Fifty Shades of the Harlequin Ladybird and a Sexually Transmitted Fungus

Abstract

The ectoparasitic fungus Hesperomyces virescens was studied on its invasive host, the harlequin ladybird Harmonia axyridis, in the Czech Republic. A primary aim was to examine the relationship between fungal infection and elytral coloration of the ladybird. Furthermore, the role of host sex and mating status of females were analyzed. Beetles (n = 1,102) were sampled during autumn migration, and then sexed, weighed, and screened for infection. Females were dissected for detection of sperm in their spermathecae. Ladybirds were sorted according to color form and absorbance spectrophotometry was used to quantify carotenoid contents in their elytra. In individuals of the nonmelanic succinea form, the degree of melanization was measured using digital photographs and putative age groups were estimated based on background color of elytra. Sexual differences in infection patterns indicated transmission during copulation: males were infected mostly on elytra and venter, and females had infection almost exclusively on elytra. Mated females had higher infection rate than virgins. There was no influence of genetic color form on the fungal infection. Putative age groups (visual sorting to yellow, orange, and red) correlated with fungal infection. Infected individuals had elevated elytral carotenoid levels in comparison to uninfected individuals, which could be explained by host age. Infection-free succinea beetles were extensively melanized because they emerged later in the season at lower temperatures which induced melanization. Overall, we highlight that H. axyridis is a multivoltine species whose age, if not taken into account in ecophysiological studies, might present a considerable confounding factor.

Fungal ectoparasites increase winter mortality of ladybird hosts despite limited effects on their immune system

“…In addition, we distinguished between potential mechanisms responsible for increased winter mortality of infected ladybirds. As ladybird age was a poor predictor of ladybird winter survival in our study, we ruled out the possibility that increased winter mortality simply results from ladybird senescence, which can correlate with infection probability in nature [29]. It should be noted that, during the growing season, He .…”

“…virescens infection mainly spreads as a consequence of ladybird mating activity, and during winter, the parasite transmission can be enhanced by the host-aggregating behaviour; thus, infection probability increases with age in promiscuous species such as Ha. axyridis [23,27,29,31]. The small effects of He .…”

“…For the following experiment, only the uninfected and heavily infected individuals were used. Prior to the start of the overwintering experiment, approximate age based on elytral coloration (yellow and pale orange = young, red = old; [29]), sex and pre-overwintering live body mass were determined for all ladybirds. Each ladybird was placed in a separate Petri dish with a watered cotton ball to preclude ladybird desiccation during the winter.…”

“…However, female ladybirds are typically infected on their elytra and males ventrally on their abdomen during the growing season, which corresponds well to the transmission of He. virescens during ladybird mating [29]. During the winter period, both males and females are frequently infected on other body parts, indicating transmission of ascospores in Ha.…”

Intraspecific and Interspecific Comparison of Toxicity of Ladybirds (Coleoptera: Coccinellidae) With Contrasting Colouration

“…However, there was no relationship between alkaloid content and either elytra redness or carotenoid pigment concentration in either sex of eld collected H. axyridis [45]. Younger orange individuals had higher number of body zones with thalli of the parasitic fungus H. virescens than red individuals [40], but older red individuals were not protected against H. virescens [47]. We suggest that some inconsistency between various studies regarding the relationship between age and toxicity can be ascribed to differences between laboratory reared and eld collected ladybirds, although Arenas et al [19] report indistinguishable toxicity of bought and wild-caught individuals of A. bipunctata.…”