Shapes of mandibles of white stemborer Scirpophaga innotata (Walker, 1863)larvae associated with different rice varieties

Abstract

Rice stem borers are considered the most serious insect pest of rice in Asia. The white stem borer Scirpophaga innotata (Walker, 1863) is the most prevalent among the different species that exist in the Philippines. This pest uses its strong mandibles to penetrate and feed on its plant host. Rice varieties of various level of resistance were deployed in different geographical locations in the Philippines but infestations were still observed and have contributed to economic losses to the farmers. Although differences in the resistance level among rice varieties makes an important factor in the control of the pest, no rice variety has been reported to be completely resistant against rice stem borer attacks. Several reports have indicated however that the level of damage caused by rice stem borer attacks differs. Thus it was the major objective of this study to determine if populations of white stem borer showed intraspecific variation between different geographical locations and between rice varieties. Since the mandible of the larvae is used in penetrating the plant, this morphological part of the insect larvae was investigated. Outline-based geometric morphometric analysis was used to test the hypothesis that the mandible shape of white stem borer differ with respect to different rice varieties and geographical location. Results of the principal component analysis showed variation in the shape of the mandible among populations of white stem borer taken from different rice varieties but not in the same variety collected from different geographical locations. Results of this study further confirm the general argument that host plant resistance play an important role in the evolution of pests.