Tag: Alfalfa weevil

Prairie Research: The Evenden Lab

*Text for this post prepared by Priyatha Sundaran, Sharavari Kulkarni and Maya Evenden, from the University of Alberta.

Dr. Maya Evenden’s lab in the Department of Biological Sciences at the University of Alberta researches insect behaviour, chemical ecology and integrated pest management. They study how insects orient and maneuver in their environment and exploit that knowledge for the development of IPM tactics. This summer the Evenden lab has multiple agriculture-based projects targeting diamondback moth, flea beetles, pea leaf weevil and alfalfa weevil. Here we highlight the work of an MSc student, Priyatha Sundaran, and a postdoctoral fellow, Dr. Sharavari Kulkarni.

Priyatha’s research focuses on the presence and distribution of alfalfa weevil (Hypera postica), in alfalfa grown for seed in southern Alberta. The study also assesses the diversity of Sitona spp. in sampled alfalfa fields. In three field seasons, alfalfa weevils have been sampled with soil and sweep samples, and emergence and pit fall traps. Soil samples at the beginning and end of each crop season estimate the density of alfalfa weevils in the soil over the winter. Sweep net samples can collect both larvae and adults to monitor alfalfa weevil density in the field for timely use of insecticides. Pitfall trap capture can indicate weevil movement in and out of the field over the course of the growing season. Emergence cages assessed the overwintering locations of weevils inside and outside the field. Initial results reinforce the effectiveness of sweep net sampling to monitor alfalfa weevil populations with peak larval activity in June-July. Alfalfa weevils were captured in equal numbers in pitfall traps placed at the edge and in the interior of the field suggesting that alfalfa weevils remain within alfalfa fields, unlike in other parts of their range. Sitona spp. bycatch consisted mostly of alfalfa curculio (Sitona lineellus) and pea leaf weevil (Sitona lineatus).

Alfalfa weevil sampling methods used in alfalfa fields grown for seed: A) Emergence cages were located inside and outside the field to reveal the overwintering sites of alfalfa weevils. B) Two hundred sweep samples were collected from four locations in each field throughout the growing season in three seasons. C) Directional pitfall traps were employed in the 2023 season to measure the direction of movement of alfalfa weevils in the field. Pictures by Priyatha Sundaran, University of Alberta.

Sharavari’s research focuses on developing weather-based stage-structured predictive models for two important canola pests, striped flea beetles, (Phyllotreta striolata (Fab.)) and crucifer flea beetles (Phyllotreta cruciferae (Goeze)). Flea beetles are oligophagous species feeding mainly on canola (Brassica napus L. and Brassica rapa L.) and mustard (Brassica juncea L.). Sharavari used field surveys to assess local phenology and laboratory bioassays to study the effect of temperature on beetle development and interspecific competition between the two species. The flea beetle surveys were conducted in the spring (pre-seeding) and fall of 2021, 2022 and 2023 across 20+ canola fields throughout Alberta. Season-long, site-specific weather data was collected for modeling and validation. None of the available monitoring methods provides accurate forecasting for flea beetles, and weather-based phenology models can help producers make informed decisions on timing and the need to apply foliar insecticides for flea beetle management. Lab assays showed a dramatic effect of temperature on the time and success of egg hatch and development time from egg to adult. On-going lab work is testing for plant-mediated interactions between the two species to understand if P. cruciferae prefers to feed and oviposit on plants previously damaged by P. striolata and to determine if inter-species interactions have fitness costs.

Flea beetle monitoring in commercial canola fields with yellow sticky cards at sites with weather stations for site-specific temperature measurements. Pictures by Sharavari Kulkarni, University of Alberta.

Predicted Alfalfa Weevil Development

The alfalfa weevil (AAW), Hypera postica, model predicts development using biological parameters known for the pest species and environmental data observed across the Canadian prairies on a daily basis. Review lifecycle and damage information for this pest.

Model simulations for alfalfa weevil (AAW), Hypera postica, indicate that oviposition should be underway across the prairies. Relative to eastern Saskatchewan and Manitoba, warmer temperatures in Alberta are predicted to have resulted in rapid development of alfalfa weevil populations. The following graphs indicate, based on potential number of eggs, that development of alfalfa weevil populations is greater near Lethbridge (Fig. 1) than Regina (Fig. 2). As of May 7, 2023, alfalfa weevil populations may have produced two or three times more eggs in the Lethbridge area than alfalfa weevil populations near Regina. The model predicts that hatch may occur across southern Alberta in mid-May and 10 days later across south-central Saskatchewan.

Alfalfa weevil

Alfalfa weevil larval populations are developing into later instars (Fig. 1). Second instar development is nearing completion and this week there larvae should be in the third instar stage. This week larvae are mostly second (26%, 52% last week) and third instars (52%, 22% last week; Fig. 1). Model output indicates that fourth instar larvae are beginning to occur in southern SK and isolated areas in southern AB and MB.

The larval stage of this weevil feeds on alfalfa leaves in a manner that characterizes the pest as a “skeletonizer”. The green larva featuring a dorsal, white line down the length of its body has a dark brown head capsule and will grow to 9mm long.

Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon). 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). The guide is available in both a free English-enhanced or French-enhanced version.

