In studies in southern England, the relative abundance of the hymenopterous parasites attacking Metopolophium dirhodum (Wlk.) and Sitobion avenae (F.) differed between their hosts, between years (1973-79) and on whether they were assessed using field or laboratory-reared mummies. Species of the complex of Aphidius uzbekistanicus Luzhetzki were usually the commonest parasites, especially from mummies of M. dirhodum, while Aphidius picipes (Nees) was less common and tended to attack mainly 5. avenae; Toxares del tiger (Hal.) was common only in 1979. Species of hyperparasites emerged most frequently from mummies of M. dirhodum, except for Dendrocerus car pent eri (Curt.), which emerged most often from 5. avenae.
Abstract. 1. The number of common carabid beetles trapped‐irr a wheat field on a clay with flint soil from May to October in.1971–77 differed greatly: Harpalus rufipes and Pterostichus melanarius were numerous every year; but the appearance of H.aeneus, P.madidus, Agonum dorsale, Nebria brevicollis, Notiophilus biguttatus, Bembidion lampros and Trechus quadristriatus was much more variable.2. The numbers caught were not correlated with rainfall. Catches of the large species were positively correlated with accumulated temperature above an assumed activity threshold of 5°C, whereas the smaller beetles were negatively correlated with accumulated temperature, suggesting that the danger of desiccation at high temperatures limits their activity.3. The egg‐laying periods of the commonest species were: B.lampros and A.dorsale from late April to June; overwintered P.melanarius, H.rufipes and H.aeneus in May and June, with the summer generation of these species and of P.madidus from July to September; T.quadristriatus during August and September; N.brevicollis from September to November; N.biguttatus and C.fossor laid in the early summer and again in the autumn.4. A few male and female H.rufipes and H.aeneus, and one female P.melanarius and N.brevicollis were each parasitized by a single tachinid larva; one P.melanarius was infested with a mermithid parasite.
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