A study of the Eugregarines of the grass-grub [larva of Costelytra zealandica (White), Melolonthinae], with a description of three new species

Abstract

1. Three new species of eugregarine are described from the mid-gut of the larva of Costelytra zealandica (White).2. Euspora zealandica occurs in the anterior region of the mid-gut near the gut caeca. Slictospora costelytrae occurs just posteriorly to E. zealandica. Euspora sp. occurs posteriorly to the malpighian tubules, but was found only rarely.3. A description of the species and the life-cycle of two species are given.4. The life-cycle of S. costelytrae takes about 8 weeks and that of E. zealandica 6 weeks.5. Gametocysts will develop only at a humidity of 95–100 %.6. The bi-associative species, E. zealandica, is more abundant in the 1st and 2nd instars than the large species, S. costelytrae. Both species are equally abundant in the 3rd instars, but the peak for incidence was in May for E. zealandica and June for S. costelytrae. This is related to the longer period of time taken for the life-history of S. costelytrae.7. The incidence of gregarines builds up in each instar to over 90% then falls off, the time of fall off corresponding with the production of gametocysts which pass out with the faeces of the grub.8. The gregarines mostly complete their cycle before the instars moult. This is borne out by the observation that cysts were not found in the smallest size group of each instar. There were many cases in the larger size group of all three instars where cysts only occurred.9. Gametocysts are produced mainly in the autumn.10. Gregarines were not found in grubs approaching metamorphosis (prepupae) nor in pupae nor adults.11. It seems unlikely from the results that the gregarines have an adverse effect on the grubs as, in general, it was found that the larger grubs had the greater number of gregarines present, but further work on this is needed.12. The life-history of the gregarines is closely correlated with the life-history of the beetle.13. The presence of the gregarines only in the larval stages is related to the different habitat and behaviour of larva and adult.I am grateful to the University Grants Committee for financial support.