Sexual maturity in the male tree weta Hemideina Crassidens (Orthoptera: Stenopelmatidae)

Abstract

The tree weta Hemideina crassidens inhabits holes in trees. Weta often live alone however they are also found in aggregations of one male to one or more females, called galleries. Male tree weta have a range of instars at maturity, eighth, ninth or tenth instars. Female tree weta all mature at the tenth instar. As males grow their head length increases allometrically with each moult, hence tenth instar males have a larger head than eighth or ninth instar males. This is unusual since male tree weta are aggressive, frequently in conflict over access to galleries with the winner mating with any females inside. These disputes involve two males facing each other and gaping their mandibles. The male with the biggest mandible gape gains access to the gallery, so early maturing males with small heads should have low reproductive success. However from observing weta behaviour in tanks I concluded that there are different mating strategies for late and early maturing males: 1. The gallery strategy, a male defends a gallery from other males preventing them from mating with the females inside. The male rarely leaves the gallery, mating frequently with the females inside. 2. The wander strategy, a male living alone spends much of the night outside in search of females, mating with any female he finds out. The gallery strategy is best suited to males with large heads which can successfully defend a gallery while the wander strategy is best suited to early maturing males which can not hold galleries. Population studies of weta on Mana Island and Crofton Downs in Wellington reveal that the ninth instar is the most common form, it has the ability to adopt either strategy as circumstances require it, unlike eighth instar males which are too small to defend a harem and tenth instar males whose large, cumbersome head is a burden to carry any distance.