Abstract
To determine the causes of the variation in the seasonal dynamics of Harmonia axyridis (Pallas) in Central Europe, numbers of adults and larvae of this invasive species were recorded on trees (Acer, Betula, Tilia) throughout the growing seasons from 2011 to 2016. Each year beetles were collected every two weeks, using a standardized sweeping method. The seasonal dynamics was expressed as plots of abundance (number of individuals per 100 sweeps) against time (Julian day) and these plots (seasonal profiles) were compared in terms of their size (area under the seasonal profile curve), range, timing and height of the mode (maximum abundance). Timing and size of seasonal profiles varied among hostplants, years and sites. Abundance of larvae paralleled aphid occurrence and peak abundance of adults followed that of larvae 10 to 20 days later. Population dynamics before and after the peak were determined by dispersal. Adults arrived at sites before the start of aphid population growth and persisted there long after aphid populations collapsed. The abundance of H. axyridis decreased from 2011 to 2013 and then increased, achieving the previous levels recorded in 2015 and 2016. The variation in seasonal profiles revealed that H. axyridis, in terms of its response to environmental conditions, is a plastic species and this flexibility is an important factor in its invasive success.
Highlights
Harmonia axyridis (Pallas) is an invasive ladybeetle (Coleoptera: Coccinellidae) that arrived in the Czech Republic in 2006 (Sprynar, 2008)
This study summarizes six years of records of the abundance of larvae and adults of H. axyridis on different species of trees in a suburban area
We address the seasonal variation in abundance of larvae and adults of H. axyridis on particular trees and analyze the relationship of this species with site, hostplant and aphid abundance
Summary
Harmonia axyridis (Pallas) is an invasive ladybeetle (Coleoptera: Coccinellidae) that arrived in the Czech Republic in 2006 (Sprynar, 2008). Between 2007 and 2009, H. axyridis became a dominant species (Nedved, 2014), at times making up more than 90% of the adult ladybird species in coccinellid communities (Honek et al, 2015). Within Europe, H. axyridis dominates coccinellid communities on trees (Honek et al, 2015) and at times in stands of wild herbaceous plants and maize, while it is rare in other crops (Vandereycken et al, 2013; Honek et al, 2014). Adult Harmonia axyridis leaves hibernacula in April, reproduces from early May until mid-September and during this period produces up to three generations (Honek et al, 2018a). Females lay their eggs from midMay until mid-September, not all of the females exploiting abundant prey populations are capable of laying eggs (Honek et al, 2018a). Scattering eggs among many plants (Osawa, 2011), laying small batches of eggs (Honek et al, 2018a), high dispersal capacity (Osawa, 2000) and weak tendency to enter dormancy (Reznik & Vaghina, 2013; Reznik et al, 2017) are characteristics that support suc-
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