| dc.description.abstract | 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 Pterosticnus 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.
.catches of Pterostictiue- femora/is Kirby and arachnids, had a significant
relationship with egg densities in fall of 1992. Catches of P. corvus and
P. lucublandus Say, had a significant relationship with sites, which also
represented relative densities of grasshopper eggs, in spring of 1992. Because
spring has higher temperatures, and offers a longer period for predation of
grasshopper eggs, than the fall, the most prevalent taxon in the spring, P. corvus,
which also had a significant relationship with relative densities of eggs, had the
greatest potential for predation of grasshopper eggs.
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. femora/is 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 at-shelter.
A one-choice feeding test of harvestmen on grasshopper eggs, in the | en |
