PROBING AND FEEDING CHARACTERISTICS OF THE GREENHOUSE-WHITEFLY IN ASSOCIATION WITH HOST-PLANT ACCEPTANCE AND WHITEFLY STRAINS

Host-plant and whitefly strain effects and their interactions on the p robing and sap feeding of the greenhouse whitefly Trialeurodes vaporar iorum (Westwood), have been investigated in this study using the DC-EP G (Electrical Penetration Graph) technique. Whiteflies generally displ ayed fewer but longer probes on highly acceptable cucumber than on les s acceptable tomato. Both whitefly strains, the T(omato)-strain and th e C(ucumber)-strain, showed a significantly lower number of phloem pha ses on cucumber than on tomato. However, the duration of total phloem phases achieved by either of the whitefly strains on these two host pl ants was not significantly different. These data indicate that a more continuous phloem feeding has occurred on cucumber plants. Indeed, the percentage of phloem feeding time after the first sustained phloem ph ase (longer than 15 min) was higher on cucumber for the C-strain white flies. When comparing these two whitefly strains, the T-strain whitefl ies probed less frequently but longer than the C-strain whiteflies did on both host plants. Also, the T-strain whiteflies displayed a longer duration of total phloem phases on tomato. An interaction between the whitefly strain and plant effects was detected on a parameter, which showed that whiteflies probed significantly longer before reaching the first phloem phase on the host plants that had been previously experi enced. In conclusion, both plant species and whitefly strains affect w hitefly's probing and feeding behaviour, though plant effects are much stronger.