Interactions of the blackcurrant leaf curling midge, Dasineura tetensi, with resistant and susceptible host plant cultivars
Oviposition behaviour Dasineura tetensi and its host plant Ribes nigrum was studied in both the laboratory and field. Monitoring of an unsprayed infested fieldsite using watertraps in S.E. Kent revealed that there were four generations occurring between the April - August 1996. 'Baldwin' (susceptible), 'Ben Alder' (susceptible) and 'Ben Connan' (resistant) Ribes cultivars were sampled for eggs in the field and assessed for midge shoot damage throughout the season. Oviposition was shown to be indiscriminate, however plant damage between cultivars varied significantly. In laboratory choice experiments using pairs of plants, mated female midges did not prefer susceptible shoots of 'Ben Alder' over resistant shoots of 'Ben Connan' for oviposition. In larval performance studies, larvae reared on resistant 'Ben Connan' shoots were significantly smaller than larvae reared on shoots of the susceptible variety of 'Ben Alder', suggesting that larval antibiosis to be the main mechanism for resistance to D. tetensi. Olfactory responses of D. tetensi to leaf volatiles of 'Baldwin' were also tested in a 4-way olfactometer. Newly emerged virgin males and females that were individually tested showed no attraction to the leaf volatiles emitted from a 'Baldwin' shoot. Mated females (2 hr post mating) however, responded positively in the olfactometer to leaf volatiles emitted from a 'Baldwin' shoot, showing that leaf volatiles play an important role in host plant finding. Scanning and Transmission electron microscopy of the antennae of D. tetensi show that males and females share five sensillum types. Sensilla chaetica have a structure typical of mechanoreceptors. They possess a single sensory neurone whose dendrite ends in a tubular body at the base of the hair.