Insect of the week: 4 September 2023

A leafhopper’s nightmare; Pseudodryinus townesi (Olmi), Family Dryinidae, Subfamily Dryininae.

Dryinidae are parasitoid wasps of true bugs belonging to the order Hemiptera, suborder Auchenorrhyncha. While adult males are fully winged, females may be winged or wingless (apterous). Hosts are commonly Cicadellidae (leafhoppers) and their relatives. Dryinids are known mainly for their extreme sexual dimorphism, the sexes so different looking that it is impossible to associate males with females of the same species. At least it was until recently when molecular methods (barcoding) were developed to sort out this once insoluble problem. A second feature unique to most dryinid females is the modified chelate (pincer-like) last tarsal segment of the foreleg (see image) that allows the parasitoid to grab and restrain its host while injecting an egg into the bug’s abdomen. The developing parasitoid larva feeds within the host and as the larva grows it forms a sac-like structure, the thylacium, that projects out from the host’s abdomen so that, in later developmental stages, most of the parasitoid’s body is actually outside the host. The presence of a thylacium on the host’s abdomen makes it possible to see with the naked eye that the bug is parasitized. Eventually, the parasitoid consumes its defenseless host, exits, and pupates in the soil or on the plant on which the host was feeding. Within the pupa the remarkable holometabolous transformation into an adult is completed.

There are close to 2000 species of Dryinidae worldwide, with 430 species found in The Afrotropical region. The most recent checklist of the number of species found in Kenya is 76. I thank Dr. Masimo Olmi, the world’s expert on Dryinidae, for identifying this week’s insect of the week, Pseudodryinus townesi. This species is one of only two species of Pseudodryinus known from the Afrotropical region. Like Seladonia jucunda, last week’s insect of the week, our collection of P. townesi was made in the Lambwe Valley in western Kenya and was the first record of the species in Kenya.

Credits: Dr Robert Copeland