Because we will be moving to Ithaca, New York tonight, we had no choice but to collect all the cecropia moth (Hyalophora cecropia) cocoons despite that not all larvae have spun.

We never thought a cecropia brood started all the way back in April would still not be finished now in mid August. We normally would have collected all the cocoons once all larvae had finished spinning, but since we will be moving tonight, we had to collect all the finished ones and resleeve up the remaining few larvae with as many leaves as possible. 

The cocoons this year are far smaller than the ones last year, despite having received nearly identical treatment (indoors on apple first three instars, and sleeved outside in the last two). The only difference was that some of the larvae this year were sleeved since birth. The larvae this year also grew much, much slower than last year's which all finished spinning at the beginning of August and began in June. We can't really understand why this year's rearing was so poor. We started off with hundreds this year and nearly all died off overtime, mostly the ones that were sleeved since birth. Last year we started with three dozen and got about the same amount through and they were respectable in size, with females at 8 g and males at 6 g. This year, the cocoons are a measly 3-6 g. We didn't imagine cecropias could even get down to 3 g without opting for a supernumerary sixth. Maybe inbreeding reduced their size?

​Authors
Alan Liang

Our final non-diapausing ♀ ​polyxenes asterius × ♂ zelicaon hybrid pupa eclosed into a crippled male. Fortunately, the important wing and body patterns are visible enough to compare to parent species, P. polyxenes asterius and P. zelicaon.

The hybrid eclosed today, and weak and small as it is, it could not expand its wins fully just like the first one. However, this one managed to expand enough for us to clearly see the wing patterns, unlike the first who's wings were completely crumpled. Below are sided by side live comparisons between the hybrid and the parent species, P. polyxenes asterius and P. zelicaon; all individuals are males. Though intermediate between the parent species and many traits, the hybrid superficially resembles polyxenes more due to the black (rather than yellow) ground color. However, all the yellow regions on the hybrid are darker than in polyxenes more closely match the shade in zelicaon.

Now let's get into the details, starting with the wings.

​Dorsal Forewing

The dorsal forewing of the hybrid is primarily black like polyxenes, though it is not quite as dark and is slightly brownish. The band of yellow spots in the middle is more or less consistent in width, unlike in polyxenes which typically tapers going upwards or like in zelicaon which is thick on both ends and narrower in the center. Also, The marginal yellow spots are somewhat intermediate of the parents, being more rectangular than polyxenes' but rounder than zelicaon's. ​

​Dorsal Hindwing

The dorsal hindwings of the hybrid are similarly intermediate between the parent species as the forewings are. They are primarily black, but the band of yellow spots is larger than in polyxenes. Also, the marginal yellow spots are larger and more crescent shaped than in the polyxenes of our lineage, more like in zelicaon.

Ventral Forewing

The central hindwing is again more polyxenes like that zelicaon, simply due to the black ground color (though again, slightly brownish rather than pitch black). However, the other traits seem more intermediate, with the band of spots in the middle being orange-yellow, rather than orange in polyxenes or yellow in zelicaon. The marginal yellow spots are longer lengthwise and more rectangular, similar to zelicaon, and not rounded or tear drop like in polyxenes.

​Ventral Hindwing

The ventral hindwing of the hybrid is perhaps the most interesting of the wings. It is again black in ground color rather than yellow. However, intermediate of the parents, it contains much more blue past the band of orange spots than in polyxenes, and less than in zelicaon. Also, the band of orange spots is lighter and more yellow than in polyxenes, and is more simplistic, lacking the orange spot on the discal cell like in zelicaon.

​Now, onto the body

Head & Thorax

Like mentioned in the previous post with the first hybrid, the yellow stripes on the head and thorax of the hybrid are short and small like in polyxenes, unlike the long, connected stripes in zelicaon. However, like other yellow regions of the hybrid's body, the yellow is darker than in polyxenes, and more like the shade in zelicaon.

​Abdomen

The hybrid abdomen is very interestingly intermediate between the parents which we briefly described it in the previous post already. On the hybrid, the abdomen very clearly has two rows of rectangular yellow spots laterally. This is intermediate between polyxenes and zelicaon, because in polyxenes, the abdomen has three rows of rounded yellow spots - two lateral and one dorsal, and in zelicaon there are two solid yellow stripes rather than  rows of spots. The placement of the top row of yellow spots in the hybrid is also intermediate between the location of the dorsal and top lateral row in polyxenes, and right in the middle of where the larger solid yellow stripe in zelicaon is.

