Drosophila bioassays are very sensitive methods to assess tarantula species venoms

Assaying venom toxicity in a suitable model system is often tricky, since normally the amount of venom is in short supply, and the assay subjects, i.e., typically mice, require large amounts. There is also no guarantee that the effects observed in the bioassay reflect the true nature of the venom's intended effects, as the animals used for assessment might not be the prey items to which the venom has evolved.

We harvested tarantula venoms from the Indian Poecilotheria regalis and the Mexican Bonnetina papalutlensis using light anesthesia and electrical stimulation. We follow the definition of venom as stated in (Nelsen et al., 2014). The recovered venom was lyophilized and reconstituted in sterile saline solution for injections. Drosophila melanogaster third instar larvae and adult flies were injected with 4.6 nanoliters of different concentrations of the venoms into the sixth abdominal segment, and scored for survival and development to adulthood.

The injected venoms were very effective in provoking lethality of injected larvae and adults, with an LD₅₀ of 1-5 nanomoles protein /gram wet weight. Comparison with other toxicity bioassays, i.e., mice and crickets -using the same P. regalis venom- renders the Drosophila bioassays three orders of magnitude more sensitive. The P. regalis and B. papalutlensis venoms have similar LD₅₀.

These bioassays use a small amount of venom compared to other bioassays, allowing characterization with far fewer starting material. As it uses insects, phylogenetically close to the intended prey victims, it also points to the efficiency of the tarantula venom for its preferred prey items, and thus, links as well to the tarantulas' ecology.