Change of Plans for Polyphemus Hosts

After a day of offering our polyphemus (Antheraea polyphemus) larvae various hosts, we have decided to change our choice of hosts based on the results.

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Looks like this a perfect example of when larvae of a particular species do not accept hosts recorded in literature. Though a widespread and polyphagous species like polyphemus may seem accepting of a large variety of hosts, the reality is that each given population of the species likely only utilizes oak and a few of the other ones listed in literature in the wild. The remainder of the list probably comes from common recordings of polyphemus hosts elsewhere in the species' range.

Our stock of polyphemus larvae readily fed on oak last year, which came to no surprise as it is likely the prime host of a once specialist feeding Antheraea ancestor. However, when offered five hosts other than oak this year - willow (Salix), alder (Alnus), hawthorne (Craetagus), plum (Prunus), and grape (Vitis) - all recorded in literature, there was minimal or no feeding on any of them after 24 hours. The plum seemed to do the best, as there were actually a few small holes and frass, and surprisingly the hawthorne wasn't too much worse as well. We thought the alder would be a surefire host of polyphemus regardless of its origins, as it is not too distant from the oak family Fagaceae, but it only looked like a few larvae had even attempted eating it. However, the species of alder we offered them had thick and glossy leaves which may have been the reason for its unpopularity among the larva. The willow, which we had planned on using as a staple due to its abundance here was completely uneaten except for maybe a minuscule nibble by one of the larva.  The grape was also completely untouched, but this came as no surprise as it is likely an obscure host anyway, though it looked like one of the larva might have been nibbling on it. 

With five unstable looking hosts, we decided to take the safe route and get some of the good old oak regardless if the leaves are always hard, dry, and in poor quality around here, as well as some birch and red alder - a softer, less glossy variety of alder we had offered them yesterday. These tree hosts - Quercus, Betula, and Alnus - should most likely be accepted by polyphemus anywhere. When we got back, there were over a hundred new born larva swarming the petri dish of eggs, and we cut small bits of the three hosts into the dish just to see how they would respond before putting them all on the hosts. The results were good - just as we thought, the larvae immediately went for all three cuttings and began nibbling holes on every piece - a far better response that the one they had towards the five hosts we offered them yesterday. So, after several minutes we felt we had seen enough and decided to place 40 some larva each to alder and birch (though it is likely they would switch between the two interchangeably if we want them to in the future), and 20 some larvae on oak.

As for the larvae that were still on the five hosts we tried yesterday, we merged the ones on alder with the new group of alder feeders, and stuffed in new cuttings of the other four hosts, just to see if giving them another day might prove them still usable. It's a risk, as they might all starve, but the plum and hawthorne actually look like they have potential - Rosaceae shouldn't be too bad compared to their favorite Fagaceae and Betulaceae. As for the willow and grape, fingers crossed that they will accept - we saw another larva begin to nibble on the willow, and at least two take a bite out of grape. Though even if these fail, all is well, as we should now have three solid staples for this years rearing.

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Authors
Alan Liang​

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