Development of Management strategies of Pulse Insect Complex in Montana

Principal Investigator: Dr. Michael Ivie

Project collaborators: Dr. Kevin Wanner and Dr. G.V.P Reddy

Project personnel: Pragya Kiju and Dr. Anamika Sharma

Montana State University, Western Triangle Agricultural Research Center, Conrad MT, 59425

Aim of the study

The different aims of this study were: 1. To develop the management strategies for pulse insect pest complex in Montana. ; 2. To perform larval and adult damage assessment of different pea varieties at two different sites. ; 3. To compare damage level by pea leaf weevil on different pea varieties. ; 4. To evaluate and establish efficacy of biopesticides. ; and 5. To develop pheromone- based low-cost technology “Attract and Kill Method”.

Location Study sites

The assessment was done at two sites, the Western Triangle Agriculture Research Center (WTARC) Conrad (48.307 ̊ N, 111.917 ̊ W), and Northern Agriculture Research Center (NARC), Havre (48.32 ̊ N, 109.40 ̊W). A total of 44 (32 at SW,12 at WR) varieties were assessed at WTARC and 54 varieties at NARC were assessed which were planted in a random block design for Statewide (SW) and Western Regional (WR) spring pea variety trails. Similarly, For the pheromone based low cost technology that is attract and kill method; the experiment was conducted on three sites; both of the above sites and at the Arthur Post agronomy farm, Bozeman (45.676998˚N, 111.042931˚W).

Materials and methods

1. Adult and larval damage assessment of different spring pea varieties:

   1. Adult damage assessment

      

      Figure 1. Adult pea leaf weevil feeding on pea leaves

      Adult pea leaf weevil feeds upon the leaf margins and the growing point of legume seedling and produce a characteristic distinct notch (Otani, 2013).The adult weevils feed on the leaves, chewing a half-moon shaped notch in the leaf edge (Fig.1) (Wanner, 2016). For the adult assessment, 10 individual plants are randomly selected from the plots of pea that were assigned according to the Random Block Design (RBD). The distinct number of notches made by pea leaf weevil are noted and recorded. Along with the notches, the nodal stage of pea and the number of leaves of the respective pea plant were also noted. The process was repeated for every plot. In WTARC, this process of recording was done from 23rd May to 28th May in both SW and WR spring pea variety. Meanwhile in NARC, the adult assessment was done from 29th May to 7th June.

       

       

       

   2. Larval damage assessment

      Pea leaf weevils lay eggs in the soil and the larva develop under the soil. They are “c” shaped milky white in color with the distinctive dark brown head capsule. After hatching, larvae enter the root nodules of the pea plant where they consume the contents of the nodules that is rhizobium bacteria of the host plant (Otani, 2013). Due to this feeding on the root nodules, it results in the complete or partial inhibition of nitrogen fixation and which therefore result in less yield due to poor growth.

       

      Figure 2. Root nodules of pea (left panel) and b. the larva found inside the root nodule (right panel).

      In both of the sites WTARC and NARC, the larval assessment was carried out with the following steps:

      5 plants were dug from each plot in a random way.

      • In WTARC, Conrad the process of taking out the samples was carried out from 22nd June to 23rd June whereas in NARC, Havre, the process was carried out from 9th July to 12th July.

      • Plants along with the soil intact were kept in the bags. All the samples were stored in a cool dry place.

      • From each bag, sample plants were taken out and put into respective buckets.

      • The buckets with the sample were filled with water. The plants were soaked to allow the soil to soften.

      • Inspection on respective bucket was done for floating larva. If larvae were present, they were scooped out with a net. The scooped larvae were taken out with the help of forceps and therefore were transferred into a labeled container.

      • The plants were rinsed through cold water until the soil intact was removed, thus exposing the root nodules. The roots with exposed root nodules were cut.

      • The cut root nodules were placed into the container and marked. Soil in the respective container were dumped on the sieve; sieve was placed above any sink or portable plastic tubs. The soil left on the screen was rinsed with the cold water.

      • The remnant on the sieve was sorted through. Root nodules or roots were accessed meanwhile. As not all the larvae float on the top of the bucket; when soil is caught in the bottom of sink or tubs, larvae if present were seen as floating on the water. Nets were used to scoop the floating larvae and were transferred to respective container. The deposits of soil were washed away. The screens, sinks, tubs were all cleaned completely. All the cut root nodules were stored in the refrigerator. The number of root nodules was counted and recorded in every plant. Each root nodules was cut and checked for larvae under a Microscope. The larvae if present were recorded and stored in 70 % ethyl alcohol.

