Effects of provision type and pesticide exposure on the larval development of Osmia lignaria (Hymenoptera: Megachilidae)

Authors: KOPIT, ANDI - Utah State University; KLINGER, ELLEN - The Ohio State University; Cox-Foster, Diana; RAMIREZ, RICARDO - Utah State University; Pitts Singer, Theresa

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2021
Publication Date: 10/29/2021
Citation: Kopit, A.M., Klinger, E., Cox-Foster, D.L., Ramirez, R.A., Pitts Singer, T. 2021. Effects of provision type and pesticide exposure on the larval development of Osmia lignaria (Hymenoptera: Megachilidae). Environmental Entomology. 51(1):240-251. https://doi.org/10.1093/ee/nvab119.
DOI: https://doi.org/10.1093/ee/nvab119

Interpretive Summary: Understanding the impacts of agricultural practices on pollinators and their development is critical to help preserve pollination of crops. For solitary bees, delayed larval development could lead to asynchronous emergence, unhealthy and inefficient pollinators, and possibly population decline. To investigate the effect of pesticides on developing solitary bee larvae and develop a methodology for larval testing, a laboratory bioassay was conducted using the mason bee, Osmia lignaria. Two pollen types (apple and almond), two provision compositions (homogenized and intact natal with spot application of treatment), and four agrochemicals (acetamiprid, boscalid/pyraclostrobin, and dimethoate) were fed to the larvae at different doses. To simulate tank mixing, one pesticide mixture (acetamiprid plus boscalid/pyraclostrobin) was examined for effects on larval development. All larvae survived to cocoon initiation when only water was added either apple or almond pollen via either injection or homogenization. The neonicotinoid acetamiprid was the most toxic. Almond pollen with acetamiprid was much more toxic than apple pollen plus acetamiprid, suggesting that plant defensive chemicals present in pollen can have a significant impact on pesticide impacts on bees. When agrochemicals were injected into pollen provisions, fewer larvae succumbed to the agrochemical treatments compared to those reared on homogenized provisions in which chemicals were mixed. Duration of Larval development was more affected by acetamiprid and when mixed with boscalid/pyraclostrobin. Optimizing testing methodology for solitary bee exposure to agricultural products is crucial for properly assessing risks for pollinators and for creating best practices for agricultural systems.

Technical Abstract: With both native and managed bee species experiencing population declines, understanding the impacts of agricultural practices on developing bees is critical. For solitary bees, delayed larval development could lead to asynchronous emergence, unhealthy and inefficient pollinators, and possibly population decline. To investigate the effect of pesticides on developing solitary bee larvae and develop a methodology for larval testing, a laboratory bioassay was conducted using Osmia lignaria Say (Hymenoptera: Megachilidae). Two pollen types (apple and almond), two provision compositions (homogenized and intact natal with spot application of treatment), and four agrochemicals (acetamiprid, boscalid/pyraclostrobin, and dimethoate) were delivered at different doses. To simulate tank mixing, one pesticide mixture (acetamiprid plus boscalid/pyraclostrobin) examined for effects on larval development (durations of the 2nd to 5th instar and of the 5th instar to cocoon initiation). All larvae survived to cocoon initiation when only water (control) was added to provisions of all types, and the least survived when acetamiprid was added. Pollen source significantly affected the survivorship with acetamiprid, suggesting that plant defensive chemicals present in pollen can have a significant impact on pesticide impacts on bees. When agrochemicals were injected into the intact natal provisions, fewer larvae succumbed to the agrochemical treatments compared to those reared on homogenized provisions in which chemicals were mixed. The treatments with the greatest effect on larval development times compared to other treatments and control were those that included acetamiprid at all dose levels and when mixed with boscalid/pyraclostrobin. These treatments resulted in significantly higher development times from the 2nd to 5th instar and significantly lower times from the 5th instar to cocoon initiation. Optimizing testing methodology for solitary bee exposure to agricultural products is crucial for properly assessing risks for pollinators and for creating best practices for agricultural systems.