STYLET ACTIVITY OF COWPEA APHID (HOMOPTERA, APHIDIDAE) ON LEAF EXTRACTS OF RESISTANT AND SUSCEPTIBLE COWPEA CULTIVARS

Electrical penetration graph recordings using direct current (DC-EPGs) were used to analyze aspects of the probing behavior of cowpea aphid, Aphis craccivora Koch, on intact plants and on hexane, ethyl acetate, and methanol extracts of leaves of aphid-resistant (ICV-12) and aphid -susceptible (ICV-1) cultivars of cowpea Vigna unguiculata (L.) Walp. In one set of experiments, recordings were done on plants with or with out parafilm wrapping, or on plants painted with raw leaf juice and ex tracts of the two cultivars. In another study, recordings were done on leaf extracts homogenized in water or in 0.5 M sucrose solution and t hen placed in parafilm membrane sachets. Electrodes were inserted into soil mix for the experiments on potted plants or into extract fractio ns and raw juice for the membrane feeding experiments on leaf extracts in parafilm sachets. Waveform signals were recorded from resistance f luctuations from interactions between aphids and substrates, and elect romotive forces generated within each preparation. ICV-12 plants with or without parafilm wrapping, and ethyl acetate extracts and raw juice of that cultivar significantly (P less than or equal to 0.05) reduced stylet penetration behavior. Thus, antixenosis as manifested by disru ption of aphid stylet activity on host substrates, appeared to be a go verning modality of aphid resistance in ICV-12.