Brazilian entomologists compared two insecticides on a native stingless bee, Melipona quadrifasciata. One was imidacloprid, a neonicotinoid from the class that got fields closed across Europe. The other was spinosad, a fermentation product of a soil bacterium and a permitted input in organic farming. The oral lethal dose came out at 23.54 nanograms per bee for imidacloprid and 12.07 for spinosad.
For that bee, the “natural” product was twice as toxic. The authors put it in the title: regrettable non-target toxicity of a bioinsecticide.
Organic is a different list, not an empty one
The most common misconception about organic produce is that nothing gets sprayed on it. Things do. Organic farming permits its own set of crop protection inputs: copper compounds against fungal disease, spinosad and pyrethrins against insects. A study from Kansas State University and the USDA Agricultural Research Service names the latter two directly as organically approved grain protectants, at 5 percent pyrethrins and 8.66 percent spinosad. The difference lies in the origin of the substances and in which list they appear on, rather than in whether spraying happens.
Those substances carry their own bills, and the bills run longer than a shopper at the shelf would guess. Take the two heaviest: copper and spinosad.
Copper stays in the soil permanently
Copper fungicides are used in organic viticulture against downy mildew, and there is still no replacement for them. The trouble is that copper is a metal: it does not break down. It builds up.
Researchers from the University of Strasbourg and the European Commission’s Joint Research Centre modeled the copper balance in European vineyard soils using machine learning. Average net export of copper from a plot came to 0.29 kg per hectare, while net accumulation reached 24.8 kg per hectare. Two orders of magnitude apart.
| Copper in EU vineyard soils | Value |
|---|---|
| Current application limit | 4 kg Cu per hectare per year |
| Net accumulation | 24.8 kg Cu per hectare |
| Net export | 0.29 kg Cu per hectare |
| Projection under the current limit | a further 2% of EU vineyard area passes the soil no-effect threshold within 100 years |
Copper is a micronutrient plants need, which is exactly why it is easy to think well of it. At high concentrations it becomes a toxicant: the vineyard review describes morphological, anatomical and physiological changes in plants that reduce both productivity and quality. Precipitation, aridity and soil organic carbon together explain 45 percent of how copper is distributed across European vineyards.
Replacements have been sought for years. The Julius Kühn-Institut, Germany’s federal crop research center, tested leaf and bark extracts of the African tree Warburgia ugandensis: in vitro the bark extract worked at 5 µg/mL, and on leaf discs and seedlings it protected for up to 48 hours. In field trials efficacy dropped off markedly, regardless of the extract’s origin or concentration. That is the usual ending for candidates meant to replace copper.
Spinosad: natural origin, thoroughly chemical action
Spinosad is produced by the soil bacterium Saccharopolyspora spinosa, which is where its gentle reputation comes from. On an insect’s nervous system it acts as decisively as any synthetic, and the Brazilian experiment put numbers on that: same dose, same route, a worse outcome than the neonicotinoid.
One detail from the same study is worth keeping. Imidacloprid impaired respiration, overall group activity and flight in worker bees, while spinosad significantly impaired flight alone. The harm profiles differ, and neither is zero. The authors framed their conclusion as a demand on regulators: bioinsecticides should not be exempted from risk assessment because of where they come from.
Spinosad also leaves traces in produce. In the Danish residue monitoring program for 2012 to 2017 it was among forty-odd substances detected for the first time, and it turned up more than a hundred times. The program covered 13,492 samples and included organic produce, but the published summary does not split the detections between organic and conventional. So the correct reading is narrow: a substance permitted in organic farming shows up in the monitoring net alongside everything else. How that net is built, and why animal products pass through three checks rather than one, is covered in our piece on antibiotics in meat and milk.
Pyrethrins: permitted, and weaker
The same Kansas study compared fresh and seven-month-old residues on corn against two storage pests. Deltamethrin, the conventional comparator, killed well. After pyrethrins there were 92 to 99 percent fewer dead maize weevils and 78 to 88 percent fewer dead larger grain borers than after deltamethrin, and plain water produced the same result. Spinosad held its own against the synthetic: from 16 percent fewer to 1.4 percent more dead insects.
Direct mortality is only part of the ledger, though. Pyrethrins, spinosad and deltamethrin all cut progeny production much the same way: by 43 to 99 percent for the weevil and 27 to 100 percent for the borer, against water-treated grain. A product permitted in organic farming can barely kill adults and still hit the population hard.
The practical consequence for a grower: weaker direct action means more applications per season, which costs money and raises pressure on non-target species.
How much residue turns up at all
The Danish program gives the scale for conventional produce: residues were found in 54 percent of fruit and vegetable samples and 30 percent of cereal samples, with limits exceeded in 1.8 percent, most often in fruit. Samples of foreign origin carried more detections than Danish ones.
Finding a residue and exceeding a limit are different events, and the gap between 54 percent and 1.8 percent is exactly that distinction. What the best known consumer list does with numbers like these is covered in our piece on the Dirty Dozen.
What switching to organic actually does
A Spanish group ran a pilot intervention: 20 volunteers spent 24 hours eating exclusively organic or exclusively conventional food, in two different seasons, after which their first-morning urine was screened for pesticides and mycotoxins at once. Of 52 compounds, four mycotoxins and seven pesticides appeared in more than a quarter of samples, and deoxynivalenol along with the organophosphate metabolite diethylphosphate appeared in every single one.
After a day of organic food two mycotoxin markers fell and a third, β-zearalenol, rose. The authors ask for caution themselves: 20 participants over 24 hours is a pilot, not a proof. The direction of thinking is still useful. Changing a diet changes which substances arrive in the body rather than switching all of them off.
The same pattern showed up elsewhere on this site from another angle: in the Canary Islands, nitrate levels in organic greens were significantly higher than in conventional ones, which is covered in a separate piece.
What follows for a shopper and for a grower
For a shopper the conclusion is plain: an organic certificate guarantees adherence to a list rather than the absence of treatments. It says a good deal about the farming method and little about the specific molecule on your plate. The extreme case of that difference is cut flowers, which have no list at all: 90 bouquets carried 107 active substances. Nor does the certificate promise fewer bacteria: studies from six countries are covered in do organic vegetables carry fewer pathogens.
For anyone growing, the other half matters more. Swapping a synthetic product for a permitted one removes none of the need to count doses, rotate modes of action and watch non-target species. The logic of “spot the pest, spray it, only organically now” leads exactly where it led before: to resistance and to losses among beneficials. What the alternative looks like is in our reference entry on IPM strategy. Soilless growers never reach that list at all: in the EU and Ukraine, hydroponics, aquaponics, and bioponics cannot be certified organic.
Key points
- Organic farming runs on its own list of inputs: copper, spinosad, pyrethrins. Spraying happens; the list of substances differs.
- Copper does not degrade. Under a limit of 4 kg per hectare per year, net accumulation in EU vineyard soils is 24.8 kg per hectare against an export of 0.29 kg.
- Under current regulation a further 2 percent of European vineyard area will pass the soil no-effect threshold within a century.
- For the stingless bee Melipona quadrifasciata, spinosad proved more toxic than imidacloprid: 12.07 against 23.54 nanograms per bee.
- Danish monitoring found residues in 54 percent of conventional fruit and vegetable samples, with limits exceeded in 1.8 percent.
- A 24-hour switch to organic food in a pilot study lowered two mycotoxin markers and raised a third. The mix changes; it does not reset to zero.
Copper products from the crop protection side are covered in our reference entry on bacterial diseases. The wider picture of fresh produce risk sits in the food safety hub.
