Deep in the archives of San Francisco-based Aquarius Records, buried between several days’ worth of “laptop glitchery” and “brutal industro-crunch,” lies this gem: Insect Noise in Stored Foodstuffs, (INRA, 2000, CD, 19:98).The CD is currently unavailable or out of stock, which is disappointing but unsurprising, given its intriguing description:
Insect Noise in Stored Foodstuffs appears to be an industrial document produced by the 5th International Working Conference On Stored-Product Protection. This CD presents the sound investigation of the French team of Bunsel and Andrieu who used sensitive microphones with narrow frequency responses made to detect and identify the sounds of insect larvae which may be inhabiting otherwise quiet containers of grains and cereals.
A handful of examples of the sounds including the grain weevil, the Indian meal moth, and the Lesser mealworm are accompanied by a running narrative both explaining the techniques used and the identification of the insects. And in case you missed the first 30 minutes of the document, the kind people at the 5th International Working Conference On Stored-Product Protection repeat the program in French.
Mysteriously, the online proceedings of the 5th International Working Conference of Stored Product Protection (IWCSPP) do not include reference to any such CD. However, in Session 8, there is a short paper entitled “Automated acoustical detection of stored-grain insects and its potential in reducing insect problems,” by D. W. Hagstrum.
From that teasing clue, it is just a short step into the world of acoustic pest detection. David Hagstrum, as it turns out, is the co-author of a major textbook on the subject of food infestation control. His 323-page Fundamentals of Stored Product Entomology, published in 2008 by the American Association of Cereal Chemists, includes a chapter specially devoted to the subject of designing an effective acoustic sampling programme.
Silos, bins, elevators, or UFO-like grain storage rings filled with wheat, oats, barley, or sorghum make an understandably attractive home for a number of insects and their larvae. The problem, as outlined by Francis Fleurat-Lessard in a paper submitted to the 9th IWCSPP, is that while “the presence of live insects in commercial grain lots is unacceptable in grain trade,” standard techniques of insect detection are slow, inaccurate, labour-intensive, expensive, or all of the above.
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However, since the larvae of many stored product pests grow inside grain kernels, where, Fleurat-Lessard notes, their “population density may be ten times more numerous than free-living adults,” a visually-inspected “clean” sample may actually be completely infested with rice weevil larvae. To look inside grains, laboratories use X-rays or resonance spectroscopy, but these techniques are too expensive and impractical to deploy in bulk grain lots.
But while rice weevil larvae are invisible, they are not inaudible: the “mean sound pressure” of rice weevil larvae feeding inside a wheat kernel is 23 dB, according to the USDA Agricultural Research Service. The idea, then, is that if you could somehow design sensitive-enough acoustic probes, combined with software to match the probes’ input against a database of field recordings, you might be able to monitor insect activity in stored grain automatically and detect infestations at the larval stage.
A fairly select group of entomologists, including several specialists at the USDA’s Insect Behavior and Biocontrol Research Unit, have thus spent the past twenty years investigating the acoustic detection of insect noise. Major steps forward, as described by Fleurat-Lessard, came with the development of ever more sensitive sound technology, as well as innovative designs for “muffle boxes” that shield acoustic sensors in grain bins.
Building a sound library of stored food insects was equally important – the field recordings on that Insect Noise in Stored Foodstuffs CD actually form the core of current acoustic pest detection databases. Years of research have gone into classifying the characteristic sonic signatures of different pest species at different stages in their lifecycles, to the point that a computer can now compare input from a grain silo’s acoustic sensor system against a library field recordings and tell you whether the rice weevil larvae eating your wheat kernels are sixteen or eighteen days old.
(For the curious, you can actually listen to the fairly revolting munching sounds of Indian meal moth and eighteen-day-old rice weevil larvae at the USDA website.)
― Elvis Telecom, Friday, 8 January 2010 11:24 (fourteen years ago) link