The Morphology and an Improvement of Breeding Efficiency of Larval Chilo suppressalis (Lepidoptera: Crambidae)

The striped stem borer Chilo suppressalis (Lepidoptera: Crambidae) is one of the destructive generalists of water-oat Zizania latifolia and is difficult to control. Resistance monitoring and new pesticide screening require large quantities of the same instar larvae, which is very important to develop sound integrated pest management (IPM). Acute identification of larvae is crucial to mass screening larvae and improvement of breeding efficiency (especially by improving replacement rates of food residue and feces) is important to guarantee larval adequacy in the lab, and they are prerequisites to ensure accuracy of bioassay results. Therefore, the present study focuses on the larval morphology of C. suppressalis, and some differences found are promising diagnostic characters for separating 1st to 6th instar larvae: the head widths, body lengths, brindles on the pronotum, stripe shapes, pigmentations, black spots on the head capsule, crochets amounts, and arrangements on abdominal prolegs. Novel food residue and feces replacement substrates based on polycarbonate tubes were developed. The transfer rate and larval mortality rate were calculated to evaluate the performance of C. suppressalis larvae under different transfer substrates (i.e., polycarbonate tubes, hair brush, placing fresh pulps on the bottom of the residual pulps, pick off by forceps, docking bottleneck). Larvae transferred by the new substrates (i.e., polycarbonate tubes) showed the best performance among the substrates. These results indicated that larval C. suppressalis adapted well to the new substrates, and the substrates could serve as a viable alternative to traditional substrates for transfer. The acute identification and optimization of the breeding system for the C. suppressalis supplies a very important tool for pest management research.