Egg production and adult longevity in Didymuria violescens (Leach) (Phasmatodea : Phasmatidae).  F.G. Neumann.  July 1973.  29 pp. (unpubl.)

SUMMARY

The variation with time in rate of oviposition and corresponding adult mortality and the fecundity of both individual insects and sample populations were studied in the laboratory and field. Fecundity in this context implies a number of eggs laid.

At constant 20°C day and 15°C night temperatures, adults took about 19 days to oviposit. In the field during 1971, oviposition commenced after the first week of February, reached a daily peak of 7-8 eggs per female within 35 days and then declined to 2-3 eggs per female by mid-April. Oviposition ceased in mid-June. Fecundity per mated female, when food was abundant, exceeded 350 eggs in the laboratory but approximated 310 in the field. Virgin females in the field laid about half as many eggs, suggesting that mating confirmed a biological advantage. Under laboratory conditions, fecundity varied little with insect size, and, as small females lived significantly longer, indications were that larger females oviposited at faster rates. There was evidence that fecundity was inversely proportional to insect population density in the field. Thus, equivalent or even greater egg production, and hence a correspondingly faster rate of population growth, from uncrowded populations is possible. Further evidence of this was obtained from the extensive annual phasmatid prediction surveys in stands of Eucalyptus regnans F. Muell.

Viability of field oviposited eggs initially exceeded 76% and, except for unfertilized eggs, varied little with month for oviposition. Adult females had a significantly longer lifespan compared with males. During 1971, first males died in late February and females about two weeks later. All males were dead in late May but some females lived until mid-June.

There are three important practical implications arising from these studies. Subject to periodic review, control of feeding stages should be completed by the first week of February for prevention of oviposition. Because appreciable egg production continues until mid-April, sampling of egg densities in litter for the assessment of potential progeny from the previous generation should not commence before May. High fecundity of uncrowded populations necessitates sampling of healthy ash-regrowth stands during winter, if potential plagues are to be detected early.

Also published:

Neuman, F.G. (1976)  Egg production, adult longevity and mortality of the stick insect Didymuria violescens (Leach) (Phasmatodea : Phasmatidae) inhabiting mountain ash forest in Victoria.  J. Aust. Entomol. Soc. 15 (2): 183-90.