Phenology, diapause, and overwintering of the wheat bug,Nysius huttoni(Hemiptera: Lygaeidae), in Canterbury, New Zealand

Abstract

Abstract At Lincoln, Canterbury, New Zealand, two generations of the wheat bug (Nysius huttoni) developed in annual weeds (Stellaria media, Coronopus didymus, and Polygonum aviculare) between October and February in 1990–91 and 1991–92. Flight trapping indicated that a proportion of the population emigrated from the weeds soon after adult emergence when new habitats, such as patches of fathen (Chenopodium album) and wheat (Triticum aestivum), were colonised. Gravid females comprised 47–80% of all females dissected during the first generation, but only 0–9.6% of second generation females. A small third generation, initiated by the latter gravida, was detected in the field. Reproductive diapause, reported for the first time in the genus Nysius, was induced by transferring second generation female nymphs of the third and fourth instars, in late summer, to short day (12 h light: 12 h dark) conditions in the laboratory, where virtually no reproduction occurred over 80 days at 23.5°C. Females transferred to long day (16 h light: 8 h dark) photoperiod, but otherwise identical conditions reproduced normally. Adults of the second generation migrated to overwintering sites in the autumn and aggregated under dead leaves of Verbascum thapsus, under bark of dead Pinus radiata, in gorse hedges (Ulex europaeus), and swards of browntop grass (Agrostis capillaris). Adult survival and maintenance of condition of internal organs during late winter was greatest in sheltered sites under pine bark. In early spring, overwintered adults migrated to patches of annual weeds, fed, and reproduced. The relationship between the timing of migration of first generation adults and damage to wheat through grain proteolysis is discussed. It is concluded that the success of the wheat bug may be linked with flexibility in habitat use, and that this occasional agricultural pest is difficult to control as it migrates to affected crops from fallow land.