Horticulture and Food Research Institute of New Zealand, Mt Albert Research Center, Private Bag 92169, Auckland, New Zealand.
Hessian fly (HF) larvae feed at the base of wheat plants. Wheat plants infested by larvae exhibit particular symptoms, such as reduced plant height and a color change from bright green to darker blue-green leaves. We have found that HF females lay fewer eggs on the leaves of wheat plants infested by conspecific larvae than on the leaves of uninfested wheat plants. It was confirmed that both plant height and leaf color are important physical factors affecting the oviposition behavior of HF females. Chemical stimuli on the leaves of infested and uninfested wheat plants were also examined. When green paper leaf models were treated with leaf extracts made from uninfested or infested wheat plants, females laid significantly fewer eggs on models treated with extracts from infested plants. Recently, two compounds found on the surface of wheat leaves, 1-octacosanal and 6-methoxy- 2-benzoxazolinone (MBOA), were identified as oviposition stimulants for HF females (Morris et. al., in press). The presence of these two oviposition stimulants on the leaves of infested and uninfested wheat plants is currently being investigated. Volatile chemicals emitted by infested and uninfested wheat plants are also being investigated using a Y-tube olfactometer.