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

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 50 μg · 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 ≤250 μg · 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 (≥500 μg · 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.