Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor "Candidatus Portiera aleyrodidarum," an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the sweet potato whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbionthousing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.

Upon initiating a research project on the role of volatile infochemicals in the tritrophic system Cotesia (= Apanteles) glomerata (L.) ‐ Pieris brassicae (L.) ‐ cabbage, a bioassay was developed to investigate the response of C. glomerata. The bioassay should be effective in terms of high responsiveness and minimum variability and constructed through a comparative approach. Twenty seven treatments, organized in a factorial randomized block design, compared the effect of three bioassay set‐ups (glasshouse flight chamber, wind‐tunnel and Y‐tube olfactometer), three parasitoid age groups (1–2, 4–5 and 8–9 days old females), three pre‐treatment experiences (naive, damage experienced and oviposition experienced wasps) and the day‐to‐day effect on response of C. glomerata to clean cabbage (CC) and plant‐host complex (PHC) in a dual choice test. The best results with regard to the strength and consistency of response to the PHC were obtained in the glasshouse flight‐chamber by 4–5 days old female wasps with either damage or oviposition experience (94 and 90%, respectively). It is therefore recommended as a suitable bioassay for studying the role of volatile infochemicals in host‐habitat location by C. glomerata. A day‐to‐day variation in response was found in the glasshouse and wind‐tunnel. It was correlated with the direction of change in barometric pressure within the time period of the experiment, showing that steadily increasing atmospheric pressure yields a significantly higher response than steadily decreasing or fluctuating barometric flux. To control for the day effect it is suggested to conduct further experiments in a block design, having day as a block. Several aspects of the infochemical ecology of C. glomerata are discussed.

Recently parasitoids were hypothesized to encounter a reliability-detectability problem relating to chemical stimuli from the first and second trophic level, when searching for hosts. The relative role of infochemicals originating from the host,Pieris brassicae (second trophic level), and its food plant, cabbage (first trophic level), have been investigated with respect to long-range host location by the larval parasitoidCotesia glomerata. Flight-chamber dual choice tests showed that uninfested cabbage plants are least attractive to female wasps. Host larvae and their feces were more attractive than clean plants but far less attractive than artificially damaged and herbivore-damaged plants. The plant-host complex, with host larvae actively feeding on the plant, was the most attractive odor source for the parasitoids. The data indicate that one of the solutionsC. glomerata uses to solve the reliability-detectability problem is to respond to infochemicals that are emitted from herbivore-damaged plants. Whether these infochemicals are herbivore-induced synomones that are produced by the plant remains to be demonstrated. Infochemicals emitted by the herbivore or its by-products are of little importance in the foraging behavior ofC. glomerata.

The effect of ultra violet (UV)-absorbing plastic sheets on the host location ability of three commercially available parasitoids Aphidius colemani Viereck (Hymenoptera: Braconidae), Diglyphus isaea Walker (Hymenoptera: Eulophidae) and Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) -was tested in the laboratory and in field trials. The parasitoids' preference between natural light and UV-filtered light was tested under laboratory conditions in a Y-shaped pipe system. The vast majority of all three species were strongly attracted to non-UV-filtered light. In field trials parasitoid's ability to locate a host-infested plant from a distance (approximately 10 m.) was tested. Host location by A. colemani and D. isaea, expressed by parasitization rates, was not affected by greenhouse covering plastic type (regular versus UV-absorbing plastic). E. mundus, on the other hand, was unable to locate the host-infested plant when the latter was placed in the center of the UV-absorbing plastic covered greenhouses. When the host-infested plants were located in the corners of the greenhouses and the wasps were released at the center, the parasitization rates were lower under the UV-absorbing plastic than under the regular plastic covered greenhouses. The significance of UV light to E. mundus host location process and the practical implications it has on the parasitoid's application in the field are discussed.