Keywords: Invasive species Ecosystem function Insect pests Invasive plants Ecological restoration Biological control Natural ecosystems a b s t r a c tOf the 70 cases of classical biological control for the protection of nature found in our review, there were fewer projects against insect targets (21) than against invasive plants (49), in part, because many insect biological control projects were carried out against agricultural pests, while nearly all projects against plants targeted invasive plants in natural ecosystems. Of 21 insect projects, 81% (17) provided benefits to protection of biodiversity, while 48% (10) protected products harvested from natural systems, and 5% (1) preserved ecosystem services, with many projects contributing to more than one goal. In contrast, of the 49 projects against invasive plants, 98% (48) provided benefits to protection of biodiversity, while 47% (23) protected products, and 25% (12) preserved ecosystem services, again with many projects contributing to several goals. We classified projects into complete control (pest generally no longer important), partial control (control in some areas but not others), and ''in progress," for projects in development for which outcomes do not yet exist. For insects, of the 21 projects discussed, 62% (13) achieved complete control of the target pest, 19% (4) provided partial control, and 43% (9) are still in progress. By comparison, of the 49 invasive plant projects considered, 27% (13) achieved complete control, while 33% (16) provided partial control, and 49% (24) are still in progress. For both categories of pests, some projects' success ratings were scored twice when results varied by region. We found approximately twice as many projects directed against invasive plants than insects and that protection of biodiversity was the most frequent benefit of both insect and plant projects. Ecosystem service protection was provided in the fewest cases by either insect or plant biological control agents, but was more likely to be provided by projects directed against invasive plants, likely because of the strong effects plants exert on landscapes. Rates of complete success appeared to be higher for insect than plant targets (62% vs 27%), perhaps because most often herbivores gradually weaken, rather than outright kill, their hosts, which is not the case for natural enemies directed against pest insects. For both insect and plant biological control, nearly half of all projects reviewed were listed as currently in progress, suggesting that the use of biological control for the protection of wildlands is currently very active.

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The population dynamics of the silverleaf whitefly (SLWF), Bemisia argentifolii Bellows and Perring (=sweetpotato whitefly, B. tabaci Biotype “B”, [Gennadius]), and its endemic parasitoids (mostly Encarsia spp. [Aphelinidae]) were monitored in a heterogeneous cropping area, consisting of cotton, cantaloupe and kenaf (tall fiber crop). To assess the suitability of the whitefly for areawide pest management, we compared estimates of population densities using different sampling methods and determined the effects of agronomic practices on the whitefly and parasitoid populations. There was no correlation between adult SLWF estimates using sticky traps and those counted directly on the leaves. However, counts of immatures using disk subsamples were found to be good predictors of whole leaf counts. SLWF counts were low in cotton, until the harvest period of cantaloupes, which may have triggered migration from cantaloupe to cotton. The determinants of emigration from cotton were less clear. High numbers of adults were migrating well before harvest or the application of a defoliant. One likely contributing factor in triggering whitefly migration was leaf senescence. Despite rather high adult densities sampled in kenaf, populations of immature SLWF were low, suggesting that it is not a preferred host. Parasitoid populations were high in the kenaf fields, causing 20 to 80% parasitism and suggesting that kenaf could serve as a reservoir of natural enemies within a larger cropping system. Parasitism in cotton was less than that in kenaf, usually at ~10 to 15%. Encarsia spp. sampled on sticky traps indicated significant activity of the adults in the cotton and kenaf fields, and much lower numbers in the cantaloupe. Because it is a dispersive and polyphagous pest, areawide suppression of SLWF must include the consequences of farming practices and cropping patterns in heterogeneous fields, especially when they are under different management.

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