Insect of the Week – Natural enemies of pea aphids

Meghan Vankosky

Week 10

Populations of pea aphids, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), can be kept below the economic threshold by their natural enemies if these are present early and in sufficient numbers. Natural enemies include parasitoids, predators, and diseases that reduce pest populations.

Predators of pea aphids include ladybird beetles (adults and larvae), syrphid fly larvae, and damsel bugs. These predators catch and eat pea aphids of all ages and sizes. They are classified as generalists because they also prey on other insect species.

The many faces of the adult harlequin ladybeetle
(aka multicoloured Asian ladybeetle) (Photo: ©Entomart)

Harlequin ladybeetle larva (Photo: cc by-sa Quartl)

Pea aphids are attacked by several species of parasitoid, including Aphidius ervi Haliday (Hymenoptera: Aphidiidae: Aphidiinae). Female parasitoids lay individual eggs inside aphid nymphs. After hatching, the parasitoid larva consumes its host, eventually killing it. The parasitoid pupates inside the dead or mummified aphid before a new adult parasitoid emerges.

Aphid mummies look bloated and discoloured compared to healthy adult aphids. Parasitism rates can be estimated by counting the number of aphid mummies on five host plants at five locations within a field.

*Aphidius ervi* parasitoid (Photo: cc by Penny Greeves)

For more information about the predators and parasitoids of pea aphids, visit the Insect of the Week page or consult Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management Field Guide.

To learn more about some of the natural enemies fighting pests in background for free, go to www.fieldheroes.ca or follow @FieldHeroes on Twitter.

Blog post submitted by Dr. Meghan Vankosky.
Follow her at @Vanbugsky.

Weekly Update

Jennifer Otani, Ross Weiss, David Giffen, Boyd Mori, Meghan Vankosky, Hector Carcamo, Erl Svendsen and Owen Olfert

Week 10

Greetings!

Field crop entomologists across the prairies are again surveying so the Weekly Update is restricted to the basics for Week 10.

Access the Weekly Update as a series of Posts for Week 10 (July 12, 2018). A similarly abridged downloadable PDF is available. Review the “Insect of the Week” for Week 10!

Questions or problems accessing the contents of this Weekly Update? Please e-mail either Dr. Meghan Vankosky or Jennifer Otani. Past “Weekly Updates” can be accessed on our Weekly Update page.

Subscribe to the Blog by following these three steps!

Weather synopsis

Ross Weiss, David Giffen, Owen Olfert and Meghan Vankosky

Week 10

Weather synopsis – This week staff were again surveying so we direct you to the AAFC Drought Watch maps in addition to the following updates.

This past week (July 2 – 9, 2018), temperatures across the prairies were warmer than long term average values (Fig. 1). The warmest weekly temperatures continue to occur across Manitoba. Compared to last week, daily average temperatures were warmer across southern Alberta and Saskatchewan. The 30-day (June 9 – July 9, 2018) average temperature was similar to the long term average.

Figure 1. Weekly (July 2 – 9, 2018) average temperature (°C).

Weekly and 30-day total precipitation was slightly above average (Figs. 2 and 3). Weekly accumulations were generally less than 20 mm with a few areas (northeast Saskatchewan, northwest Manitoba and the south of the Peace River region) reporting greater than 40 mm. The wettest (30-day) regions were across eastern areas in Saskatchewan, and isolated areas in southern Manitoba and the south of the Peace River region. A large region across Saskatchewan and Alberta continues to be dry.

Figure 2. Weekly (July 2 – 9, 2018) cumulative precipitation (mm).

Figure 3. The 30-day (June 9 – July 9, 2018) cumulative precipitation (mm).

The growing degree day map (GDD) (Base 10ºC, March 1 – July 8, 2018) is below:

The growing degree day map (GDD) (Base 5ºC, March 1 – July 9, 2018) is available below:

The maps above are all produced by Agriculture and Agri-Food Canada. Growers may wish to bookmark the AAFC Drought Watch Maps for the growing season.

