Systemic pesticides are absorbed through the leaves or roots and translocated to every part of the plant. Unlike contact pesticides, which need to touch pests to kill them, systemic pesticides don’t need direct contact; so long as the pest eats or sucks enough of the crop, death is assured. The downside is that the pesticide is in the edible parts of the plant too, giving you no chance of washing or peeling it off.
When I studied agriculture in the early ‘80s, I became an advocate of integrated pest management (IPM) whereby intelligent and minimal interventions are based on the ecological interactions (assumed to be well-studied and understood) of crop, pest, predator and the wider environment. An ‘intervention’ could be a pesticide (ideally well-targeted and short-lived), or (in theory at least) introducing a parasitic wasp, planting a hedge to encourage lacewings, or timing sowing to avoid peak pest egg-laying.
If things had progressed as my lecturer anticipated, we would now see non-organic farmers using minimal, highly targeted, low persistence sprays with a full understanding of their ecological impacts. But we were wrong. Farming didn’t get that smart, it just found more sophisticated, powerful ways of
being stupid. We failed to invest in ecology or to acknowledge the dangers of pesticides; the chemicals were too cheap, their use too simple and the sales patter too alluring. Threatening bees and other pollinators with systemic neonicotinoids is the latest example of the dangers of power without ecological understanding. Despite being systemic, 95% of neonicotinoid seed treatments end up in the soil, disrupting soil life or getting dispersed in dust to nearby crops. They are fairly persistent in the environment (half-lives typically between 200-1000 days), toxic to all insects, and harmful to most other animals. In trials bees didn’t die fast enough, so we didn’t anticipate neonicotinoids would reduce their ability to find their way back to the hive; that was just too subtle for the methodology. Intelligent regulation must accept there is no safe level for a nerve toxin or endocrine disrupter, only degrees of risk and levels of benefit. The job of legislation is to balance the two, not to fob us off with reassurance of long-lost safety.