Wireworms, the larval stage of click beetles (Coleoptera: Elateridae), are serious soil dwelling pests of small grains, corn, sugar beets, and potatoes. Limonius californicus and Hypnoidus bicolor are the predominant wireworm species infesting wheat in Montana, particularly in the 'Golden Triangle' area of north-central Montana. Wireworm populations in field crops are increasing, but currently available insecticides provide only partial control, and no alternative management tools exist. In our study, three entomopathogenic fungi were tested for their efficacy against wireworms in spring wheat at two field locations (Ledger and Conrad, Montana, USA) in 2013. The three fungi (Metarhizium brunneum F52, Beauveria bassiana GHA, and Metarhizium robertsii DWR 346) were evaluated as seed-coat, in-furrow granular, and soil band-over-row drench applications in addition to imidacloprid (Gaucho® 600) seed treatment (as a chemical check), the approach currently being used by growers. Wireworm damage in these treatments was evaluated as standing plant counts, wireworm population surveys, and yield. The three fungi, applied as formulated granules or soil drenches, and the imidacloprid seed treatment all resulted in significantly higher plant stand counts and yields at both locations than the fungus-coated seed treatments or the untreated control. Significant differences were detected among the application methods but not among the species of fungi within each application method. All three fungi, when applied as granules in furrow or as soil drenches, were more effective than when used as seed-coating treatments for wireworm control, and provided an efficacy comparable or superior to imidacloprid. The fungi used in this study provided significant plant and yield protection under moderate wireworm pressure, supporting their value in the management of this pest.
The objectives of this study were to quantify the virulence of four entomopathogenic fungal species to pupae of Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) and to determine the potential to combine entomopathogenic fungi (EPFs) and entomopathogenic nematodes (EPNs) for biological control of this pest. The four species of EPFs included Beauveria bassiana (strain GHA), Metarhizium brunneum (strain F52), Isaria javanica (wf GA17), and Isaria fumosorosea (Apopka 97 strain). In laboratory assays, all fungi reduced adult emergence but there were no differences between fungal species. Isaria javanica and M. brunneum were examined further in a EPFs and EPNs bioassay that also included the EPNs Steinernema carpocapsae (ALL strain) and S. riobrave (355 strain). All nematodes and fungi were applied either alone or in combination (fungus + nematode). There were no differences between species within the same entomopathogen group (fungi and nematodes). However, the treatment with S. riobrave resulted in lower R. pomonella emergence than either fungal species. The combination of S. riobrave and I. javanica resulted in the lowest R. pomonella emergence (3%) at fourth-week interval, which was significantly lower than any of the single-agent applications, yet virulence of the other three combination treatments was not different from their respective nematode treatments applied alone. Additive interactions were detected for all fungus–nematode combinations. This study suggests that application of entomopathogenic nematodes and fungi could be an effective option to suppress R. pomonella populations.
The cabbage butterfly, Pieris melete hibernates and aestivates as a diapausing pupa. We present evidence that the optimum of low temperature and optimal chilling periods for both summer and winter diapause development are based on a similar mechanism. Summer or winter diapausing pupae were exposed to different low temperatures of 1, 5, 10 or 15°C for different chilling periods (ranging from 30 to 120 d) or chilling treatments started at different stages of diapause, and were then transferred to 20°C, LD12.5∶11.5 to terminate diapause. Chilling temperature and duration had a significant effect on the development of aestivating and hibernating pupae. The durations of diapause for both aestivating and hibernating pupae were significantly shorter when they were exposed to low temperatures of 1, 5 or 10°C for 50 or 60 days, suggesting that the optimum chilling temperatures for diapause development were between 1 and 10°C and the required optimal chilling period was about 50–60 days. Eighty days of chilling was efficient for the completion of both summer and winter diapause. When chilling periods were ≥90 days, the durations of summer and winter diapause were significantly lengthened; however, the adult emergence was more synchronous. The adaptive significance of a similar mechanism on summer and winter diapause development is discussed.
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