Dynamics ofSitotroga cerealella (olivier) (lepidoptera: gelechiidae) andSitophilus zeamais motschulsky (Coleoptera: Curculionidae) populations in a small bulk of stored corn |
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Authors: | Richard T Arbogast and Michael A Mullen |
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Institution: | (1) Stored-Product Insects Research and Development Laboratory, Agric. Res. Serv., USDA, 31403 Savannah, Georgia, U.S.A. |
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Abstract: | Summary The dynamics of Angoumois grain moth,Sitotroga cerealella (Olivier), and maize weevil,Sitophilus zeamais
Motschulsky, populations breeding in a small bulk (initially 5.36 t) of shelled corn were studied over an 8-year period by monthly sampling.
The weevil population showed wide fluctuations in density superimposed on a general decline with time. The moth population
showed no upward or downward trend for the first 60 months, although it fluctuated widely. Following a decline that occurred
between 56 and 60 months, the moth population fluctuated within a much narrower range, and there was a general decrease in
density with time. The decline of the weevil population paralleled deterioration of the corn as did that of the moth population
after ca 60 months, and the decline of both species probably resulted from increasing scarcity of suitable breeding sites.
Both populations exhibited seasonal variation in density with minima in late summer and early fall, following periods of adversely
high temperatures in the storage shed. The populations increased during the fall, leveled off or declined slightly during
the winter months, and then increased to maximum levels in late spring or early summer. It thus appears that high temperatures
had a greater adverse effect on the populations than low temperatures. The grain moth and the maize weevil both tended to
be randomly dispersed at low population levels and moderately aggregated at intermediate and high levels, although the degree
of aggregation was not correlated with population density when low population levels were considered separately, and the maize
weevil showed a greater tendency for aggregation than did the grain moth. Analysis of individual samples at fixed points in
time showed a conspicuous bias for negative correlation between numbers of the two species within sampling quadrats, suggesting
a tendency for the two species to segregate within the grain mass. This process could have resulted from behavioral differences
or from the destruction of one species by the other. Competitive displacement of the grain moth by the maize weevil has been
demonstrated in laboratory experiments but has rarely been observed under natural conditions, and in our study the two species
coexisted for 8 years in a relatively small grain bulk. |
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