Fungicide ingestion reduces net energy gain and microbiome diversity of the solitary mason bee

Abstract

Fungicides are frequently used during tree fruit bloom and can threaten insect pollinators. However, little is known about how non-honey bee pollinators such as the solitary bee, Osmia cornifrons, respond to contact and systemic fungicides commonly used in apple production during bloom. This knowledge gap limits regulatory decisions that determine safe concentrations and timing for fungicide spraying. We evaluated the effects of two contact fungicides (captan and mancozeb) and four translaminar/plant systemic fungicides (cyprodinil, myclobutanil, penthiopyrad, and trifloxystrobin) on larval weight gain, survival, sex ratio, and bacterial diversity. This assessment was carried out using chronic oral ingestion bioassays where pollen provisions were treated with three doses based on the currently recommended field use dose (1X), half dose (0.5X), and low dose (0.1X). Mancozeb and penthiopyrad significantly reduced larval weight and survival at all doses. We then sequenced the 16S gene to characterize the larvae bacteriome of mancozeb, the fungicide that caused the highest mortality. We found that larvae fed on mancozeb-treated pollen carried significantly lower bacterial diversity and abundance. Our laboratory results suggest that some of these fungicides can be particularly harmful to the health of O. cornifrons when sprayed during bloom. This information is relevant for future management decisions about the sustainable use of fruit tree crop protection products and informing regulatory processes that aim to protect pollinators.

Keywords: Fungicide risk assessment; Host-microbial diversity; Mortality; Osmia cornifrons; Pollen provisions.

Figure 1

Mean fresh weights of Osmia cornifrons larvae measured at three-time points across four diet treatments (homogenized pollen provisions + fungicides: control, 0.1X, 0.5X, and 1X dosage. (a) Low dose (0.1X): First time point (1st day): χ²:30.99, DF = 6; P < 0.0001, second time point (5th day): 22.83, DF = 6; P = 0.0009; third time point (8th day): χ²:28.39, DF = 6; P < 0.0001. (b) Half dose (0.5X): First time point (1st day): χ²:35.67, DF = 6; P < 0.0001, second time point (1st day): χ²:15.98, DF = 6; P = 0.0090; third time point (8th day) χ²:16.47, DF = 6; P = 0.0041. (c) Field or full dose (1X):First time point (1st day) χ²:20.64, DF = 6; P = 0.0326, second time point (5th day): χ²:22.83, DF = 6; P = 0.0009; third time point (8th day): χ²:28.39, DF = 6; P < 0.0001. Two-way nonparametric anovas, followed by pairwise comparisons (α = 0.05) (n = 16). Bars represent mean ± S.E. *P ≤ 0.05, **P ≤ 0.001, ***P ≤ 0.0001.

Figure 2

Comparison of Osmia cornifrons larvae mortality after ingestion of pollen provision individually treated with six different fungicides. Susceptibility of O. cornifrons larvae by oral exposure was high with mancozeb and penthyopirad (GLM: χ² = 29.45, DF = 20, P = 0.0059) (line, slope = 0.29, P < 0.001; slope = 0.24, P < 0.00, respectively).

Figure 3

Percent of females and males of Osmia cornifrons after exposure to fungicides during larval stage. (a) Low dose (0.1X). (b) Half dose (0.5X). (c) Field or full dose (1X).

Figure 4

Comparisons of the Shannon richness and observed richness at the phylum level based on SAV profile for 16S sequences. (a) Principal coordinate analysis (PCoA) based on the overall structure of microbial communities in untreated pollen-fed larvae or control (blue) and mancozeb-fed larvae (orange). Each data point represents an individual sample. PCoA was calculated using Bray–Curtis distances with a multivariate t-distribution. Ellipses represent an 80% confidence level. (b) Boxplots, raw data (points) of Shannon richness, and c. observed richness. Box plots display the median line, interquartile range (IQR) boxes, and 1.5 × IQR (n = 3).

Figure 5

Composition of microbial communities in larva fed on mancozeb-treated and untreated pollen provisions. (a) Relative abundance of reads of microbial genera in larvae. (b) Heatmap of microbial communities identified. Delftia (odds ratio (OR) = 0.67, P = 0.0030) and Pseudomonas (OR = 0.3, P = 0.0074), Microbacterium (OR = 0.75, P = 0.0617); Rhodococcus (OR = 1.5, P = 0.0060). Heatmap rows are clustered using correlation distance and average linkage.