By Richard Levine
If you want to do lab research on insects, you need to be able to keep them alive, sometimes for many generations. That means you need to know how and what to feed them, even if it means giving blood to bed bugs.
Many moths in the family Noctuidae are subjects of research because they are serious agricultural pests. They include bollworms, corn earworms, tobacco budworms, stalk borers, armyworms, and many other pest species.
In 2011 a group of Canadian entomologists wanted to assess the potential of a parasitoid wasp (Cotesia vanessae) as a biocontrol agent for different species of noctuid moths, which meant they had to raise caterpillars in the lab. They began by taking semiloopers in the subfamily Plusiinae and feeding them on the McMorran diet, which is named after Arlene McMorran, who created it back in 1965. The McMorran diet turned out to be so useful that Natural Resources Canada actually sells a slightly modified version of it (they add linseed oil) on their website, which claims that the diet is suitable for the rearing of spruce budworm, cabbage looper, fir coneworm, and eight other moths.
The Canadian researchers soon realized that, in addition to those mentioned above, many other species readily fed on the modified McMorran diet. In fact, they successfully reared 39 different moth species on the diet — some for multiple generations — and they also tested it on other field-collected caterpillars that they reared until they metamorphosed into adults.
“[The McMorran diet] allowed us to quickly handle high numbers of field collected caterpillars of various species,” the authors wrote. “It saved us tremendous time, space, and money because we did not need to grow plants, and we did not need to develop species based rearing knowledge as we were pretty much ensured that any Noctuidae would develop on this diet.”
Their methodology and results are published in an article in the open-access Journal of Insect Science, which also includes a literature review of other insects that were previously reared using the McMorran diet.
“Because we believed that, like us, other entomologists may be interested in using the McMorran diet to ease their laboratory rearing of insects, we decided to do a literature search to find out the species that have previously been reared on this diet and publish this information,” said Dr. Vincent Hervet, one of the co-authors. “Our paper highlights the use of an easily-prepared and stored artificial diet on which to rear a broad variety of phytophagous insects species, including 39 new species that we report in our study. According to information we found in the literature, it seems that the success of this diet is particularly associated with the use of wheat germ and linseed oil as ingredients.”
Their literature review revealed that at least 103 Lepidoptera species have been reared on the McMorran diet, including species that belong to the families Erebidae, Gelechiidae, Geometridae, Lasiocampidae, Noctuidae, Pieridae, Pyralidae, Saturniidae, Sphingidae, and Tortricidae. They also learned that grasshoppers in the genus Melanoplus had been reared on the McMorran, and that many other insects had been reared on slightly modified versions, including the white pine weevil (Pissodes strobi) and more than 49 species of longhorn beetles.
These slight modifications “could potentially be used to rear many more phytophagous insect species that do not readily feed on the McMorran diet,” Dr. Hervet believes.
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Richard Levine is Communications Program Manager at the Entomological Society of America and editor of the Entomology Today Blog.