By Richard Levine
One hundred years ago this month, an entomologist at the Washington Agricultural Experiment Station named A. L. Melander published an article in the Journal of Economic Entomology called “Can Insects Become Resistant to Sprays?” It is widely regarded as the first ever published article on arthropod resistance to insecticides.
“Melander’s 1914 paper not only reported the first case of field-evolved insecticide resistance, it also foreshadowed the refuge concept for delaying resistance,” said Dr. Bruce Tabashnik, head of the Entomology Department at the University of Arizona. “It’s remarkable!”
Melander noticed that certain populations of insects — but not all of them — were becoming less susceptible to sulphur-lime than they had been in the past. While the chemical was documented to be very effective at killing scale insects in a previous experiment in Wawawai, WA, Melander found that 90% of the specimens that he had sprayed in Clarkston had survived. Even when he increased the amount of active ingredient by ten times, 74% of them still survived.
“That the San Jose scale should become acclimatized to a sulphur-lime environment is not altogether a strange thing,” he wrote, noting that a colleague had observed that moths in his lab could become resistant to arsenic.
“By consuming repeated small amounts of arsenic the body becomes immune to many times the normal lethal dose,” he wrote. “When arsenic spraying for leaf-eating insects is imperfectly done it is quite possible for the insects to get daily homeopathic doses of arsenic and to become progressively resistant. Indeed, Mr. R. W. Glaser of the Bussey Institution, has experimentally verified this supposition in his work with the gipsy moth [sic]. By successively administering more and more spray, he tells me that he has succeeded in rearing a series of moths from larvae that finally were feeding on heavy dosages of arsenate of lead. Indeed, these larvae were especially hardy, and developed as strong an immunity to disease as they did to the arsenic.”
As Dr. Tabashnik said, Melander also predicted that entire populations would not become resistant as long as some non-resistant insects survived, because their non-resistant genes would be passed on to future generations.
“If only the resistant individuals survived to reproduce then a pure [resistant] line might result after repeated sprayings,” he wrote. “But always there are some scales missed by the spraying, and these, during the ten generations between sprayings, will produce a population in part, at least, non-resistant … Thus we may make the strange assertion that the more faulty the spraying this year, the easier it will be to control the scale the next year.”
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Richard Levine is Communications Program Manager at the Entomological Society of America and editor of the Entomology Today Blog.