The effects of some insecticides on populations of frit fly (Oscinella frit) and its enemies.
The following is based almost entirely on the author's summary. In investigations in southern England, nearly twice as many eggs were laid by females of Oscinella frit (L.) on oat plants in plots protected from ground predators by DDT-treated barriers as on plants in untreated plots and 2.5 times as many were laid on plants in protected plots that were also sprayed twice with parathion in May. Young larvae were killed by the spray, and few adults developed in the tiller stage [cf. RA.E., A 47 219] of the sprayed plants. Just over 10 per cent. more adults of O. frit and just over a third more of all flying insects emerged from tillers during July on the protected plots than on the unprotected ones. Only about half as many adults of O. frit emerged from the panicles of plants [cf. loc. cit.] in sprayed plots as from those in unprotected ones. The proportion was similar for parasites and for the total number of flying insects. Adults of O. frit emerging from grass stems in May were preyed upon by Empidids and by spiders, which were especially abundant in the oats when the tiller generation emerged. At the time of the panicle generation, spiders were still numerous and there was a species of Anthocorid among the glumes. Adults of the four main Hymenopterous parasites of the larvae and pupae, Rhoptromeris eucera (Htg.), Halticoptera fuscicornis (Wlk.), Callitula bicolor Spin. and Loxotropa tritoma (Thoms.), were caught in the emergence traps, but the proportion of parasites of O, frit in the catch was small. An apterous Braconid, Chasmodon apterus (Nees), attacked the larvae and pupae of the overwintering generation. Many predacious beetles and spiders were caught in pitfall traps, especially in May, when females of O. frit were laying eggs. The yield of grain from late-sown oat plants sprayed twice with parathion was about one-third greater than that of untreated plants, and fewer adults of O. frit emerged from the panicles of the treated plants.