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Bemisia tabaci (Gennadius) is a serious pest of vegetable, ornamental, and agronomic crops throughout the world. To control B. tabaci, Eretmocerus eremicus Rose & Zolnerowich, and Eretmocerus mundus Mercet are considered the most effective parasitoids in dry tropical regions. In parasitoids, choosing the `right` hosts has direct consequences for their reproductive success and efficiency as biocontrol agent. Therefore, being able to discriminate a parasitized host from an unparasitized one would be important to prevent wasting time, eggs, and to reduce the mortality risk for their offspring. We evaluated intra- and interspecific host discrimination and the chance of super-parasitism or multi-parasitism in two populations of E. mundus (sexual and asexual) and E. eremicus. Different combinations and sequences of female introduction were carried out for the various populations and species. Experienced females avoided super-parasitism. However, naïve females did lay eggs under hosts that were previously parasitized by conspecific females. E. eremicus females avoided to multi-parasitize hosts parasitized by E. mundus. However, E. mundus females did multi-parasitize the hosts that had been parasitized earlier by E. eremicus. In the case of super-parasitism, the outcome showed that neither of the E. mundus populations was stronger, whereas in the case of multi-parasitism E. mundus appeared stronger than E. eremicus. Since those populations and species are morphologically similar a molecular method had to be developed to identify the outcome of super- or multi-parasitism, which is presented in Appendix A.

The authors most frequently credited for the European discovery of the parasitoid life cycle are Antoni van Leeuwenhoek, John Ray and Antonio Vallisnieri around the year 1700. Many other European authors published works on entomology in the 17th century and mentioned insects that we now recognize as parasitoids. Most of them were supposed until recently not to have understood the parasitoid life cycle. After rereading much of the old literature, we suggest this supposition is correct for, among others, Aldrovandi, Goedaert, Malphighi, and Redi. However, Lister, Merian, and Swammerdam (with the help of the painter Marsilius) all arrived at the correct interpretation of insect parasitism after observing most or all life history stages. The first correct interpretation of parasitism that we can trace, but which does not include the critical observation of oviposition by the adult female, is that of Swammerdam in 1669. The first recorded observation of oviposition that we can find is by the painter Marsilius but described by Swammerdam in 1678. However, this observation was not published until 1737-1738 by which time van Leeuwenhoek's influential 1700-1701 description had rendered it obsolete. Provisionally, we thus suggest Jan Jacob Swammerdam (assisted by Otto Marsilius) should be credited with the description of the discovery of the parasitoid life cycle in Europe. © 2004 Elsevier Inc. All rights reserved.

Foraging behavior of Encarsia formosa was analyzed with a stochastic simulation model of the searching parasitoid during a single visit to a tomato leaflet infested with immatures of the greenhouse whitefly, Trialeurodes vaporariorum,from which the parasitoid can fly away. The model is based on host searching, host selection, host handling, and patch leaving behavior and on the physiology of the parasitoid. Outputs of the model were the residence time of the parasitoid on the leaflet and the number of hosts encountered, parasitized, or killed by host feeding. The mean residence time and the mean number of encounters, ovipositions, and host feedings on the leaflet increased with host density to a maximum of 14.0 h, 209.3 encounters, 15.6 ovipositions, and 2.9 host feedings. The shape of the curves resembles a Type II functional response. The relationship between ovipositions per unit of residence time and host density showed a dome-shaped curve. The most important parameters affecting the number of ovipositions at low host densities were the parasitoid’s initial egg load, the walking speed, the walking activity, and the leaf area. At high densities, the maximum and initial egg loads and the egg maturation rate were most essential. r 1997 Academic Press

