The behaviour and aspects of the reproductive ecology of the Raukumara tusked weta, Motuweta riparia

Abstract

The 1995 discovery of the Raukumara tusked weta, Motuweta riparia (Orthoptera: Anostostomatidae), has provided new opportunities for the study of tusked weta. Previous research on tusked weta has been limited due to the rarity of these species, in particular Motuweta isolata. This study investigated captive behaviour, with particular focus on male agonistic interactions, and aspects of breeding biology in M. riparia. A description of the field collection site illustrates the forested riparian habitat of this species and is in agreement with previous accounts of its habitat. The methods used to capture individuals and maintain them in the laboratory were based on previous studies of tusked weta and proved suitable for M. riparia. These methods also introduce the use of artificial burrows to enable the transfer of individuals between terrariums with a minimum of disturbance. M. riparia spends the majority of the night concealed in a refuge. Activity patterns are similar to most other weta being unimodal and dominated by long periods of 'Sitting' and 'Movement'. These and other observed behaviours are discussed. The amount of time spent active differs between the sexes but does not between females in the presence or absence of a male. Residency and female presence or absence does affect the amount of behaviour exhibited by males. These differences may be explained by a combination of territoriality, mate-guarding and search behaviour for females by unpaired males. Observed behaviours in male agonistic interactions were ranked in four levels of increasing aggression. The proportion of encounters at each level is similar to previous studies of aggression in Orthoptera. Interactions were generally resolved with only moderate levels of aggression. The repertoire of actions used in agonistic encounters differs from previous studies of aggressive behaviour in weta (Hemideina) because of differences in cephalic weaponry and the orientation of opponents towards one another. Resident Males are more successful in encounters than Intruder Males however this effect can be overridden by the physical attributes of the males involved. Male aggression does not occur over direct access to females, as the presence or absence of a female has no affect on the outcome or the level of aggression exhibited in an interaction. Examination of aspects of breeding ecology met with only limited success. A study of the sediment preferences of females for oviposition sites was inconclusive regarding substrate choice although it indicated that humidity levels are more important in the selection of an oviposition site than sediment type. Trials examining incubation at different temperatures were also inconclusive due to extremely poor hatching success. This outcome may be explained by a number of factors including infertility, inappropriate temperature or moisture levels, quiescence or diapause and potential damage to eggs.