Monday, April 2, 2018

BacterioFiles 334 - Measuring Mycelial Moth Muncher Management

Gypsy moth caterpillar
By CharlesC, CC BY-SA 4.0
This episode: Figuring out the best way to study the spread of a fungus that kills an invasive tree-eating caterpillar pest!

Download Episode (8.2 MB, 8.9 minutes)

Show notes:
Microbe of the episode: Pasteurella aerogenes

News item

Journal Paper:
Bittner TD, Hajek AE, Liebhold AM, Thistle H. 2017. Modification of a Pollen Trap Design To Capture Airborne Conidia of Entomophaga maimaiga and Detection of Conidia by Quantitative PCR. Appl Environ Microbiol 83:e00724-17.

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    Episode outline:
    • Background: Invasive species can be incredibly harmful, no matter what size
      • Kudzu in US south
      • Rabbits in Australia
      • Aedes albopictus mosquito all over the place
    • Whenever they can get plenty of resources
      • And lack of predators or disease
    • Another problem species in US is gypsy moth, Lymantria dispar
      • Introduced from Europe long time ago
      • Caterpillars eat tree leaves, create bags of webbing
      • Can defoliate whole trees and kill them
      • Many different trees affected: oaks, birch, willow, etc
      • Sometimes called “bagworms”, can get so abundant almost dripping from trees
    • Top 5 costliest invasive insects in world, $3.2 billion yearly in US
      • How to control? Could try introducing biocontrol
        • Disease or predators
        • Doesn't always work, like myxoma virus in Australian rabbits
        • Parasitoids tried, also fungus called Entomophaga maimaiga from Japan
    • What’s new: Now, scientists publishing in Applied and Environmental Microbiology have looked at how this fungus spreads through the air to infect and kill these invasive insects!
    • Methods: Set up sampling near fields with known infected caterpillars
    • Tested different ways of sampling to see which was best
    • Just flat pieces of plastic
      • Fungus DNA detected in 15/22 samples
      • But didn’t last too long; DNA signal had decreased after 2 days, gone by 7
      • Dry surfaces don’t maintain well
    • So set up another type: wet traps modified from kind used for pollen
      • Like jar with cup in bottom, topped by lid like lampshade (sloped) with screened opening
      • Worked better
    • So detected fungal DNA in PA through June
      • Peak at mid-June; no more larvae after June
      • Less fungus farther from defoliation; limit to spread
      • But spread can be up to ~40 miles (64 km)
        • Most 6-12miles, ~10-20 km, 
      • Killed up to 86% of caterpillars around, but often not that much
    • Applications and implications: Better understand fungal spread
      • Predict how bad caterpillars will be in a given year
      • Then modify pesticide spraying programs as needed
    • One spore can make 1 million more from caterpillar
      • Could try to help more spread
    • Fungus seems spreading at same rate as caterpillars are, but 3 years lag
    • What do I think: Not clear why DNA didn’t last long on dry surface
      • Could be degrading, or getting washed off by rain, or fungus launching more spores
      • Wet traps work better
    • Overall biocontrol doesn’t seem super-effective, but better than nothing
      • If too effective, resistance probably develop quickly
      • This way can limit spread somewhat and use other methods of control in addition
      • Resistance less likely
    • Important that it is specific to these caterpillars, not likely to get out of control
    • Still a long way from solving problem of invasive species


    1. You mentioned the gypsy moth being on the top 5 costliest invasive species. Are the kudzu, rabbits, and mosquitos in the top 5 as well or are they just some of the more known invasive species?

      1. The gypsy moth is in the top 5 insects globally. Not sure where it places among all categories of invasive species though, or where those other species place.

        The other 4 costly invasive insects, depending on who is counting, are:
        Plutella xylostella, the diamondback or cabbage moth, that feeds on cruciferous crops such as cabbage, broccoli, etc;
        Tetropium fuscum, brown spruce longhorn beetle, that kills pine trees;
        Anoplophora glabripennis, the Asian long-horned beetle, that kills different kinds of trees;
        and Haemotobia irritans, the horn fly, that bites and drinks blood mainly from cattle, irritating them and reducing milk production.
        From here: