Field Evaluation of Bio-pesticides Against Wheat Midge, Sitodiplosis mosellana

Principle Investigator: Dr. Gadi V.P. Reddy

Project personnel: Govinda Shrestha, Dan Picard, John Miller, Julie Prewitt and Debra Miller 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 aim of this study was to examine the commercially available bio-pesticides against wheat midge management.

Materials and methods

Spring wheat fields

The experiments were conducted at three field locations: East Valier (N 48o 30.206 W112 o14.350), North Valier (N 48o 35.192 W112 o 21.169) and East Conrad (N 48o 14. 403 W111o 60.119), in the Golden Triangle area of Montana, United States, during summer of 2016. This area is situated in an important cereal growing region in Montana. Three field locations were selected based on the high level of infestations caused by S. mosellana in previous years (https://pestweb.montana.edu/Owbm/Home). A randomized complete block design with four replicates was used, with 8 × 4 m treatment plots separated from other plots by 1 m buffer zones to avoid any overlap of treatment effects. The trials were conducted in a spring wheat field with the cv. “Duclair”.

Monitoring of wheat midge adults flights using a pheromone trap

To select the best date for application of bio-pesticide products, S. mosellana adults (male) flights were monitored using pheromone traps, as a method described by Gries et al. (2000). Wheat midge populations were monitored using delta traps baited with pheromone lures ((2S, 7S)-nonadiyl dibutyrate) (Great Lakes IPM, Inc., Vestaburg, MI), with sticky card inserts (Scentry®) at experimental fields. Delta traps were painted green to reduce non-target insect catch and positioned at the height of the wheat canopy (Thompson and Reddy, 2016). At each experimental field, a single trap was placed 20 m inside from the field edge, and the trap height was adjusted weekly to match the height of the wheat canopy. The trap was set on June 10 at each experimental location and monitored almost every day from Monday to Friday and continued until wheat plants crossed the susceptible stages.

Bio-pesticide products treatment application

Commercial formulations of five bio-pesticide products were used for the study. Mycotrol ESO® (Beauveria bassiana GHA) and Xpectro OD® (Beauveria bassiana GHA + pyrethrin) were obtained from Lam International (Butte, MT), entomopathogenic nematode Steinernema feltiae from Sierra Biological Inc. (Pioneer, CA), jasmonic acid from Sigma-Aldrich (St. Louis MO) and, PyGanic EC® 1.4 (pyrethrin) from McLaughlin Gormley King (Minneapolis, MN). The established concentrations of these products in the study were based on the product dose recommendation from company or the studies that have shown effective control against several insect pest species (Table 1).

Table 1. Materials and application rates of bio-pesticides used for the field studies against wheat midge Sitodiplosis mosellana.

All bio-pesticide products were mixed with normal tap water, however: for jasmonic acid product, it was first dissolved in acetone and then mixed with water (Wakeil et al. 2010) and; for entomopathogenic nematode product, 1 % polymer gel was added further in mixture of entomopathogenic nematode and tap water (Antwi and Reddy 2016). Two controls were included in the study: 1) water served as a negative control and, 2) Lorsban worked as a positive control/reference chemical, since this chemical has been widely used by spring wheat growers in Montana to control wheat midges (Thompson and Reddy 2016; Stougaard et al. 2014).

All bio-pesticide product treatments including controls were applied on the same date at all field experimental trail locations. However, at East Conrad location, the wheat midge adults population was found extremely low based on pheromone trap data and the spring wheat plants were also found to cross wheat midges’ susceptible stages. This field location was, therefore, decided to discard for bio-pesticide treatment applications. The treatments were sprayed using a SOLO backpack sprayer (SOLO, Newport News, VA), delivering the volume of 408 L mixture/ha. The plots were sprayed at 29th June, 2016, when the wheat plants were at midge susceptible stage (early boot) and the peak emergence of wheat midge adults was occurring. Furthermore, scouting was performed to determine wheat midge threshold level for treatment. The spraying activity was performed between 7- 9 pm as adult’s activity seems to be high in the fields.

Wheat midge larvae in white traps

White traps were used to assess the wheat midge larval population in the treatment plots and the method was adapted from El-Wakeil et al. (2010). The traps, made of plastic dishes (diameter =12.5 cm; height = 6.5 cm), were placed on the soil surface among wheat plants in each plot. Each trap was partly filled with tap water (100-150 ml) and 3-4 drops of soap detergent. Four days after treatment, two traps were placed in each treatment plot. Samples were collected from traps every week, immediately brought to lab and the presence of midge larvae in each sample was identified under a binocular or stereomicroscope.

