A Papilio rutulus Victory

Our female western tiger swallowtail (Papilio rutulus), originally found as an egg in Spring 2017 and hand-paired to a wild male, has begun to lay eggs.

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After so many years of searching and searching for western tiger swallowtails (Papilio rutulus) in the wild with horrible luck, we have achieved the unthinkable (at least for us). The survivor of our two rutulus females that we painstakingly captured male mates for and hand-paired on Monday 7/3 has begun to lay eggs. She has already laid over 40 eggs. 

Our success was more technique than the actual oviposition cage setup. After hand-pairing, we kept the female in the dark in a box for four days straight, only taking out twice a day in the morning and night for feeding of a strong honey water solution. She has an incredible appetite, so all we needed to do was prompt her by uncurling her proboscis without having to actually force her to drink. Over the days the abdomen got progressively plumper and firmer. Even though she was surprisingly calm inside the box (we don't think she ever flapped her wings once inside there), by the third day, she must have been exasperated and restless. Every time we opened the box and exposed her to the light, she would very sudden fly out frantically and it would be a hassle to try to catch her and introduce her to the food. When we finally released her this afternoon, she started going berserk the second she touched the potted willow (Salix) we had in our cage, which was actually a camping tent. She would curl her abdomen violently everywhere she went, and at times it seemed like she might lay on the screen of the tent. In fact, she did lay an egg on the nectar source (Asclepias curassavica) when we accidentally bumped her down from it as she was on the actual host plant, plum (Prunus​). When we realized that she was going insane, we considered using a laundry bag rather than a huge tent so that we wouldn't have to keep putting her back onto the host plant to lay, but we didn't want to risk her beating herself up and it was much easier to take pictures while we were inside the tent with her.

Another plus about the tent was that it was a just a much more natural setting. . . she drank furiously when she came in contact with the flowers after she spent so much energy laying eggs.

Through today, we learned quite a bit about the ovipositing preferences of our rutulus population, or at least the preferences of the one individual we have. For the choices, we had a potted willow (Salix) and large cuttings of plum (Prunus), sycamore (Platanus), apple (Malus), and privet (Ligustrum lucidum) that were stuck together in the same bucket of water. 

It was quite clear after some time that she had the greatest response to the plum (Prunus). Now, there are a lot of different varieties of Prunus and the preference for each is undoubtedly different, but the kind we used is something we have found rutulus on two years ago. Prunus is obviously a well-liked host among the tiger swallowtails and the ovipositing preference, a trait that is often retained after speciation, may be ancestral. She did not actually like the willow as much as we had thought and only laid a lot in the beginning when she was basically doing it uncontrollably. Afterwards she would only lay on the plum. Again, this probably has something to do with the fact that willow is a very new host for tigers (not all of them have the genetics to eat it) and probably not a rutulus ancestral host. However, it seems that the populations where we live and other places where willow grows are especially well adapted to the stuff and, despite the oviposition preferences of the adults, the larvae likely perform best on it. The female only laid one egg on sycamore, which is reportedly a very commonly utilized host in urban areas but that is probably the result of it being the only host available. Sycamore seems to be quite an obscure plant and is obviously also relatively new in their host plant palate.  No eggs were laid on the privet, which is exotic but works for anything that can normally eat the related ash (Fraxinus). Rutulus and other tigers oviposit on both plants but we saw no response by our female at all. Even though the apple also received no eggs, it was something that we put in after she had already laid a hefty amount and was starting to lose steam. Had we put it in from the start, we would have expected her to lay a few on it. Malus (exotic like privet), when used by Prunus eaters, is typically a poor substitute but still should work. Clearly, it seems to be a novel host for rutulus after it became popular to plant in gardens since many older reports claim that they cannot survive on them, but we have found rutulus on Malus on it on two separate occasions before and records now exist of larvae completing development on it successfully. 

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Authors
Brian Liang

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