Effect of the lectin PHA on the feeding behavior of the grain aphid

Abstract

The electrical penetration graph (EPG) method was used to quantify the effect of the lectin PHA (phytohemagglutinin) on the
feeding behavior of the grain aphid Sitobion avenae F (Hemiptera: Aphididae). Addition of PHA to an artificial diet affected aphid probing behavior. In general, increasing concentrations
of PHA in sucrose-agarose gels significantly reduced the number of aphid probes and extended their duration. Aphids feeding
on the gels with lectin (without concentration 50μg· cm−3) had a prolonged activity (EPG pattern C) that was corresponded to prolonged penetration of the epidermis and mesophyll for
aphids feeding on plants. Such insects also showed a significant reduction in salivation and passive ingestion from gels and
a reduction in the total number of gel penetrations. At concentrations ≤250μg ·cm−3, PHA reduced feeding behavior on gels, and the EPG data were interpreted to correspond with reduced salivation into phloem
sieve elements (EPG pattern E1) and reduced ingestion of phloem sap (EPG pattern E2). PHA also delayed the onset of the first
E1 and E2 patterns. At higher concentrations (≥500μg· cm−3), PHA completely stopped salivation and passive ingestion from gels. Similarly, higher concentration of PHA strongly reduced
activity on gels that corresponded to activity in xylem (EPG pattern G); high PHA delayed the onset of the first G pattern
and reduced total time of pattern G activity.

KeywordsPhytohemagglutinin-Sitobion avenae-EPG-Artificial diet-Protein toxicity