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On the trail of the lily beetle invasion

6/27/2013

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The first lily leaf beetle recorded in North America was observed in Montreal in 1943.  It wasn’t until about 40 years later that the beetle started appearing elsewhere in North America, and since then, its spread has been rapid. In the US, it is now found in New York, New Jersey and all six New England states, as well as in the state of Washington on the west coast.  In Canada, it has been recorded in every province except Saskatchewan and Newfoundland (update July 13, 2016: it is now found in both these provinces).

Did the lily beetle spread throughout its current range from its established base in Montreal?  Or were multiple introductions from Europe responsible for the beetle’s present distribution?  And where exactly in Europe did the North American populations originate from?

These are the questions that University of Montreal student Alessandro Dieni is addressing as his Master’s research topic. With the help of collaborators, Alessandro has obtained samples from throughout the North American and European ranges.  Using a technique called AFLP (Amplified fragment length polymorphism), he will be able to detect differences and similarities among the populations.  His preliminary results suggest that the populations from Montreal and Quebec City form one genetically similar group, distinct from the New Brunswick samples, pointing to the possibility of more than one invasion.  Still to be determined is the European origin of the invasion, as the North American populations are quite distinct genetically from the Swedish and Swiss beetles he has analyzed.   

Understanding invasion routes can help us pinpoint hotspots from which invaders tend to originate.  These areas can then be targeted for increased surveillance of imported goods.  Studies such as Alessandro’s can also provide valuable information to aide biological control efforts.  Biocontrol agents imported from an invader’s region of origin share a coevolutionary history with the invader, and are expected to be better suited to attack their host. 

We’ll look forward to hearing about the results of this important study!

This post is based on Alessandro’s essay published in Antennae, the Bulletin of the Quebec Entomological Society (Bulletin de la Société d’entomologie du Québec, 2013, vol. 20, no. 2, pp 3-6), which, in turn, was based on his poster, which won the Prix Melville-Duporte for the best scientific poster at the Society’s annual meeting.


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Lily Beetle numbers down in eastern Ontario this year

6/18/2013

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I've been getting reports from gardeners throughout eastern Ontario that lily beetle numbers appear to be down this year compared to last year.  In Ottawa, many gardens that were hit hard in previous years have had very few adults this year.  It would be nice to be able to say that this was a result of successful biological control, but there simply hasn't been enough time for the wasp Tetrastichus setifer to have spread throughout the region since its release in 2010.  Here's my hypothesis: the severe drought we had last summer affected larval or pupal survival.  I've noticed that the larvae have a hard time forming a cocoon out of soil particles when the soil is too dry.

Reports of low numbers in Massachusetts (and possibly Connecticut?) are likely due to the spread of the biocontrol agents from the release sites.  

Reports from Manitoba and from the Maritime Provinces indicate that lily beetle populations are going strong in those areas.

Write and let us know whether your beetle infestation seems more or less severe this year compared with previous years!
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Biological control agents at work

6/2/2013

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Picture
Our biological control agent, Tetrastichus setifer, is emerging in the lab from cocoons sent to us from Switzerland.  The females will happily parasitize larvae in Petri dishes and small cages.  They don't seem to mind having to lay an egg through all that poop. In fact, they appear to have trouble finding their host if the fecal shield has been removed!


We are letting the wasps do their work in the lab, instead of releasing them into the field. Larvae naturally occurring in our experimental garden will be collected every week to see if they are parasitized by wasps that have successfully overwintered. That way, we will know if our population from our 2010 release is still going strong.  Some of the larvae parasitized in the lab, like the one in the picture, will be released into the garden when they are ready to form their cocoons, to bolster the population.  Others will be overwintered in the lab. Our goal is to have a big enough population in a couple of years to support releases at other sites.

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    Naomi Cappuccino was a member of the Department of Biology at Carleton University in Ottawa, Ontario, Canada. She is now retired and no longer updating this site.

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