Shifts in dynamic regime of an invasive lady beetle are linked to the invasion and insecticidal management of its prey

Abstract

The spread and impact of invasive species may vary over time in relation to changes in the species itself, the biological community of which it is part, or external controls on the system. We investigate whether there have been changes in dynamic regimes over the last 20 years of two invasive species in the midwestern United States, the multicolored Asian lady beetle Harmonia axyridis and the soybean aphid Aphis glycines. We show by model selection that after its 1993 invasion into the American Midwest, the year-to-year population dynamics of H. axyridis were initially governed by a logistic rule supporting gradual rise to a stable carrying capacity. After invasion of the soybean aphid in 2000, food resources at the landscape level became abundant, supporting a higher year-to-year growth rate and a higher but unstable carrying capacity, with two-year cycles in both aphid and lady beetle abundance as a consequence. During 2005-2007, farmers in the Midwest progressively increased their use of insecticides for managing A. glycines, combining prophylactic seed treatment with curative spraying based on thresholds. This human intervention dramatically reduced the soybean aphid as a major food resource for H. axyridis at landscape level and corresponded to a reverse shift towards the original logistic rule for year-to-year dynamics. Thus, we document a short episode of major predator-prey fluctuations in an important agricultural system resulting from two biological invasions that were apparently damped by widespread insecticide use. Recent advances in development of plant resistance to A. glycines in soybeans may mitigate the need for pesticidal control and achieve the same stabilization of pest and predator populations at lower cost and environmental burden.

The harlequin ladybird, Harmonia axyridis: global perspectives on invasion history and ecology

“…Coleomegilla maculata (DeGeer) (Coccinellidae) (Bahlai et al 2015). However, this last study also 266 noted that declines of several species reported previously from the same site (Colunga-Garcia, Gage 267 1998) appear to have stabilized or reversed, having become statistically undetectable (Bahlai et al 268 2015).…”

Rapid spread of Harmonia axyridis in Chile and its effects on local coccinellid biodiversity

“…In this year, native species tended to increase in abundance to values similar to those in 2010 and 2011. Similar trends have been observed in Michigan where previous reports of declines of several species of native coccinellids are no longer observed (Bahlai et al ., ). Long‐term monitoring is critical to derive robust distribution and population trends for coccinellids, and this in turn will enable assessment of when the loss of biodiversity in coccinellid assemblages may have serious consequences for biological control.…”

Assessing the value and pest management window provided by neonicotinoid seed treatments for management of soybean aphid (Aphis glycines Matsumura) in the Upper Midwestern United States

“…A previous study, analyzing data from the initial phase of soybean aphid colonization of North America, found that high‐aphid and low‐aphid years often alternated, resulting in an approximately even chance that a given year will be a high‐aphid year. Since the initial invasion, a combination of increased insecticide applications and predation by the predacious ladybird beetle Harmonia axyridis have resulted in a loss of this trend . In fact, correlative data analysis by Bahlai et al .…”