Papilio glaucus Female Finally Starts to Lay Eggs!

4/15/2017

On the third day of attempting to get one of our Papilio glaucus females to lay eggs, she finally laid one!

Beginning on 4/13, after we set up a homemade little oviposition light box as described in this post, we have been hoping each day to get some of our hand-paired swallowtails to lay some eggs.

After a quick feed of honey-water this morning at 9 AM, we decided to put the older of our two eastern tiger swallowtail (Papilio glaucus) females paired on 4/3 into the box with just a small sprig of plum (Prunus cerasifera) and switched on both lamps (our female pipevine swallowtail [Battus philenor hirsuta] escaped in the basement yesterday and still has yet to be recovered and the other glaucus has only just eclosed two days ago). Based on the activity of the previous two days with this female, there didn't seem to be much hope since she was already very worn and weak with brutally torn/crippled wings and a missing leg. We knew that if she really was going to lay eggs, it would take time and were not optimistic that she would be in the proper condition--or even alive for that matter--by the time she was ready. But when we checked on her about two hours later, we were quite taken aback that she had indeed finally laid a single egg right on the top of a fresh little leaf!

Being the first time that we have ever gotten any swallowtail outside of the machaon-group to actually oviposit in captivity, this has truly got to be one of the most exciting events in all our of years of rearing. What makes this even more exciting, or at least interesting, is that the female that laid the egg had been hand-paired with a wild caught western tiger (Papilio rutulus). We will admit that we aren't positive that the egg is actually fertile, but based on the behavior and abdomen girth of the female it at least seems that the pairing was successful.

Given the unexpected success of this oviposition setup, we'll take this opportunity to analyze just what was different about this and the multitude of other occasions we have attempted to get Papilio glaucus to oviposit in captivity. In the past, we have always taken the roomy approach in terms of the setup size, thinking that it was necessary that the female have enough room to fly in order to stimulate natural conditions and get her to lay. This time we used the smallest possible enclosure that could fit a sprig of host plant such that contact of the plant was essentially unavoidable unlike in the larger setup. Also different was that we used the heat lamps this time instead of natural sunlight. As you probably know, the weather here doesn't get very hot here so the lamps added a significant amount of heat that would be unachievable otherwise. However, we did realize this time that it probably was not necessarily the heat that got our female to start laying. Simply put, heat is not a direct stimulus for egg-laying; it seems only to hasten the process just as it hastens all other processes of these cold-blooded insects. Based on experience, very high heat is certainly not an absolute requirement for the swallowtails to lay so if our female was not planning on laying from the start she would not lay no matter how hot it is (the opposite is true in that if she is going to lay, she will do so even without higher than normal temperatures).

It is also important to note that our female is an old one, having eclosed on 4/4 (paired on 4/13). Tiger swallowtails are notorious for taking very long time to develop their eggs. Obviously, the adult females begin with a handful upon emerging, but the higher the egg load, the more willing it seems that they are to lay. There is also some unconclusive research saying that females with higher egg loads are less picky when choosing host plants, which if true is something that we probably need to count on given the hosts that we used and have available to us. Our particular female very evidently had built up a generous supply of eggs based on how old she was and just by taking a look at the fullness of her abdomen. It is certainly much fuller than our younger female that eclosed on 4/3. Insufficient egg load is one of the primary reason why it might take a long time before females begin laying in captivity.

Anyway, we are hoping that now that our female has gotten started, she will lay a some more in the coming days. Even a few eggs would be more than enough to please us if they all hatch and assuming they don't die for mysterious genetic reasons.

Authors
Brian Liang

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