Methoxyfenozide has minimal effects on replacement queens but may negatively affect sperm storage

Authors: Carroll, Mark; Corby-Harris, Vanessa; Brown, Nicholas; Snyder, Lucy; Reitz, Dylan

Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2022
Publication Date: 6/23/2022
Citation: Carroll, M.J., Corby-Harris, V.L., Brown, N.J., Snyder, L.A., Reitz, D.C. 2022. Methoxyfenozide has minimal effects on replacement queens but may negatively affect sperm storage. Apidologie. 53. Article 33. https://doi.org/10.1007/s13592-022-00940-7.
DOI: https://doi.org/10.1007/s13592-022-00940-7

Interpretive Summary: Honey bees are often exposed to toxic pesticides during the pollination of agricultural crops and often carry pesticide-contaminated pollen and nectar back into their colonies, where it is stored as food. The Insect Growth Regulator (IGR) methoxyfenozide (MEOF) kills pest larvae and pupae by disrupting their hormone balances and causing molt failures in immature insects. Methoxyfenozide primarily affects lepidopteran pests (butterflies and moths) but is not very toxic to honey bees because it doesn’t interact as much with their hormone receptors. Honey bee workers can accidently store methoxyfenozide in the colony wax, stored pollen, and honey where it might be consumed later by other bees. We examined the effects of methoxy-contaminated pollen supplement and methoxyfenozide contaminated wax on the rearing and production of new replacement queens from young worker larvae. Colonies must rear replacement queens when their queen is killed, lost, or no can longer lay eggs for the colony. We examined the effect of MEOF exposure on colony rearing of emergency replacement queens from worker larvae. MEOF-treated colonies were given pollen patty supplement and wax that contained average field levels of methoxyfenozide (500 ppb and 171 ppb). Treatment colonies were exposed to MEOF-contaminated pollen (supplemental pollen patty) and queen cup wax at sublethal field-relevant levels before and during a queen replacement (after removal of the resident queen) cycle. MEOF-exposed colonies were able to rear and support new replacement queens of similar physiological and reproductive quality as unexposed colonies. MEOF-treated colonies produced mated, ovipositing queens from grafted larvae at similar rates as unexposed colonies. Queens that developed in MEOF colonies also showed similar levels of development of key reproductive and non-reproductive tissues as unexposed queens. MEOF-exposed queens did not differ from control queens in their body mass, ovary ovariole development, and the levels of nutrients (total protein and fatty acid contents) in both ovaries and fat bodies. Queens from both treatments had similar proportions of nutrient resources split between ovaries and non-reproductive fat bodies. MEOF also did not affect queen production of two sets of key pheromones essential for obtaining queen care and retaining the resident queen without replacement. Queens reared in MEOF-exposed colonies had similar amounts of QMP (Queen Mandibular Pheromone) and QRP (Queen Retinue Pheromone) components in their gland-containing heads. However, MEOF exposure did appear to affect a key factor that might shorten how long a queen could lay eggs. Queens reared in methoxyfenozide-exposed colonies stored marginally less sperm in their spermathecae than unexposed queens. Given that production of female workers from fertilized eggs ultimately depends on sperm availability, methoxyfenozide contamination may lead to more frequent queen failure (inability to produce fertilized eggs/female workers) and queen replacement in developing queens.

Technical Abstract: Honey bees are often incidentally exposed to pesticides such as the IGR methoxyfenozide (MEOF) during the pollination of agricultural crops, an exposure that extends into the colony via stored food and hive material residues. We examined the effect of MEOF exposure on colony rearing and production of replacement queens. Treatment colonies were exposed to MEOF-contaminated pollen (supplemental pollen patty) and queen cup wax at sublethal field-relevant levels before and during a queen replacement (queen grafting) cycle. MEOF-exposed colonies were largely able to rear and support replacement queens of similar physiological and reproductive quality as unexposed colonies. MEOF-treated colonies produced mated, ovipositing queens from grafted larvae at similar rates as unexposed colonies. Queens that developed in MEOF colonies also showed similar levels of development of key reproductive and non-reproductive tissues as unexposed queens. MEOF-exposed queens did not differ from control queens in their body mass, ovary ovariole development, and the levels of nutrient provisioning (total protein and fatty acid contents) in both ovaries and fat bodies. Queens from both treatments had similar partitions of nutrient resources between ovaries and non-reproductive fat bodies to support oviposition. MEOF also did not affect queen production of key pheromones essential to worker solicitation of queen care and queen retention. Queens reared in MEOF-exposed colonies had similar contents of QMP (Queen Mandibular Pheromone) and QRP (Queen Retinue Pheromone) components in their gland-containing heads. However, MEOF exposure did appear to impact a key factor that might shorten the functional lifespan of an ovipositing queen. Queens reared in MEOF-exposed colonies stored marginally less sperm in their spermathecae than unexposed queens. Given that production of female workers from fertilized eggs is ultimately limited by sperm availability, methoxyfenozide contamination may lead to more frequent queen failure and queen replacement in affected developing queens.