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The scaling of insect respiratory systems with body size has important implications for ecology and evolution of insects, ranging from allometry of aerobic performance to current and past environmental constraints on insect body size. Previous work examining scaling across beetle species and during ontogeny of grasshoppers suggests strong tracheal hypermetry, with larger insects investing relatively more volume in their tracheal systems. However, these approaches potentially confound body size differences with species or life stage differences in morphology or physiology. To circumvent these issues, we took advantage of large body size variation within bumblebee nests. Workers with 75% genetic similarity nevertheless varied in body size from under 50 mg to more than 250 mg, and queens exceeded 500 mg. We estimated respiratory volume, dimensions of pronotal spiracles, and body size of individual bumblebees (Bombus impatiens) from lab-reared nests. Among workers, tracheal system volume scaled hypermetrically with mass(2.6), whereas overall scaling of the cross-sectional area of the pronotal spiracular tracheae scaled isometrically with mass(0.67). Queen bumblebees had tracheal systems similar in size to those of workers 1/3 their body mass but had larger-than-expected cross-sectional area of spiracular tracheae. Given space constraints within the rigid exoskeleton, the strong hypermetry of the tracheal system among bumblebee workers may impose an upper limit to body size as the tracheal system occupied 25% of total body volume for the largest workers.

Strip tillage, in which tillage and seedbed preparation are limited to a narrow band where the subsequent crop is planted, provides many potential agronomic benefits, including reduced fuel and labor costs, reduced erosion, and improved soil tilth. Lower soil disturbance and enhanced water retention associated with strip tillage also may affect density and diversity of predatory arthropods, which have been little studied in sugar beet. We examined the effects of tillage (conventional versus strip) on the predatory epigeal arthropod fauna in sugar beet. Studies were conducted over three growing seasons (2010–2012) in Idaho using both fenced and unfenced pitfall traps to sample arthropods. Unfenced pitfall traps often captured a greater activity density and richness of predators, and showed no bias of higher captures in conventionally tilled plots as has been shown elsewhere. Total density of predators was higher in strip tillage only during 2011. Density and species richness of carabid beetles did not differ between tillage treatments during the course of the study. Density of the other major taxa (staphylinid beetles, spiders, and Opiliones) was higher under strip tillage during some years, especially early in the season, but richness showed little or no relationship with tillage. Predaceous arthropods might be favored by enhanced ground cover, higher humidity, more moderate temperatures, and/or less habitat disturbance associated with strip-tilled plots. The results suggest that certain groups of soil-dwelling predatory arthropods can be favored by strip tillage in sugar beet, which further adds to the benefits of conservation tillage in this system.

Despite the many agronomic benefits of conservation tillage, little is known regarding the effects of reduced tillage on the pest complex in sugar beet. We examined the effects of two types of tillage (strip till versus conventional) and different irrigation rates on yield as well as densities of insect pests, weeds, and a soil-borne plant pathogen in sugar beet. Yields were similar between tillage treatments for two of the three years, but were greater for conventional tillage during one year in which a wet spring may have slowed seedling development in strip-tilled plots. The low irrigation treatment exhibited lower yields in one of three years, regardless of tillage treatment. Eggs of beet leafminer flies were more abundant in conventional tillage on three of eight observation dates, but larval densities did not differ by tillage treatment. Bean aphid incidences generally were positively related to irrigation rate. Total weed counts within beet rows did not

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