In field populations of cereal aphids parasitism levels declined through the season as fungal infection increased. In laboratory trials the fungus Erynia neoaphidis Remaudiere & Hennebert took 3 to 4 days to kill the rose-grain aphid, Metopolophium dirhodum (Walker), whereas the parasitoid Aphidius rhopalosiphi De StefaniPerez took 8 to 9 days at 20 ~ When aphids were infected by the fungus less than 4 days after being parasitized the parasitoids were prevented from completing their development. Conversely, when infection-occurred more than 4 days after parasitization development of the fungus was significantly impaired. There was no histological evidence that the fungus invaded the tissues of the parasitoid when both attacked the same aphid.Interference between parasitoids and fungal pathogens must be taken into account when estimating the impact of these mortality agents on pest populations.

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Western flower thrips (Frankliniella occidentalis) develops from an active larval stage through to a non-feeding, almost immobile, pre-pupal and pupal stage. This generally occurs in the compost or soil below the plant on which the larvae fed. Control of thrips at this stage in their development offers a chance of utilising pathogens or pesticides not suitable for use in an integrated control programme aimed at adult and larval stages. Trials were done with F. occidentalis pupae and pre-pupae in a soil/peat based compost using 11 pesticides, three fungal pathogens and four species of insect parasitic nematodes. The pesticides malathion and chlorpyrifos-methyl gave the most promising result with 97.5% and 96.5% control, respectively. The fungal pathogen Metarhizium anisopliae proved better when applied as a pre-pupation rather than as a post-pupation treatment (74.5% : 26.6% control), The insect parasitic nematode Steinernema carpocapsae gave 76.6% control when applied at 25 x lo4 nematodes litre-' of compost. The results are discussed in relation to control of thrips in glasshouses.

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SummaryFifty‐one pesticides currently registered for use in the UK were tested in the laboratory against Western Flower Thrips (Frankliniella occidentalis) maintained on chrysanthemum leaf discs. In an initial screening trial of the pesticides against larval thrips, 14 caused more than 75% mortality three days after exposure. These were tested further against adults and pupae and retested against larvae. A series of glasshouse trials were conducted using the most efficacious pesticides evaluated earlier. Granular and systemic compounds were included in the glasshouse trials since these could not be evaluated satisfactorily in the laboratory. Malathion proved to be the most potent chemical currently registered for control of thrips on a wide range of horticultural crops.