Control of adult striped cucumber beetle with a natural enemy parasitoid and an insect parasitic nematode

Grower survey of interest in biological control:
In 2004, a survey was taken on pumpkin crop management during the Pumpkin Field Day held at the Western Agricultural Research Station in South Charleston, Ohio. Twenty-five growers were personally handed a one-page questionnaire and 20 of those growers returned the questionnaire with responses to some or all of the questions.

Resource enhancement of the effects of C. setosa:
The field experiments in 2004 were designed as a randomized complete block with two treatments and two blocks. One experimental block had three replications of 470 square meter pumpkin fields at an agricultural research site, and the other experimental block had three replications of 470 square meter pumpkin fields, one at each of three commercial vegetable farms. The agricultural research site was located at the Western Agricultural Research Station in Clark County, Ohio, and the other three replicates were located on separate commercial farms in Clinton, Licking, and Franklin Counties. The control treatment and experimental treatment were applied at each site. The experimental treatment was a habitat created by planting a mixed flowering border of purple tansy, Phacelia tanacetifolia, and nasturtiums, Trapoleum majus, planted on two edges of a pumpkin field. The control treatment was the natural habitat of weeds and grasses at the edge of the pumpkin field. The two flower species were chosen for their known high nectar production, tolerance of poor soils, and horticultural availability.

The variety ‘Magic Lantern’ pumpkin was used at all sites, and plot dimensions of 27 meters by 20 meters were used for each treatment. Pumpkin seeds were planted 0.3 to 1 meter apart within the row, and rows were spaced as four pairs with 1.5 meters spacing and a large 5 meter space as a driving lane in the middle of each plot. The buffer between treatment plots in Clark County was 67 meters of soybean, and the sites located on commercial farms had buffers of 30 meters of pumpkin. Flowering border treatment plots on commercial farms were modified to plant flowering borders in an L-shape along the field due to the need for sprayer access for weed and disease management. At the research station, pre-emergent herbicide was used immediately after pumpkin seed planting, but no insecticides were used on the pumpkin fields. Two of the three commercial farms sprayed their pumpkin fields with a broad spectrum insecticide at planting and in the late season, depending on severity of beetle infestations. In Licking County, the commercial farm was under organic crop management practices and used no chemicals.

To compare parasitism in pumpkin plots with flowering borders to plots without flowering borders, beetles were collected by hand-held aspirator from pumpkin flowers in September. Beetle collection was delayed until the end of the season, early September, to allow parasitism in the beetle population of each plot to accumulate undisturbed. In treatment plots where stands of flowering borders did not properly establish, beetles were not collected and the block was omitted from analysis. One hundred beetles was the target sample size for the end of the season beetle evaluations. Beetles were collected down each row of pumpkins and across the entire plot and held for observation.

Calculations and statistical tests were attempted to detect difference between the percentage parasitism of beetles found in pumpkin fields that had flowering borders versus beetles found in unaltered pumpkin fields.

Inundative application of insect parasitic nematodes:

The randomized complete block design of the experiment included six replicates and four spray treatments:
1. water control
2. high rate nematode solution (15 nematodes per 10 microliters water)
3. low rate nematode solution (5 nematodes per 10 microliters water)
4. standard rate of carbaryl, Sevin XLR (1 quart per acre)

Treatment sprays were scheduled for the late season only, to target the summer generation of striped cucumber beetle. The experiment was designed to have approximately 24 plants per treated plot, with 6 meters within row spacing and 10 meters between rows. Each plot was 75 meters by 45 meters and adjacent plots were separated by 30 meters of bare-ground or untreated pumpkins. In June 2004, field plots at Waterman Research Laboratory in Columbus, Franklin County, OH and the Western Agricultural Research Station in South Charleston, Clark County, OH were direct seeded with ‘Magic Lantern’ pumpkin with imidacloprid (Admire 2F®) applied in furrow. Imidacloprid was applied as a low rate solution, 16 fluid ounces per acre, to protect cotyledons from defoliation by the overwintering generation of striped cucumber beetle and other pests and to allow pumpkin establishment. Curbit® was used to control weeds and bimonthly sprays of a fungicide mix (Quadris, Bravo Ultra, Nova, Ridomil Gold, Terronil, or Amistar) were applied in rotation from July 21 until August 27 to control fungal diseases. These chemical were used to ensure good pumpkin stand development, and therefore allow us to collect beetle data. Experimental treatments were applied and data were collected during the flowering and fruiting stages.

Nematode solutions were based on rates used to control turfgrass grubs by foliar backpack application. The recommended rate for turf is 25 infective juvenile (IJ) nematodes per square centimeter, and the high rate is 50 IJ nematodes per square centimeter, equivalent to 2500 IJ /m² and 5000 IJ /m² respectively (Grewal 2004). In this experiment, approximately four liters of nematode solution was applied to each site for each spray. By calculation, low and high treatments were 2500 IJ /m² and 7500 IJ /m². Before applying nematode solution, concentrations of nematodes were verified under the microscope, and the high rate nematode solution for this field experiment was 15 IJ / 10 µl of water and low rate was 5 IJ / 10 µl of water. Sprays began after weekly field scouting showed that flowers were present and beetles were infesting the pumpkin fields at both sites at a minimum density of one beetle per flower. Four inundative sprays were applied at each site at 1 to 2 week intervals, which covered the flowering stage of the crop. Time intervals between sprays varied due to weather and availability of Hb GPS-11 infective juveniles. Nematode sprays were applied by backpack sprayer (Deluxe model 425, SOLO Inc., Newport News, VA) operated at 15 psi with a size 10 cone nozzle and a size 50 screen. Nematode sprays were directed into open flowers in the morning from 9 to 10 AM. Carbaryl sprays (56 milliliters of Sevin XLR in 5.8 liters of water per 8640 square feet) were also applied by backpack, but sprays were full coverage sprays that covered the entire canopy in the treatment plot. Carbaryl sprays were applied in the afternoon, when flowers were closed and bees were not active. Sprays began in early August and ended in mid-September.

Scouting for adult beetles in flowers was performed in each plot 48 hours after sprays were applied. The number of beetles in 30 flowers was recorded for individual species: A. vittatum; western corn rootworm, Diabrotica virgifera virgifera; spotted cucumber beetle, Diabrotica undecimpunctata howardi; and northern corn rootworm, Diabrotica barberi. The number of flowers present in each plot varied from a high of 30 in early August to 10 flowers by mid-September. At harvest, for each treatment plot, pumpkins were weighed in kilograms with a sample size of 20 fruit at Clark County, where productivity was higher and 10 fruit at Franklin County, where fruit production was lower. Pumpkins were evaluated for beetle feeding damage on the rind and stem using a 0, 1, 2, and 3 rating. Striped cucumber beetle density, expressed as the mean number of beetles per flower, was calculated by the scouting data for each treatment plot and for each spray. The sum of all beetle species (including western corn rootworm and spotted cucumber beetle) density was calculated as the mean number of beetles, any species, per flower for each treatment plot and each spray. For each research site, striped cucumber beetle density and the sum of all species density for each scouting date were statistically analyzed by two-way ANOVA using MINITAB 14.