The rearing system of Sclerodermus brevicornis, a potential biocontrol agent of flat faced Longhorn beetle : perspective and difficulties

Sclerodermus brevicornis (Hymenoptera Bethylidae) is a gregarious quasi social parasitoid. After its detection in association with exotic longhorn beetles, a rearing system, aimed to study the biology, ethology and the potential of the parasitoid was set up. It was immediately clear the complexity of the rearing system as foundresses cooperate in attacking a victim, and looking after their brood until emergence. Studies have been focused on the maximisation of the offspring production and on the strategies to overcome the encountered difficulties. Currently, a stable mass rearing system is active at the University of Milan, and over the years various aspects have been evaluated. The first one was to find the best number of females per host to maximise the success of parasitization and to obtain the best per-female production: tests with a progressive number of females in relation to host dimension were set up. Main problems associated with desiccation of small larvae or with the decay of the bigger ones, led to the search for the best rearing system condition (temperature, containers, host development, and substrates). Since the rearing system on natural hosts is long and difficult, different factitious hosts (Coleoptera and Lepidoptera) were evaluated. Another important factor considered was the influence of different temperatures. The survival at 4.5°C (cold storage) was compared with the one at higher temperatures (23; 28.5; 34°C, all ±1). At the same time the influence of these temperatures on subsequent oviposition was evaluated throughout the lifetime of S. brevicornis females. As a result 4.5°C was considered a valuable tool for the storage. However, as males emerge before females to allow mating and avoiding the presence of arrenothocous females, it was established the necessity to wait at least 3 days after first emergence before the storage at cold temperature. Obtained results provide different solutions for the application of mass rearing in the biofarms.