Commercial biological control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood) through releases of the parasitoid Encarsia formosa Gahan is used at present on about 5000 ha in most countries with an important greenhouse industry.Although other types of natural enemies of greenhouse whitefly are known (predators and entomopathogenic fungi), it is mainly introductions of parasitoids that have led to economically feasible control. Fundamental research on the relationship among E. formosa, greenhouse whitefly, and host plants, has provided information on how the parasitoid locates and attacks its hosts and how greenhouse climate and plant architecture influence finding of the hosts and parasitization efficiency. The parasitoid is not able to locate infested plants from a distance. Searching is random on all levels, and after a host has been found the search pattern does not alter. The only important change in foraging behavior which was observed is that, in comparison with search times on an uninfected leaf, a parasitoid keeps searching considerably longer (2‐10 times) on a leaf once a whitefly larva has been found or when other indicators of whitefly presence were discovered (e.g., honeydew, exuviae, dead hosts). On a number of important crops, a single E. formosa or her offspring is able to kill more whiteflies per unit of time than an individual whitefly female can produce. On other plant species, the development of whitefly is so fast that seasonal inoculative releases of E. formosa are not sufficient for reliable control and inundative releases have to be made. A stochastic simulation model, which includes (a) the detailed search behavior of the parasitoid and (b) the demographics and distribution of whitefly and parasitoid in relation to host plant and greenhouse climate, is developed to be able (1) to explain the capability ofE. formosato reduce whiteflies in large commercial greenhouses on crops like tomato, (2) to improve introduction schemes of parasitoids for crops where control was difficult, and (3) to predict effects of changes in cropping practices (e.g., greenhouse climate, choice of cultivars) on the reliability of biological control. r 1996 Academic Press, Inc.

The perspective of the use of hymenopterous parasites for pest control is discussed. First, the planning of a biological control project is given, together with a description of the disagreement which exists about the necessity and predictive value of studies conducted prior to the introduction of a natural enemy. Although several contributing factors of parasites to the depression of pest numbers have been identified, the practical value of extensive pre-introductory research is still limited. Parasites have been used successfully against a large variety of pests occurring in completely different cropping systems and in all major climates. Success seems largely to have been the result of the amount of research directed to the solution of a pest problem. The ratio of successes obtained with parasites compared to those achieved with predators and pathogens is 82:17:1, respectively. The rate of success after introduction is high for natural enemies (± 6%) when compared with that for chemicals (± 0.1–0.05% of the tested chemicals is marketable). Data on economic aspects are also positive for biological control programs. The risks of using parasites for pest control are minimal, especially when compared with chemical pesticide use. In the second part of the article an example is presented of the recent development of biological control programs for pest control in greenhouses, an expensive cropping system in which growers will not risk damage from pests. During a 15-year period, biological control programs for six major pests were developed and several species of natural enemies became commercially available; this success was partly the result of good cooperation between several working groups of the International Organisation for Biological Control (I.O.B.C.), mainly in Western Europe. The causes that limit the application of biological control are also discussed. The article is concluded with optimism: many effective natural enemies await discovery, and the development of biological control programs deserves more effort.

The parasitoid Encarsia formosa is commonly applied to control the greenhouse whitefly Trialeurodes vaporariorum in glasshouse tomatoes and cucumbers. Nevertheless, in some cases the control capacity of this natural enemy is insufficient and an additional selective pest-suppressing agent is desirable. The entomopathogenic fungus Aschersonia aleyrodis was applied to cucumber plants carrying whiteflies in different developmental stages. After spraying each leaf with 2 ml of spore suspension (4 × 10 6 spores/ml) the plants were kept at 100% RH for 24 hr; thereafter the humidity was lowered to 70% RH at 20°C and the photoperiod was 16 hr. Treated eggs did not become infected, but larvae that hatched from these eggs and settled on the treated abaxial leaf surface were infected at the same rate and to the same degree as treated first instar larvae. This suggests that the spores persist for at least 7 days. The final percentages of infection over all instars when treated as young eggs, old eggs, and first larval instars were 94, 93, and 90%, respectively. The final percentages of infection when treated as third and fourth larval instars and prepupae were 76, 28, and 12%, respectively. The older instars were less susceptible and adults were seldom infected by the fungus. Several applications of A. aleyrodis as a microbial insecticide are needed to achieve sufficient control of whitefly populations in glasshouses.