Results

Table 1. Average number (x̄ ) of notches/leaf with the respective average number of larvae per plant ± Standard Error (SE) in the spring pea-variety trial of Western region at NARC, Havre.

The variety with the highest to lowest number of Notches/Leaf along with the respected number of larvae are arranged in the above Table 1. PS08101004 seems to have highest average number of Notches/Leaf that is 1.74 ± 0.17 standard error along with the respective average larvae of 2.50

± 1.89. PS16100102 has the lowest average number of Notches/Leaf that is 0.9 with 0.23 standard error with average larvae of 3.25 with the standard error of 2.29.

Table 2. Average number (x̄ ) of notches/leaf with the respective average number of larvae per plant ± Standard Error (SE) in the spring pea-variety trial of Western region at WTARC, Conrad.

Location:

The variety with the highest to lowest number of Notches/Leaf along with the respected number of larvae are arranged in the above Table 2. PS071000925 seems to have highest average number of Notches/Leaf that is 4.28±0.41 standard error along with the respective average number of larvae 10.75± 4.37. DS Admiral has the lowest average number of Notches/Leaf that is 3.06 with 0.33 standard error with average larvae of 11.25 with the standard error of 2.39.

Table 3. Average number (x̄ ) of notches/leaf with the respective average number of larvae per plant ± Standard Error (SE) in the spring pea-variety trial of Western region at NARC, Havre (SW)

The variety with the highest to lowest number of Notches/Leaf along with the respected number of larvae are arranged in the above Table 3. CDC Spectrum seems to have highest average number of Notches/Leaf that is 0.83± 0.28 standard error along with the respective average number of larvae 0. PS0877MT632 has the lowest average number of Notches/Leaf that is 0.23 and with 0.11 standard error with average larvae of 0.50 with the standard error of 0.5.

Table 4. Average number (x̄ ) of notches/leaf with the respective average number of larvae per plant ± Standard Error (SE) in the spring pea-variety trial of Statewide at WTARC, Conrad

Location:

The variety with the highest to lowest number of Notches/Leaf along with the respected number of larvae are arranged in the above Table 4. PS0877MT076 seems to have highest average number of Notches/Leaf that is 0.47± 0.08 standard error along with the respective average number of larvae 6.00± 5.02. DS-Admiral has the lowest average number of Notches/Leaf that is 0.20 and with 0.02 standard error with average larvae of 0.75 with the standard error of 0.25.

2. Development of pheromone -based monitoring and mass trapping for pea leaf weevil Materials and methods

• Insecticide (Deltamethrin) (0.03 gram)

• Aggregation Pheromone (4–methyal-3,5-heptanedione) (used in pellet form and rubber

  septa form, Manufactured from ChemTica International, Costa Rica)

• Soil sampler

• Stakes

Figure 3. Pellet in the pit and fall trap (left panel); b. granular insecticide used (right panel).

Figure 4. Demonstration of attract and kill method strategy in NARC, Havre.

The main principle of this project is to attract mass number of pea leaf weevils and then kill through the insecticide. The trial was laid out with a Complete Randomized Block Design (CRBD) with 5 Treatments and 8 Replications in both WTARC, NARC. At every 10 m of distance, one treatment was set. Also, the same experiment was carried on the Arthur Post agronomy farm MSU, Bozeman.

Table 5. Number of treatments with the materials used

For every treatment (Table 5), 2-inch deep hole was dug. At every hole, same weight of insecticide was spread evenly. With respective design in (Table 6) each treatment was completed. Long stakes were put at every treatment for identification. At intervals of 7-8 days, observations were recorded.

Experimental Design

Table 6. Design for “Attract and Kill” project in NARC, Havre

Results

No result for this experiment was obtained. At this later date pea leaf weevil migration and attraction to aggregation pheromone may vary. No pea leaf weevil was collected during this experiment at either of the sites. This experiment will be repeated in 2020 earlier in the spring season when pea leaf weevils are actively migrating into pea fields.

Acknowledgements

This work was supported by USDA-NIFA-Montana. We would like to thank summer interns Ryan, Carley Ryes, Johnathan Blanchard for assistance with field work. We would also like to thank the producers, John Miller and Peggy Lambert for providing the fields to establish experiments.

References

Wanner, K.W. Pea leaf weevil. MontGuide : Montana State University: Bozeman , MT, USA, 2016; pp.1-2

Otani, J. Pea Leaf Weevil: Sitona lineatus Linnaeus Monitoring Protocol, 2013