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Challenges in Rearing Galerucella Beetles

July 13, 2011

Every project that involves live animals, live plants and the outdoors will have challenges, and our Galerucella rearing project is no exception. Here I’ll detail some of the challenges we came up against in rearing our beetles; hopefully others can gain from our experiences!

The first challenge was collecting the beetles; continuous poor weather in May meant collecting beetles was delayed until late May. The weather the day we collected was questionable, at best, but it was also the only day that entire week that wasn’t threatening thunderstorms.

Galerucella beetles are most active on sunny, warm days, and while our collecting day was warm, it was cloudy. The beetles had to be carefully hunted out, and there was ample evidence they had already begun breeding (both eggs and larvae were visible in the field). While this was excellent news for the release site, it raised concerns that we would have beetles totally finished laying eggs, meaning our releases in July or August would be scanty.

Thankfully, we were able to collect enough beetles to inoculate 18 plants, and they laid quite a few eggs which have hatched into quite a few larvae. I was lucky enough to get to work with the West Virginia Department of Agriculture on the beetle collecting, and was thankfully smart enough to trust their guidance that the weather was good enough for collection. Had I waited for a more favorable day I might have missed the egg-laying window for the beetles. Thank you, WVDA!

The cages were taped down with duct tape, but this proved unreliable during the incredibly wet spring we had. I found a few escaped beetles on the bare plants we left in each pool, and found a gap in the tape holding down a sleeve cage as the culprit. After returning the beetles to a different cage, I re-taped the sleeve cage, and added a rubber band seal to each pot (tying together several rubber bands to reach around the pot). This has worked well so far, but in the heat the rubber bands may snap. A higher-strength tape like Gorilla tape may be the answer to keeping the cages firmly affixed to the pots, or using a large zip-tie.

For a few of the smaller loosestrife plants, the beetles were a little too successful in laying eggs, as the larvae have nearly obliterated the plant and as a result started squeezing through even the no-see-um netting in search for new plants. My solution to this was to examine the cages daily to find escaped larvae, and transplanting them to a cage with a larger plant that can sustain more larvae; a little time consuming, but it meant that few if any larvae were lost and they could still be released into the field. Next time I may attempt to only use larger plants or larger root masses, or perhaps grow two plants per pot to increase the mass of the loosestrife available for the beetles.

While there have been a few challenges in raising the beetles, it has been fascinating and rewarding to watch them grow and demolish purple loosestrife. It will be worth the time spent raising them to see a large patch of loosestrife brought down to a manageable few plants a few years after the beetles are released!

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