oa African Entomology - Effects of insect growth regulators on Chilacorus nigritus (Fabricius) (Coleoptera: Coccinellidae), a non-target natural enemy of citrus red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae), in southern Africa: evidence from laboratory and field trials
Chilocorus nigritus (Fabricius) is one of the major coccinellid predators of the citrus pest Aonidiella aurantii (Maskell) in southern Africa. Laboratory and field experiments were carried out on eggs, larvae and adults of this ladybird to determine the effects of three insect growth regulators (IGRs) used against citrus pests in the region. Two chitin synthesis inhibitors, buprofezin and teflubenzuron, and a juvenile hormone analog, pyriproxyfen, were applied to C. nigritus populations at the recommended dosages. Mortality and development of egg and larval stages, as well as mortality and fecundity of the adults were recorded. Laboratory experiments indicated that, of the three IGRs tested, buprofezin was the most detrimental compound, especially to larval stages, irrespective of whether the larvae were fed IGR-treated A. aurantii directly or sprayed with IGRs. Immediate larval mortality from pyriproxyfen and teflubenzuron was not significantly different from the controls. None of the larvae that were fed with IGR-treated A. aurantii pupated. By contrast, larvae that had only been sprayed with IGRs pupated, but no adults emerged. Adult fecundity was not affected by exposure to IGRs, either in the laboratory or in the field, but all eggs exposed to IGRs failed to hatch. Although larvae developed to the adult stage in the field experiments, the IGRs' ovicidal activity and effects on immature stages still had a detrimental effect on C. nigritus population levels. As a result, spraying of IGRs is likely to impede C. nigritus population increases in citrus orchards. This emphasizes the need to avoid spraying during C. nigritus population increases should the use of IGRs be unavoidable. Insect growth regulator's impact on non-target species still requires further consideration, especially with the incorporation of these chemicals into integrated pest management programmes.
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