Wheat midge

Ross Weiss, Owen Olfert and Meghan Vankosky

Week 10

Wheat Midge (Sitodiplosis mosellana) – As of July 9, 2018, the model runs indicate that wheat midge oviposition is well underway across a large area of Manitoba and Saskatchewan. Populations in this region are primarily in the egg stage (Fig. 1) with larvae appearing as well.

Figure 1. Percent wheat midge in the egg stage based on model simulations for April 1 – July 9, 2018.

Monitoring:

When monitoring wheat fields, pay attention to the synchrony between flying midge and anthesis.

In-field monitoring for wheat midge should be carried out in the evening (preferably after 8:30 pm or later) when the female midges are most active. On warm (at least 15ºC), calm evenings, the midge can be observed in the field, laying their eggs on the wheat heads (photographed by AAFC-Beav-S. Dufton & A. Jorgensen below). Midge populations can be estimated by counting the number of adults present on 4 or 5 wheat heads. Inspect the field daily in at least 3 or 4 locations during the evening.

REMEMBER that in-field counts of wheat midge per head remain the basis of economic threshold decision. Also remember that the parasitoid, Macroglenes penetrans (photographed by AAFC-Beav-S. Dufton below), is actively searching for wheat midge at the same time. Preserve this parasitoid whenever possible and remember your insecticide control options for wheat midge also kill these beneficial insects which help reduce midge populations.

Economic Thresholds for Wheat Midge:

a) To maintain optimum grade: 1 adult midge per 8 to 10 wheat heads during the susceptible stage.

b) For yield only: 1 adult midge per 4 to 5 heads. At this level of infestation, wheat yields will be reduced by approximately 15% if the midge is not controlled.

Inspect the developing kernels for the presence of larvae and the larval damage.

Click here to review the 2018 wheat midge forecast map.

Information related to wheat midge biology and monitoring can be accessed by linking to your provincial fact sheet (Saskatchewan Agriculture or Alberta Agriculture & Forestry). A review of wheat midge on the Canadian prairies was published by Elliott, Olfert, and Hartley in 2011. Additionally, more information can be found by accessing the pages from the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Field Guide”. View ONLY the Wheat midge pages but remember the guide is available as a free downloadable document as both an English-enhanced or French-enhanced version.

Predicted grasshopper development

Ross Weiss, Owen Olfert and Meghan Vankosky

Week 10

Grasshopper Simulation Model Output – The grasshopper simulation model will be used to monitor grasshopper development across the prairies. Weekly temperature data collected across the prairies is incorporated into the simulation model which calculates estimates of grasshopper development stages based on biological parameters for Melanoplus sanguinipes (Migratory grasshopper).

As of July 9, 2018, the grasshopper model output indicates that development is approximately 10 days ahead of normal with populations consisting of 4th and 5th instar stages and adults. The most rapid grasshopper development occurred across southern and central regions (Fig. 1).

Figure 1. Grasshopper development (average instar) based on model simulations, for April 1 – July 9, 2018.

Grasshopper Scouting Steps:

● Measure off a distance of 50 m on the level road surface and mark both starting and finishing points using markers or specific posts on the field margin.

● Starting at one end in either the field or the roadside and walk toward the other end of the 50 m making some disturbance with your feet to encourage any grasshoppers to jump.

● Grasshoppers that jump/fly through the field of view within a one meter width in front of the observer are counted.

● A meter stick can be carried as a visual tool to give perspective for a one meter width. However, after a few stops one can often visualize the necessary width and a meter stick may not be required. Also, a hand-held counter can be useful in counting while the observer counts off the required distance.

● At the end point the total number of grasshoppers is divided by 50 to give an average per meter. For 100 m, repeat this procedure.

● Compare counts to the following damage levels associated with pest species of grasshoppers:

0-2 per m² – None to very light damage

2-4 per m² – Very light damage

4-8 per m² – Light damage

8-12 per m² – Action threshold in cereals and canola

12-24 per m² – Severe damage

>24 per m² – Very severe damage

* For lentils at flowering and pod stages, >2 per m² will cause yield loss.

