Observations on some Parasites of Oscinella frit Linn. Part II.

Abstract

It has already been shown (Imms, 1930) that the stem generation of the frit-fly in the Harpenden district is subjected to natural destruction, to a marked degree, by the agency of certain hymenopterous parasites. Among these, two species, viz. the Cynipid Rhoptromeris eucera Htg. and the Chalcid Halticoptera fuscicornis (Walk.) were found to predominate in numbers. Parasitisation, to a lower degree, by the Proctotrypid Loxotropa tritoma Thoms. was also noted and the Chalcid Callitula bicolor Spin. was recorded for the first time as having been reared from this same host. Evidence was also brought forward which o appeared to indicate that the parasitisation of frit-fly by the above combination of species increases in intensity as the season advances. In other words the stem generation of frit-fly, attacking late sown oats, is subjected to markedly heavier parasitisation than when it attacks oat sown earlier in the same season.