Western Corn Rootworm Adults Research Articles

Model of the Biotic Potential of Western Corn Rootworm (Coleoptera: Chrysomelidae) Adult Populations, and Its Use in Studying Population Dynamics

A model of the biotic potential of western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, adult populations was developed from data presented in the literature. Adult emergence, adult populations, and egg populations were measured in a total of five continuous cornfields in 1982 and 1983. The simulations made with the model suggested that the observed populations of WCR adults and eggs were far below their potential (one-third and one-fifth, respectively). With the use of the biotic-potential model, adult population sizes were simulated by using different mortality (including dispersal) regimes. The results of these simulations suggest that age structure may be important in determining the potential of WCR adult populations. A regime that allowed the earlier emerging adults to remain in the field for a longer period fit the observed adult and egg population data better.

Effects of Adult Western Corn Rootworm (Coleoptera: Chrysomelidae) Ear Feeding on Irrigated Field Corn in Colorado

Effects of adult western corn rootworm, Diabrotica virgifera virgifera LeConte, feeding on corn yield were assessed over a 4-year period by confining beetles in various densities to corn ears. Corn rootworm survival was good under conditions of the study and generally resulted in a direct positive correlation between beetle number and superficial injury. However, analysis of yield parameters (kernel weight, and kernel number per ear quarter and per ear) indicated that densities of up to 20 beetles per ear did not significantly reduce yield. Some evidence of compensation was observed, with the tip quarter of the ear often exhibiting a positive linear response to beetle density, and the other ear quarters exhibiting nonlinear responses. Similarly, mechanical defoliation studies suggested that moderate levels of silk clipping could be tolerated.

Susceptibility of Western Corn Rootworm Adults From Illinois to Carbofuran, Terbufos and Fmc 67825, 1985

Abstract Adult beetles were collected from nine separate locations in northern Illinois from fields with organophosphate, carbamate and mixed insecticide use histories as well as from an untreated field on 25-27 Jul. Control problems had been reported for the organophosphate fields. The beetles were caged, provided with fresh corn silk, and treated within 24h at the FMC Research Farm at Champaign, IL. Individual beetles were topically treated with 1.0 microliter of acetone: insecticide solution (technical grade) on the ventral abdomen using a Burkard microapplicator. At least 4 or 5 dosages were of carbofuran, terbufos, or FMC 67825 were used to determine 24h LD50‘s. Each test was replicated twice (10 beetles per replication) and the tests were repeated 2 or 3 times on separate days. Beetles were considered dead if they did not move or regain a standing position 24h after treatment. Dosage-mortality data were calculated by a logit analysis program and the LD50‘s corrected for beetle weight.

Influence of Population Density of Immatures on Size, Longevity, and Fecundity of Adult Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Field tests with controlled infestations of eggs of Diabrotica virgifera virgifera LeConte showed that larvae at higher infestation rates were stressed for food. The percentage of insects reaching the adult stage was significantly reduced at infestation rates above 600 eggs per 30.5 cm of row. Adults were significantly smaller at infestation rates above 300 eggs, they were shorter-lived at rates above 600 eggs, and they were less fecund at infestation rates above 1,200 eggs per 30.5 cm of row. These results indicate that high densities of immatures have a deleterious effect on number, size, longevity, and fecundity of adult western corn rootworms.

Response of Western Corn Rootworm (Coleoptera: Chrysomelidae) Adults to Several Semiochemicals in Cornfields

We conducted studies in corn fields to examine the response of western corn rootworm, Diabrotica virgifera virgifera LeConte, beetles to slices of a bitter Cucurbita sp. fruit and microtubes containing either western corn rootworm sex pheromone or crude extracts of a bitter Cucurbita sp. stems and leaves. Sticky traps were used to measure beetle populations. Plots treated with Cucurbita sp. fruit slices or pheromone lures had significantly (P <0.05) higher catches than control plots for ca. 15 days after treatment. Foliage extract lures did not successfully attract beetles to a treated plot. Both sex pheromone lures and bitter Cucurbita sp. fruit may be useful to manage western corn rootworm populations in corn fields.

