Paraquat also induces oxidative stress in invertebrates such as "Drosophila melanogaster". Another virus is Nora virus from "Drosophila melanogaster". The signalling pathway is also crucial for eye development in the fruit fly ("Drosophila melanogaster"). They were shown to be able to visually distinguish between different mutations of "Drosophila melanogaster". Triethylamine is the active ingredient in FlyNap, a product for anesthetizing "Drosophila melanogaster". Merck is studying recombinant subunit vaccines expressed in Drosophila cells. They can be found in mice, humans, "Xenopus", zebrafish, "Drosophila" and many others. One approach of inserting foreign genes into the "Drosophila" genome involves P elements. The "Scr" gene is responsible for cephalic and thoracic development in "Drosophila" embryo and adult. S2 cells were then transfected with "Drosophila" cyclin E dsRNA. "Drosophila", like all insects, has eight Hox genes. A single nematocyst has been shown to suffice in paralyzing a small arthropod ("Drosophila" larva). These genes exist in two ordered groups on "Drosophila" chromosome 3. Three major genes are involved in determination of "Drosophila" sex. Other species however (notably "Drosophila") exhibit homologous pairing much more frequently.