The effects of the odoriferous volatile matter produced by Scaptocoris talpa Champ on the activity of Fusarium oxysporum f. cubense (E.F.S.) Sny. and Hans., F. oxysporum f. lycopersici (Sacc.) Sny. and Hans., and Meloidogyne incognita in soil, and its phytotoxicity to tomato seedlings, were investigated.The results obtained indicated that 50–75 insects per pot protected tomato seedlings (Bonny Best) and banana plants (Gros Michel) from attack by their respective fungus pathogens and one insect per 2 grams of soil protected tomato seedlings from attack by root-knot nematode.The apparatus especially constructed to study the phytotoxicity of odoriferous volatile matter to tomato seedlings and its effect on microbial population of the soil was described. By means of this apparatus it was found that 6 days of a weak flow of a mixture of air and volatile matter produced by 350–400 insects was not phytotoxic to six tomato seedlings. Furthermore, it was also found that volatile matter produced by 800 insects, under the same conditions, was not toxic to one tomato seedling. Under similar conditions the non-phytotoxic concentration of volatile matter produced by 350–400 insects reduced the density of F. oxysporum f. cubense population in soil samples containing 25 and 15% (w/w) of moisture by 61.20 and 45.78% respectively.It was also demonstrated that one insect per 2 grams of soil infested with the root-knot nematode during 16 hours' incubation produced a nematocidal concentration of volatile matter.The possibility of selective toxicity of volatile odoriferous matter to various bacteria is also discussed.