This week’s Insect of the Week is a beneficial wasp from the Family Pteromalidae named Macroglenes penetrans. It is an important natural enemy of wheat midge. The wasp is a parasitoid that lives within the wheat midge larva and overwinters within the host. In the spring, the parasitoid larva develops to emerge from the wheat midge cocoon buried in the soil and seeks out wheat midge eggs.
Ross Weiss, David Giffen, Owen Olfert and prairiepest_admin
Weather synopsis – This past week our average temperatures were cooler than last week, and 2 – 3°C cooler than long term averages for mid-June (Fig. 1). The second map presents the 30-day average temperature (Fig. 2).
Figure 1. Average temperature across the Canadian prairies from June 4-11, 2017.
Figure 2. Average temperature across the Canadian prairies from May 19-June 19, 2017.
Temperature – The seven-day accumulated precipitation was greater than 15 mm with southeast Saskatchewan and southwest Manitoba reporting amounts in excess of 40 mm (Fig. 3).
Figure 3. Accumulated precipitation across the Canadian prairies from June 11-18, 2017.
Compared to last week, the 30-day rainfall amounts are similar to long term average values for southern Manitoba, southeast Saskatchewan and southwest Alberta (Fig. 4). A large region in south and central Saskatchewan is reporting well below normal precipitation.
Figure 4. Percent of average precipitation from May 20-June 18, 2017.
The following is the accumulated precipitation for the growing season up to June 18, 2017.
The updated growing degree day map (GDD) (Base 5ºC, March 1 – June 18, 2017) is below:
While the growing degree day map (GDD) (Base 10ºC, March 1 – June 18, 2017) is 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.
Alfalfa Weevil (Hypera postica) – The model output for alfalfa weevil is not signficantly different that that posted last week for June 22nd (Week 7).
Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon) and additional information can be accessed by reviewing the Alfalfa Weevil Page extracted from the “Field crop and forage pests and their natural enemies in western Canada – Identification and management field guide” (Philip et al. 2015). That guide is available in both a free English-enhancedor French-enhanced version.
Grasshopper Simulation Model Output – Predicted hatch was 71% (52% last week) with 30% of the population in the first instar, 26% second instar, 12% third instar and 2% in the fourth instar. Across the prairies, the mean developmental stage was second instar. The greatest development was predicted to be across southern regions in all three provinces.
Grasshopper populations near Saskatoon were predicted to be primarily in the second instar this week with the appearance of third and fourth instars. Model output suggests that grasshopper development is slightly ahead of average development. Based on long term meteorological data, populations should be predominantly in the first and second instars with a low number being third instars. This week’s survey (SW of Saskatoon) indicates that most melanopline grasshoppers are already in the second and third numbers.
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 grasshopers:
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.
Bertha armyworm (Lepidoptera: Mamestra configurata) – Bertha armyworm should be in the adult stage across the prairies this week. The map illustrates predicted appearance of adults (percent of the population) across the southern prairies.
For those monitoring BAW pheromone traps, compare trap “catches” to the following reference photo kindly shared by Saskatchewan Agriculture:
Wheat Midge (Sitodiplosis mosellana) – Reminder – The previous Insect of the Week (Week 7) features wheat midge!
Simulation modelling is used to predict wheat midge emergence across the Canadian prairies. The model has not changed significantly from last week. The map below predicts the geographic distribution and corresponding accumulation of heat units necessary for wheat midge to emerge from puparia developing in the soil.
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.
More information about Wheat midge 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.
Cabbage seedpod weevil (Ceutorhynchus obstrictus) – There is one generation of CSPW per year and the overwintering stage is the adult which is an ash-grey weevil measuring 3-4mm long (Refer to lower left photo). Adults typically overwinter in soil beneath leaf litter within shelter belts and roadside ditches.
Monitoring: ● Begin sampling when the crop first enters the bud stage and continue through the flowering. ● Sweep-net samples should be taken at ten locations within the field with ten 180° sweeps per location. ● Count the number of weevils at each location. Samples should be taken in the field perimeter as well as throughout the field. ● Adults will invade fields from the margins and if infestations are high in the borders, application of an insecticide to the field margins may be effective in reducing the population to levels below which economic injury will occur. ● An insecticide application is recommended when three to four weevils per sweep are collected and has been shown to be the most effective when canola is in the 10 to 20% bloom stage (2-4 days after flowering starts). ● Consider making insecticide applications late in the day to reduce the impact on pollinators. Whenever possible, provide advanced warning of intended insecticide applications to commercial beekeepers operating in the vicinity to help protect foraging pollinators. ● High numbers of adults in the fall may indicate the potential for economic infestations the following spring.
