The action of some systemic aphicides on the eggs of Anthocoris nemorum (L.) and A. confusus Reut

Comparisons were made of the systemic action of phorate, menazon and dimethoate on Aphis fabae Scop, and on the eggs of the aphidophagous Anthocoridae Anthocoris nemorum (L.) and A. confusus Reut., which are laid within plant tissue. Against 4th-instar apterous A. fabae the order of toxicity of the insecticides taken up by roots of the field bean Vicia faba L. was: menazon > dimethoate > phorate. Phorate concentrations needed to kill all A. fabae (10–15 ppm of wet weight of plant) killed most A. nemorum eggs but did not harm A. confusus eggs. Few A. nemorum eggs were killed by 15 ppm of menazon or 5 ppm of dimethoate. In the field a commercial in-row treatment of 1·5 lb/acre of phorate applied as granules in the seed drill of field beans sown in late April killed 86 % of eggs laid in June by overwintered A. nemorum and 30% of those laid in late July by second-generation females. Plants initially treated with 6 lb of in-row phorate per acre killed 74% of A. nemorum eggs in late July but did not harm A. confusus eggs. A. nemorum eggs laid in early June were unharmed by 1·5 lb/acre of in-row menazon. Of the A. nemorum eggs, 92–96% were inserted into the stipules and leaf margins of young bean plants, i.e. in the region (peripheral and distal part of the leaf) where most ³²P from labelled phorate accumulates after root uptake. The egg-laying sites of A. nemorum in potatoes and brussels sprouts (edges of the leaves) and in oats (the leaf tips) are also where most of the ³²P accumulates. In contrast, 98% of A. confusus eggs were laid in the stems, petioles and leaf midribs of field beans, where there was generally much less ³²P from labelled phorate.