Parasitylenchus bifurcatus n. sp. Tylenchida: Allantonematidae parasitizing Harmonia axyridis Coleoptera: CoccinellidaeReport as inadecuate

Parasitylenchus bifurcatus n. sp. Tylenchida: Allantonematidae parasitizing Harmonia axyridis Coleoptera: Coccinellidae - Download this document for free, or read online. Document in PDF available to download.

Parasites and Vectors

, 5:218

First Online: 01 October 2012Received: 20 September 2012Accepted: 26 September 2012


BackgroundThe harlequin ladybird, Harmonia axyridis Pallas Coleoptera: Coccinellidae is native to central and eastern Asia and was purposely introduced into Europe to control aphids. While it proved to be a good biological control agent, its rapid spread and buildup of large populations made it a nuisance, since it overwinters in homes, emits unpleasant odors, stains fabrics, occasionally bites humans and feeds on apples, pears and grapes. Aside from the above, the ravenous appetite of H. axyridis results in their consumption of harmless native insects, including even other ladybird beetles. A study of the natural enemies of H. axyridis in Denmark revealed the presence of nematodes. The present study describes this nematode parasite and discusses aspects of its development and ecology.

MethodsAdult harlequin ladybird beetles were collected from March to November from four localities in Copenhagen on different plant species. In addition, groups of last-instar larvae and pupae n = 50 were examined for the presence of nematodes. Living and recently dead nematodes were removed from adult H. axyridis in 0.5% saline solution, the nematodes were then heat killed at 75C, fixed in 5% formalin and transferred to glycerin on slides for further examination and measurements.

ResultsA new species of Allantonematidae Tylenchida, Parasitylenchus bifurcatus n. sp., is described from adults of the harlequin ladybird, Harmonia axyridis in Denmark. The new species is characterized by a straight stylet lacking basal thickenings, a bursa and a forked tail tip in the vermiform infective females and juvenile males. The new species is compared with P. coccinellinae previously described from ladybird beetles in France. Parasitism resulted in depletion of the fat body and partial or complete atrophy of the reproductive organs of the beetles. Infections occurred throughout the year with rates of parasitism reaching up to 35%. The rate increased to 60% when field-collected ladybirds were incubated for 30 days in the laboratory.

ConclusionsThe production of subsequent generations within the host with only the fertilized females not the males leaving the hosts and the absence of parasitism of the larvae and pupae is an impressive developmental modification of P. bifurcatus. It is proposed that the vermiform infective females pass from one adult host to another when the beetles are hibernating or in assemblage groups. Rates of parasitism show that P. bifurcatus could be a significant biological control agent of H. axyridis.

KeywordsCoccinellidae Parasitic nematodes Allantonematidae Ladybird beetles Multicolored lady beetle Electronic supplementary materialThe online version of this article doi:10.1186-1756-3305-5-218 contains supplementary material, which is available to authorized users.

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Author: George O PoinarJr - Tove Steenberg


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