* For flax at boll stages, >2 per m² will cause yield loss.

Biological and monitoring information related to grasshoppers in field crops is posted by Manitoba Agriculture, Saskatchewan Agriculture, Alberta Agriculture and Forestry, the BC Ministry of Agriculture and the Prairie Pest Monitoring Network. Also refer to the grasshopper pages within the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” as an English-enhanced or French-enhanced version.

Lygus in canola

Ross Weiss, Owen Olfert and Meghan Vankosky

Week 10

Lygus bugs (Lygus spp.) – Due to warmer temperature data, the Lygus model output has predicted rapid a increase in development across southern and central prairie regions with Lygus adults forecast to occur across most of this area (Fig. 1).

Figure 1. Lygus development (average instar) based on model simulations, for April 1 – July 9, 2018.

Remember – The economic threshold for Lygus in canola is applied at late flower and early pod stages.

Adult *L. lineolaris* (5-6 mm long) (photo: AAFC-Saskatoon).

Fifth instar lygus bug nymph (3-4 mm long) (photo: AAFC-Saskatoon).

Damage: Lygus bugs have piercing-sucking mouthparts and physically damage the plant by puncturing the tissue and sucking plant juices. The plants also react to the toxic saliva that the insects inject when they feed. Lygus bug infestations can cause alfalfa to have short stem internodes, excessive branching, and small, distorted leaves. They feed on buds and blossoms and cause them to drop. They also puncture seed pods and feed on the developing seeds causing them to turn brown and shrivel.

Begin monitoring canola when it bolts and continue until seeds within the pods are firm. Since adults can move into canola from alfalfa, check lygus bug numbers in canola when nearby alfalfa crops are cut.

Sample the crop for lygus bugs on a sunny day when the temperature is above 20°C and the crop canopy is dry. With a standard insect net (38 cm diameter), take ten 180° sweeps. Count the number of lygus bugs in the net.

Repeat the sampling in another 14 locations. Samples can be taken along or near the field margins. Calculate the cumulative total number of lygus bugs and then consult the sequential sampling chart (Figure C). If the total number is below the lower threshold line, no treatment is needed. If the total is below the upper threshold line, take more samples. If the total is on or above the upper threshold line, calculate the average number of lygus bugs per 10-sweep sample and consult the economic threshold table.

Sequential sampling for lygus bugs at late flowering stage in canola.

The economic threshold for lygus bugs in canola covers the end of the flowering (Table 1) and the early pod ripening stages (Table 2). Once the seeds have ripened to yellow or brown, the cost of controlling lygus bugs may exceed the damage they will cause prior to harvest, so insecticide application is not warranted.

Consider the estimated cost of spraying and expected return prior to making a decision to treat a crop.

Remember that insecticide applications at bud stage in canola have not been proven to result in an economic benefit in production. The exception to this is in the Peace River region where early, dry springs and unusually high densities of lygus bug adults can occasionally occur at bud stage. In this situation, high numbers of lygus bugs feeding on moisture-stressed canola at bud stage is suspected to result in delay of flowering so producers in that region must monitor in fields that fail to flower as expected.

Table 1. Economic thresholds for lygus bugs in canola at late flowering and early pod stages (Wise and Lamb 1998).

1 Canola crop stage estimated using Harper and Berkenkamp 1975).
2 Economic thresholds are based on an assumed loss of 0.1235 bu/ac per lygus bug caught in 10 sweeps (Wise and Lamb. 1998. The Canadian Entomologist. 130: 825-836).

Table 2. Economic thresholds for lygus bugs in canola at pod stage (Wise and Lamb 1998).

3 Economic thresholds are based on an assumed loss of 0.0882 bu/ac per lygus bug caught in 10 sweeps (Wise and Lamb. 1998. The Canadian Entomologist. 130: 825-836).

