Table 1.

Densities of cereal aphids and parasitoid mummies (individuals per 100 shoots) in winter wheat fields in three consecutive years.

(Arithmetic mean±s.d., minima and maxima are given for 18 fields in 2001, for 10 fields in 2002 and for 12 fields in 2003.)

	mean±s.d.	minimum	maximum
number of aphids at wheat flowering
2001	23.7±14.5	1	53
2002	257.6±161.7	30	596
2003	121.7±63.9	7	229
number of aphids at wheat milk ripening
2001	46.9±32.2	13	140
2002	101.6±63.9	18	228
2003	492.6±297.4	258	1371
number of mummies at wheat flowering
2001	0.9±1.5	0	5
2002	5.8±5.4	0	14
2003	0.3±0.6	0	2
number of mummies at wheat milk ripening
2001	8.8±6.4	0	23
2002	13.2±8.1	4	26
2003	8.0±6.0	0	23