Arrestment responses ofEretmocerus species andEncarsia deserti (Hymenoptera: Aphelinidae) toBemisia tabaci honeydew

The responses of Eretmocerussp. and Encarsia deserti(Gerling & Rivnay), parasitoids of Bemisia tabaci(Gennadius) to host secretions were investigated. Upon contact with honeydew excreted from the host, the parasitoids' walking speed decreased, whereas the rate of angular turning increased (the walking speed of Eretmocerussp. and Encarsia desertidecreased from 2.0 to 0.8 and from 0.8 to 0.3 mm/s, respectively, and the respective angular turning rates increased from 123.3 to 489.6 and from 267.9 to 979.2 deg/cm). Moreover, the wasps generally turned back toward the secretion as soon as they lost contact with it. This induced arrestment responses resulted in increased searching time by the parasitoids. Laboratory bioassays were conducted in which paper disks in petri dishes containing different amounts of honeydew, equivalent to the secretions of 1, 5, or 50 larvae, were offered to female wasps. The wasps responded by arrestment even to honeydew produced by a single larva. While the response of Eretmocerussp. was quantity dependent, being more intense at higher amounts of honeydew, that of E. desertiwas of equal intensity at all honeydew quantities assayed.