The effect of various levels of nitrogen, phosphorus and potassium on the fecundity of the two-spotted spider mite Tetranychus Bimaculatus Harvey.

The two-spotted spider mite Tetranychus bimaculatus Harvey has long been one of the most serious pests attacking cucumber in greenhouses. This pest is of particular economic importance in Essex County, Ontario, where cucumber culture under glass is a major commercial practice. Each year mite infestations result in a ten to fifteen per cent loss of a $3,000,000 crop. The recently developed aerosols of parathion and related phosphoric acid esters have been highly effective against active forms but have had little or no ovicidal effect. Such controls are costly as they must be repeated at intervals of time to prevent further mite population build-up from the unaffected eggs. The most effective of these chemical controls have on occasion resulted in the selecting out of resistant strains of the pest, thus defeating their own effectiveness. Many workers have, therefore, turned their attention to the investigation of non-chemical methods of controlling these mites on greenhouse plants. One suggestion has been that controls might be effected by the manipulation of plant nutrients in the soil (Page, 1946; Rodriguez and Neiswander, 1949). This led the writer to undertake a controlled nutritional experiment at the Dominion Entomological Laboratory, Harrow, Ontario, in an attempt to ascertain the effect of various levels of nitrogen, phosphorus and potassium on the fecundity of the two-spotted spider mite Tetranychus bimaculatus Harvey. [...