Monitoring Populations of Corn Rootworm Beetles (Coleoptera: Chrysomelidae) with a Trap Baited with Cucurbitacins

A trap is described that uses cucurbitacins and carbaryl to capture and kill northern and western corn rootworm beetles ( Diahrotica barberi Smith and Lawrence and D. virgifera virgifera LeConte, respectively). The trap is consistent in numbers of beetles captured per trap per day, and it should be useful in integrated pest management programs that monitor the population density of corn rootworm beetles in cornfields. Captures in 1981, 1982, and 1983 in Illinois showed that western corn rootworm adults that disperse into first-year cornfields were predominantly females.

Comparison of Adult Corn Rootworm (Coleoptera: Chrysomelidae) Trapping Techniques as Population Estimators

Eight trapping methods were compared for their ability to sample populations of adult northern and western corn rootworms, Diabrotica barberi Smith and Lawrence and Diabrotica virgifera virgifera LeConte, respectively. Comparisons of sampling efficiency, fidelity with standard sampling methods (ear zone and plant counts), sampling precision, and sex and species capture ratios were made among these sampling techniques. Two of the trapping techniques, the unbaited Pherocon AM trap and the ear level, cylindrical sticky trap, were found to have the best adult corn rootworm sampling characteristics. These trapping techniques were significantly correlated with the standard sampling methods, and their sampling precisions were the highest of all the traps tested. Also, both techniques sampled corn rootworm populations similarly with respect to sex and species captured. Therefore, either the unbaited Pherocon AM trap or the ear level, cylindrical sticky trap could be used effectively as a relative sampling method for adult corn rootworms.

Influences of Rainfall and Sprinkler Irrigation on the Residual Activity of Insecticides Applied to Corn for Control of Adult Western Corn Rootworm (Coleoptera: Chrysomelidae)

A western corn root worm, Diabrotica virgifera virgifera LeConte, adult bioassay technique using insecticide-treated corn leaves was used to determine the influence of moisture on the residual activity of several insecticides. Results of the studies indicated that moisture (rainfall or sprinkler irrigation) was a major factor influencing the decline in residual activity of carbaryl, carbaryl-oil, phosmet, and Penncap-M. Residual activity of dlazmon and malathIOnwas neghgible at 7 days, regardless of the amount of moisture. In tests comparing dry land and sprinkler-irrigated treatments, there was a significant negative correlation (r = −0.91) between percent control and the amount of water applied. Both linear and quadratic effects were highly significant (P <0.005). There were no significant linear or quadratic effects detected between percent control and days post application. Carbaryl-oil, diluted with ¼ part diesel fuel, and carbaryl-XLR provided slightly shorter residual activity than undiluted carbaryl-oil treatments. However, all three treatments provided considerably longer residual activity than other insecticides tested.

Eugenol, a New Attractant for the Northern Corn Rootworm (Coleoptera: Chrysomelidae)1

Eugenol, a component of the best commercially available, food-type lure for Japanese beetles, Popillia japonica Newman, was attractive to adults of the northern corn rootworm (NCR), Diabrotica barberi Smith and Lawrence. Captures of NCR increased significantly as concentrations of eugenol in traps increased, and more beetles were attracted to eugenol-baited traps placed outside of a cornfield than to traps placed within the field. Adult western corn rootworms, Diabrotica virgifera virgifera Le Conte, which feed almost exclusively on corn, were not attracted to eugenol. Attraction of NCR to eugenol, a compound distributed widely in the plant kingdom, may indicate the extent to which NCR is adapted to feed on hosts other than corn.

