Effects of field-weathered residues of insect growth regulators on some Coccinellidae (Coleoptera) of economic importance as biocontrol agents.
Use of the insect growth regulator (IGR) pyriproxyfen (Nemesis®) for the control of the diaspidid Aonidiella aurantii on Citrus in southern Africa has led to extensive disruption of the biological control of the margarodid Icerya purchasi by the coccinellids Rodolia cardinalis and other indigenous Rodolia spp. Similar effects on field populations of Chilocorus nigrita, a coccinellid 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 were determined in a laboratory bioassay. Residues of pyriproxyfen, a juvenile hormone analogue, and 2 chitin synthesis inhibitors, buprofezin (Applaud®) and triflumuron (Alsystin®), were tested. Exposure to residue-bearing leaves did not affect the number of eggs laid by Chilocorus nigrita, but a complete, or near-complete failure of eggs to hatch ensued 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 for Citrus in southern Africa, where coccinellid biological control agents play an important role.