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Lily Beetle by Ian Wise

  

UPDATES 2021

 

This spring is shaping up like the past few years, in which the red lily beetle is, for most areas of Manitoba, noticeable by its absence. 

Our province is not unique as beetles also have been harder to find in previously infested spots in Canada. It obviously begs the question:  ‘What is happening’?  The best way to answer the question is to undertake an ecological study of the beetle in Canada, but that can take time (15-20 years or more) in a research environment dedicated to publication frequency.

What can be done at present is to make a reasonable estimate based on previous studies of insects with similar ecological histories.  Firstly, what is known is the red lily was introduced into Canada from Europe in the 1940’s, and did not begin to spread outside its original introduction site until humans facilitated it distribution on potted plants.  The beetle was suddenly deposited into environments, which had many similarities, but also subtle differences than its ancestral homeland of Eurasia.  These subtle differences often are infrequent climatic factors that can reduce an insect’s ability to reproduce at a level to maintain the species survival. The result is the insect can either slowly or quickly disappear. Insect species with a very narrow ecological niche, like the red lily beetle, are most susceptible. It is quite likely that the red lily beetle was introduced into the prairies on more than one occasion. The insect probably managed to get a foothold because climatic changes made it possible for the beetle to survive. But the prairies are continuing to undergo a rapid change, one that is not as obvious to humans as it is to the beetle; a change that has reduced its ability to reproduce at a level needed for the species survival. If I had to make a guess, it is the reduction in snowfall coupled with early springs that has caused overwintering sites of the adults to warm up earlier more frequently. This results in the adults emerging too quickly relative to the emergence of lilies. The subsequent lack of sufficient food resources lessens the ability of females to buildup sufficient fat reserves needed to optimize egg production. Insects are masters of evolutionary adaptation to counteract climatic change.  But it is a slow process and it is utterly impossible to apply in today’s rapidly changing environment.
Does this spell the end of the beetle in the prairies? That is not a guarantee because continued climatic changes in the future may tip the balance back in favour of its survival.

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The research program on the lily beetle during 2020 was hampered by a continued scarcity of beetles at the research sites and in areas where beetles had been collected in past years.
In the two sites where the parasitic wasp has been released beetle populations have yet to recover. Unfortunately, it is diffi-cult to determine if the lack of beetles at these sites is caused by the parasitic wasp or because of the same factors that have eliminated beetles elsewhere.
What will be done in 2021 is continued to monitoring of these sites, and, possibly, introduction of the parasitic wasps at sites where beetles have re-established. A third research site has set up a which we hope to provision with beetles collected from areas where the beetle is at densities insufficient to support the establishment of the wasp.
I request that all MRLS members contact me once they find adults so I can immediately add them to the research sites. COVID could undoubtedly impact the research program, particularly if the availability of the parasite is affected by the con-tinued lockdown of Concordia U.
 

UPDATE 2020

The primary objective this year is to distribute the parasitic wasp, Tetrastichus setifer, of the lily beetle into as many sites with suitable lily beetle populations to measure the ability of the parasite to migrate from these sites.  Beetles where the parasite has been added need to be allowed to complete their development, so damage to the lilies will occur. 

The past two years have seen unexpectedly lower beetle populations than in previous years.  It is not known why populations have not remained higher, but is likely being caused by the beetle continuing to adapt to environmental changes.  Western Canada is the most northerly climate the beetle inhabits in its world distribution so changes in the weather patterns can greatly influence its survival.

(Update 2019)

The scarlet lily leaf beetle Lilioceris lilii, was first found in Manitoba in Portage la Prairie in 1997, and spread to Winnipeg in 2004. It has most recently been found in Brandon. Its distribution is aided by the commercial movement of infested potted lily plants.

A parasitic wasp is being tested to determine if it can reduce the presence of the lily beetle. It was just found to be able to overwinter in Manitoba, which opens up the opportunity to disburse the wasp into areas infested by the beetle.

In the interim, lily growers are advised to control the beetle by observing areas where lilies grew the previous year, and then killing the beetles as they emerge. Remove any leaf litter once snow melts from these areas to hasten beetle emergence.

Larvae on plants can be controlled safely with spray applications of insecticides that contain pyrethrum. There are a number of products with pyrethrum that are available at Home and Garden shops. Use a sprayer that enables the spraying of the under surface of the leaves where the larvae feed. Direct spray contact of the larvae is needed for pyrethrum products to be effective.

 

Life Cycle of the Red Lily Beetle (Lilioceris lilli)

(With suggested Controls)

  • Over wintering adult beetles emerge in early spring from the surrounding soil to mate and lay 200 to 400 eggs on the underside of the leaves of the lily plant.

  1. Handpick the adult beetles (6-8 mm ¼ inch in length) as soon as they appear on the emerging lilies.
  2. Spray the adults with any pyrethrum based (0.5%) insecticide or any other registered pesticide. Rotenone may also be effective.
  3. Destroy the egg cases on the underside of the leaves.  Eggs are in yellow/orange clusters or in irregular rows. The eggs are quite small, approximately 1 mm.
  • Eggs usually hatch in about 7-10 days.

 Photo by: Paul Mabbott

  • Emerging larvae will begin feeding on the underside of the leaves and then move to the top. This stage lasts for about 16-24 days. They will cover themselves with their own feces to discourage predators.

 

  1. Remove the larvae.  Can be very messy.  Use rubber gloves.
  2. Dust or spray with Rotenone or any pyrethrum based pesticide at 5-7 day intervals.
  • Larvae drop to the ground and pupate for about 20-25 days.  Pupae cases are dark brown or black in color and very hard to find in the soil.
  • Emerging adults climb plants and feed until fall but do not normally mate or lay eggs until spring,
  1. Handpick the adult beetles.
  2. Spray the adults with any pyrethrum based (0.5%) insecticide or any other registered pesticide. Rotenone may also be effective.
  • Adults over winter in the surrounding soil or under plant debris.  Some adults may survive over two seasons.  Stir up the surrounding soil or the mulch in early spring and kill any emerging beetles before they have a chance to lay their eggs.


Note: The lily beetle has no known natural enemies in Canada. It is up to each gardener to check their lily plantings at least weekly for signs of the beetle. Because the beetles are strong fliers and can move around the neighborhood, inform your neighbors and help them to control this pest. The beetles have been reported  in most parts of Winnipeg as well in various provincial locations.

 

Note: All information in this article has been obtained from various sources on the Internet.  Use your own discretion in controlling beetles on your property and use only the methods with which you are comfortable with.  All organic or chemical pesticides should be handled as directed by the manufacturer.  There are no pesticides specifically registered for use on lily beetles in Canada.