Effects of crowding on larval diapause and adult body size in Monochamus alternatus alternatus (Coleoptera: Cerambycidae)

Abstract

AbstractTo determine the effect of larval crowding on induction of diapause in Monochamus alternatus alternatus Hope (Coleoptera: Cerambycidae), newly hatched larvae were inoculated singly (density 1) or in pairs (density 2) on Pinus thunbergii Parlatore (Pinaceae) bolts and reared at 25 °C and 16 light:8 dark hour photoperiod. Adults emerged at density 1 and 2 between 75 and 139 days after the inoculation. About 150 days after larval inoculation, dissection of pine bolts indicated the incidence of larval diapause was greater at density 1 (0.536) than at density 2 (0.222), indicating inversely density-dependent induction of diapause. For both larval densities, the probability of entering diapause increased as bark surface area per larva (a proxy for per capita amount of food available) increased, showing that diapause induction can be explained by the amount of food available per larva. Adults that emerged at density 1 were heavier than those at density 2. When diapause and nondiapause insects occurred in the same pine bolts, six heavy adults had experienced diapause whereas three heavy adults had not, indicating that bark surface area affected the induction of diapause indirectly through larval interaction. The relationship between two different manners of density-dependent diapause induction and food supply is discussed.