Oviposition and egg studies on the spur-legged phasmatid Didymuria violescens (Leach) (Phasmatodea : Phasmatidae) from mountain ash forests in the Victorian Central Highlands.  F.G. Neumann.  February 1972.  29 pp. (unpubl.)

SUMMARY

Variation in rate of oviposition with time and the fecundity of both individual insects and sample populations of the phasmatid Didymuria violescens from mountain ash forests in the Victorian Central Highlands and some aspects of its egg stage were studied in the laboratory and field.

At constant day and night temperatures, adults took about 19 days to oviposit. Irrespective of mating and crowding, oviposition in the field commenced after the first week of February, reached a daily peak of 7-8 eggs per female within 35 days, then declined to 2-3 eggs per female by mid-April and ceased in mid-June. Actual fecundity, with ample food provided, exceeded 350 eggs per female in the laboratory but approximated 300 in the field. Density-induced food shortage appears to be a critical factor in lowered egg production. Hatching occurred during a three month period. Viability of field-oviposited eggs initially exceeded 76% and, except for unfertilised eggs, varied little with month of oviposition. Desiccation of egg embryos appears significant in the more open or younger stands where factors of weather can readily dry out the litter during summer. Pre-platelet diapause in egg-embryos, which is responsible for predominantly biennial life cycles in the central Highlands, is likely to be largely by-passed during warm dry summers at autumns.

Sampling of egg density in litter to predict phasmatid populations over two years ought not to commence prior to May and litter from apparently undefoliated stands must also be sampled. Heavy thinning and priority clear filling in most affected stands may give measurable control of phasmatids. When aerial control with short persistence insecticides is programmed, low altitude forest should ideally be sprayed first and the operation completed by the first week of February.

Also published:

Neuman, F.G., Harris, J.A. and Wood, C.H.. (1977)  The phasmatid problem in mountain ash forests of the Central Highlands of Victoria.  For. Comm. Vic., Bull. 25, 43 pp.