Parasa lepida, the Blue-streaked Nettle Grub: 3. Parasitoid wasps

Small wasps were always flying around my Blue-streaked Nettle Grubs (Parasa lepida) when they were feeding on leaves of the Calabash Tree (Crescentia cujete) or the Lipstick Palm (Cyrtostachys renda) (above). These are parasitoids wasps whose larvae live as parasites in the body of the host that eventually kill the latter.

I first noticed a young grub with white silk growing out of its body. A small black wasp was nearby (above and video below). Obviously the wasp’s eggs inside the grub had hatched and the larvae had emerged.

A dead grub with similar outgrowths was also seen. A larva was seen emerging from the mass of silk (below, arrowed).

On another occasion a wasp was caught on video (below) landing on the thorax of the grub and injecting its eggs into it. The grub reacted to the attack by raising its anterior portion before returning to feed.

The largest of these parasitoid wasps seen was the Ensign Wasp (Family Evaniidae) (below).

Prof Cheong Loong Fah kindly identified this wasp, adding that its characteristic feature as “…the gaster (abdomen) sticks out of the thorax and is repeatedly raised high above the wings.”

Loong Fah further added: “The members of this family parasitise oothecae of cockroaches (or at least for those with known hosts); I have not heard of it parasitising eggs of moth, so yours could be an interesting record!” The image above shows the wasp approaching the grub but the actual attack was not captured in the video below.

According to Ng et al. (2011), Evania appendigaster is the only Ensign Wasp that has been recorded for Singapore. As it is relative common, it is possible that the wasp is Evania appendigaster.

YC Wee & Prof Cheong Loong Fah
Singapore
15th October 2016

Reference:
Ng, P.K.L., R. Corlett & H.T.W. Tan (eds.) 2011. Singapore Biodiversity: An encyclopedia of the Natural Environment and Sustainable Development, pp. 303. Editions Didier Millet & Raffles Museum of Biodiversity Research, Singapore.