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Pollinators make foraging decisions based on numerous floral traits, including nectar and pollen rewards, and associated visual and olfactory cues. For insect-pollinated crops, identifying and breeding for attractive floral traits may increase yields. In this study, we examined floral trait variation within cultivated sunflowers and its effects on bee foraging behaviours. Over 2 years, we planted different sunflower inbred lines, including male-fertile and male-sterile lines, and measured nectar volume, nectar sugar concentration and composition, and corolla length. During bloom, we recorded visits by both managed honey bees and wild bees. We then examined consistency in relative nectar production by comparing field results to those from a greenhouse experiment. Sunflower inbred lines varied significantly in all floral traits, including the amount and composition of nectar sugars, and in corolla length. Both wild bee and honey bee visits significantly increased with nectar sugar amount and decreased with corolla length, but appeared unaffected by nectar sugar composition. While wild bees made more visits to sunflowers providing pollen (male-fertile), honey bees preferred plants without pollen (male-sterile). Differences in nectar quantity among greenhouse-grown sunflower lines were similar to those measured in the field, and bumble bees preferentially visited lines with more nectar in greenhouse observations. Our results show that sunflowers with greater quantities of nectar sugar and shorter corollas receive greater pollination services from both managed and wild bees. Selecting for these traits could thus increase sunflower crop yields and provide greater floral resources for bees. [ABSTRACT FROM AUTHOR]

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is one of the most economically important insect pests threatening the production of corn, Zea mays (L.), in the United States. Throughout its history, this insect has displayed considerable adaptability by overcoming a variety of pest management tactics, including the cultural practice of annual crop rotation. Since first reported in Illinois in the late 1980s, populations of the rotation-resistant western corn rootworm have spread over a wide area of the eastern Corn Belt. Currently, little information is available concerning the interaction of rotation resistance with the use of genetically modified corn expressing insecticidal toxins from Bacillus thuringiensis Berliner (Bt), a popular tactic for preventing larval injury and its associated yield loss. The goal of this greenhouse experiment was to determine whether rotation-resistant and rotation-susceptible western corn rootworm larvae differ with respect to survival or development when exposed to single- or dual-toxin (pyramided) Bt corn. Individual corn plants were infested with 225 near-hatch eggs at the V5 (five leaf collar) growth stage. Larvae developed undisturbed on the root systems for 17 days, after which they were recovered using Berlese-Tullgren funnels. Surviving larvae were counted to estimate mortality, and head capsule widths were measured to assess development. Rotation-resistant and rotation-susceptible larvae had statistically similar mean levels of mortality and head capsule widths when exposed to both single-toxin (Cry3Bb1 or Cry34/35Ab1) and pyramided (Cry3Bb1+ Cry34/35Ab1) Bt corn, suggesting that these two populations do not differ with respect to survival or development when exposed to Bt corn. Additionally, the statistically similar mean levels of mortality for larvae exposed to single-toxin and pyramided Bt corn suggest that pyramided Bt hybrids containing the Cry3Bb1 and Cry34/35Ab1 toxins do not result in additive mortality for western corn rootworm larvae. Implications for management of this economically important pest are discussed. [ABSTRACT FROM AUTHOR]

The ability of the biomass crop Miscanthus ( Miscanthus × giganteus Greef and Deuter ex Hodkinson and Renvoize) to support larval development for both United States and European populations of the western corn rootworm, Diabrotica virgifera virgifera Le Conte, suggests an avenue for interactions with corn ( Zea mays L.). To provide context to survival of D. v. virgifera on Miscanthus, adult activity and oviposition of Diabrotica spp. were monitored in central Illinois in 2010-2011 in Miscanthus, corn and switchgrass ( Panicum virgatum L.). For D. v. virgifera, vial traps within corn plots captured 3-10 times as many adults as in Miscanthus or switchgrass, while soil samples showed females laid approximately 10 times as many eggs in corn as in the perennial grasses. Adult southern corn rootworms, Diabrotica undecimpunctata howardi Barber , were the most abundant species in 2010 and clearly preferred switchgrass as an adult habitat, with vial traps in switchgrass capturing 5-10 times as many D. u. howardi as those in corn or Miscanthus. Based on the small production areas for Miscanthus and switchgrass (and low use of both by D. v. virgifera), it seems likely that there are no current impacts of these perennial grasses on pest status of Diabrotica spp. in corn or other crops. However, adaptations by Diabrotica spp. to pest management practices suggest they could be a source for interactions between biomass and food or feed crops. Early-season soil samples did not recover eggs of D. u. howardi, but their use of switchgrass as an adult habitat suggests additional research in areas where switchgrass may be grown near peanuts, alfalfa or other hosts may be needed. Also, investigation of other candidate bioenergy crops known to support Diabrotica spp. larval development is needed to better understand the possible effects of a changing agricultural landscape on corn rootworms. [ABSTRACT FROM AUTHOR]

For their simplicity and effectiveness, pitfall traps have become a standard technique to measure the activity and relative abundance of ground-dwelling arthropods. Permeable screen or mesh bags filled with plant material, referred to as litter bags, have also recently been employed as a complementary sampling technique for epigeal taxa. The anticipated need for increased field research on arthropod populations, particularly in transgenic crops with insecticidal properties, suggests that a relative assessment of both sampling methods could contribute to the design of future studies. Comparisons among pitfall traps, and litter bags placed above- or below-ground indicated that above-ground litter bags most frequently succeeded in collecting certain groups of arthropods associated with moisture and sheltered areas, including centipedes (Chilopoda) and beetle larvae (Carabidae, Staphylinidae). Conversely, pitfall traps most often captured taxa considered active at ground level, such as adult carabids or harvestmen (Opiliones). For taxa collected in >40% of all three trap types, bootstrap confidence intervals for the coefficient of variation (CV; used to assess precision or sampling efficiency) showed that above-ground litter bags were significantly more precise than pitfall traps for sampling elongate springtails (Collembola) and adult rove beetles (Staphylinidae), but only during the first year of sampling. While below-ground litter bags often appeared similar to one or both of the other trap types, in no case were below-ground litter bags best based on frequency of collection or CV. Though differences were not always consistent between years, results suggest that the additional effort required to sample using litter bags may be justified for the collection of some ground-dwelling taxa. [ABSTRACT FROM AUTHOR]