Criteria for host-plant acceptance by aphids

Abstract

Aphid probing or stylet penetration behaviour is needed (1) to get appropriate chemical information by internal gustation (Wensler, 1977) and (2) to reach the sieve elements in the vascular bundle for actual feeding. Transmission electron microscopy (TEM) showed that Aphis fabae (Scop.) on its host Vicia faba (L.) punctured many, if not all plant cells along the stylet track (Hogen Esch & Tjallingii, 1990; Tjallingii, 1990b). The stylet path, however, remained completely extracellular and the cells generally survived. It was intriguing that 11 sieve elements were reached and punctured before sap feeding started from the last one, which had evidently been punctured earlier, as we inferred on basis of saliva tracks. These data suggest that once a sieve element is reached its acceptability is not nessecarily self-evident. Presumably, its suitability might depend on the plant’s reactions to aphid activity. Whether sap ingestion from a sieve element had taken place could not be concluded from the histology, but from an electrical penetration graph (EPG), recorded from this aphid previous to TEM processing. EPGs can record aphid activity during plant penetration (Tjallingii, 1988). Moreover, mechanical work, punctures of plant cells, saliva secretion, active and passive ingestion and other activities can also be derived from EPGs. So, the EPG from this aphid was able to show a number of sieve element punctures without ingestion preceding the final puncture with sustained sap ingestion.