A fungus infecting goldenrod soldier beetles can alter their behaviour before death and cause changes to their bodies afterwards. Researchers investigating Eryniopsis lampyridarum found infected Chauliognathus pensylvanicus beetles clamped their mandibles tightly onto flower heads shortly before dying. Between 15 and 22 hours after death, the fungus caused the beetles to raise their hardened forewings and expand their hind wings, with these changes occurring mainly between midnight and 7 am. The researchers recorded infected beetles on frost aster, common boneset and Canada goldenrod during investigations in Arkansas. In one 1996 collection of 446 beetles, 90 were infected, producing an overall prevalence of 20.2%. The study found that infected beetles developed either conidia or resting spores, but not both. The researchers said the positioning of infected beetles on flowers may increase opportunities for fungal spores to reach other hosts, although the mechanism behind the pre-death gripping behaviour remains unknown.
How does the fungus turn beetles into zombies
According to the study published ScienceDirect titled ‘Zombie soldier beetles: Epizootics in the goldenrod soldier beetle, Chauliognathus pensylvanicus (Coleoptera: Cantharidae) caused by Eryniopsis lampyridarum (Entomophthoromycotina: Entomophthoraceae)’, infected beetles displayed a striking behaviour shortly before death. They tightly clamped their mandibles into flower heads, firmly attaching themselves to plants. Such behaviour, also seen in other fungal infections, may help fungal spores reach new hosts. Goldenrod soldier beetles normally feed on pollen from Asteraceae plants and gather on flowers for mating.Researchers found infected beetles attached to frost aster, common boneset and Canada goldenrod. At the University of Arkansas Experiment Station, large numbers of dead beetles were found attached to frost aster flowers on 3 October 1996, with fungal structures covering their abdomens. Similar outbreaks occurred in Washington County, Arkansas, between 25 September and 19 October in four different years.
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Why do zombie beetles raise their wings after death
The fungal effects continued after the beetles had died. Researchers observed the insects periodically for 24 hours after death and recorded changes in their bodies. About 15 to 22 hours after the beetles died, usually between midnight and 7 am, the fungus caused the dead insects to raise their elytra, the hardened forewings found in beetles, and expand their metathoracic wings. These changes occurred after death rather than before it. The researchers specifically noted that the mechanism responsible for the beetles’ flowers before death remained unknown.The position of the dead beetles on flowers is relevant to fungal transmission because the fungus produces spores from the infected host. The study’s introduction explains that some fungal pathogens alter host behaviour so infected insects remain in locations where spores have a greater chance of contacting other hosts. In E. lampyridarum, the beetles died while firmly attached to flower heads, with their bodies positioned on the plants where the fungus could develop and produce its reproductive structures. The researchers described the study as providing the first detailed information on the plants associated with infected beetles and the first detailed observations of the fungus’s resting spores.
Why does the fungus appear in autumn
Infections mainly occur during the autumn, when adult goldenrod soldier beetles are present on flowering plants. The researchers reported fungal outbreaks in Arkansas between late September and October across several study years. Because the beetles are univoltine, meaning they have one generation each year, the timing of infection occurs during the adult stage of their annual life cycle. Adults feed on pollen-producing plants, while their larval stages have been reported to prey on ticks and on eggs and larvae of tiger beetles.The researchers did not establish a direct mechanism showing that the fungus specifically infects the next beetle generation. However, they documented several features relevant to transmission: infected adults attach to flowers before death, fungal structures develop on the dead insects, and outbreaks occur in the autumn period when adult beetles are found on flowering plants. The study concluded that the interaction provides information on fungal prevalence, beetle-plant associations and the effects of the fungus on its host. It also recorded the production of both conidia and resting spores, providing evidence of different fungal stages within infected beetles.