Biological and monitoring information related to Lygus in field crops is posted by the provinces of Manitoba or Alberta fact sheets or the Prairie Pest Monitoring Network’s monitoring protocol. Also refer to the Lygus pages within the new “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” – both English-enhanced or French-enhanced versions are available.

Abundant parastioids in canola!

Jennifer Otani

Week 10

The cabbage seedpod weevil is a chronic pest of canola in southern Alberta and south western Saskatchewan; it has recently reached Manitoba as well. The pest is managed with insecticides, which are sprayed at early flower. This year, in some canola fields around Lethbridge AB, an abundant parasitoid wasp was noticed at the time when fields may be sprayed. The wasp was identified as Diolcogaster claritibia (Fig. 1; thanks to Vincent Hervet and Jose Fernandez for confirming identification).

The wasp is a parasitoid that attacks diamondback moth larvae and recently abundant in some fields in 2017. In some of the fields sampled, as many parasitoids as cabbage seedpod weevil (i.e., nearly one per sweep) were observed. In the fields sampled (i.e., around 10), cabbage seedpod weevils were below thresholds on average, though some spots may have been close to the threshold of 2-3 weevils per sweep.

The above observation emphasizes the value of beneficial arthropods like Diolcogaster claritibia. It is important to recognize that foliar applications of insecticides kill beneficial insects like this small wasp (about 2 mm) which attacks and helps regulate pest populations of diamondback moth or other Lepidoptera, including cutworms and cabbage worms. Thus, think beneficials before you spray!

Figure 1. *Diolcagaster claritibia* adult measuring ~2mm in length (Photo credit J. Fernandez, AAFC-Ottawa).

Learn more about beneficials by accessing Field Heroes and all the Blog’s Parasitoid posts.

Download the Field Guide

Jennifer Otani

Week 10

If you haven’t downloaded the FREE field guide yet, please do so now!

Field Crop and Forage Pests and their Natural Enemies in Western Canada: IDENTIFICATION AND MANAGEMENT FIELD GUIDE

The 152-page, full-colour field guide, now available online, is designed to help you make informed decisions in managing over 90 harmful pests of field and forage crops in Western Canada. Better decision making helps save time and effort and eliminates unnecessary pesticide applications to improve your bottom line. The guide also helps the reader identify many natural enemies that prey on or parasitize pest insects. Recognizing and fostering populations of natural enemies will enhance their role in keeping or reducing pest populations below economic levels.

Find links to download the FREE Insect Field Guide.

Provincial Insect Pest Reports

James Tansey, John Gavloski and Scott Meers

Week 10

Provincial entomologists provide insect pest updates throughout the growing season so we link to their most recent information:

Manitoba‘s Insect and Disease Updates for 2018 can be accessed here. Issue #6 (posted July 4, 2018) included reports of grasshoppers, low numbers of aphids in peas and cereal crops, and importance of protecting and preserving pollinators in any flowering crop.

Saskatchewan‘s Crop Production News for 2018 is posted with Issue #4 now available. This issue includes a report from the Crop Protection Lab summarizing disease and insect samples submitted this growing season. Saskatchewan growers can review articles on how to scout for cutworms, how to assess plant stand densities in flax or canola, and for flea beetles, pea leaf weevils. Also note the following diamondback moth pheromone trap interception counts from across the regions (updated June 27, 2018):

Alberta Agriculture and Forestry’s Call of the Land regularly includes insect pest updates from Scott Meers. The most recent Call of the Land (posted July 12, 2018) identified that SOME bertha armyworm pheromone traps over a wide geographic range have started to intercept higher numbers of moths. This means in-field scouting will be critical in 10-14 days (as larvae move up from leaves to feed among canola pods). Processing of canola survey samples has begun; initial samples suggest lower diamondback moth and Lygus bug numbers so far compared to 2017 but higher numbers of small parasitoid wasps associated with diamondback moths, and a pocket of grasshoppers (clearwinged) near Carmangay AB.