A sliver of gold. This week’s Insect of the Week (95), the sleek and striking Aeptencyrtus bruchi De Santis, was captured about 50 m from where I’m sitting in my office at the International Centre of Insect Physiology and Ecology (icipe) in Nairobi. It was collected in a yellow pan trap set in degraded riverine woodland. The trap is simply a yellow-coloured shallow bowl with water and a few drops of liquid detergent added. The latter helps to break the surface tension of the water so that the insect sinks to the bottom.
The genus Aeptencyrtus is one of three small genera of Encyrtidae in the tribe Acroaspidiini, all species of which are presumed to be parasitoids. Holcencyrtus contains 9 species, while Aeptencyrtus and Pelmatencyrtus are monotypic, each containing only a single species. Aeptencyrtus bruchi females can be distinguished from those of the other two Acroaspidiini genera by their shiny, concave scutellum. Female, but not male, Acroaspidiini are myrmecomorphous (i.e. possessing an ant-like form with reduced wings and an abdominal petiole). Ant mimicry probably reduces hostile encounters between female Acroaspidiini species that parasitize mealy bugs and the normally aggressive ants which tend and protect the mealy bugs in return for access to their sweet honeydew excreta.
Before our collection of Aeptencyrtus, all Acroaspidiini were thought to be new world endemics, although A. bruchi had been recorded from Hawaii, probably together with its presumptive mealybug host. In addition to the type locality in Argentina, the species is known from Peru, Trinidad, St. Vincent, Cuba and recently also from Florida. The record from Peru provides the only example of its biology. Aeptencyrtus bruchi was reared from two species of mealybugs (Hemiptera, Sternorrhyncha), pests of two commercially important grass species, the Rhodesgrass mealybug Antonina graminis and the Pink Sugarcane Mealybug, Sacchricoccus sacchari. Aeptencyrtus is a “farmer’s friend”.
The answer to the question of how Aeptencyrtus made it to Nairobi is probably a simple one, international trade. Sugarcane (Saccharum officinarum) is native to south and southeast Asia and New Guinea. The Pink Sugarcane Mealybug probably also originated in New Guinea and today is a pest of sugarcane wherever it is grown. It isn’t hard to imagine the sugarcane mealybug traveling together with its parasitoids on sugar cane plants being traded and shipped throughout the tropics. Sugarcane stalks are even sold today by street vendors throughout Africa, including just across the road from icipe.
Aeptencyrtus bruchi was described by the celebrated Argentinian entomologist Luis De Santis (1914 –2000). Over his career he authored 273 scientific publications. He was an international expert on the microhymenoptera, particularly the Encyrtidae.