Aldrin and dieldrin residues in Nebraska soils as related to decreasing LD50values for the adult western corn rootworm ‐ 1962–1981

Abstract Aldrin was recommended and used to control the western corn rootworm (Diabrotica virgifera LeConte) (WCR) in Nebraska from 1952 to 1961. During that period, LD50 values for adult WCR tested against aldrin were determined for 19 collection sites in Nebraska. Mean 24 h LD50 values for these sites decreased from 1,539 μg/g in 1962 to 355 μg/g for 1981. A correlation existed between the amount of aldrin used for soil treatments and the aldrin and dieldrin residues, with decreasing LD50 values for the WCR over the observation period.

Spectral Response of the Adult Western Corn Rootworm (Coleoptera: Chrysomelidae) to Selected Wavelengths1

Adults of Diabrolica virgifera LeConte were placed in choice boxes whose tops consisted of filters of six different wavelengths ranging from ultraviolet to red. Observations to determine the most attractive wavelengths, made five times daily, indicated that wavelengths in the yellow spectral region were significantly more attractive than those in the red region; additionally, red was more attractive than other wavelengths tested. The use of colored traps for assessing field populations of adult western corn rootworms is indicated.

Sampling Plan for Population Estimation of Northern and Western Corn Rootworm Adults in Iowa Cornfields 1

Sample sizes were determined for three adult corn rootworm sampling techniques. Sources of variation in the sampling plan used were analyzed with a nested analysis of variance. Plant-to-plant, ear-to-ear, and trap-to-trap variation accounted for the greatest percentage a variability, on a within-field basis, in their respective analyses. Optimum allocations of sample units were two plants per site, five ears per site, and one trap per site. Comparisons of precision and cost of the three methods revealed that plant counts provide the most precise estimate of beetle populations for the least cost.

Spatial Dispersion Patterns of Northern and Western Corn Rootworm Adults in Iowa Cornfields 1

Three adult corn rootworm sampling techniques were employed in 59 Iowa cornfields during August 1976 and 1977. Northern and western corn rootworm beetle counts were analyzed by Green's coefficient, Cx, and Iwao's regression method, m* = a + b m, to determine spatial dispersion patterns. Both indices indicated that most rootworm beetle populations sampled were characterized by aggregated dispersion. Spatial behavior in rootworm beetles tended to be density dependent. Some populations with large mean densities, however, did not differ significantly from randomness.

Topical Toxicity of Soil Insecticides to Western Corn Rootworm Adults in NE, 1981

Abstract Western corn rootworm beetles were collected between Jul 13 and Aug 6 from corn at 19 geographical sites throughout NE and returned to the laboratory in Lincoln for testing. Mean weights for beetles from each collection site were determined prior to tretment. Unsexed beetles were individually treated by topical application of 1 ml of an acetone solution of the test insecticides to the posterior ventral abdominal area. Beetles were anesthesized with CO2 prior to treatment. Treatment solutions were prepared with reagent grade acetone using technical grade insecticides. Six to eignt dosages, plus an acetone check, were used to determine 2 hr LD50. values for all insecticides from all collection sites; 2 replicates of 10 insects each were used for each dosage rate tested. Insects were declared dead if they could not regain their footing 2 hr post-treatment. Dosage-mortality data were calculated in mg/g of insect weight using a FORTRAN computer program.

Influence of Constant and Changing Temperatures on Locomotor Activity of Adult Western Corn Rootworms ( Diabrotica virgifera ) 1 in the Laboratory 2

An actograph was used to determine diel locomotor periodicity and influence of constant and changing temperatures on adult western corn rootworm ( Diabrotica virgifera LeConte) locomotor activity in the laboratory. Diel periodic fluctuations in activity occurred with reduced activity from 9 a.m. to 5 p.m. and a high level of activity from 5 p.m. to 8 a.m. Maximum activity for males and females occurred at 23°–25° and 25°–27°C, respectively, with negligible activity for both sexes at 10° and 40°C. Males were generally more active than females, especially in the maximum activity temperature range. Female activity exceeded male activity at high temperature ranges. Decreasing temperature conditions increased activity levels over constant-temperature comparisons at low temperatures for both male and female beetles.

