The Reason For The Migration
Dr. Patrick Dale has suggested this possible reason for the migration to the sea of Pericoptus truncatus, the sand scarab larva.
“My understanding of the habits of Pericoptus truncatus larvae is that they tend to move towards the sea as the sand they are in gets drier, and away from the sea after a period of rain. But they also suffer from mites around the spiracles, and it may be that the salt water has some effect in reducing mite numbers. I don’t know. Perhaps you can check it out.”
Well that makes perfect sense. I have seen these mites crawling over pericoptus larvae, saved some in alcohol & intended to take photos down the microscope, though never found the time. Ideally, I would love to do this but as you can see years have passed, it is now 2017 and I am still busy on many other matters. Perhaps someone else will find time…
I imagine it is highly likely that all five New Zealand Pericoptus species exhibit the same ‘cleansing’ in water. It was becoming evident before I had to curtail my beach studies, that a golden chafer beetle, sand-hoppers, pericoptus larvae & Agrotis innominata -sandcut worm/moth larvae, all tended to be attempting this nocturnal cleansing ritual.
Anybody, young or old are able to pick the correct times to verify all the facts I have discovered by reading what is written in these pages & going out to the dunes & sandy banks to observe for themselves.
Agrotis innominata displays an emergence pattern that is effectively trans-winter. Adults are known to emerge first in May (late autumn) and adults continue to emerge in small numbers throughout the winter months, although the largest numbers emerge from August to December. This pattern of emergence is known in another New Zealand noctuid species, Meterana vitiosa (Butler) of forest and shrubland areas (B. H. Patrick unpublished data). As both experience quite different climatic and ecological regimes the resemblance may well be coincidental. K. J. Green (unpublished data) observed that the large coastal scarab beetle Pericoptus truncatus began emerging as an adult in May on the Dunedin coast and continued to emerge in small numbers throughout the winter months but with peak emergence in August-October showing that this type of emergence pattern is not limited to moth species.