SEARCHING BEHAVIOR OF ENCARSIA-FORMOSA AS MEDIATED BY COLOR AND HONEYDEW

The habitat- and host-searching behaviour of female Encarsia formosa G ahan (Hymenoptera: Aphelinidae) was assessed using an airflow olfactom eter and a filter paper test. Responses to different odour cues, colou rs, host-produced honeydew, non-host honeydew and single carbohydrates were determined. The parasitoid was not attracted to or arrested by o dours emanating from clean tobacco leaves, tobacco leaves heavily infe sted with the host Trialeurodes vaporariorum (Westwood) (Homoptera: Al eyrodidae) and covered with honeydew, or honeydew alone. However, E. f ormosa females showed a significant response to green light transmitte d through a tobacco leaf. The yellow part of the spectrum was partly r esponsible for this response. Thus, the long-range orientation is rand om with respect to the presence of hosts. Filter paper tests showed th at the short-range searching behaviour is influenced by water soluble, non-volatile contact-kairomones contained in the host-produced honeyd ew. Contact with honeydew excreted by L3/L4 TT: vaporariorum um result ed in longer searching times than honeydew from adult T vaporariorum o r L3/L4 Bemisia tabaci Gennadius (Homoptera: Aleyrodidae). No differen ce was found between the response to honeydew excreted by adult and L3 /L4 B. tabaci. The parasitoids' response to honeydew was unaffected by the host plant on which the whiteflies had fed. Non-host honeydew and single carbohydrates also affected the searching behaviour of E. form osa but to a lower extent than host honeydew. The possible differences in the carbohydrate and amino acid composition of the honeydew excret ed by different life-stages of T. vaporariorum and B. tabaci are discu ssed.