Alfalfa weevil

This past week warmer temperatures in southern MB advanced alfalfa weevil development. Weevils are predicted to be primarily in the second (53%) and third instars (22%) across most of southern areas in MB and SK (Fig. 1).

Alfalfa weevil

Weather conditions continue to be favourable for development of alfalfa weevil, if alfalfa weevil are present in your area. First instar development is nearing completion (Fig. 1) and the more individuals in the population should be in the second instar stage (Fig. 2).

Model runs for Brooks AB (Fig. 3) and Swift Current SK (Fig. 4) were projected to June 21, 2019. In alfalfa fields near Brooks AB larvae should start to reach the third instar stage late this week. At Swift Current SK third instar larvae will begin to appear approximately 5-7 days later.

Alfalfa weevil

Model runs for Brooks AB and Swift Current SK were projected to June 15, 2019. The model runs indicate that second instar AAW should begin to appear over the next few days. Third instar larvae are predicted to occur one week later. The warm weather over the next few days may speed up development.

Alfalfa weevil

Model output indicates that alfalfa weevil hatch has begun and first instar alfalfa weevils should be present across most of AB (Fig. 1). Model runs for Brooks AB (Fig. 2) and Swift Current SK (Fig. 3) were projected to June 15, 2019. Second instar larvae will begin to occur late next week in fields near Brooks and 3-5 days later in the Swift Current region.

Alfalfa weevil

Model runs for Brooks AB (Fig. 1) and Swift Current SK (Fig. 2) were projected to June 15, 2019. Model output indicates that initial hatch should occur late next week in fields near Brooks. Hatch should be 5-7 days later in the Swift Current region. Compared to last year’s runs for Swift Current, development is predicted to be 10 days later than 2018. Compared with long term normal weather data, egg development is 1 – 2 days later than average.

Alfalfa weevil

AAW model runs indicate that oviposition should have begun in the Brooks (Rosemary) AB (Fig. 1) and Regina SK regions (Fig. 2). Note that this week’s cool temperatures have reduced oviposition rates (based on model predictions).

Alfalfa weevil

The AAW model runs indicate that oviposition has begun in fields near Swift Current SK (Fig. 1). Compared to last week, oviposition rates are predicted to have increased.

Alfalfa weevil

Alfalfa Weevil (Hypera postica) – Degree-day maps of base 9°C are produced using the Harcourt/North Dakota models (Soroka et al. 2015). Models predicting the development of Alfalfa weevil (Hypera postica) across the prairies are updated weekly to help growers time their in-field scouting for second-instar larvae. Compare the following predicted development stages and degree-day values from Soroka (2015) to the map below (Fig. 1).

Alfalfa weevil (AAW) model runs indicate that oviposition may have begun in fields near Swift Current SK.

Alfalfa weevil

Alfalfa Weevil (Hypera postica) – Approximately 70% of the population should be in the third or fourth instar stages and pupae may be occurring as well. AAW populations near Winnipeg, Brandon, Regina, Saskatoon and regions in southern Alberta are predicted to be primarily in the fourth instar (Fig. 1).

Access last week’s update to view photos and descriptions of all stages of alfalfa weevil.

Alfalfa weevil

Alfalfa Weevil (Hypera postica) – The AAW model runs for Swift Current SK indicate that oviposition is well underway in southern Saskatchewan (Fig. 1). Larvae should be primarily second and third instars. Fourth instar larvae may be occurring as well.

Use the photo below as a visual reference to identify alfalfa weevil larvae. Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.

Alfalfa weevil

Figure 1. Predicted alfalfa weevil phenology at Swift Current SK.
Values are based on model simulations (April 1-May 28, 2018 and projected to June 21, 2018).

Degree-day maps of base 9°C are produced using the Harcourt/North Dakota models (Soroka et al. 2015). Models predicting the development of Alfalfa weevil (Hypera postica) across the prairies are updated weekly to help growers time their in-field scouting for second-instar larvae. Compare the following predicted development stages and degree-day values from Soroka (2015) to the map below (Fig. 2).

Figure 2. Predicted development of alfalfa weevil as of May 30, 2018.

Use the photo below as a visual reference to identify alfalfa weevil larvae. Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.

Alfalfa weevil

Figure 1. Predicted development of alfalfa weevil as of May 21, 2018.

Use the photo below as a visual reference to identify alfalfa weevil larvae. Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.

Alfalfa weevil

The alfalfa weevil model predicts that oviposition is well underway in southern Saskatchewan. Figure 1 shows model output for Swift Current where first instar larvae should appear early next week.

Figure 1. Predicted alfalfa weevil (Hypera postica) phenology at Swift Current SK.
Values are based on model simulations for April 1-May 6, 2018.

Use the photo below as a visual reference to identify alfalfa weevil larvae. Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.

Alfalfa weevil

The AAW model predicts that oviposition may have begun in southern areas of the prairies. Current oviposition rates are predicted to be higher than oviposition rates based on LTN climate data (Fig. 1).

Figure 1. Predicted AAW oviposition at four prairie locations. Values are based on
model simulations, for April 1 – May 6, 2018.

Use the photo below as a visual reference to identify alfalfa weevil larvae. Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.