Can the species and numbers of lady beetles within field crops be affected by the types of habitats that surround those fields? That was the question researchers sought to address in a two year study conducted in southwestern Michigan. To determine the answer, they sampled lady beetles using sticky traps in 62 acre2 blocks on the Kellogg Biological Station. Each of the three study areas contained a mixture of crops (corn, alfalfa, and wheat) and non-crop habitats (abandoned fields, and woodlots) in varying ratios.
In total, thirteen species of lady beetles were captured during the two seasons of weekly sampling. The seven-spotted lady beetle, Coccinella septempunctata, was the most abundant lady beetle in the study and was equally numerous in all sites. Coleomegilla maculata lengi was significantly more abundant in the site that contained a corn habitat, while three other species (Cycloneda munda, Chilocorus stigma, and Brachiacantha ursina) were more abundant in the site with a woodlot habitat. Overall, the presence of a deciduous woodlot significantly increased the number of species found in that site.
The researchers then examined the number of species of lady beetles in alfalfa, the one crop common to all sites. They found that even though aphids were present in alfalfa at each site, the site with the most diverse mixture of crop, woodlot and abandoned field habitats contained the greatest number of species and abundance of lady beetles. Increasing habitat diversity has previously been suggested as a means to enhance biological control of pests. This study supports part of that hypothesis--the number of predaceous lady beetles was greater in diverse habitats--but more study is needed to see if this will result in a lower frequency of pest outbreaks.
M. Colunga-Garcia, S. H. Gage and D. A. Landis. 1997. Response of an assemblage of Coccinellidae (Coleoptera) to a diverse agricultural landscape. Environ. Entomol. 26: 797-804.
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