Y.C. Drost

Life-history parameters of different biotypes of Bemisia tabaci (Hemiptera: Aleyrodidae) in relation to temperature and host plant: a selective review

Life-history parameters of different biotypes of the whitefly Bemisia tabaci (Gennadius) species complex were reviewed. This included the B-biotype of B. tabaci , identified as B. argentifolii (Bellows & Perring). Comparisons were made among different biotypes on cotton, among host plants for biotype B and among the whitefly species B. tabaci and Trialeurodes vaporariorum (Westwood), the greenhouse whitefly. The biotype identification of different populations of B. tabaci was 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 of B. tabaci in 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 as sustainable biological control agents in greenhouses

Aphelinid parasitoids have been used for control of pests in greenhouses since the 1920s, 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, Trialeurodes vaporariorum, with the aphelinid Encarsia formosa. Encarsia is applied on 5000 ha of vegetable crops worldwide. Weekly, more than 20 million individuals of E. formosa are mass reared and shipped to growers in 20 countries. About 10 years ago, another whitefly species, Bemisia 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.

Comparison of searching strategies of five parasitoid species of Bemisia argentifolii Bellows and Perring (Hom., Aleyrodidae)

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.

Life‐history and oviposition behaviour of Amitus bennetti, a parasitoid of Bemisia argentifolii

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.