The new wasp species Bracon predatorious Ranjith & Quicke. Credit: Ranjith A. P.

Biologists have discovered a new species of parasitic wasps that show obligate predatory behavior, an uncommon trait that makes the wasps feed on a specific host1.

The wasps survive by feeding solely on specific mites that make galls on the leaves of Cinnamomum verum, a commercially important plant. The leaf galls are abnormal growths that reduce plant vigour. The wasp larvae devoured the mites, significantly reducing their number.

The scientists, led by A. P. Ranjith at the Ashoka Trust for Research in Ecology and the Environment in Bangalore, collected mite-induced leaf galls from two locations in Kerala. In the lab, they dissected the leaf galls under a microscope to count the number of mites and studied the predatory behaviour of the wasps by observing their different developmental stages.

The team, collaborating with researchers from Thailand, found that the female wasps laid eggs inside the galls by inserting their egg-laying organs through the gall walls. A female wasp laid multiple eggs in each gall.

After hatching, the larvae began to hunt mites, using their sickle-shaped mandibles. They ate voraciously, devouring five to seven mites a minute. The larvae completed their entire life cycle inside the galls before emerging as adults by cutting through the gall walls.

The wasps, named Bracon predatorious Ranjith & Quicke, can be considered as effective biological control agents against gall mites, the researchers say.