Morphometric differences between rice and water-oats population of the striped stem borer moth, Chilo suppressalis (Lepidoptera: Crambidae)

Abstract

The striped stem borer moth, Chilo suppressalis, has two major host plants; rice, Oryza sativa, and the water-oats, Zizania latifolia. It has been suggested that there is reproductive isolation between the populations feeding on rice (rice population) and water-oats (water-oats population). We compared the morphological characteristics of the two populations using multi variate analyses based on eight genital and ten non-genital traits in male adults. Body size differed between the two populations as shown previously. However the results of a principal component analysis (PCA) based on genital traits showed a proportional difference between the two populations, but not on the non-genital traits. This shows the existence of a morphological difference in the genitalia of male adults between the populations. We also conducted a discriminant function analysis (DFA) based on seven genital and five non-genital traits. The discriminant function obtained could classify the two populations with 94.3% accuracy. Another discriminant function using only four genital traits also could distinguish the two populations with 88.6% accuracy. DFA would be of use in the practical forecasting of occurrence.

Differences in timing of the emergence of the overwintering generation between rice and water-oats populations of the striped stem borer moth, Chilo suppressalis (Lepidoptera: Crambidae)

“…Trapped males were individually classified into a population by the discriminant function method (Matsukura et al, 2006). This discriminant function was constructed from morphometric data of the overwintering generation of the two populations; however, this method was applied to all generations.…”

“…This discriminant function was constructed from morphometric data of the overwintering generation of the two populations; however, this method was applied to all generations. Moreover in this study, we adopted the simple discriminant function consisting four variables: the length of two of three lines of the valva (Va and Vb), the length of the juxta (JL), and the width of the juxta (JW) as a descriminant method, as described in Matsukura et al (2006), because it seemed to be suitable for analyzing large numbers of samples. Only males trapped in 2004 were classified into their respective populations.…”

“…In addition to apparent differences in body size between the two populations (Maki and Yamashita, 1956), morphometric differences in male genitalia have been detected (Matsukura et al, 2006). Furthermore, differences in mating time between populations have been reported by different investigators (Konno and Tanaka, 1996;Samudra et al, 2002;Ueno et al, 2006).…”

“…After comparing the ecology of individuals feeding on rice and water-oats, many researchers believe that this species is in the course of diverging into two populations: a rice population and a wateroats population (Samudra et al, 2002;Matsukura et al, 2006;Ueno et al, 2006). In addition to apparent differences in body size between the two populations (Maki and Yamashita, 1956), morphometric differences in male genitalia have been detected (Matsukura et al, 2006).…”

“…In our previous study, we created a morphometric discrimination method that classifies the population of individual adult males at high accuracy according to a proportional difference in genitalia (Matsukura et al, 2006). Using this discrimination method, we verified differences in seasonal occurrence between rice and water-oats populations of C. suppressalis.…”