Abstract
Aphidophagous coccinellids (ladybeetles) are important providers of herbivore suppression ecosystem services. In the last 30 years, the invasion of exotic coccinellid species, coupled with observed declines in native species, has led to considerable interest in the community dynamics and ecosystem function of this guild. Here we examined a 24-year dataset of coccinellid communities in nine habitats in southwestern Michigan for changes in community function in response to invasion. Specifically we analyzed their temporal population dynamics and species diversity, and we modeled the community’s potential to suppress pests. Abundance of coccinellids varied widely between 1989 and 2012 and became increasingly exotic-dominated. More than 71% of 57,813 adult coccinellids captured over the 24-year study were exotic species. Shannon diversity increased slightly over time, but herbivore suppression potential of the community remained roughly constant over the course of the study. However, both Shannon diversity and herbivore suppression potential due to native species declined over time in all habitats. The relationship between Shannon diversity and herbivore suppression potential varied with habitat type: a positive relationship in forest and perennial habitats, but was uncorrelated in annual habitats. This trend may have been because annual habitats were dominated by a few, highly voracious exotic species. Our results indicated that although the composition of the coccinellid community in southwestern Michigan has changed dramatically in the past several decades, its function has remained relatively unchanged in both agricultural and natural habitats. While this is encouraging from the perspective of pest management, it should be noted that losses of one of the dominant exotic coccinellids could result in a rapid decline in pest suppression services if the remaining community is unable to respond.
Highlights
Aphidophagous coccinellids are a well-studied group of insects [1,2]
Prior to 1996, C. maculata was frequently observed to be co-dominant with C. septempunctata, but has declined in importance since, typically only representing greater than 20% of the captures in years when maize is planted at the site
Coccinellid community dynamics The pattern of long-term co-dominance between several species observed in this study is common in coccinellid communities the composition of the group of dominant species may vary with location and time [35]
Summary
Aphidophagous coccinellids (ladybeetles, order Coleoptera) are a well-studied group of insects [1,2]. Coccinellids are economically important for their ability to suppress pest herbivores, and their ubiquity and charismatic appearance has led to public interest in their conservation [1]. Over the last 30 years the addition of multiple exotic species to the North American coccinellid community, coupled with observed declines in native species, has led to renewed interest in the ecosystem function of this guild [2]. Aphidophagous coccinellids have been under systemic surveillance at the Long Term Ecological Research (LTER) site at Kellogg Biological Station since 1989. This community has been invaded four times in the last 28 years. Coccinella septempunctata, a European species [3], arrived in 1985; Harmonia axyridis, an Asian species [4], was first detected in 1994; Hippodamia variegata, a Eurasian species [5], was first captured in 1999; and Propylea quatuordecimpunctata, a European species [6], has been in the region since 2007
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