The Insects We Counted, And The Ones We Lost

AFew animals have been recruited into a public argument as quickly as the insects that carry pollen between flowers. The reasoning is easy to state: roughly three-quarters of the world's leading food crops set more or better fruit when insects visit them, and the value placed on that service is now quoted in national accounts. The alarm, however, rests on figures that do not describe the same thing. The number of managed honeybee colonies worldwide rose by about forty-five per cent between 1990 and 2020, since colonies are livestock and can be bought; over the same decades, counts of wild bees and hoverflies in the intensively farmed lowlands of northern Europe fell, and in several long-running schemes fell steeply. What has been added and what has been lost are therefore different populations. The dispute that now organises the field concerns the second of them: whether the decisive change is what growers have sprayed onto their fields or what has been cleared from between them.

BHiroshi Petrosyan, an entomologist at the Boreal Pollination Laboratory in Uppsala, argues that the headline numbers have been read too loosely. Between 2009 and 2021 her group reworked 96 monitoring transects in four countries, a series covering some 1.1 million identified individuals. Total insect biomass on those transects fell by 22 per cent, a figure widely quoted since. Underneath it the losses were not shared out evenly. Species that gather pollen from a single plant family declined by 61 per cent, while generalists able to work whatever happened to be in bloom were close to stable, and about three-quarters of the whole decline was contributed by roughly eight per cent of the recorded species. An average, on her reading, is the wrong instrument here, because it allows a large number of adaptable insects to disguise the disappearance of the narrow feeders on which many wild plants and several orchard crops depend. The transects themselves, she adds, had been laid out along field edges for ease of access, and it was there that the specialists thinned out first.

CThe shape of the loss suggested a mechanism, and Petrosyan set out to test it. A specialist returns to the same few plants day after day, so any residue those plants carry arrives in concentrated form, whereas a generalist dilutes what it takes. At 24 farms her group installed nesting units of a solitary bee and counted the offspring each female produced. Where treated seed had been used, output fell from 5.4 offspring per female to 2.1. The result was confined, however, to farms where uncropped flowering habitat made up less than three per cent of the surrounding land; at farms above that share the difference between treated and untreated ground was too small to measure. Petrosyan reports the limit without disguising it and calls it uncomfortable, since the harm she attributes to chemistry appeared only where her opponents' variable had already gone missing. She maintains that exposure is nonetheless the trigger rather than the background condition.

DTomas Reguera, who studies agricultural landscapes at the Institute for Rural Land Use in Valencia, replies that a field with nothing in flower starves an insect long before it poisons one. His survey covered 40 districts selected so that spray regulations and application rates across them were equivalent, which he presents as a way of holding chemistry constant. Districts where uncropped flowering habitat, on the same measure Petrosyan had adopted, exceeded eight per cent of the area retained a median of 74 wild bee species; those where it had fallen below two per cent retained 31. Regulation, he notes, was tightened in most of these districts while the survey ran, and the species figures did not respond. He accepts two limitations. All 40 districts lie within one climatic region, so the range of flowering seasons is narrow, and his habitat share was read from satellite classification, which separates a mown verge from a flowering margin poorly.

EThe disagreement stopped being academic in 2022, when pollination clauses attached to farm support payments began to require growers to report counts of wild species on their land rather than the number of colonies they had brought in, and applications submitted without those counts were returned unpaid. Reguera observes, awkwardly for his own case, that a restriction on spraying takes effect within a single season and can be checked against an invoice, whereas a flowering margin takes years to establish and cannot be produced on the morning an inspector arrives, so the remedy with the weaker evidence behind it is the easier one to legislate. Petrosyan answers that this appetite for a visible intervention is exactly what has kept habitat out of the accounts, and that her own findings are being cited in support of prohibitions she has never endorsed. What both dislike is the convention still in use across much of the industry, under which pollination is reported as colonies installed rather than as species persisting.

FA settlement is taking shape in which the two accounts are sorted by circumstance instead of being ranked against each other. Where flowering habitat remains plentiful, the variation still to be explained is largely chemical, and restricting exposure ought to recover it; where forage has collapsed, no restriction on spraying will hold a specialist fauna in place, because the insects concerned have nothing left to specialise on. The question neither line of work has answered is whether habitat that has been restored comes to carry the same range of species as habitat never removed, across the decades over which payments are made, and no series of counts yet runs long enough to say. What both researchers reject is the assumption behind the original alarm, that a pollination shortfall is something a country can buy its way out of by importing colonies.