Management of plant bugs in Europe under greenhouse condition
1Department of Plant Protection Biology, The Swedish University of Agricultural Sciences (SLU), Alnarp
2Swedish Board of Agriculture (SJV), Alnarp and
3Swedish University of Agricultural Sciences (SLU), Swedish Species Information Centre, Uppsala
Correspondence: Birgitta.Ramert@vpe.slu.se
In Sweden infestation of plant bugs Lygus spp. and Liocoris tripustulatus (Fabricius) (Heteroptera: Miridae), the common nettle capsid bug, in greenhouse production of cucumber is an increasing problem. Feeding damage on young shoots may cause plant deformations and developing fruits may become unmarketable. Today there is no selective insecticide available for use against mirids in cucumber production in Sweden. However, the use of bio insecticides, such as insect pathogenic fungi may be a promising alternative to conventional chemicals. To develop a management program of mirids in greenhouse production, pilot studies were undertaken. During February – September 2004 a survey was carried out in several greenhouses to find out which species dominated and how early they occurred and if any species could overwinter in the greenhouses. Yellow and blue sticky traps (Catch-it) were placed in half of the greenhouses from the week after planting until the end of March to see if the traps could be used as indicators of plant bug infestations. During spring and early summer, mirids was also surveyed on herbaceous vegetation surrounding the greenhouses. Thereafter, the susceptibility of one of the Lygus species Lygus pratensis (L.) (Heteroptera: Miridae) towards the commercially bioinsecticide BotaniGard ES (Beauveria bassiana strain GHA) was evaluated both in a laboratory and in a greenhouse study. In all greenhouses Lygus rugulipennis (Poppius) (Heteroptera: Miridae), the European tarnished plant bug, and L. tripustulatus, were found, with L. rugulipennis as the dominating species. The same two species were also the most common ones on the vegetation surrounding the greenhouses, with L. tripustulatus dominating on nettles. In some of the greenhouses adult bugs were found already in February and feeding damage was obvious on plants within two weeks after planting. The sticky traps were not useful as indicators for adults overwintering in greenhouses. Symptoms of bug activities were already developing on the plants when the first specimen of L. tripustulatus was trapped. The pathogenicity of BotaniGard ES was tested at different concentrations on hibernated L. pratensis sampled in May and on adults sampled from the summer generation in August to calculate LC 50 values. The BotaniGard ES was pathogenic to adults from both the hibernated and summer generation. The LC50 value for total mortality of L. pratensis 8 days after treatment was higher for the hibernated generation compared to the summer generation, indicating that the summer generation is more susceptible. In the greenhouse experiments BotaniGard ES was applied at two different dosages (250 and 125 ml/L) on Lygus spp. nymphs feeding on cucumber plants. An application with only water was also made as a control. At termination 8 days after treatment the total mortality of the nymphs was significantly higher on the nymphs treated with the higher dose compared to the nymphs feeding on the control plants (just water application) but the mortality was the same between the control and the lower dose treatment. To be able to discover and remove the overwintering and migrating insects early in the season and during replanting in July further studies are needed to find suitable and efficient traps or trap crops. More efficient application techniques using BotaniGard for both adults and nymphs is in need of development. The suppression of mirids using different formulations and doses of BotaniGard is in need of refinement.
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