Figure 1. Wheat midge populations at three study locations

Midge-damaged wheat kernels

Wheat midge-damaged kernels in the biologically based or control treatment plots were assessed when the wheat kernels were about ready to harvest. Ten wheat ears were randomly sampled from each treatment plot, placed in a brown paper bag, transported immediately to the laboratory and dried at room temperature for 7 days. Wheat ears were subsequently threshed individually by hand to obtain the total number of wheat kernels and midge-damaged kernels per wheat ear. The midge- damaged kernels were characterized based on the criteria (such as shriveled, cracked or deformed kernels) reported by Kondel and Ganehiarchchi (2008) and Stougaard et al. (2014).

Parasitoid Macroglenes penetrans population

This study was performed to determine whether the bio-pesticides or Lorsban treatment had a significant impact on parasitoid populations as it has recently stated the presence of M. penetrans in the Golden Triangle area of Montana (Reddy and Thompson 2016). To obtain parasitoid population estimate, sweep net method was used. Sweeping was conducted with a standard sweep net, and 20 sweeps were made per treatment plot.

Yield and quality of wheat kernels

Hege 140 plot combine was used to thresh the wheat grains from treatment plots. The precautions were used to avoid the borders and any overlap of treatment effects on wheat yield and quality. Each plot was trimmed from edges, plot length was measured and the wheat grain threshing was done only from the center of each plot. Wheat grains were cleaned with a seed processor (Almaco, Nevada, IA) and weighed on a scale to determine yield and test weight. The protein and moisture content of seed was determined with NIR grain analyzer IM 9500 (Perten Instruments, Springfield, IL).

Statistical analysis

One-way analysis of variance (ANOVA) was performed to test the bio-pesticide treatments had significant abilities to protect kernels from wheat midge damages and, to improve yield and qualities (test weight, protein percentages and moisture percentages) of spring wheat in comparison with two controls; water and Lorsban treatment at each trial location. A normal quantile-quantile plot was performed to confirm normality of data and equality of the variance. No transformation of data was required to achieve normal distribution. Tukey’s post hoc test was used for multiple comparisons among the treatment means. Similarly, for the sweep net data set, one way analysis of variance (ANOVA) was performed to examine the effect of treatments on total population of parasitoid M. penetrans adults at each trail location.

The water traps data was found to be non-normally distributed even after the log transformation, and the non-parametric one-way analysis of variance (Kruskal-Wallis test), was consequently used to examine effect of treatments on wheat midge larvae per sampling time across the treatments on each sampling date. A Mann-Whitney U-test was used as a post hoc test for multiple comparisons between the means followed by a Bonferroni correction.

Results

Wheat midge adult activities based on pheromone trap catch

In all three field sites, the flight activities of wheat midge adults began in about the same time, June 15-21 of the year 2016 (Fig 1). Within the two weeks, adult activity accelerated sharply at East Valier, gradually at North Valier and presented very low at East Conrad (Fig 1). The economic threshold levels of wheat midge adults’ activity that warranted the application of control measures in relation to susceptible stages of spring wheat were only found at the East Valier and North Valier locations, while it was not observed in the East Conrad location (Fig 1). The cumulative number of adult midges observed in East Valier, North Valier and East Conrad were: 2397, 855 and 121 respectively.

Larval populations

Irrespective of treatments or trial locations, no wheat midge larvae were caught in water traps until the first three sampling dates with exception of few larvae (0.25-0.50) caught in Lorsban and entomopathogenic nematode treatments at the East Valier location but without significant differences (Table 2). However, at fourth and fifth sampling dates, wheat midge larvae were found in all treatment plots at both trial locations. The significant differences in midge larvae were recorded between treatment plots at fourth (χ2 = 23.42; df =6; P < 0.001, Kruskal-Wallis test) and fifth sampling (χ2 = 18.43; df =6; P < 0.01, Kruskal-Wallis test) dates in the East Valier location while only at fourth sampling (χ2 = 22.82; df =6; P < 0.001, Kruskal-Wallis test) date in the North Valier location.

Table 2. Effect of bio-pesticides on wheat midge larval populations (two traps/plot)

Mean values within columns bearing the same letter within each location are not significantly different (Mann Whitney-U test, P > 0.05).

