DO APHIDS SURVIVE OVER SUMMER IN MAIZE CROPS IN BELGIUM - A TEST OF THE APHID RESERVOIR HYPOTHESIS

In late summer, maize is the main crop available for cereal aphids in Belgium, and constitutes a possible transition between two consecutive winter wheat cultures. Moreover, this crop is generally left unspraye d throughout the season. In order to verify this ''aphid reservoir hyp othesis'', aphid populations and the abundance of their main predators and parasitoids were recorded over two years. Aphid development on ma ize began in June and reached a peak in mid-July. Afterwards, the popu lation declined abruptly and disappeared in early August. This drop wa s unexpected as, at that moment, maize plants are still suitable for a phid nutrition. This decline corresponds to the peak period of many ap hid predators and parasitoids. This plethora of antagonists can sharpl y reduce aphid populations. However, other factors such as plant physi ology, temperature and fungus development are to be taken into account . Instead of being an ''aphid reservoir'', untreated maize is a crucia l period in the cereal aphid life cycles and allows the multiplication of many auxiliaries.