Spotted Stem Borer Chilo partellus: Occurrence, Biology and Relative Resistance in Erianthus arundinaceus

In this paper, we report the first occurrence of the spotted stem borer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) in Erianthus arundinaceus (Retz.) Jeswiet (Poales: Poaceae) at Coimbatore, Tamil Nadu State, India. We also examined the developmental biology, larval instar determination from head capsule measurements and sources of resistance among selected germplasm. Infestation began in 4–5-month-old plants when young larvae caused characteristic irregular chlorotic windows and shot holes on leaves. Older larvae bored into internodes of 6–7-month-old plants and tunneled extensively in the internodes. While the borer completed seven instars in E. arundinaceus, larval and pupal durations, and total life cycle did not vary significantly in comparative biology studies on E. arundinaceus, sugarcane and artificial diet. The number of egg masses deposited and eggs laid was significantly lowest in E. arundinaceus. Relative suitability ratio was the lowest in E. arundinaceus and similar in the other two substrates. Mean head capsule width (HCW) and head capsule length (HCL) followed normal distribution for most instars and differed among the seven instars. HCW of the seven instars showed a mean Brook–Dyar ratio of 1.34 (range: 1.28–1.44) and Crosby ratio of less than 10%; the corresponding figures for HCL were 1.36 (range: 1.23–1.48) and < 10%. The correlations between instar number and natural log of HCW and HCL were significant. In the screening trials, percent incidence of C. partellus in 2018–2019 did not differ among the 15 accessions of E. arundinaceus, whereas in 2019–2020, the accession IND 02–1260 had significantly lowest incidence level, but the two accessions IND 10–1591 and Lakshadweep had significantly highest levels; percent intensity did not differ among the accessions in both years. Relative resistance ratio in both 2018–19 (range: 0.333–0.700) and 2019–2020 (range: 0.250–0.783) did not differ significantly among the 15 accessions. When the accessions were grouped into three categories of resistance, IND 99-884 and Bethuadahari emerged as least susceptible. Among the plant characteristics examined, cane thickness showed negative correlation with percent of infestation and leaf width had positive correlation with percent of intensity. The present studies pave the way for further screening and utilization of accessions in breeding program for C. partellus resistance.