Pipevine Swallowtail First Brood is Ending

It is evident that the first brood of pipevine swallowtails (Battus philenor hirusta) is now ending here.

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Despite the haphazard diapausing pattern of our "California" pipevine swallowtails (Battus philenor hirsuta), their broods are still fairly distinct. Starting as early as February, the first largest flight of the year begins and peaks sometime around April. By the start of June, for a brief moment there are few adults or eggs being laid and the first brood is usually ending. Then, simultaneously, the second flight begins and eggs are once again seen alongside last instar larvae and recently formed pupae. 

Today, when we went into the Berkeley Hills (Berkeley, California) to check on the status of flight, we found hordes of last instar larvae. More than half of the larvae we found were in this stage. The youngest larvae we found were mature third instars. We only found a single egg cluster, either laid by a first flight straggler or by an early second flighter. 

This is consistent with what we observed last year at this time. Many of the larvae look just about ready to pupate and, undoubtedly, many of them already did before we got there. At the same time, we are suddenly seeing a lot of fresh eggs being laid at Albany Hill. . .

What we also noticed was how much the pipevines (Aristolochia californica) had declined overtime and how overcrowded they were with larvae. We found a number of late instar larvae that were evidently disease with symptoms identical to what we have seen from our own home rearing. The larvae stop eating and just crawl around or sit there as they "liquify", eventually become completely flaccid, and die. Two years ago in August, we also found larvae like this. 

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Authors
Brian Liang

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