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Manitoba Agriculture, Food and Rural Initiatives

Manitoba Insect Update

June 29, 2009                   

Compiled by: John Gavloski, Entomologist, Manitoba Agriculture, Food and Rural Initiatives, Crops Knowledge Centre,
Phone: 204-745-5668; Fax: 204-745-5690

To report observations of insect activity or control that may be of interest or importance to others in Manitoba, please send messages to the above contact addresses.

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Summary

High populations of juvenile grasshoppers were noticed in some areas. There is still some cutworm activity, although reports of high populations are fewer.

Recent Insect Concerns and Observations

Cutworms: Some cutworms and cutworm feeding damage is still being noticed, but we are getting out of the period when cutworm feeding is most severe. Most of our damaging species of cutworms go into pupae or resting stages this time of year, so they will cease feeding on plants. As well, the crops are getting to a stage where they are less susceptible to cutworms. The picture below shows 2 redbacked cutworm pupae and a larva. Once the pupa stage has been reached they will no longer be a threat to crops this year, and control becomes uneconomical once most larvae are fully grown.

 
Redbacked Cutworm Pupae and Larva  

Grasshoppers: High populations of grasshoppers were noticed around field edges in the Portage la Prairie area, and in fields in the Melita area.
Impact of heavy rain on young grasshoppers: One positive aspect to the heavy and at times intense rains we had last Friday and Saturday is that heavy rains can be harmful to grasshoppers that have recently hatched. While grasshopper eggs are very tolerant to waterlogged and even flooded conditions, the newly hatched young grasshoppers are not. After grasshoppers hatch they have few fat reserves, and must feed to build up these reserves. If these weaker grasshoppers are subjected to flooded or muddy conditions, they can be killed directly, become bloated, and are more susceptible to disease. So heavy rainfall just after hatching can have a big impact on grasshopper populations. Grasshopper eggs do not all hatch at the same time however, and hatch is occurring throughout much of June in Manitoba for those 3 or 4 species that potentially could be pests. Eggs that may still be unhatched would survive quite well, and older grasshoppers would be a less risk of being killed by the rain than those recently hatched. However, the hatch was late this year, and most of the grasshoppers we have been seeing recently were still quite small. So don’t assume that because certain fields or field edges seemed to have a lot of grasshoppers last week that the situation will still be the same. It may be worthwhile having another look at these areas again once they are accessible.

 

Surveys and Forecasts

Diamondback Moth Forecasting: Counts of diamondback moth continue to be generally low. However, counts have increased in the eastern part of Manitoba. Data and interpretations can be viewed at: https://www.gov.mb.ca/agriculture/crops/insects/db/index.html

I did notice some diamondback moth larvae on canola and volunteer crucifers at the University of Manitoba research farm near Carman last week, but only in very low numbers. So larvae are around, but at this point you have to look hard to find them, so they are far from being an economical problem.

Bertha Armyworm Forecasting: So far, counts from the traps for bertha armyworm are also very low. Data can be viewed at:
https://www.gov.mb.ca/agriculture/crops/insects/bertha/index.html

 

Insect Identification Quiz

The beetles below were found feeding on cruciferous vegetables in the Swan River area. They will feed on other crucifers as well, including canola. What are they?

 

This is red turnip beetle. Although they will feed on canola, they are rarely economical, and usually when they are there is a heavy edge effect. They overwinter as eggs, and emerge early in the year as larvae. The adults, which you see in this photo, feed for 2 or 3 weeks after emerging. Then go into a resting and nonfeeding phase for several weeks before reappearing later in the summer. Only feeding to seedling plants is likely to be a concern, and as mentioned economical problems are not common.