Ecology and biocontrol of aphids feeding on cypress trees

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EFFECTS OF TEMPERATURE AND RELATIVE HUMIDITY ON Nephapsis bicolor, A PREDATOR OF Aleurodicus spp.

The spiralling whitefly Aleurodicus dispersus Russell was introduced to Africa and Asia during the 1990s. Among its potential biological control agents is the predatory coccinellid, Nephaspis bicolor Gordon. Since the coccinellid may be required to control A. dispersus under variable climatic conditions, four temperature (20-34°C) and two RH (78% and 90%) (55% RH at 26°C only) regimes were evaluated under laboratory conditions in Trinidad and Tobago. Temperature (but not RH) had significant effects on the development rate of all stages of N. bicolor and on the pupal and adult sizes. Interactions between temperature and RH were significant only for egg incubation and total duration and for size of the pupa. Mortality during development was highest at 30°C/90% RH and lowest at 23°C/78% RH. Both temperature and RH significantly affected the preoviposition period, while temperature alone affected longevity and lifetime fecundity. Adult survival at 26°C and 55% RH as well as 90% RH was significantly higher compared to all the other treatments. Based on the life table statistics, the best performance of female N. bicolor was at 26°C and 55% RH. Although feeding, survival, development and reproduction occurred under all the temperature and RH regimes, constant low and high temperatures were not conducive to the coccinellid since the survival of immature stages and adults was greatly reduced. Thus, the introduction of N. bicolor into such environments may not result in long-term establishment. It may be necessary to ‘thermally adapt’ the beetles prior to release and/or to time the field releases to coincide with favourable environmental conditions. Another solution may lie in maintaining laboratory cultures of N. bicolor and making periodic (inoculative/augmentative) releases

Classical biological control for the protection of natural ecosystems

Of 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