Probing Behavior of the Pea Aphid, Acyrthosiphon pisum. II. Comparisons of Salivation and Ingestion in Host and Non-Host Plant Leaves1

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Abstract
Differences in probing behavior of the Chualar pea aphid biotype of Acyrthosiphon pisum (Harris) became evident when salivation and ingestion activities in host and nonhost plants were electronically recorded on strip charts. Leaves of healthy broadbean, Vicia faba L., and V. faba plants infected with the Geneva 2 strain of bean yellow mosaic virus were used as hosts. Cowpea, Vigna sinensis Endl., and lettuce, Lactuca saliva L., were used as the non-host plants. Lettuce and cowpea were judged to be non-host plants when young adult pea aphids confined to leaves of these plants were unable to survive for more than 5 days. During this period, these aphids produced about 20 times fewer offspring than did aphids of comparable age on the V. faba plants. Specimens from 1 group of pea aphids were allowed to ingest for 10 minutes. Waveform sequences and the study of histological preparations showed that 70% of the aphids ingested fluid during their first probe regardless of whether the leaf was from a host or a non-host. Of the aphids probing host plant leaves, 78% ingested sap from the sieve elements during their first probe. Sixty-one percent of the aphids probing V. sinensis and 53% probing L. sativa ingested sap from epidermal or sulxjpidermal cells during their first ingestion probes. None of the aphids probing non-host plants ingested sap from the sieve elements during the first probe. Salivation and ingestion activities of another test group of aphids were continuously recorded for 24 hours. Twelve activity parameters were analyzed statistically. Significant differences in probing behavior occurred between aphids on host and non-host plants. Some differences in ingestion behavior were evident between aphids on lettuce and aphids on cowpea. There were some statistical differences in probing behavior between aphids on healthy V. faba and those on diseased V. faba. Aphid probing behavior is discussed in light of the results and some hypotheses are presented in explanation of these phenomena.