Kernel damage

Regardless of treatments, higher kernels damage percentages inflicted by wheat midges was observed at East Valier as compared to North Valier (Fig 2) and this result was further supported by number of wheat midge adults caught on pheromone traps in study sites (Fig 1). Kernel damage percentages recorded in bio-pesticide treatment plots including the water and Lorsban varies from 20-48 % and 11-23 % at East Valier and North Valier respectively (Fig 2). However, bio-pesticide treatments had found significant impact on wheat midge kernel damage at both field sites: East Valier (df = 6, 258; F = 11.7; P ˂ 0.001) and North Valier (df = 6, 267; F = 7.40; P ˂ 0.001).

Among the biopesticide treatment plots, interestingly, the significantly lower kernel damage percentages were observed when wheat plots were treated with jasmonic acid, entomopathogenic nematode or Xpectro over water control plots at both field sites. In contrary, other two biopesticides treatments: pyrethrin and Beauveria bassiana had not protected the wheat kernels from wheat midge damages and the kernel damage levels were similar to water treated plots.

Fig 2. Wheat kernel damage percentages inflicted by wheat midges in bio-pesticide treatments. Bars bearing the same uppercase and lower case letters are not significantly different (Tukey test, P > 0.05).

Yield

To assess the impact of bio-pesticide treatments on wheat grain yield, the obtained yield data of each bio-pesticide treatment plot was compared with yields from the untreated (water control) and Lorsban treatments (positive control) plots. The result clearly depicted that bio-pesticide treatments had a significant impact on wheat grain yield at both field sites: East Valier (df = 6, 21; F = 8.03; P ˂ 0.001) and North Valier (df = 6, 21; F = 11.27; P ˂ 0.001). Grain yield at the East Valier site was significantly higher for treatments with the entomopathogenic nematode or jasmonic acid as compared to the treatment with water control (Fig 3). The yield of these two biopesticide treatments were also similar to treatment with Lorsban control, with no significant difference (Fig 3). In contrast, B. bassiana (Mycotrol) or B. bassiana in conjunction with pyrethrin (Xpectro) treatments had not improved the wheat grain yield as compared with yield obtained from Lorsban control treatment (Fig 3), while there was no significant difference in grain yield between the pyrethrin or Lorsban treatment groups (Fig 3). Similarly, at the North Valier site, significantly improved yield production was also observed with entomopathogenic nematode, jasmonic acid or B. bassiana in conjunction with pyrethrin treatments over the untreated control. In contrast, B. bassiana (Mycotrol) or pyrethrin treatments had not impact on wheat grain yield (Fig 3).

Fig 3. Yield of spring wheat treated with bio-pesticides. Bars bearing the same uppercase and lower case letters are not significantly different (Tukey test, P > 0.05).

Quality

Test weight, protein content % and moisture % were measured as a part of wheat kernel quality to determine whether the biopesticide treatments had an effect on these parameters compared with the untreated (water control) and Lorsban (positive control) treatments. Test weight across the treatments varies from 58 to 62 (lbs/bushel) and from 59 to 62 (lbs/bushel) at East Valier and North Valier respectively (Table 3). Treatments had a significant impact in test weight at East Valier (F = 8.96; df = 6, 21; P ˂ 0.001) while no significant differences at North Valier (F = 2.26, df = 6, 21; P = ˃0.05). With respect to other quality parameters, treatments had not shown any impact on protein or moisture percentages at both field sites: East Valier (protein: F = 0.52; df = 6, 20; P = 0.79 and moisture: F = 0.95; df = 6, 20; P = 0.49) and North Valier (protein: F = 0.74; df = 6, 20; P = 0.62 and moisture: F = 0.60; df = 6, 20; P = 0.73). The overall average protein and moisture percentages were: 16-17 and 10-11 respectively, irrespective of treatments and field sites (Table 3).

Table 3. Quality of spring wheat treated with bio-pesticides

Mean values within columns bearing the same letter within each location are not significantly different (Tukey test, P > 0.05).

Parasitoid population

Regardless of locations, bio-pesticide or Lorsban treatments had no significant impact on examine on total population of parasitoid M. penetrans adults (P > 0.05). The total mean number of parasitoid adults per treatment plot recorded at two locations; North Valier and East Valier ranged from 1.25 – 3.00 and 1.00 – 4.00 respectively.

Acknowledgements

This work was supported by Montana Wheat and Barley Committee. This material is also based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, Multistate Project W3185, # The Working Group Biological Control of Pest Management Systems of Plants under Accession # 231844. We would like to thank cooperator growers (Cory Crowford and Jody Hobel) for allowing their fields for the study.

References

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