EFFECTS OF TREATMENTS FOR ELECTRICAL PENETRATION GRAPH RECORDINGS ON BEHAVIOR AND BIOLOGY OF APHIS-CRACCIVORA (APHIDIDAE)

Two laboratory studies were conducted to investigate effects of treatm ents for direct current electrical penetration graph (DC-EPG) recordin gs or 'tether effect', on behaviour and reproductive performance of co wpea aphid Aphis craccivora Koch. The experiments constituted a contro l study in application of DC-EPGs to analyse cowpea aphid feeding beha viour and host plant resistance mechanisms. Resistant (ICV-12) and sus ceptible (ICV-1) cultivars of cowpea Vigna unguiculata (L.) Walp were used. EPG treatments included two groups of aphids: tethered aphids th at were exposed to DC electricity via an attachment of a thin, flexibl e gold wire on their dorsum using a droplet of adhesive silver paint, and 'free' (untethered) aphids with a dorsal spot of silver paint only . EPGs of the tethered aphids were recorded continuously for c. 1 h, w hereas from the 'free' aphids recordings were done only for brief peri ods of 2-5 min, by temporarily contacting a gold wire to the spot of s ilver paint. Waveform signals generated from resistance fluctuations a nd electromotive forces, and representing aphid styler penetration beh aviour were recorded. A separate experiment was conducted to investiga te effects of EPG treatments on aphid survivorship and population grow th. Overall, EPG treatments did not significantly affect aphid styler penetration behaviour or life-table parameters. However, effects of cr op cultivar on those characteristics were significant, Waveform E2, wh ich denotes aphid ingestion in phloem sieve elements, and non-penetrat ion behaviour were important indicators of aphid resistance in ICV-12. Also, apart from the number of aphid generation, other life-table par ameters were useful indicators of ICV-12 resistance. Thus, DC-EPGs pro vided a reliable technique for studying aphid stylet behaviour, and in vestigation of aphid resistance in cowpeas.