BIONOMICS OF THE DAMSEL BUG, NABIS AMERICOFERUS CARAYON (HEMIPTERA: NABIDAE), A PREDATOR OF THE ALFALFA BLOTCH LEAFMINER (DIPTERA: AGROMYZIDAE)

Abstract

AbstractThe damsel bug, Nobis americoferus Carayon, develops through two generations a year in eastern Ontario. In early fall, females of the second generation develop a reproductive diapause but both sexes continue to feed until freeze-up. Post-diapause development begins in late March. Eggs are deposited singly in plant stems but several may be laid in close proximity. In alfalfa, most eggs were found where stem diameter measured from 0.8 to 1.9 mm but height of oviposition site was not related to length of stem. Females reared at 23°C laid an average of 157 eggs during a 3-week oviposition period. The immature stages of the first generation occurred from mid-April to mid-July and those of the second generation from mid-July to early September. The duration of each stage of N. americoferus, fed pea aphids, Acyrthosiphon pisum (Harr.), and held at four constant temperatures, 18, 23, 28, and 31°C, decreased with increasing temperature. There was a highly correlated linear relationship between rate of development and temperature for all stages. The theoretical temperature threshold for development of eggs was 11.1°C and that for the nymphal stage was 10.6°C; degree-day requirements for these stages were 123.5 and 370.4, respectively. Developmental rate of nymphs varied with host as well as temperature; nymphs fed larvae of the alfalfa blotch leafminer, Agromyza frontella (Rondani), developed significantly faster than those fed pea aphid.