The use of egg counts and suction trap samples to forecast the infestation of spring‐sown field beans, Vicia faba, by the black bean aphid, Aphis fabae

Abstract

SUMMARYDaily suction trap samples at a height of 12·2 m collected throughout the year, winter egg and ‘spring’ population counts on the spindle tree, Euonymus europaeus, and initial infestations of the black bean aphid, Aphis fabae, on field bean, Vicia faba, crops are available from Southern England since 1970. In different areas, estimates of the sizes of the autumn migrations, the over‐wintering egg populations, the spring fundatrigeniae and the spring migrations, have been used to forecast field bean crop infestation levels which, in turn, project subsequent trap catches of alatae.The forecasts of crop infestation become progressively more accurate from the autumn migration to the following spring migration, accounting for 28%, 54%, 54% and 64% of the variance respectively. In areas where traps are sited, the spring migration trap samples give the most accurate estimate of the size and timing of crop infestation.Autumn trap catches are particularly useful as very early forecasts of likely very large or very small populations on field beans about 8 months later, but otherwise they lack precision. Egg sampling in winter provides a considerably more accurate forecast approximately 5 months before crop infestations. In spring (May), fundatrigeniae sampled on spindle are most useful for predicting time of migration, and provide approximately 2 weeks' warning for insecticide application, if needed. Finally, trap sampling of the spring migration provides the latest estimate of both the sizes of crop infestations and the timing of insecticide treatment.The E. europaeus and aerial sampling systems are complementary, the traps providing systematic, continuous information and the E. europaeus samples greater detail. Combined, they can provide excellent long‐term fore‐warning of the need for chemical control and short‐term warning of control timing. Forecasts have been 90% correct in eight years out of nine. The error in the ninth year may be due to immigration from the European mainland.