RECOGNITION BEHAVIOR OF THE CASSAVA MEALYBUG PHENACOCCUS-MANIHOTI MATILE-FERRERO (HOMOPTERA, PSEUDOCOCCIDAE) AT THE LEAF SURFACE OF DIFFERENT HOST PLANTS

The testing behavior and test probing which are a part of host-plant a cceptance behavior were studied in P. manihoti. Attention was focused on the testing behavior of three plants of the Manihot genus (Incoza, M'Pembe, and Faux-caoutchouc) and a weed of the cassava fields (Talinu m). This enabled us not only to characterize the associated behavior b ut also to show that the mealybug is able to distinguish between diffe rent host plants when walking on the leaf. The video description of th e test probing of first- and fourth-instar larvae on M'Pembe mid on th e Faux-caoutchouc shows that the succession of the phases is similar. After a first phase characterized by the repeated intervention of the mealybug sensorial organs, a second phase, more mechanical, with up-an d-down head movements, is observed. At this time, the stylets pass thr ough the epidermic and inner tissues. Finally, a third phase, during w hich the mealybug becomes more agitated, is observed: it stands up usi ng its rear legs and pushes the upper part of its body against the pla nt. The stylets continue their progression, which is principally inter cellular, until they reach the phloem. Longer and longer immobility pe riods are observed over a period of time. We used the coupled videocam era and electrical penetration graph technique to see the relations ex isting between outer and inner plant events, i.e., between the behavio ral items and the electrical signals characteristic of the stylers pat hway in the plant. We observed that the stylet progression in the plan t was more difficult in the resistant hybrid Faux-caoutchouc than in t he sensitive M'Pembe variety.