​Authors
Alan Liang

Rearing Notes 8/6/17-8/14/17:

​Authors
Alan Liang

Rearing Notes 8/10/17-8/15/17:

​Authors
Alan Liang

Rearing Notes 8/10/17-8/??/17:

​Authors
Alan Liang

And another brood finished. The last of the larvae finished spinning, so like always, we collected all of them in a tub and weighed them. There are 20 in total, and this time they are quite large compared to previous rearings. This is our fourth rearing of Samia ricini; summary stats are listed below for this brood, as well as two previous broods (the third brood of winter 2016 was never recorded, but was very small). Note that this brood was reared on Liquidambar while the other two were on Prunus, and the fall 2016 brood was of a different lineage.

Summary Statistics for Samia ricini Cocoon Mass:
                                  Mean     Std Dev     Median     Min     Max     N 
Fall 2016                 2.221       0.356          2.1               1.6         2.8        14
Spring 2017            1.773       0.337           1.7               1.2         2.5       33
Summer 2017        2.218       0.294          2.19            1.78       2.86     20

The majority of cocoons this time were 2 g or larger which is quite good, and masses were less variable than in previous broods. Of the three broods, both the fall 2016 and summer 2017 broods were significantly larger in mean mass than the spring 2017 brood (p=0.0002 and p<0.0001, respectively), and between those two larger broods, there was no significant difference in mean mass. 

​Shown above are this brood's cocoons compared to the fall and spring cocoons. The spring are visibly much smaller, and the silk was thinner and and more papery, rather than thick and fluffy. The fall cocoons look about the same size visually as this time's cocoons, but as they were of a different lineage, the shape of the cocoons were flatter and less round.

Most likely the spring rearing produced small cocoons because of much more severe overcrowding in the final instar compared to in the other two and the food quality was not as good. Or, maybe it was the host plant species that made the difference, as this time we used Liquidambar for the first time rather than Prunus. Perhaps Liquidambar was a better host than Prunus, and the reason why the fall brood was on par with the summer brood because that lineage was larger or utilized Prunus more efficiently.

​Authors
Alan Liang

​Rearing Notes 8/4/17-8/13/17:

Our luna moth (Actias luna) larvae have all finished spinning cocoons.

Since all the larvae have spun up, we went ahead and collected all the cocoons from the tubs and ripped off all the leaves. There are just 19 cocoons total which is very few for how many we started with, but we're not too worried though as it is not the most valuable species.

While rearing the larvae, we had put them in an opaque tub starting in the fourth instar which blocked out light when closed, allowing us to limit the light to only a few hours a day. Thus, we expected that all the cocoons would diapause and be made of tough, brown silk than the thin beige of the normal, non-diapausing ones. However, after inspecting all the cocoons, we saw that there was a very large variation in silk color, with some being extremely dark brown, others being almost white, and many being an intermediate orange-brown. The dark brown and probably also orange-brown ones should be in diapause, but we can't be sure about the beige ones. They look just like the spring cocoons that did not diapause, but perhaps the silk just hasn't hardened and tanned yet.

Some other interesting things about this rearing's cocoons are that one of the cocoons is extremely large, thin, and baggy, rather than the normal round and compact. It sort of resembles the baggy form of Hyalophora cecropia cocoons, though this form is not supposed to exist in luna. Perhaps something about the way the available attachment points were arranged while the prepupa was spinning caused it to produce such an odd cocoon. Other unusual cocoons were two pairs of fused cocoons due to the larvae spinning right next to each other. We were able to split them apart without damaging them with some difficulty. 

Anyway, on to the mass data. After collecting the cocoons, we weighed and recorded their masses and calculated some summary statistics, shown below: 
​
Summary Statistics for Actias luna Cocoon Mass (Summer 2017):
Mean     Std Dev    Median     Min     Max      N
2.750      0.541          2.68            1.98      3.86       19

For comparison, we pulled up the spring stats as well:

 Summary Statistics for Actias luna Cocoon Mass (Spring 2017):
Mean     Std Dev    Median     Min     Max      N
3.525      0.411            3.4              3.0        4.2        12​

What's the first thing we noticed? That's right - a ridiculously lower summer cocoon mass compared to spring. Sample size is small, but the difference is still quite extreme. A two-sample t-test for the difference of means between spring and summer cocoon mass also supports that the difference is statistically significant (t = 4.2357; df = 29; p=0.0002).

