Monitoring of Wheat Midge and its Parasitoids Macroglenes penetrans and Platygaster tuberosula in Irrigated and Dryland Spring Wheat in Golden Triangle, Montana

Principal Investigator: Gadi V.P. Reddy, Dr. Michael Ivie Project personnel: Ramadevi L. Gadi and Anamika Sharma

Western Triangle Agricultural Research Center, Montana State University, 9546 Old Shelby Rd., P.O. Box 656, Conrad, MT 59425, USA

Aim of the study

The objectives of this study were: 1) to assess the wheat midge population trend in Golden Triangle, Montana, 2) the wheat midge population dynamics in irrigated and dryland spring wheat fields and 3) to monitor the wheat midge parasitoid M. penetrans and Platygaster tuberosula population in spring wheat fields.

Materials and methods

Wheat midge populations

Western Triangle Agricultural Research team installed 16 delta traps baited with wheat midge pheromone lures (2S, 7S)-nonadiyl dibutyrate in spring wheat fields (dryland and irrigated) in multiple locations of Pondera, Toole, Teton and Chouteau Counties of Golden Triangle, Montana (Table 1). Pheromone traps were installed on June 07, 2019. Traps were checked at 1-3 days interval in Pondera (Valier and WTARC trap sites) and Toole (Ledger), while at 15 days interval in Teton and Chouteau Counties locations. The monitoring work was wrapped up on August 13, 2019.

Parasitoids Macroglenes penetrans and Platygaster tuberosula population levels

The parasitoids adult population levels were monitored using the sweet net at spring wheat fields located at Valier, WTARC and Ledger locations. For sweep net sampling, 150 sweeps were made per field and the sampling was done at least 15 m from inside fields. The sweep net sampling was begun on June 24 and completed in July 23, 2019. Parasitoid adults were monitored at 15 days interval throughout the wheat midge adult activity period. The collected samples were stored at - 20 °C until processing. The parasitoids were identified under a microscope.

Results

Wheat midge population levels in the Golden Triangle, Montana

Total cumulative midge count observed in our trap established locations are shown in Table 1.

Table 1. Total cumulative wheat midge count per trap observed in Pondera, Toole, Teton and Chouteau Counties of Montana in 2019.

In 2019, wheat midge populations were monitored in seven counties (Liberty, Toole, Teton, Chouteau, Glacier, Cascade and Pondera) at the Golden Triangle, Montana. A portion of the wheat midge count data was extracted from PestWeb Montana. The total number of wheat midge pheromone traps installed in wheat fields was 32 in 2019. Among the seven counties, the highest wheat midge population level per trap was observed in Pondera County (Fig. 1). The second highest wheat midge populations were noticed at Liberty County followed by Toole, Cascade and Teton Counties (Fig. 1). Compared to the last year, wheat midge population was low in Liberty County but higher in Pondera and Toole Counties.

Figure 1. Wheat midge population levels in the Golden Triangle, Montana from 2014-2019.

Wheat midge population level: Irrigated vs. dryland spring wheat fields.

In overall, the flight activity of wheat midge adults began about one and half weeks earlier (June 19-June 26) in 2019 when compared to 2018 with emergence occurred on June 30-July 5 in Pondera County (Fig. 2). The midge adult activity reached a peak on August 04, 2019 both in dryland and irrigated fields and which is similar to 2018 (Fig. 2). In 2019, we had similar results as in 2018 regarding wheat midge population levels in irrigated and dryland wheat fields. Wheat midge populations were relatively at higher levels in irrigated fields compared to dryland spring wheat fields. However, it is interesting to report that wheat midge population levels were nearly twelve-fold higher in irrigated compared to dryland fields in 2019. The total cumulative numbers of male adults captured per pheromone trap were: 746 and 65 in irrigated and dryland fields, respectively (Fig. 2). Similarly in 2018, wheat midge population levels were fourteen folds higher in irrigated compared to dryland fields. The total cumulative numbers of male adults captured per pheromone trap were: 700 and 50 in irrigated and dryland fields, respectively (Fig. 2). Environmental factors could be the main triggering factors for wheat midge population dynamics in irrigated and dryland spring wheat fields in Montana.

Figure 2. Wheat midge adult activity based on pheromone trap catch in dryland and irrigated spring wheat fields (2018-2019).

Parasitoids:

Sweep net samples collected on June 24 did not show any parasitoids in Valier and WTARC locations but P. tuberosula was present (6) in samples collected from dryland Ledger locations. We have observed some M. penetrans and P. tuberosula on midge trap sticky liners collected from all location on June 28. Later collected sweep net samples on July 08 and 22 contain both

M. penetrans (40) and P. tuberosula (18) in Valier, WTARC and Ledger locations. In 2019, the total cumulative parasitoid numbers per 150 sweeps were 51 and 14 compared to 48 and 12 in 2018 in irrigated and dryland fields, respectively.

M. penetrans has been established with adequate population level and P. tuberosula has been seen in some of the spring wheat fields. To improve P. tuberosula and E. error population establishment, 20,000 wheat heads will be collected again from spring wheat fields of Saskatchewan, Canada during the second week of August, 2019 and will be transported to WTARC. The same procedures will be followed for storing the wheat midge larvae, rearing and release of the parasitoids during the spring of 2020.

Acknowledgements

This work was supported by Montana Wheat and Barley Committee. We would like to thank summer interns for assistance with field work.