Notonecta maculata: more than just a model predator of mosquito larvae

Notonecta species, commonly known as backswimmers, are often employed as model predators of rotifers, annelids, zooplankton, crustaceans, molluscs, juvenile fish, frog tadpoles, and all the developmental stages of water insects. Indeed, they have a relevant impact on the size, structure, and richness of aquatic communities. Relative to mosquito populations, juvenile and adult backswimmers are more than just predators of larvae: their solely presence can also discourage the oviposition of gravid females. In this study, we selected a backswimmer of Western Palearctic distribution, Notonecta maculata (Hemiptera: Notonectidae), as a predator and deterrent of the highly invasive and health threatening Asian tiger mosquito, Aedes albopictus (Diptera: Culicidae). From our biological observations on N. maculata, we assumed that, in central Italy, the species is univoltine and overwinters as an adult. Females oviposit from the following February to the end of May, and the new adults emerge in late June after 44.5 ± 3.1 days of nymphal development. Through different predation evaluations, we observed that the number of Ae. albopictus larvae preyed on by N. maculata increases while growing, starting from an average of 0.40-3.36 larvae per day for first, second, and third instar nymphs up to about 20 for adults. In the oviposition deterrence trial, a single N. maculata nymph in a mosquito ovitrap was sufficient to significantly discourage Ae. albopictus oviposition by 66 to 88% for five days. Overall, limiting or suppressing mosquito populations involving a biological control agent such as N. maculata might sound promising.