Developmental Biology and Effects of Adult Diet on Consumption, Longevity, and Fecundity of Colaspis crinicornis (Coleoptera: Chrysomelidae).

The chrysomelid beetle Colaspis crinicornis Schaeffer (Coleoptera: Chrysomelidae) occurs primarily in the Great Plains region of the United States. Little is known about the biology and ecology of this species, but over the last decade, it has become increasingly common in the corn, Zea mays L., and soybean, Glycine max (L.) Merrill, agroecosystem of southeastern Nebraska. As part of a larger comprehensive project to understand the natural history and pest potential of this species, laboratory experiments were conducted to study the developmental biology, morphological characters of immature stages, and the effect of adult diet on consumption, longevity, and fecundity. Females readily deposited egg clusters in the soil, and percentage egg hatch was high under laboratory conditions. Larvae and pupae were confirmed to be soil-dwelling stages. C. crinicornis has relatively short egg, pupal, and adult stages with the majority of its life cycle spent in the larval stage. Results of choice and no-choice adult feeding experiments indicate that diets of corn or soybean leaves did not significantly affect consumption, longevity, or fecundity of adult C. crinicornis, suggesting that corn and soybean leaves are similarly suitable food sources for adults. The ability to effectively utilize tissues from very different plant families as adult food sources suggests that C. crinicornis is polyphagous in the field.

Measuring Bee Effects on Seed Traits of Hybrid Sunflower.

In hybrid sunflower, bee pollination can improve productivity, but the contribution of bees to productivity may be over or underestimated. To estimate bee effects (seed trait gains from exposure to bees during anthesis), single capitula are commonly covered with a porous material to exclude bees. However, depending on the exclosure porosity, estimates of the magnitude of bee effects will vary. In two studies, porosity size and bee effect gains in two sunflower types were tested. In the exclosure study, Delnet exclosures severely reduced seed set and exclosures with larger porosities and had smaller and similar effects. However, since a few small bees penetrated the largest porosity size tested, exclosures with porosity sizes < 7 mm are recommended. With an exclosure porosity of 5 X 5 mm, the estimated bee effect contribution to the yield was 323 kg per hectare. Effects of exclosures on seed traits were similar in the oilseed and confectionary hybrids tested. Insecticide use did not affect seed traits but did lower insect damage to seeds. Bees from three families, mostly Apidae, were collected while foraging on sunflower. In summary, we recommend the use of exclosures with porosities of about 3 to 5 mm to avoid over or underestimating bee effects. And we recommend holistic insect management for sunflower cropping systems that balances the benefits of bee effects on seed traits with management of pest insects.

Seasonality of Colaspis crinicornis (Coleoptera: Chrysomelidae) and its Injury Potential to Corn in Southeastern Nebraska.

Colaspis crinicornis Schaeffer (Coleoptera: Chrysomelidae) primarily occurs in the Great Plains, United States. Although C. crinicornis has historically been considered a non-pest and is rarely found in agricultural systems, population densities of this species have been increasing in corn, Zea mays L., and soybean, Glycine max (L.) Merrill, over the last decade in southeastern Nebraska. As part of a comprehensive project to understand the life history and pest potential of C. crinicornis, a field study was conducted to: understand adult seasonality of C. crinicornis using emergence cages and whole-plant-count sampling in cornfields and sweep-net sampling in soybean fields; confirm voltinism and the overwintering stage; and evaluate the potential of larvae to cause economic injury to corn roots. Data indicate that C. crinicornis is univoltine in southeastern Nebraska and overwinters as medium-large larvae at least 20 cm deep in the soil. Adults were present from June through August with peak emergence in July. The C. crinicornis lifecycle is similar to related Colaspis species. Root injury to corn was minor at population densities encountered in the field, and therefore, C. crinicornis is unlikely to cause economic loss. C. crinicornis may be an example of an insect species that has exploited open niches in crops that have been created by changes in agricultural and pest management practices. The lifecycle and polyphagous nature of the insect, annual crop rotation, the shift to minimum tillage, and replacement of insecticides with Bacillus thuringiensis Berliner (Bt) traits may have collectively facilitated establishment and increased survival in agroecosystems.

Diel Patterns of Colaspis brunnea and Colaspis crinicornis (Coleoptera: Chrysomelidae) in Southeastern Nebraska.

A field study was conducted to increase our understanding of diel activity patterns of Colaspis brunnea (F.) and Colaspis crinicornis Schaeffer (Coleoptera: Chrysomelidae) in key crop habitats. Within 24-h periods, C. brunnea was sampled in clover fields (primarily red clover, Trifolium pretense (L.), with some sweet clover, Melilotus officinalis (L.) Pallas, and downy brome, Bromus tectorum (L.)) and soybean, Glycine max (L.) Merrill, fields, using a sweep-net, while whole-plant-count sampling was used to monitor C. crinicornis densities in field corn, Zea mays (L.). Sweep-net captures of C. brunnea were significantly greater at night than during the day, suggesting possible vertical movement within the canopy during a 24-h period. Colaspis crinicornis densities on corn plants were fairly constant throughout a 24-h period, but beetle activity (e.g., walking, mating) was significantly greater at night than during the day. Results suggest that both Colaspis species may be exhibiting similar increases in activity at night that facilitates movement from more protected to more exposed areas within a habitat. It is unclear what mechanisms drive this diel pattern, but vegetation architecture and associated interactions with environmental conditions may play a role. Sweep-netting in clover or soybean fields and use of whole-plant-counts in cornfields were effective sampling methods for Colaspis adults. However, because activity and behaviors of Colaspis beetles were influenced by time of day in this study, use of a consistent sampling time within a diel period would be recommended for future population studies or integrated pest management decision-making.