each plant and identified by spectroscopic techniques. The development of cotton aphid treated with various globe cucumber extracts as well as the isolated cucurbitacins was also evaluated. Ethanol extract of globe cucumber caused higher mortality and affected on the biological aspects of cotton aphids when compared with all extracts. The importance of acetyl group and the double bond in the position 1 and 2 in different cucurbitacins on aphid’s mortality was studied. A field study showed a remarkable reduction (82.0 %) of cotton aphid induced by spraying the cucumber with 4 % ethanol extract of globe cucumber.