Tag: Phylotreta striolata

Flea beetles

Two species, Phyllotreta striolata and P. cruciferae, are the most chronic and economically important flea beetle pests of cruciferous crops in western Canada. Bioclimate simulation models for the two flea beetle species were developed to assess how climatic factors influence shifts in their geographic distribution and relative abundance. Economic risk was associated with populations in the orange and red zones (Figs. 1-4). It is crucial to note that the following information is NOT based on flea beetle densites BUT IS INSTEAD reflecting the suitability of environmental factors for P. striolata and P. cruciferae to prosper in highlighted areas of the following maps.

This spring has been approximately 1 °C cooler than normal. Recent rain (May 23-24) has resulted in precipitation amounts that are normal to above normal (30-day total) across Alberta and Saskatchewan. Simulations were run to determine how the two flea beetle species might respond to cooler, wetter conditions (compared to average growing seasons). Based on average temperature and precipitation (based on long term climate normals) risk associated with P. cruciferae is most prevalent across the southern prairies and risk related to P. striolata tends to be greatest across the Parkland and Peace River regions (Figs. 1 and 2).

Figure 1. Predicted risk for P. cruciferae, for model simulations based on long term climate normals. Red and orange regions may
be associated with economic crop losses.

Figure 2. Predicted risk for *P. striolata*, for model simulations based on long term climate normals. Red and orange regions may
be associated with economic crop losses.

For both species, cooler/wetter conditions generally could result in reduced risk and southward shifts in distribution (Figs. 3 and 4). Cooler and wetter than average growing seasons were predicted to have less negative impact on P. striolata than P. cruciferae. For example, Peace River populations of P. striolata are predicted to present reduced risk with cooler, wetter conditions (compared to average climate). Under similar conditions, P. cruciferae was predicted to have significantly reduced risk in the Peace River region. Wetter than average conditions in Manitoba may result in reduced risk from P. cruciferae and P. striolata. Olfert et al. (2017) reported that both species were more sensitive to temperature than moisture. Potential risk related to warmer temperatures was greater for P. cruciferae than P. striolata. Producers should monitor flea beetle species composition, crop stage and weather to assess potential flea beetle risk to cruciferous crops.

Figure 3. Predicted risk for *P. cruciferae*, for model simulations based on conditions that are cooler and wetter than current climate. Red and orange regions may be associated with economic crop losses.

Figure 4. Predicted risk for *P. striolata*, for model simulations based on conditions that are cooler and wetter than current climate. Red and orange regions may be associated with economic crop losses.

If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding. Review photos of flea beetle feeding damage posted earlier in the Weekly Update (Wk 02 – May 14, 2021) to help assess percent defoliated and to apply the action threshold of 25 % leaf area of cotyledons consumed plus flea beetles were the Insect of the Week (Wk 02 – May 10)!

Access biological and pest management information posted by Alberta Agriculture and Forestry, Saskatchewan Agriculture, or Manitoba Agriculture and Resource Development, or the Canola Council of Canada’s Canola Encyclopedia. Refer to the flea beetle page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” (Philip et al. 2018) as an English-enhanced or French-enhanced version.

Flea beetles

Newly emerging Brassicaceae but especially canola is attractive to overwintered flea beetles that emerge and become active early in the spring. As canola seedlings emerge, in-field scouting becomes crucial! If flea beetle densities are high, seedling damage levels can advance quickly – even within the same day! The cotyledon stage of canola is vulnerable to flea beetle feeding. Be sure to check out the Insect of the Week – Week 2 featured flea beetles!

Several species of flea beetles are present across North America. Be on the lookout for flea beetle damage resulting from feeding on canola cotyledons but also on the stem (Fig. 1). Two species, Phyllotreta striolata (Fig. 1) and P. cruciferae, will feed on all cruciferous plants but they can cause economic levels of damage in canola during the seedling stages.

Figure 1. Flea beetle feeding damage (L) and striped flea beetle (R).

The Action Threshold for flea beetles on canola is 25% of cotyledon leaf area consumed. Watch for shot-hole feeding in seedling canola but also watch the growing point and stems of seedlings which are particularly vulnerable to flea beetle feeding.

Estimating flea beetle feeding damage can be challenging. Using a visual guide to estimate damage can be helpful. Canola Watch circulated this article but also use the two images (Figs. 2 and 3; copied below for reference) produced by Dr. J. Soroka (AAFC-Saskatoon) – take it scouting!

Figure 2. Canola cotyledons with various percentages of leaf area consume owing to flea beetle feeding damage (Photo: Soroka & Underwood, AAFC-Saskatoon).

Figure 3. Percent leaf area consumed by flea beetles feeding on canola seedlings (Photo: Soroka & Underwood, AAFC-Saskatoon).

Two other favourite flea beetle resources relevant to field crop protection include:

Those armed with a stereomicroscope who are keen to monitor flea beetle species may wish to bookmark the “Common flea beetles of North Dakota” (Fauske 2003) which an excellent online resource and includes many of the commonly observed species of flea beetles also present across the Canadian prairies.

Soroka, J., Grenkow, L., Otani, J., Gavloski, J., & Olfert, O. (2018). Flea beetle (Coleoptera: Chrysomelidae) species in canola (Brassicaceae) on the northern Great Plains of North America. The Canadian Entomologist, 150(1), 100-115. doi:10.4039/tce.2017.60

Flea beetles active already

In canola, the most common flea beetles are either bluish black (crucifer flea beetle or Phyllotreta cruciferae) or black with two wavy yellow lines running down the length of its back (striped flea beetle or P. striolata). They overwinter as adults under plant material along field margins and females lay eggs in the soil near host plants.

Striped and crucifer flea beetles feed on canola, mustard and related cruciferous plants and weeds. Canola is highly susceptible to feeding damage at the cotyledon stage – damage appears as ‘shot-holes’ in cotyledon leaves. Flea beetles also feed on stems and very young seedlings may wilt or break off under windy or damp conditions. New generation adults feed on maturing pods late in the summer. Remember, the Action Threshold for flea beetles on canola is when 25% of cotyledon leaf area is consumed (see post from 2019 on estimating flea beetle damage and action threshold and the Flea Beetle Monitoring Protocol).

According Dr. Tyler Wist (@TylerWist1), who makes it his business to know, striped flea beetles are already active.

More information about these pests (lifecycle, damage, control options, etc.) and others is available in the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien)