Body temperature changes can modify an insect's ability to fight infections by altering its immune activity. This work evaluated the impact of mild cold and heat thermal stress on the expression of different immune and heat shock genes in the species Bombus terrestris . Additionally, a thermal treatment was repeated under starvation to analyze a possible compromise of immune gene expression in favor of a thermal stress response when energetic resources are limited. Results pointed to a role of Hsc70 and Aha1 genes in tolerance to moderately high temperatures. Expression of the immune genes was not negatively affected by the cold or the heat treatments, and the receptor gene BGRP1 was upregulated with cold, possibly indicating an increase in the cellular immune activity. Under starvation, the effect of the heat and the cold treatments caused a higher upregulation in all genes analyzed, suggesting a synergistic effect of starvation and thermal stress on the activation of heat shock and immune gene expression.bumblebee / temperature variation / heat shock genes / immunity / RT-qPCR Electronic supplementary material The online version of this article (

Gut microbial communities confer protection against natural pathogens in important pollinators from the genera Bombus and Apis. In commercial species B. terrestris and B. impatiens, the microbiota increases their resistance to the common and virulent trypanosomatid parasite Crithidia bombi. However, the mechanisms by which gut microorganisms protect the host are still unknown. Here, we test two hypotheses: microbiota protect the host 1) through stimulation of its immune response or protection of the gut epithelium and 2) by competing for resources with the parasite inside the gut. To test them, we reduced the microbiota of workers and fed part of them with microbiota supplements. We exposed them to an infectious dose of C. bombi and characterised gene expression and gut microbiota composition. We examined the expression of three antimicrobial peptide (AMP) genes and Mucin-5AC, a gene with a putative role in gut epithelium protection, using qPCR. Although a protective effect against C. bombi was observed in bumblebees with supplemented microbiota, we did not observe an effect of the microbiota on gene expression that could explain alone the protective effect observed. On the other hand, we found an increased relative abundance of Lactobacillus bacteria within the gut of infected workers and a negative correlation of this genus with Gilliamella and Snodgrassella genera. Therefore, our results point to a displacement of bumblebee endosymbionts by C. bombi that might be caused by competition for space and nutrients between the parasite and the microbiota within the gut.

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Bombus magnus (Vogt, 1911) (Hymenoptera: Apidae) es una de las tres especies crípticas pertenecientes al complejo lucorum junto con B. lucorum (Linnaeus, 1761) y B. cryptarum (Fabricius, 1775). En la península Ibérica solo se encuentran B. lurocum y B. magnus pero la presencia de esta última no ha sido confirmada al sur de los Pirineos. Dada su similitud morfológica, usamos la región del código de barras de ADN para identificar 113 individuos de este complejo de especies en un muestreo ibérico. Los resultados confirman la presencia de B. magnus en los Pirineos y amplían su distribución actual hacia la meseta Norte ibérica. Dados estos resultados, sugerimos que ha de revisarse su distribución y el estado de conservación de esta especie en la península Ibérica.