No abstract

The effect of wind and rain on initiation of dispersal and subsequent distances moved by apterous Sitobion auenae was quantified in five laboratory experiments. Wind duration and type (steady and gusting), rain duration and intensity, and a combination of wind and rain were investigated. With increased duration of wind there was an increase in the average distance aphids moved. There was less movement when aphids were exposed to gentle gusting, than to steady wind or strong gusting. With increased duration of rain there was an increase in the proportion of aphids lost from plants. Under heavy rain, the proportion of aphids off the release plant, the distance moved by them and the proportion of aphids lost, was greater than for drizzle or light rain. When wind and rain were compared, rain had the greater impact on aphid dispersal. It was concluded that leaf disturbances caused by strong gusts of wind or large rain droplets are of considerable importance in the initiation of aphid dispersal, but that wetness alone is not.

Parasitoid development, parasitoid-induced host mortality and parasitoid progeny emergence were determined at five constant temperatures for Muscidifurax raptor Girault and Sanders, Muscidifurax zaraptor Kogan and Legner, Spalangia cameroni Perkins and Spalangia endius Walker using pupae of the house fly, Musca domestica L., as hosts. At temperatures of 20, 25, 30 and 35 degrees C the median development times (days from oviposition to adult emergence), respectively, were M. raptor (28.4, 20.7, 14.3, 14.5), M. zaraptor (30.6, 22.8, 14.1, 14.2), S. cameroni (55.6, 35.2, 21.8, 25.0) and S. endius (52.4, 31.5, 16.3, 14.6). All species failed to emerge at 15 degrees C. Using densities of five parasitoids and 100 hosts and a 24 h exposure period, Muscidifurax species oviposited at a greater rate over a wider range of temperatures than Spalangia species. At 15, 20, 25, 30 and 35 degrees C the mean number of pupae killed per parasitoid were, respectively, M. raptor (1.4, 7.4, 10.5, 13.7, 14.1), M. zaraptor (0.0, 3.3, 8.9, 14.4, 15.0), S.cameroni (0.0, 7.8, 11.0, 11.9, 7.4), S.endius (0.6, 4.0, 7.5, 12.0, 11.7), and means of the number of parasitoid progeny per parasitoid were, respectively, M.raptor (0.2, 5.2, 7.9, 11.8, 11.6), M.zaraptor (1.3, 4.4, 8.2, 13.0, 13.7), S.cameroni (0.0, 2.4, 4.7, 5.1, 1.0), S.endius (0.0, 0.9, 3.4, 7.5, 4.9). Development and ovipositional activity in S.cameroni was strongly inhibited at 35 degrees C. The model by Sharpe & DeMichele (1977) was used to describe temperature-dependent development and the number of parasitoid progeny produced per parasitoid at temperatures of 15-30 degrees C in all species.

No abstract

In autumn 1991, aphid parasitoids of the genus Praon (Hymenoptera; Braconidae) were caught in water traps with lures containing synthetic aphid sex pheromone components at three sites in England and one in Germany. At two of the English sites and at the German site, the traps were placed in winter cereal fields whilst the third English site was in woodland. Three species were caught, P. volucre, P. dorsale and P. abjectum. Those caught in cereal fields were almost entirely P. volucre, whilst P. dorsale dominated at the woodland site. Of the known aphid sex pheromone components, the most effective lure was the (+)‐(4aS,7S,7aR)‐nepetalactone. Nepetalactone traps placed at the woodland site in spring and summer caught few Praon females, and attraction may be confined to the autumn, when sexual female aphids are present in the field. Male parasitoids did not respond to the aphid pheromones at any time, although they were caught in suction traps operated at the woodland site during the autumn. At the cereal sites height had a significant influence on the efficiency of the pheromone traps, those placed just above the crop canopy being most effective. There was no evidence that any other genus of parasitoid responded to aphid sex pheromones at these sites.