Abstract
The ectoparasitic fungusHesperomyces virescensThaxter (Ascomycota: Laboulbeniales) commonly infects the invasive lady beetleHarmonia axyridis(Pallas) and several other aphidophagous lady beetles in North America and Europe. We tested the hypothesis that bodily contact between adults of different lady beetle species supports horizontal transmission ofH. virescens. We used laboratory assays to determine whetherH. axyridisorOlla v-nigrum(Mulsant) harboringH. virescens(i.e., source beetles) transmit the fungus to noninfected target beetlesH. axyridis,O. v-nigrum,Coccinella septempunctataL.,Coleomegilla maculata(De Geer), orHippodamia convergensGuerin-Meneville. Results indicate that intraspecific transmission (i.e., for the source beetlesH. axyridisandO. v-nigrum) was common but interspecific transmission (i.e., from sourceH. axyridisorO. v-nigrumto target species) was low. Interspecific transmission occurred at low rates fromH. axyridisto bothC. septempunctataandO. v-nigrumand fromO. v-nigrumto bothC. septempunctataandH. convergens. Based upon our laboratory assays of forced pairings/groupings of source and target beetles, we predict that horizontal transmission ofH. virescensbetween species of aphidophagous coccinellids is possible but likely rare.
Highlights
Laboulbeniales (Ascomycota) are ectoparasitic fungi and most 2,000 described species are obligate parasites that grow on the integument of living arthropods, mostly insects, and usually on the adult stage [1, 2]
When H. axyridis was the source, the only target species found with mature thalli was H. axyridis, and the proportion of infected beetles was significantly higher than no infection observed for C. maculata or O. v-nigrum (χ02.05,2 = 10.59; P = 0.0050) (Table 1)
From the January 2010 trial when source H. axyridis had different thalli density, 25, 50, and 25% of the newly infected target beetles had been housed with source beetles rated with low, moderate, and high thalli densities, respectively
Summary
Laboulbeniales (Ascomycota) are ectoparasitic fungi and most 2,000 described species are obligate parasites that grow on the integument of living arthropods, mostly insects, and usually on the adult stage [1, 2]. Within the ten insect orders that contain host species, about 80% of these parasitic fungi are on beetles (Coleoptera) [2]. Four species of Hesperomyces (H. chilomenis, H. coccinelloides, H. hyperaspidis, and H. virescens) attack entomophagous Coccinellidae [1, 3, 4]. Of these species, H. virescens Thaxter infects more coccinellid species than the other three species [4]. Negative impacts of parasitism by H. virescens on lady beetle populations are not well defined, but Kamburov et al [5] found that infected Chilocorus bipustulatus L. adults suffered premature mortality
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