The Structure of the Apparent Pheromone-Secreting Cells in Female Diabrotica virgifera1,2

Secretory-type epithelial cells of the adult female western corn rootworm, Diabrotica virgifera LeConte (Chrysomelidae), apparently responsible for releasing the sex pheromone, are composed of 2 groups of cells. One group is columnar, arranged in a “U” shape, and located dorsally between tergites 7 and 8; the cells of the 2nd group are cuboidal and located ventrally between sternites 7 and 8. Individual cuticular pore openings occur on the 7th abdominal segment and correlate spatially with the epithelial secretory cells.

Corn Rootworm Cholinesterase Activity as Influenced by Species, Sex, Age, and Cold Storage12

Cholinesterase (ChE) activity was determined for larval and adult whole body homogenates of the western corn rootworm (WCR), Diabrotica Virgifera LeConte, and the southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber. Significant differences (P<0.001) existed in enzyme activity levels between the species at the 3 stages of comparison (3rd-instars, adult females, and adult males). Third-instar WCR had considerably higher ChE specific activity levels than WCR adults and 2nd-instar WCR when expressed on an individual basis. Third-instar SCR had less specific activity than 3rd-intar WCR. Enzyme levels of 3rd-instar SCR were similar to those of adult SCR enzyme levels. In WCR, ChE activity differences between the sexes were minimized when dimorphism by weight was considered. ChE was not stable beyond one day when the supernatant was refrigerated at 8°C, whereas freezing the supernatant at −12°C for 8 weeks caused no significant change when compared to fresh material. Storage of the supernatant at −12°C for 24 weeks reduced ChE activity by 6%

Adaptation of a Dry Diet for Adults of the Western Corn Rootworm1

A dry diet used routinely for maintenance of adults of the southern corn rootworm, Diabrotica undecimpunctata howardi Barber, was altered for use with western corn rootworm, D. virgifera LeConte, adults. The alteration was accomplished by ball milling the diet to a fine powder and then either forming it into a pellet or texturizing it. Longevity of western corn rootworm adults on the dry diet was some what reduced compared to those on a diet of fresh com leaves, but fecundity was not significantly affected. Tests with various oviposition schemes indicated that the western corn rootworm adult preferred to oviposit at a coveredsite either in soil or moist gauze.

Comparison of Gut Contents of Adult Western and Northern Cora Rootworms 1 in Northeast Nebraska 2

Tests were made to determine if apparent feeding differences observed in the field between adult western corn rootworms (WCR), Diabrotica virgifera LeConte, and northern corn rootworms (NCR), D. longicornis (Say), actually exist. Beetles were collected from corn plants and weeds in northeast Nebraska cornfields, and the gut contents examined and identified. Several significant feeding differences were demonstrated between species and between sexes within species: gut contents contained different proportions of corn leaf tissue, corn pollen, corn silks, weed pollen, fungal spores, and gregarine sporonts. The NCR fed more extensively on pollens of other plants in addition to corn than did the WCR. A higher percentage of WCR contained gregarine sporonts than did the NCR and more males of each species contained sporonts than did females. Gut contents indicate that males are more mobile within a field than females.

Diel Activity and Vertical Flight Distribution of Adult Western Corn Rootworms in Iowa Cornfields12

Vertical yellow sticky traps, 3.048 m long and 10.160 cm diam, were utilized at 5 locations during 1973 and 1974 to ascertain the diel periodicity and vertical flight distribution of Diabrotica virgifera LeConte in cornfields ( Zea mays L.). Western corn rootworm flight activity is bimodal with flight activity peaks occurring in the 2–3 h periods after sunrise and before sunset. Flight activity peaks were further characterized by a temperature range of 22.2 to 27.0°C. Statistical differences (0.05 level) in height of flight activity between the sexes were not observed below 182.88 cm where the majority of the insects was captured. Significantly more (0.05 level) females than males were captured between 182.88 and 304.80 cm. The 2 sexes fly at the same time and height of flight showed no relationship with time of day.