AbstractsBiology & Animal Science

1. Two populations of D. siricidicoZa and one of D. rudyi which had been maintained continuously in monoxenic culture for 1 year (D. siricidicoZa (S), D. rudyi (T)) and 6 years (D. siricidicoZa (H)) were used to study the effects of a range of environmental conditions on the egg phase of the free-living form of DeZadenus. 2. For each population the rate of egg development increased 0 0 with tempera.ture from 5 C to 25 C. 3. The abortion rate of each population was related to temperature but the nature of the relationship varied from one population to the next. In each case, abortion rate was lowest 4. There were no significant differences in the relationships of abortion rate and eclosion failure to temperature. 5. Examination of the effects of pH on the rate of egg development was inconclusive. 6. Abortion rate varied with pH from pH 2·5 to pH 8•0. Different reactions were recorded for each population. Optimum pH was about pH 5·5 for D. siricidicoZa (H) and D. rudyi (T), about pH 5 • 0 for D. siricidicoZa (S). 7. \i'i.thin each population, abortion rate and eclosion failure follm.;reC. a similar pattern of change with pH. 8. Considerable variati.on occurred between replicates in the estimation of fecundity but, on the average, D. siricidiaoZa (S) were more fecund than D. siricidico Za (H). D. rudyi (T) were more fecund when cultured on CMA rather than !t; PDA. - IV - 9. The mean volume of the eggs of D. siricidicoZa (H) was significantly greater than that of D. siricidicoZa (S) which was also significantly greater than that of D. ruayi (T). 10. The variance of egg volume of D. rudyi (T) was considerably less than that of either of the D. sirvicidicoZa populations for which the variances were not significantly different. 11. There was no correlation between the variance of the egg volume of these populations and the time interval between hatching of the first and last eggs. 12. Cross-breeding trials conducted with seven species of DeZadenus produced a wide range of results; from the parent female depositing only few eggs, all of which were abortive, to completely unimpeded production of the Fz generat:ton. 13. With only one exception, intraspecific crosses produced hybrids without reduced fecundity. 14. Interspecific crosses sometimes resulted in reduced fecundity among the parents and always among the hybrids produced. 15. The crosses, D. ruayi (UJ7) x D. rudyi (T) and D. rudyi (UJ7) J1 x D. imperiaZis !f., produced aberrant results suggesting a close relationship benveen D. rudyi and D. imperiaZis. 16. Differences between D. siricidicoZa (H) and the other two populations indicated that considerable changes can result from continuous cultures of the type used for DeZadenus. 17. Differences between D. sirim:dicoZa (S) and D. siricidicoZa (H) inr:lic12te that the cultures of these populations should be regarded as differen': strains.