Impact of Diflubenzuron on Bombus impatiens (Hymenoptera: Apidae) Microcolony Development.

Reliance on the honey bee as a surrogate organism for risk assessment performed on other bees is widely challenged due to differences in phenology, life history, and sensitivity to pesticides between bee species. Consequently, there is a need to develop validated methods for assessing toxicity in non-Apis bees including bumble bees. The usefulness of small-scale, queenless colonies, termed microcolonies, has not been fully investigated for hazard assessment. Using the insect growth regulator diflubenzuron as a reference toxicant, we monitored microcolony development from egg laying to drone emergence using the Eastern bumble bee Bombus impatiens (C.), a non-Apis species native to North America. Microcolonies were monitored following dietary exposure to diflubenzuron (nominal concentrations: 0.1, 1, 10, 100, and 1,000 µg/liter). Microcolony syrup and pollen consumption was significantly reduced by diflubenzuron exposure. Pupal cell production was also significantly decreased at the highest diflubenzuron concentration assessed. Ultimately, diflubenzuron inhibited drone production in a concentration-dependent manner and a 42-d 50% inhibitory concentration (IC50) was determined. None of the dietary concentrations of diflubenzuron tested affected adult worker survival, or average drone weight. These data strengthen the foundation for use of this methodology, and provide valuable information for B. impatiens; however, more work is required to better understand the utility of the bumble bee microcolony model for pesticide hazard assessment.

Characterization and localization of an aldehyde dehydrogenase to amacrine cells of bovine retina.

An enzyme of bovine retina that catalyzes oxidation of retinaldehyde to retinoic acid was purified to homogeneity and a monoclonal antibody (mAb H-4) was generated. MAb H-4 recognized a single component (Mr = 55,000) in extracts of bovine retina and other bovine tissues. The antibody showed no cross-reactivity with extracts of rat, monkey, or human retinas. A 2067 bp cDNA was selected from a retina cDNA expression library using mAb H-4. The cDNA hybridized with a similarly sized, moderately abundant mRNA prepared from bovine retina. Nucleotide sequence analysis indicated that the cDNA contained a single open reading frame encoding 501 amino acids that have 88% sequence identity with the amino-acid sequence of human hepatic Class 1 aldehyde dehydrogenase. Amino-acid sequence analysis of purified enzyme demonstrated that the cDNA encodes the isolated enzyme. MAb H-4 specifically labeled the somata and processes of a subset of amacrine cells in bovine retinal sections. Labeled amacrine somata were located on both sides of the inner plexiform layer, and their processes ramified into two laminae within the inner plexiform layer. The inner radial processes of Müller (glial) cells were weakly reactive with mAb H-4. Weak immunostaining of amacrine cells was found in monkey retina with mAb H-4, but no signal was detected in rat or human retina. The results provide further evidence for metabolism and function of retinoids within cells of the inner retina and define a novel class of retinal amacrine cells.