Damage: Adult feeding damage to buds is more evident in dry years when canola is unable to compensate for bud loss. Adults mate following a pollen meal then the female will deposit a single egg through the wall of a developing pod or adjacent to a developing seed within the pod (refer to lower right photo). Eggs are oval and an opaque white, each measuring ~1mm long. Typically a single egg is laid per pod although, when CSPW densities are high, two or more eggs may be laid per pod.
There are four larval instar stages of the CSPW and each stage is white and grub-like in appearance ranging up to 5-6mm in length (refer to lower left photo). The first instar larva feeds on the cuticle on the outside of the pod while the second instar larva bores into the pod, feeding on the developing seeds. A single larva consumes about 5 canola seeds. The mature larva chews a small, circular exit hole from which it drops to the soil surface and pupation takes place in the soil within an earthen cell. Approximately 10 days later, the new adult emerges to feed on maturing canola pods. Later in the season these new adults migrate to overwintering sites beyond the field.
Nysius niger(Lygaeidae) – Agrologists in Saskatchewan have been querying a greyish-black bug spotted this week in some fields of canola, soybeans and flax. Photos and descriptions suggest Nysius niger, an ~4mm long lygaeid, is being observed (Fig. 1 and 2). Reports of damage in canola have been matched with observations of these insects active on plants growing in good conditions with no apparent damage. Reports of damage in canola and flax indicate the bugs are feeding on the main stem near the soil surface.
Growers should be cautious – there is no data confirming whether or not Nysius niger is a pest causing consistent levels of economic damage. Insects can feed on field crop species yet never inflict measurable levels of damage and are therefore not worth managing. Careful scouting is warranted to assess how these insects are feeding AND if damage is occurring and to what extent. Also remember our @FieldHeroes who benefit from less insecticide use and instead reserve insecticide use for economically important pests that cause well-researched levels of damage.
Figure 1. Nysius niger adult on the soil surface in a canola field in Saskatchewan photographed by J. Bogden.
Figure 2. Lygaeid nymphs observed in the above canola field photographed by J. Bogden.
Scarabaeidae – Reminder – Each June brings scattered reports across the Prairies of white grubs associated with crop damage. In fact, several species of Aphodius, Phyllophaga, Polyphylla or even small Aetenius produce larvae described as “white grubs”.
Recently, crop damage reports have been associated with a grub identified as the larvae of the beetle Aphodius distinctus (see below). This common beetle is not known to be a pest, but there is an ongoing effort to gather information to develop a ‘pest’ profile. Additional information is online at Top Crop Manager. Please send reports of this insect and associated information to Dr. Kevin Floate (Agriculture and Agri-Food Canada, Lethbridge, AB).
@Field Heroes – Western Grains Research Foundation is supporting a new initiative to help growers, agrologists and the general public learn more about beneficial arthropods active in field crops. Provincial entomologists from Manitoba, Alberta, and Saskatchewan, along with input from AAFC researchers, are working with Synthesis, a communications company, to promote and increase awareness of these incredible arthropod heroes! Follow @FieldHeroes for great information on these beneficials.
The website includes scouting guides to help identify and link pest/beneficial combinations – all aimed at helping growers and agrologists understand and preserve the many arthropods hard at work in fields across the Canadian prairies.
Provincial entomologists provide insect pest updates throughout the growing season so we have attempted to link to their most recent information:
● Manitoba’s Insect and Disease Update for 2017 is prepared by John Gavloski and Pratisara Bajracharya and read Issue #5 (June 21, 2017) noting alfalfa weevil and lingering cutworm issues in that province.
● Saskatchewan’s Crop Production News – 2017 – Issue #2 prepared by Scott Hartley and Danielle Stephens is now posted. It includes updates on how to scout for pea leaf weevil and aster yellows that can occur in all crops. Additionally, very low DBM numbers have been intercepted in pheromone traps deployed throughout Saskatchewan (e.g., seasonal cumulative totals of 10-14 moths per trap were reported “peaks”.
● Watch for Alberta Agriculture and Forestry’s Call of the Land and access the most recent Insect Update (June 22, 2017) provided by Scott Meers. That report notes cabbage seedpod weevil scouting has begun in southern Alberta, isolated reports of red turnip beetle in a few fields in east-central Alberta, the appearance of early instar grasshoppers (1-3 instar stages) west of Edmonton and in the Peace River region despite the weather, and low pea aphid numbers so far in southern Alberta.
We again track the migration of the Monarch butterflies as they move north by checking the 2017 Monarch Migration Map! A screen shot of the map has been placed below as an example (retrieved 22Jun2017) but follow the hyperlink to check the interactive map! They’ve migrated into southern Manitoba and into southeast Saskatchewan!