Right now the first explanation to come to mind is simply the severe overcrowding the summer larvae experienced in later instars. But really, it wasn't too much worse by the fifth instar compared to in the spring rearing. Food quality should have been about the same, so the only other difference was the temperature and humidity. The spring larvae were incubated at constant 27°C and high humidity during the first three to four instars while the summer larvae were at room temperature their entire lives. However, this seems to be a contradictory factor, since from what we've seen, the high constant temperature of the incubator tends to speed larval growth drastically at the cost of size. Plus, by the fifth instar - the critical growing period, both spring and summer larvae were at room temperature. The only other factor that could have played a significant role in size reduction was inbreeding. The summer larvae were inbred offspring of the outbred spring larvae. It is hard to say how exactly the recessive gene stacking affects the larvae, but from what we suspect and what some other hobbyists claim based on observation is that inbreeding tends to reduces size. We only inbred for one generation, but perhaps that was enough to cause this extreme drop in size.

Our male ♀ Papilio ​polyxenes asterius × ♂ Papilio zelicaon hybrid finally eclosed, but unfortunately did not expand its wings.

We are extremely disappointed to say that our ♀ Papilio ​polyxenes asterius × ♂ Papilio zelicaon hybrid male eclosed today but could not expand its wings fully. We don't know why it became crippled or if hybridization could have caused it, though usually the males of machaon group hybrids should have no problem eclosing. Despite the crumpled wings, it is still possible to see the body and the general pattern on the wings. We tried to get shots from many different aspects, shown below.

From what we can see, the hybrid appears to resemble polyxenes more so than zelicaon. Both fore and hind wings have a considerable amount of yellow, but it is hard to say exactly how much since they are not fully expanded. The males of the parent species both have yellow on their wings, with zelicaon having more. The hybrid definitely seems to have less yellow than a zelicaon would have and looks more like polyxenes. However, perhaps if the wings were expanded, there would actually be a lot more yellow than it looks, and perhaps some of the grayish looking parts could expand to a yellow-gray, intermediate of the parent species. We do not know.

As for the ventral aspect the wings, they again seem to resemble polyxenes more, with the forewing having only small amounts of yellow and the hindwing having orange spots. However, probably the orange spots on the hind wing will expand into a pale yellow orange based on how light they are even when not expanded, which would be intermediate of the parent species, since polyxenes' spots are well-defined and dark, while zelicaon only have traces of orange.

Looking at the body - mainly the abdomen, the hybrid again resembles polyxenes slightly more. In the parent species, polyxenes has several rows of yellow spots down the length of its abdomen while in zelicaon, it is a single solid yellow stripe on each side with a poorly defined solid stripe on the ventral side. The hybrid very clearly has rows of spots rather than solid yellow, but the spots appear to be slightly larger and more rectangular and "dash" like than than in polyxenes. The head and thorax region looks more polyxenes as well. In polyxenes, there are broken pale yellow spots on the thorax while in zelicaon it is two solid dark yellow stripes. The hybrid has spots rather than solid stripes, but they appear slightly thicker and darker than normally would be in polyxenes. 

​Authors
Alan Liang

We spotted a red admiral (Vanessa atalanta) flying around our backyard.

It's always nice to see a butterfly that you haven't seen in awhile. Of the three Vanessa species in Albany, atalanta tends to be most common in midsummer while the painted lady (V. cardui) comes in spring and west coast lady (V. annabella) comes in fall and winter. Atalanta doesn't seem to be too common here in the city as there are no hosts accept exotic pellitory (Parietaria), but the little weed is only found spottily and often removed by the city. We saw many eggs on them earlier in the summer (see Red Admiral Eggs on Pellitory), but they've since then disappeared and most of the pellitory has been removed anyway. We never collected any then because our time here in Albany is short and supplying them with enough pellitory would be difficult. Maybe one day we'll rear up some of these nice little butterflies again, but our chance for this year has past.

Authors
Alan Liang
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