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Reproductive fitness of honey bee queens exposed to thiamethoxam during development.

ABSTRACT: The productivity and survival of honey bee (Apis mellifera) colonies depend on queen bee health. Colony-level neonicotinoid exposure has negative effects on reproductive fitness of honey bee queens. However, it is unclear if the observed effects are a direct outcome of neonicotinoid toxicity or result from suboptimal care of developing queens by exposed workers. The aim of this study was to evaluate larval survival, reproductive fitness, and histopathology of honey bee queens exposed to incremental doses (0, 5, 50 ng) of the neonicotinoid thiamethoxam (THI) applied directly to individual late larvae (7 days post-oviposition) of queens. The 5 ng dose represents a calculated high environmental level of exposure for honey bee queen larvae. Morphometric evaluation revealed that the total area of mandibular gland epithelium in queens exposed to 5 and 50 ng THI was reduced by 14% (P = .12) and 25% (P = .001), respectively. Decreased mandibular gland size may alter pheromone production, which could in part explain previously observed negative effects of THI on the reproductive fitness of queens. We also found that late larval exposure to THI reduced larval and pupal survival and decreased sperm viability in mated queens. These changes may interfere with queen development and reproductive longevity.

SUBMITTER: Kozii IV

PROVIDER: S-EPMC8581721 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Varroa destructor is one of the most common parasites of honey bee colonies and is considered as a possible co-factor for honey bee decline. At the same time, the use of pesticides in intensive agriculture is still the most effective method of pest control. There is limited information about the effects of pesticide exposure on parasitized honey bees. Larval ingestion of certain pesticides could have effects on honey bee immune defense mechanisms, development and metabolic pathways. Europe and America face the disturbing phenomenon of the disappearance of honey bee colonies, termed Colony Collapse Disorder (CCD). One reason discussed is the possible suppression of honey bee immune system as a consequence of prolonged exposure to chemicals. In this study, the effects of the neonicotinoid thiamethoxam on honey bee, Apis mellifera carnica, pupae infested with Varroa destructor mites were analyzed at the molecular level. Varroa-infested and non-infested honey bee colonies received protein cakes with or without thiamethoxam. Nurse bees used these cakes as a feed for developing larvae. Samples of white-eyed and brown-eyed pupae were collected. Expression of 17 immune-related genes was analyzed by real-time PCR. Relative gene expression in samples exposed only to Varroa or to thiamethoxam or simultaneously to both Varroa and thiamethoxam was compared. The impact from the consumption of thiamethoxam during the larval stage on honey bee immune related gene expression in Varroa-infested white-eyed pupae was reflected as down-regulation of spaetzle, AMPs abaecin and defensin-1 and up-regulation of lysozyme-2. In brown-eyed pupae up-regulation of PPOact, spaetzle, hopscotch and basket genes was detected. Moreover, we observed a major difference in immune response to Varroa infestation between white-eyed pupae and brown-eyed pupae. The majority of tested immune-related genes were upregulated only in brown-eyed pupae, while in white-eyed pupae they were downregulated.

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Reproductive fitness of honey bee queens exposed to thiamethoxam during development.

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