I live in central Pennsylvania and gypsy moth caterpillars have been very evident this summer. Today I noticed numerous caterpillars on the trunks of our many oaks. When I went to collect them I discovered that many were desiccated, some broke in two when I touched them, and others literally exploded when touched. We are in a suburban area and I am sure that no spraying has occurred. Any idea what could cause this welcome development?
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There should be parasitoids enjoying vast numbers of caterpillars!
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They have likely been killed by Entomophaga maimaga fungus, one of the introduced control agents for gypsy moths: https://www.canr.msu.edu/ipm/Invasive_species/Gypsy-Moth/virus-and-fungus-disease-cause
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Likely some sort of disease/parasite mix. As moth/caterpillar populations increase, so do the parasitoids and pathogens. When the population crashes from that, the cycle starts over again as the parasitoids/pathogens have no host, so then they die off. With most moths, it is about a 7 year cycle. BTW, the exploding ones were likely caused by a virus! The larvae turn into bags of black goo.
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I used to work in the Tuscarora State Forest in south-central Pennsylvania. Gypsy moths there were infected with a polyhedrosis virus (https://en.wikipedia.org/wiki/Lymantria_dispar_multicapsid_nuclear_polyhedrosis_virus). It was quite dramatic as the population munched its way toward final instars but then the caterpillars would hang themselves onto tree trunks, liquefy, collapse into a V shape and then dry into powder. Biocontrol at its finest!
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wow so cool! I remember seeing hundreds of those V shaped carcasses on the (outside) walls of a place I was staying a few years ago—I had assumed they’d sprayed something beforehand. not sure how I never was aware of this
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Great information. Thanks much.
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