Biological control of grasshoppers (Orthoptera: Acrididae) in Manitoba with emphasis on predators and parasitoids of the eggs

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Songa, Josephine M.
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Studies were conducted to examine the occurrence of potential predators of grasshopper eggs, and their relationship with egg density in the field, at Aubigny Manitoba, in spring and fall of 1992 and 1993. Assessment of potential predators was done by pitfall trapping and soil sampling. Three sites were established in preliminary surveys of egg densities in farmers' fields. Egg densities in each site were assessed by quadrat sampling. Grasshopper egg densities were higher in the spring and fall of 1992 than 1993; this was attributed to the cool wet weather that prevailed in 1993. The most commonly caught groups of potential predators in the spring of 1992 and 1993, were staphylinids, arachnids and carabid beetles. Carabids were the most abundant group in the spring, and Pterostichus corvus Lec. was the most prevalent species. The common potential predators caught in fall of 1992 and 1993, were staphylinids, arachnids, crickets and carabid beetles. Crickets were the most prevalent group in the fall... The influence of vegetative cover, soil moisture and soil compaction, on the density of grasshopper eggs was examined at the field, in fall of 1992. None of these factors had a significant relationship with egg density; this was attributed to the low egg densities that season. In a two-choice feeding test of grasshopper eggs and cat food (Tender Vittles@) in the laboratory, both P. corvus and P. femoralis preferred grasshopper eggs to cat food. Of the two species P. corvus ate more eggs. A study on the preferred depth of feeding of P. corvus on grasshopper eggs in soil in terraria showed that, P. corvus preferred to feed below the soil surface to depths up to 5 cm. The predation of grasshopper eggs by P.corvus was studied under three types of ground cover: Nicotiana, barley and bare ground, in the laboratory. A significantly higher percentage of eggs was eaten under the Nicotiana ground cover than in the other types of ground cover. The higher predation in the Nicotiana treatment was attributed to the more favourable environment provided in terms of shelter. A one-choice feeding test of harvestmen on grasshopper eggs, in the laboratory, showed that harvestmen feed little on grasshopper eggs. A laboratory study on the parasitism of grasshopper eggs collected from the field in the spring ol 1992 and 1993, showed that scelionid wasps were the only parasitoids of the eggs, and the percentage parasitism was low. The scelionids, Scelio opacus (=calopteni) Provancher and S. striativentris Kieffer were found to occur in the field site.