'Monstrous' wasps could reveal their species' secrets

9 December 2016

Close-up of Genaemirum phacochoerus head

Female Genaemirum phacochoerus, one of the newly identified wasps. The unusual shape of its head is reminiscent of a warthog.

Scientists have identified three new species of parasitoid wasp - including two that previously lay undescribed in the Museum's collections.

All three species belong to the genus Genaemirum, which is found across Kenya, Tanzania, Uganda and South Africa.

The finds bring the total number of species in the genus to eight - and offer more clues to the genus' biology, which is poorly understood.

Deadly dinner guests

Parasitoid wasps lay their eggs in or on a host animal, eventually killing it when the larvae hatch and eat their host. This lifestyle has seen some parasitoid wasp species used as pest control, particularly if the hosts cause destruction to economically important crops.

Their fatal effect on the host also distinguishes parasitoids from parasites, which live off a host but don't usually kill them.

'Until now, we knew almost nothing about the biology of Genaemirum species,' says Dr Gavin Broad, Principal Curator of Hymenoptera at the Museum, and a co-author of the research. 'They were first described in 1936, but since then we've only been able to guess at the hosts that they parasitise.'

However, one of these three new species, G. phagocossorum, was reared from a log infested by the cossid moth Coryphodema tristis.

'This suggests that members of the Genaemirum genus live on wood-boring moths - something that was suggested, but never confirmed, as long ago as 1967,' says Dr Broad.

'It's exciting to think that these specimens could finally help us answer that 80-year-old question.'

Warthog wasp

It's not just the mystery of its host species that has made Genaemirum an interesting genus to study.

'They have the most extraordinary head structures,' says Dr Broad. 'Gerd Heinrich, who originally described the genus, characterised them as "monstrous".

'In fact, one of the species we found in the Museum's collections has the most extreme head I've ever seen.

'It has massively expanded genae, or "cheeks", a long lower face and horns above the antennae. We named it G. phacochoerus, after the genus name for the warthog, because of its striking appearance.'

Still digging

This unusual head shape lends weight to the suggestion that the genus parasitises wood borers, according to Dr Broad.

'It looks like the female's head has developed into a shovel shape,' he explains. 'This could help her shovel her way through piles of frass - the waste produced by the moth larvae as they bore through the wood - to get to a host for her eggs.'

The hunt for answers isn't finished yet, however. The research, a collaboration with Dr Simon van Noort, Curator of Entomology at Iziko South African Museum, is part of ongoing efforts to document African parasitoid wasps in the family Ichneumonidae.

'If we had a male G. phacochoerus specimen to compare to the female, that would tell us even more,' says Dr Broad. 'The shape of its head could support or refute the wood-borer host theory, since males don't need to access a host.'

'But for now, we're one step closer to understanding these strange species.'

  • By Conor McKeever

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