Egg production across a 40-week period in the phasmid Sipyloidea sp. (Diapheromeridae) from a tropical rain forest, north Queensland, Australia

Abstract

In this study we report the results from the first long-term (40 weeks) study of stick-insect fecundity and distribution under natural conditions of which we are aware. We used the number of eggs falling into 72 × 0.5 m^2 traps to ask: 'Was egg production in Sipyloidea sp. uniform across the sample period'? and 'Was there evidence of host plant species preference or avoidance'? We collected a total of 213 Sipyloidea sp. eggs. The number of eggs caught per week was not uniform and an exponential decay model was the best-fit relationship between egg production and time, indicative of a steep decline from high to low (but continuous) egg production across the study period. Continuous egg production differs from other insect species in tropical areas that often show distinct seasonal differences between wet and dry seasons, timed to leaf production in host plants. The distribution of eggs within traps was aggregated, and more traps than expected from Poisson probabilities received no eggs, or six or more eggs. The concentration of eggs within particular traps was not related to the identity of canopy plant species, however. We suggest that continuous egg production in Sipyloidea sp. may be related to the wider range of plant species available as food resources for the polyphagous Sipyloidea, compared with other tropical insect species.