Quantitative genetic analysis of diamide resistance in Australian Spodoptera litura (Fabricius) (Lepidoptera:...

Spodoptera litura is a major insect pest of horticulture, cotton and legume crops which has developed resistance to insecticides from many chemical classes. Chlorantraniliprole is an important option for selective control of S. litura, and in 2023 a population established from grain legume fields in northwest Western Australia (BM28x) was found to have > 1000-fold resistance to chlorantraniliprole compared with laboratory reference strain (KSL). Following its establishment in the laboratory, the BM28x strain was found to be homozygous for resistance to chlorantraniliprole and subsequent characterisation by quantitative genetic analysis showed that resistance was autosomal, incompletely recessive (D_LC = 0.185) and conferred by one or a few closely linked loci. Chlorantraniliprole resistance in the BM28x strain conferred major cross-resistance to cyantraniliprole (262-fold) and tetraniliprole (591-fold). However, there was minimal cross-resistance (≤ 3.3-fold) in the BM28x strain to broflanilide, emamectin benzoate, spinetoram, methoxyfenozide and the Vip3A protein expressed by the bacterium Bacillus thuringiensis, indicating that resistance could be managed effectively using chemical rotational strategies which incorporate transgenic technologies. Inhibition bioassays using the synergists piperonyl butoxide, triphenyl phosphate and diethyl maleate indicate that metabolic detoxification is not involved in resistance to chlorantraniliprole in the BM28x strain. The implications of high level diamide resistance for management of Australian S. litura is discussed.