Weekly Update

Meghan Vankosky, Erl Svendsen, Ross Weiss, David Giffen, Jennifer Otani and Owen Olfert
Week 14


We’re doing a bit of catch-up with the Weekly Update….

Please view the Weekly Update FOR WEEK 14 (August 9, 2018) which is available only as a PDF.  Also review the Insect of Week for Week 14 featuring both the Natural enemies of wheat stem sawfly plus the English grain aphid.

The Weekly Update FOR WEEK 15 (August 16, 2018) is available as either as a series of Posts  OR a downloadable PDF version.  Also review the “Insect of the Week” for Week 15!

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.

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Insect of the Week – Natural Enemies of the wheat stem sawfly

Jennifer Otani
Week 14

This week’s Insects of the Week are the natural enemies (@FieldHeroes) of the wheat stem sawfly, namely Bracon cephi (Gahan) and B. lissogaster (Hymenoptera: Braconidae).

Nine species of parasitic wasps are known to attack wheat stem sawfly but Bracon cephi and B. lissogaster are the main species that help regulate this pest in North America.  These closely related wasp species are described as idiobiont ectoparasitoids meaning the parasitoid larva, after hatching from an egg laid on the surface of the sawfly larva, feeds on the exterior of the host. Normally, both Bracon species will complete their development (i.e., pupates) inside the wheat stem within the integument of the sawfly larva or just beside the consumed host.  There are two generations of B. cephi and B. lissogaster per year.  The first generation normally completes its lifecycle then escapes from the wheat stem to locate a new sawfly larva to parasitize.  The second generation of these wasps will overwinter within the wheat stem.

These wasps are 2-15 mm long and are usually brown in colour. They have a narrow waist connecting the abdomen to the thorax and the combined length of head plus thorax is equal to the length of the abdomen.  These parastiod wasps have long antennae and two pairs of transparent wings. Females have a noticeable ovipositor protruding from the end of the abdomen.

For more information about the natural enemies of the wheat stem sawfly, check out our Insect of the Week page!

Bracon cephi (Gahan) (H. Goulet)

Extra Insect of the Week – English grain aphid (Hemiptera: Aphididae)

Tyler Wist and prairiepest_admin
Week 14

The English grain aphid (Sitobion avenae) has started to appear across the Prairies in various cereal crops this past week so the time to scout is now. Look for this aphid infesting wheat heads (favourite host) as well as barley, oat, rye, Timothy and canaryseed.

This aphid can also be a vector for barley yellow dwarf virus. You might see the green, red colour morph or both morphs in fields this year (Fig. 1). You will probably also see ladybeetle (@FieldHeroes) adults and larvae hunting the aphids (Fig. 2). The economic threshold for aphids in spring wheat in Western Canada is 12-15 aphids per head prior to the soft dough stage. 

Agriculture and Agri-Food Canada, with funding from the Pest Management Centre, has developed a smartphone app called Cereal Aphid Manager (CAM) to facilitate scouting for aphids in cereals that also allows you to record the beneficial insects in the field that can keep aphid populations below the economic threshold – available at Apple iTunes and Google Play app stores. CAM information and download links.

For more information on the English grain aphid, check out our Insect of the Week page!

Submitted by Dr. Tyler Wist (Tyler.Wist@agr.gc.ca).

Fig. 1 Green and red morph English grain aphid
(Tyler Wist, AAFC)
Fig. 2 Seven-spotted lady bird larva hunting aphids
(Tyler Wist, AAFC)