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Issues Regarding Release of Exotic Beneficial Insects

QUESTION: What are some of the issues and concerns regarding the release of exotic predators, such as Harmonia axyridis, the Asian Ladybird?

See Tom Bellows’ work on native ladybug research. Riverside, CA

See Peter Karieva’s writings on the invasion of ladybugs. Univ. of Wash, Seattle, WA

Read Newsweek, Aug 1998 issue, titled "Aliens Invade America!"

What is Harmonia’s potential to spread and what indirect effects might arise if it is mass-released? Harmonia has a wide host range on conifers, vegetables, and weed pests. Harmonia is a voracious, omnivorous predator on soft-bodied pests including aphids, adelegids, whiteflies, thrips, and scales. This ladybird could be a tremendous benefit in reducing pest populations in greenhouses, nurseries, and in the field.

Typically, it is difficult to measure impact of an introduced species on native populations. To my knowledge there are no quantitative data or supportive evidence from before or presently showing direct impact of Harmonia on the abundance of native Coccinellid species. Peter Karieva, Univ. of Washington, reported greater ‘success’ and a higher abundance of Harmonia compared to native species, but could not measure their impact or see any fundamental differences in the Asian ladybug from the natives.

We must evaluate if releases of Harmonia, an exotic ladybug, may decrease the biodiversity and density of other native Coccinellid species. Could Harmonia contribute to the decline in the quality of life of the native species by competing for space or food? And the exotic may have aggressive foraging behaviors and intraguild predation. Many aliens have been known to threaten the very existence of the native species. However many initial impacts could in time be reversed.

One of the most important questions for "invasion ecology" is measuring the impact of releasing a generalist predator with a broad host range. (And it should be noted that many of the ladybug natives are generalist feeders also.) It is important to document current population levels and potential future negative impacts of exotic predator releases on natives. Will Harmonia displace native species or will populations fluctuate with seasons and cycles and the species balance out?

It is believed that the number of native Coccinellid species have not necessarily decreased per unit area, but perhaps Harmonia numbers are higher at different times of the year. Harmonia does not migrate to the mountains like other species, it remains in the valley. Possibly, is has a jump start in the spring.

Harmonia was introduced and released in large numbers in the early 90’s by USDA-APHIS and now this ladybird appears well-established and naturalized in the Willamette Valley.

What are the consequences if Harmonia is mass produced and released again? Presently, other ladybugs are taken from their wintering habitat and stored in refrigerators and sold to the public in the spring and released in random places all over the United States. Is this displacement sending the system off balance?

Can we assume that native ladybirds have declined due to the invasion of exotics? Other confounding factors that reduce populations might include plant succession, heavy pesticide use, and removal of native ladybirds from wintering sites. All these factors must be taken into consideration.

Insecta LogoCopyright 1998 Amy J. Dreves, Entomologist: Researcher, Consultant, and Educator (
All rights reserved.

Created: August 25, 1998
Last Modified: August 26, 1998

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