Body size dependency of ovariole number and timing of reproductive maturation in Semanotus japonicus (Coleoptera: Cerambycidae)

Abstract

ABSTRACTSemanotus japonicus larvae feed on the phloem of living trees of Cryptomeria japonica and Chamaecyparis obtusa, and newly emerged adults stay in xylem from August through the following April when they emerge from the trees. A positive correlation is known between the female body mass and lifetime fecundity in this insect. To determine the timing of maturation in reproductive organs and the relationships of female body size to the total number of ovarioles of a female (ovariole number) and egg production per ovariole, we dissected adults taken from dead trees from October through the following April. Dissecting females showed that well-developed eggs began to appear in the calyx in April, that the ovariole number ranged from 34 to 79, and that the ovariole number per female and egg production per ovariole increased as the female body mass increased, indicating that the body size-dependent lifetime fecundity was attributed to greater ovariole number and greater egg production per ovariole for large females. Dissecting males taken from dead trees and reared on C. obtusa bolts showed that a great deal of sperms were found in testes and seminal vesicles in October and that a long-term exposing to 25°C at a photoperiodic regime of 16-h photophase and 8-h scotophase broke down the testes internally in which sperms disappeared. Body-size dependency of ovariole number was discussed in relation to the adult feeding and phylogeny.