Study on host plants for reproduction of Chilo suppressalis

• The classification that Chilo suppressalis is commonly considered as a polyphagous pest has been challenged.
• C. suppressalis adults laid most eggs on water-oat and rice in a multiple-choice cage test.
• Field surveys showed that no egg laid on plants other than rice and water-oat.
• Larval survival rates were much higher on rice and wheat than on other plants tested in field or lab inoculation experiments.
• It suggests that the effective reproduction host of the rice population of C. suppressalis is rice.

The rice stem borer, Chilo suppressalis, is generally considered to be a polyphagous pest. The current study challenges this view by investigating its oviposition preference, larval survival and development on different host plants under both laboratory and field conditions. Rice and water-oat populations of the borer inhabiting on corresponding plants respectively have partial reproductive isolation based on previous studies. In a laboratory multiple-choice test, C. suppressalis adults from rice population laid most of eggs on water-oat (46.5% of total eggs) and rice (43.8%), with very few laid on wheat (3.6%), sugarcane (4.0%) and maize (2.0%). Field surveys supported the laboratory study and found no egg on the plants other than rice and water-oat. Neonate inoculation experiments performed in field and laboratory showed that larval survival rate was much higher on rice (49.1%–51.2%) and wheat (36.5%–44.1%) than that on water-oat (10.7%–10.8%), maize (1.2%–7.2%), sugarcane (0–1.5%) and weeds (2.4%). These results were discussed with the data reported from water-oat population and it was concluded that C. suppressalis is not a typical polyphagous pest. Rice population mainly reproduces on rice and use water-oat only as minor host, and water-oat population breeds better on water-oat than on rice as reported. Neither population could thrive on the other recorded host plants, which are used for the supplementary nutrition sources of larvae. These findings provide useful information for the development of control strategies to prevent C. suppressalis laying eggs on rice seedlings in early spring, hence effectively reducing population density of this pest in rice fields.

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