Efficiency of Trissolcus basalis (Hymenoptera: Scelionidae) as an egg parasitoid of Nezara viridula (Heteroptera: Pentatomidae) in central Italy

The natural control exerted by Trissolcus basalis (Wollaston), a solitary egg parasitoid of Nezara viridula (L.), in soybean fields in central Italy over 6 yr has been assessed. T. basalis was the only egg parasitoid attacking N. viridula egg masses. In total, 260 N. viridula egg masses were collected. Of these, 105 contained at least 1 egg parasitized by T. besalis. Approximately 20% of egg masses were parasitized during the first 2 yr (1986 and 1987), increasing to 50% in the following years (1988, 1990, 1991, and 1992). Parasitism efficiency (the percentage, of eggs parasitized over the total egg masses discovered) was approximate to 65% in 1986 and 1987, significantly less than in 1988 and 1990 (approximate to 92%). The impact of the parasitoid on the N. viridula population was low, <13%, for the first 2 yr, and much higher, approximate to 40%, in the following years.