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(R)) for the control of red scale Aonidiella aurantii (Maskell) (Homoptera: Di aspididae) on citrus in southern Africa has led to extensive disruptio n of the biocontrol of cottony cushion scale Icerya purchasi Maskell ( Homoptera: Margarodidae) provided by the coccinellids Radolia cardinal is (Mulsant) and other indigenous Rodolia spp. Similar effects on fiel d populations of Chilocorus nigrita (Fabricius), a coccinellid predato r of A. aurantii, have also been observed. The adverse effects of fiel d-weathered residues of IGRs on the fecundity and egg viability of the coccinellids C. nigrita and Cryptolaemus montrouzieri Mulsant were de termined in a laboratory bioassay. Residues of pyriproxyfen, a juvenil e hormone analogue, and two chitin synthesis inhibitors, buprofezin (A pplaud(R)) and triflumuron (Alsystin(R)), were tested. Exposure to res idue-bearing leaves did not affect the number of eggs laid by Chilocor us 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 weathere d residues from a single application of pyriproxyfen or triflumuron. T hree week old residues of buprofezin had the same effect, but both 7 a nd 19 week old residues no longer significantly reduced egg viability. Adults of both C. nigrita and Cryptolaemus montrouzieri commenced lay ing viable eggs within 20 days of being separated from all residue-bea ring leaves. One week old residues of pyriproxyfen and triflumuron bot h significantly reduced progeny production by C. montrouzieri. Ten wee k 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 citr us in southern Africa, where coccinellid biocontrol agents play an imp ortant role.