Megachile rotundata larval guts Targeted Locus (Loci)
Megachile rotundata is the second most important field crop pollinator, but is stricken by chalkbrood, a disease caused by the fungus Ascosphaera aggregata. To test the hypothesis that some microbes inhibit the growth of other microbes, we applied four treatments to the pollen provisions of M. rotundata eggs and young larvae: antibacterials, antifungals, A. aggregata spores, and a no-treatment control. We allowed the larvae to develop and used 454 pyrosequencing to quantify fungal and bacterial communities in the larval gut. Antifungals lowered the abundance of A. aggregata and correspondingly increased the relative diversity of surviving fungi. Antibacterials altered the bacterial community, but not the fungal community. Interactions between A. aggregata and other fungi, but not between bacteria and fungi, appear to be important for fungal community structure in the larval gut. Lactobacillus kunkeei clade bacteria were common members of the larval gut microbiota, and exhibited antibiotic resistance. Because L. kunkeei is also found in honey bees and is likely transferred between bee lineages at flowers, the observed antibiotic resistance may have originated from exposure to pesticides applied to honey bee colonies. This suggests that pesticide application to honey bees can have far-reaching effects on the microbiota of native bee populations.  Guts from Megachile rotundata larvae that had been treated with either: 1) antibacterials 2) antifungals 3) Chalkbrood (a fungal pathogen) spores 4) No-treatment control.