Culturable enteroviruses were detected by applying concentration techniques and by inoculating the concentrates on the BGM cell line. Samples were obtained from a wide variety of environments, including raw sewage, secondary effluent, coagulated effluent, chlorinated and UV-irradiated effluents, river water, coagulated river water, and lake water. The virus concentrations varied widely between 0.001 and 570/liter. The same cell line also supported growth of reoviruses, which were abundant in winter (up to 95% of the viruses detected) and scarce in summer (less than 15%). The concentrations of three groups of model organisms in relation to virus concentrations were also studied. The concentrations of bacteria (thermotolerant coliforms and fecal streptococci) were significantly correlated with virus concentrations in river water and coagulated secondary effluent, but were relatively low in disinfected effluents and relatively high in surface water open to nonhuman fecal pollution. The concentrations of F-specific RNA bacteriophages (FRNA phages) were highly correlated with virus concentrations in all environments studied except raw and biologically treated sewage. Numerical relationships were consistent over the whole range of environments; the regression equations for FRNA phages on viruses in river water and lake water were statistically equivalent. These relationships support the possibility that enteric virus concentrations can be predicted from FRNA phage data.

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Life-history parameters of different biotypes of the whiteflyBemisia tabaci(Gennadius) species complex were reviewed. This included the B-biotype ofB. tabaci, identified asB. argentifolii(Bellows & Perring). Comparisons were made among different biotypes on cotton, among host plants for biotype B and among the whitefly speciesB. tabaciandTrialeurodes vaporariorum(Westwood), the greenhouse whitefly. The biotype identification of different populations ofB. tabaciwas summarized in a table. Biotypes discussed were A, B, Indian and biotypes of the Old World group. Temperature dependent relationships were estimated for egg development rate, development rate from egg to adult, immature mortality, adult longevity, sex-ratio, pre-oviposition period and fecundity. The fitted curves will be used as input for a simulation model of the population dynamics ofB. tabaciin a greenhouse when parasitoids are released. The model makes it possible to evaluate the integrated effect of different life-history parameters and behavioural parameters of parasitoids on whitefly population levels in a greenhouse.

Aphelinid parasitoids have been used for control of pests in greenhouses since the 192Os, but large scale application started only some 25 years ago. Today, several aphelinid parasitoids are commercially used for the biological control of scale, aphid and whitefly pests in greenhouses. A success story is the biological control of greenhouse whitefly, Triulrurodes cuporuriorum, with the aphelinid Encursiu formom. Encursiu is applied on 5000 ha of vegetable crops worldwide. Weekly, more than 20 million individuals of E. jortnosu are mass reared and shipped to growers in 20 countries. About 10 years ago, another whitefly species, Bemisiu sp., developed to pest status and a search for control of scales and aphids in greenhouses is summarized, as well as the status of commercial biological control with aphelinid parasitoids. Further, the questions whether effective natural enemies can be identified before introduction and if autoparasitoids should be imported and released are addressed. Finally, the usefulness of parasitoid biotype studies to recognize suitable candidates for biological is considered.

Abstract. Mated female Brachymeria intermedia (Hymenoptera: Chalcididae) deprived, since emergence, from pupae of their host Lymantria dispar (Lepidoptera: Lymantriidae), accumulated eggs but had a very low rate of hostacceptance. Parasitoids that were host‐deprived after encountering pupae early in life also accumulated eggs, but maintained a high acceptance rate. Thus early exposure to hosts promoted active reproductive behaviour. Total egg production depended on the total number of pupae encountered, indicating that B.intermedia adjust their egg production to host availability. Hence, in B. intermedia both the physiological state of the parasitoid (age and egg load) and the informational state (in this case host‐availability and experience) interact to shape oviposition behaviour.

Amitus bennetti Viggiani & Evans (Hymenoptera: Platygasteridae) is a recently described parasitoid of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae). Behaviour and life history of the parasitoid are described. The first nymphal instar of B. argentifolii is preferred by the parasitoid, but the 1st through 4th instar may be parasitised. Females first investigate hosts with their antennae, then walk over the host, and eventually step with their front legs on the leaf and insert their ovipositor inside the host facing away from the host, while the hind legs are still on the host. The time from encounter to oviposition (=latency to oviposition) is shortest on the 1st instar. Oviposition duration (mean=39 s) comprises 50% of the handling time. Development time from egg to adult decreases from 72 days at 15 °C to 42 days at 20 °C to 28 days at 25 °C. We estimate that 400 degree days is required for development, with a development threshold of 10 °C. Adult longevity in the absence of hosts was 29, 26 and 19 days and with hosts present 8, 8 and 5 days at 15, 20 and 25 °C, respectively. Amitus bennetti is proovigenic and oviposits most eggs shortly after adult emergence. During the first day of their adult lives females laid 1, 31 and 49 eggs at 15, 20 and 25 °C, respectively. Compared with other parasitoid species, the development time of A. bennetti is very long, and the implications of this for management of B. argentifolii are discussed.

Oriented responses ofMicroplitis croceipes (Cresson) to airborne odors of actively feedingHeliothis zea (Boddie) larvae were observed in a flight tunnel. The behavior ofM. croceipes prior to and during sustained, oriented flights was videotaped and analyzed in detail. Preflight exposure of the parasitoid to feces and other components of the plant-host complex were found to be vital in effective flight behavior, while maturation of the parasitoid had little effect. The increased frequency of oriented flight that resulted from preflight exposure of a plant-host complex persisted for at least 24 hr.

Amitus bennetti Viggiani and Evans, Encarsia formosa Gahan (two strains), Eretmocerus eremicus Rose and Zolnerowich, Eretmocerus mundus Mercet and Eretmocerus staufferi Rose and Zolnerowich, which are parasitoids of Bemisia argentifolii Bellows and Perring were compared with respect to their searching behaviour as part of a pre‐introduction evaluation programme. Within a 5 cm arena, host‐finding time was independent of the release distance from the host. Before oviposition, A. bennetti walked fastest, the E. formosa strains walked slowest and the Eretmocerus species intermediate. Leg length was not the most significant factor determining the differences in walking speed. After oviposition, A. bennetti and Er. eremicus had a lower walking speed and higher turn rate which is an indication of area‐restricted search. The effect was strongest for A. bennetti. All species showed preference for counter‐clockwise turns. Based on the walking speed alone, it is expected that A. bennetti will be the most efficient natural enemy of B. argentifolii, the Eretmocerus species intermediate and the E. formosa strains the least.