Effects of field-weathered residues of insect growth regulators on some Coccinellidae (Coleoptera) of economic importance as biocontrol agents

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Abstract
Use of the insect growth regulator (IGR) pyriproxyfen (Nemesis®) for the control of red scale Aonidiella aurantii (Maskell) (Homoptera: Diaspididae) on citrus in southern Africa has led to extensive disruption of the biocontrol of cottony cushion scale Icerya purchasi Maskell (Homoptera: Margarodidae) provided by the coccinellids Rodolia cardinalis (Mulsant) and other indigenous Rodolia spp. Similar effects on field populations of Chilocorus nigrita (Fabricius), a coccinellids predator of A. aurantii, have also been observed. The adverse effects of field-weathered residues of IGRs on the fecundity and egg viability of the coccinellids C. nigrita and Cryptolaemus montrouzieri Mulsant were determined in a laboratory bioassay. Residues of pyriproxyfen, a juvenile hormone analogue, and two chitin synthesis inhibitors, buprofezin (Applaud®) and triflumuron (Alsystin®), were tested. Exposure to residue-bearing leaves did not affect the number of eggs laid by Chilocorusnigrita, but a complete, or near complete failure of eggs to hatch ensured when adults were exposed to either 3, 7 or 19 week old weathered residues from a single application of pyriproxyfen or triflumuron. Three week old residues of buprofezin had the same effect, but both 7 and 19 week old residues no longer significantly reduced egg viability. Adults of both C. nigrita and Cryptolaemus montrouzieri commenced laying viable eggs within 20 days of being separated from all residue-bearing leaves. One week old residues of pyriproxyfen and triflumuron both significantly reduced progeny production by C. montrouzieri. Ten week old triflumuron residues were still detrimental to this species but pyriproxyfen residues of the same age were not. It was concluded that IGRs are not compatible with integrated pest management (IPM) for citrus in southern Africa, where coccinellid biocontrol agents play an important role.