The probing behaviour of nymphs of Vanduzeea arquata and Enchenopa binotata (Homoptera: Membracidae) on host and non‐host plants

. 1. Nymphs of Vanduzeea arquata Say have been found to be more host‐specific in nature and to show a higher degree of selectivity in host discrimination experiments than nymphs of Enchenopa binotata (Say), It was hypothesized that this differential selectivity would be reflected in the probing behaviour of individuals placed on twigs of host and non‐host plants. Probing behaviour was examined by direct observation of nymphs and by sectioning and staining the probed plant tissues. 2. All nymphs probed readily and for extended periods on both host and non‐host twigs. E.binotuta nymphs showed no consistent differences in probing behaviour on hosts versus non‐hosts, but V.atquuta nymphs were more likely to withdraw their stylets within 60 s when on non‐host twigs and produced honeydew only when on their host species. V.urquatu nymphs reached the phloem sieve elements only when on host twigs and broke many cells in peripheral plant tissue layers while probing. E.binotata nymphs broke few cells and often reached the phloem of non‐host as well as host plants. 3. Nymphs of V.arquata always reject non‐host plants, apparently in the course of probing and prior to encountering the phloem sap. Chemical compounds released from ruptured parenchyma cells may act as probing stimulants or inhibitors. E.binotura nymphs often feed on non‐host plants in a non‐choice situation; their preferential settling on host twigs in discrimination experiments may reflect a tendency to abandon non‐host twigs more readily than host twigs.