Abstract.
We describe a new technique for sampling arthropods from grassland and other vegetation, using a modified petrol‐driven suction apparatus called a‘Blow & Vac’.
The new apparatus was tested by comparing its efficiency in extracting arthropods from vegetation with that of a conventional Dietrick, or‘D‐Vac’, suction sampler.
Unimpeded air velocity inside the suction tube was approximately 4 times that of the D‐Vac.
In field trials on semi‐natural grasslands, the Blow & Vac caught more individuals of most spider and certain beetle species compared to the D‐Vac and approximately equal numbers of Auchenorrhyncha.
We conclude that the‘Blow & Vac’has considerable potential for sampling arthropod populations. Its low cost and weight make it a suitable alternative to the conventional D‐Vac apparatus.
The abilities of the aphid parasitoids Aphidius ervi Haliday and A. rhopalosiphi De Stefani Perez (Hymenoptera: Braconidae) to transfer between different known host species and the implications for the use of alternative hosts in pest control strategies Abstract A series of host-transfer trials using both laboratory-cultured and fieldcollected individuals of the aphid parasitoids Aphidius ervi Haliday and A. rhopalosiphi De Stefani Perez were done in order to clarify inconsistent results from several previous studies. A. ervi cultured on Acyrthosiphon pisum (Harris) produced very few mummies when confined with Microlophium carnosum (Buckton), whereas those cultured on M. carnosum produced as many mummies on A. pisum as they did on their original host. Mummy production was correlated with the attack rate of adult parasitoids on potential hosts. The production of mummies on M. carnosum by parasitoids reared on A. pisum was often greatly improved if their male parent had been reared on M. carnosum, suggesting that genotype strongly influences host preference. Aphidius rhopalosiphi from laboratory cultures produced significantly more mummies on Metopolophium dirhodum (Walker) than on Sitobion avenae (F.) regardless of their original host, but this preference was not shown by parasitoids from field populations. It is concluded that inadvertent selection occurs in laboratory cultures of aphid parasitoids as a result of low founder numbers, genetic drift and genetic bottlenecks and that this can strongly influence experimental results in biology and behaviour studies, which has important implications for biological control workers.
The attack rate of four parasitoids against different aphid species was investigated in the absence and presence of leaves from aphid food plants. The parasitoids used, Aphidius ervi Haliday, A. rhopalosiphi De Stefani, A. picipes (Nees) and Ephedrus plagiator Nees, varied in the extent of their host ranges. The presence of plant leaves significantly influenced the attack rate of A. ervi and A. rhopalosiphi, the two parasitoids with the most restricted host ranges, but did not appear to affect attack rates by the more polyphagous A. picipes and E. plagiator. Consideration of these results together with those from previous studies on the host preferences of laboratory populations of A. ervi and A. rhopalosiphi leads to the conclusion that genotype is probably determining the responses of individual parasitoids to semiochemicals involved in host recognition. It is proposed that field populations of oligophagous aphid parasitoids consist of a mixture of specialist and generalist individuals.
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.
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