Chronic high glyphosate exposure delays individual worker bee (Apis mellifera L.) development under field conditions

Abstract

<jats:p>The ongoing debate about glyphosate-based herbicides (GBH) and their implications for beneficial arthropods give rise to controversy. This research was carried out to cover possible sublethal GBH effects on brood and colony development, adult survival, and overwintering success of honey bees (Apis mellifera L.) under field conditions. Residues in bee relevant matrices such as nectar, pollen and plants were measured in addition. To address these questions, we adopted four independent study approaches. For brood effects and survival, we orally exposed mini-hives housed in the "Kieler mating-nuc" system to sublethal concentrations of 4.8 mg glyphosate/kg (T1, low) and 137.6 mg glyphosate/kg (T2, high) over the period of one brood cycle (21 days). Brood development and colony conditions were assessed after a modified OECD method (No. 75). For adult survival, we weighed and labeled freshly emerged workers from exposed colonies and introduced them into non-contaminated mini-hives to monitor life span for 25 consecutive days. Results from these experiments showed a trivial effect of GBH on colony conditions and survival of individual workers, even though hatching weight was reduced in T2. The brood termination rate (BTR) in the T2 treatment, however, was more than doubled (49.84%) when compared to the control (22.11%) or T1 (20.69%). This was surprising as T2 colonies gained similar weight and similar numbers of bees per colony compared to the control, indicating equal performance. Obviously, the brood development in T2 was not "terminated" as expected by the OECD method terminology but rather "slowed down" for an unknown period of time. In light of these findings, we suggest that chronic high GBH exposure is capable of delaying worker brood development to a significant extent while no further detrimental effects seem to appear at the colony level. Against this background, we discuss additional results and possible consequences of GBH for honey bee health.</jats:p>

Chronic High Glyphosate Exposure Delays Individual Worker Bee (Apis mellifera L.) Development under Field Conditions

“…The results of the residue analyses from all experiments (1–4) for glyphosate and its metabolite aminomethylphosphonic acid (AMPA) are presented as an overview in Table 1 . A total of 176 samples were measured, including controls (experiment 1: six samples, experiment 2: 92 samples, experiment 3: 66 samples, experiment 4: 12 samples) (see raw data [ 46 ]). It could be confirmed that all experimental colonies from the respective treatments were exposed to glyphosate, respectively.…”

“…In experiments 1, 2, and 3, irrespective of the time interval after the application (short term: three days, or long term: 170 days), glyphosate residues remained constant in all the sugar matrices. In experiment 2, a 15.9-fold average increase, and a 24-fold peak increase (see raw data [ 46 ]) was measured in stored pollen (beebread) when compared to stored nectar. In plants, a range similar to experiment 4 (tunnel tents) was measured shortly after the application on DAT0.…”

No evidence of effects or interaction between the widely used herbicide, glyphosate, and a common parasite in bumble bees

“…Glyphosate helps reduce the need for tilling and mechanical weeding, which helps protect against soil erosion and boosts farmers yields and profits ( Beckie, Flower & Ashworth, 2020 ). Bees are exposed to glyphosate frequently in nature through spraying of weeds, contamination of water, and application onto glyphosate resistant flowering crops ( Odemer et al, 2020 ; Straw, Carpentier & Brown, 2021 ). Glyphosate-based herbicide products typically do not carry any mitigation measures aimed at reducing bees exposure to them.…”

A Qualitative Analysis of Beekeepers’ Perceptions and Farm Management Adaptations to the Impact of Climate Change on Honey Bees

“…Apart from the aspects strictly related to climate change, other issues dealing with bee hive and farm management and honey production have also emerged. These include intensive agriculture including continuous cropping with crops not useful for pollinating insects [ 62 , 63 , 64 , 65 ]; the reduction of pasture meadows with the consequent loss of blooms widely present in the past such as dandelion ( Taraxacum officinale ) or white clover ( Trifolium repens ) all providing forage for typical honey; the use of chemicals (e.g., neonicotinoids) and herbicides (e.g., glyphosate) [ 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ] applied in pre-flowering or flowering without respecting the imposed restrictions; the cultivation of hybrids, such as sunflower ( Helianthus annuus ) and buckwheat, important resources during the summer, which do not provide nectar; the release of the parasitoid Neodryinus typhlocybae (Ashmead), controlling M. pruinosa populations [ 75 ], and consequently the production of honeydew and honeydew honey; and the loss of plant biodiversity. On the other hand, the abandonment of the woodlands may allow the spread of useful plants such as cherry ( Prunus avium ) and ivy, offering an important nectar flow for honey bees, as one beekeeper observed: “Recently, an important source of nectar is the cherry tree, which was not very common until ten years ago.…”