The Repellency of Mature Citrus Leaves to Probing Aphids2

Abstract

Individuals of the cowpea aphid, Aphis craccivora Koch; the melon aphid, A. gossypii Glover; the spirea aphid, A. spiraecola Patch; and the green peach aphid, Myzus persicae (Sulzer), were allowed to probe on leaves of bean, crotalaria, and citrus. The probing response of all 4 aphid species to the various leaves was similar. More than 65% of probes on upper or lower surfaces of mature citrus leaves were less than 15 seconds in duration, whereas, less than 35% of probes were of that duration on leaves of other hosts. Virus transmission from bean and crotalaria leaves was considerably lower from probes under 15 seconds in duration than from probes exceeding 15 seconds, suggesting that more than 15 seconds are usually necessary before aphid stylets are able to reach virus-containing regions in the epidermis. Frozen sections of leaves cut with a microtome failed to reveal any obvious anatomical differences that would account for the brevity of aphid probes on mature citrus leaves. We suggest that, upon maturity, the cuticle and/or cell walls of citrus leaves develop a condition that renders them repellent to aphids, and that this condition accounts for the brevity of probes by aphids placed on these leaves.