Tuesday, 18 June 2013

A spectacular cranefly and a deadly fungus

When I collected the catch of flies from the moth traps at Pitsford last week, Mischa Furfaro, one of the wardens on the reserve, gave me an unusual-looking cranefly that she had found on a tree trunk whilst checking the nest boxes. The cranefly turned out to be Ctenophora pectinicornis. This species is one of three British species of cranefly that mimic large ichneumons or wood wasps. They are all rather scarce. Apart from their smart black and yellow colouration, the males are distinctive because of their peculiar pectinate antennae, as can be seen in the photo below.

These craneflies breed in dead wood, typically high in trees and so tend to be associated with ancient woodland. The male that Mischa found may well have been searching for a female around the nest box.

On Sunday I visited a local wood and swept the fly shown below from the ride-side vegetation. It was dead and furry-looking growth was coming out from around the abdominal segments. This fly had been infected by an entomopathogenic fungus. There are several species of fungus that kill flies and other insects. Typically a spore is picked up on the surface of the insect. The spore then develops hyphal threads which eventually penetrate the insect's exoskeleton and continue to develop inside the insect. Toxins released by the fungus kill the insect. The fungus then produces its fruiting bodies on the outer surface of the insect and the next generation's spores are released. It normally requires conditions of high humidity for this cycle to complete. There is currently scientific research being undertaken to see if this could be developed as a biological control for certain pest fly species, including mosquitoes.

Wednesday, 12 June 2013

Portevinia maculata and Ramsons

At this time of the year a number of woodlands contain carpets of ramsons Allium ursinum, which scent the air with garlic. At the beginning of June I visited two such woods at Fawsley as part of the Wildlife Trust's Bioblitz. I was particularly keen to find the hoverfly that is associated with ramsons, Portevinia maculata. It is not a particularly striking species, with its grey dusted spots but it is not frequently recorded in Northants. According to "The Flora of Northamptonshire and the Soke of Peterborough", recently compiled by Gill Gent and Rob Wilson, ramsons occur in about 75 tetrads in Northants. However I only have records of P. maculata from three.  It is almost certainly present in most sites where there is an extensive and well established population of ramsons so must be well under-recorded in the county. The fly's association with ramsons is strong. It's larvae are miners of the bulbs of ramsons and adults can be easily found when the ramsons is in flower and the weather is warm enough for the hoverflies to seek nectar. I have attached a couple of photos in the hope that more records will be made. It is easily recognised from the grey spots on the abdomen, so long as you make sure it is a hoverfly you are looking at. Similar-looking higher flies will have bristly bodies, whereas this hoverfly does not have prominent bristles and shows the "false margin" on the wings created by the two outer cross-veins running parallel to the outer hind edge.

Portevinia maculata on ramsons flowers.

Portevinia maculata showing grey dusted abdominal spots and the "false margin" on the outer edge of the wing, seen more easily in the lower wing.

Ramsons in a wood in Northants in early June.