Bean leaf beetle: Dispersion and dispersal

The bean leaf beetle is common throughout the northcentral United States and has been recorded from Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, Ohio, South Dakota, Wisconsin, and the Canadian provinces of Manitoba and Ontario (Riley et al. 2003).

Bean leaf beetle dispersion: Bean leaf beetle dispersion pattern from two fields from two years across four dates [(after Krell (1999)]. This figure describes the changing patterns of beetles across fields of soybean as the growing season progresses. The numbers in parenthesis beneatBean leaf beetle dispersion: Bean leaf beetle dispersion pattern from two fields from two years across four dates [from Krell (1999)]. The patterns describe the changing spatial dispersion of beetles across fields of soybean as the season progresses. The numbers in parenthesis beneath the dates are the range of average beetle abundance within that date and location. Light shading equals few beetles dark shading equals more beetles.

On average, these beetles have the physiological capacity for flying short distances < 167 ft (Krell et al. 2003) and populations at the field scale are highly aggregated (Kogan et al. 1974, Boiteau et al. 1979, Smelser and Pedigo 1992c). The spatial relationship between the first and second generations are highly correlated to each other with the second generation showing the greatest aggregation pattern in soybean fields (Krell 1999).

Dispersion patterns and flight potential of bean leaf beetles are both related and relevant for understanding how these beetles affect soybean. They are related because short flights within each generation increase the likelihood of establishing aggregated populations. Because bean leaf beetles generally fly short distances and establish aggregated populations within fields there is potential for site-specific management (Krell 1999). Additionally, if this same pattern and flight potential is true regardless of population size, local beetle populations should be predictable from year to year. Lastly, short flights and highly aggregated populations should result in very localized infections of diseases that might be transmitted by bean leaf beetles (e.g., Bean pod mottle virus). However, it is unknown if the very large populations in recent years follow these same patterns in dispersal and dispersion. The distribution of some organisms tend to have random or uniform dispersion patterns as population abundance increases. If this were true for bean leaf beetles it may help explain the outbreak potential for Bean pod mottle virus in Iowa.