Effects of a field-sprayed antibiotic on bee foraging behavior and pollination in pear orchards

Abstract

Broadcast spraying of antibiotics in crops is widely used for controlling bacterial plant pathogens. The effects of antibiotics on non-target (and especially beneficial) organisms in cropping systems, however, are not well studied. Pollinators are of particular concern because in pear and apple crops, antibiotics for controlling fire blight (Erwinia amylovora) are sprayed during bloom, likely exposing pollinators. This is especially relevant as laboratory evidence suggests that antibiotics could have sublethal effects on bee foraging behavior and colony health. But to our knowledge these potential impacts have not been studied in field settings. Here, we compared the effects of two fire blight control methods, a single spray of an antibiotic (oxytetracycline) and a biological antagonist (Aureobasidium pullulans), on honey bee (Apis mellifera) foraging, pollination, and fruit set in pear orchards. Complementing these field assessments, we conducted laboratory experiments to examine the effects of these treatments on locomotion and foraging behavior of the bumble bee species, Bombus vosnesenskii. We found that honey bees visited fewer flowers and foraged longer on each flower in orchards sprayed with antibiotics than with biological product, but there were no differences in pollination and seed set. The pear cultivars we worked in, however, can self-pollinate. In the lab, we found that feeding on high doses of either the antibiotic or the biological antagonist reduced bumble bee foraging behavior relative to controls. The limited impact of antibiotics on pear pollination observed in this study suggest that antibiotics pose a low economic risk to pear growers, especially for self-compatible cultivars. Still, crops with higher pollinator dependence may be more affected by reductions in pollinator visitation. Future studies should examine the impacts of multiple antibiotic sprays within a season, which are common during warm springs, and their long-term health impacts on both individual bees and colonies. HighlightsO_LIAntibiotics are sprayed on many crops to control plant bacterial pathogens. C_LIO_LIThe impacts of antibiotics on beneficial organisms in agriculture are unknown. C_LIO_LIWe studied antibiotic impacts on bee behavior and pollination function in pears. C_LIO_LIBees exposed to antibiotics visit fewer flowers and this could impact bee fitness. C_LIO_LIDespite decreased bee visitation, we did not detect a reduction in crop pollination. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=83 HEIGHT=200 SRC="FIGDIR/small/528407v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@17c2189org.highwire.dtl.DTLVardef@7dd952org.highwire.dtl.DTLVardef@4696beorg.highwire.dtl.DTLVardef@52b7fd_HPS_FORMAT_FIGEXP M_FIG C_FIG