Mediterranean Katydids Hatching at the end of July?

Today were surprised to find a second instar Mediterranean Katydid (Phaneroptera nana) nymph on wild mallow (Malva) at the Albany Middle School garden (Albany, CA).

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For a while now (about a month) we haven't really been collecting any more Mediterranean Katydid (Phaneroptera nana) or Mexican Bush Katydid (Scuderria mexicana) nymphs since we can't find them. Based on personal observations of the years, we have always assumed that these insects are strictly univoltine since they take so long to mature and their adults have a relatively long lifespan. In the spring, starting around April or May, we would find young nymphs (though the Mexican Bush Katydids seem to tend to hatch about a month earlier than the Mediterraneans). The adult males can be heard chorusing as soon June for Mexican Bush Katydids and the July for Mediterraneans.

This all aligns quite well with our captive raised katydids as seen in the rearing notes. In April, we found our first Mexican Bush Katydid nymph which was in third instar. By June, the katydid has grown to fifth instar and the wild caught katydids we found were also either in fifth or sixth instar. We first found Mediterranean Katydid nymphs at the end of May which were no older than third instar. By June, we were finding fourth and fifth instars while our captive ones were also approaching these instars. At the beginning of this month we are mostly finding fifth and sixth instars and now we are hearing the adult males buzzing around while our own are molting into adult. From this, it is easy to assume that they follow a very typical annual schedule: hatch in spring and die in the winter (eggs overwinter) with only one brood a year. 

But then why in the world did we step upon a second instar Mediterranean Katydid nymph today when our first adult had already molted back on 7/10? The little guy was resting all by itself on a crawling wild mallow plant (Malva) growing directly under a fence with a huge grape vine (Vitis) in the Albany Middle School garden at around 4 PM. In the same area at the same time, we heard adult males chirping. The first thought that came to mind was that this species is not univoltine as we had previously thought, but probably bivoltine with two broods per year. It certainly is possible and the time allows for it since we do not have very distinct seasons around here; if it takes the nymphs about two months to grow, the second instar we found would be an adult by the end of September which wouldn't be bad at all since it is actually the warmest month here, historically. It would still have plenty of time to mate and reproduce before dying sometime in November or December. 

But it could be more complicated than that when we began considering the diapausing strategies of the overwintering eggs. Like most insects under diapause or developmental arrest, katydid eggs are hormonally programmed to only respond to certain environmental cues to break diapause, develop, and hatch. The eggs of some species are not designed to hatch until three or four months after being laid to ensure that eggs laid during midsummer (such as June) do not complete development soon enough to start a new brood and instead enter diapause once winter hits; eggs laid during late summer or fall may diapause for two seasons and hatch in the second spring after being laid cued by photoperiod or day length. In other species, eggs undergo obligate diapause in which they enter diapause no matter what time of year it is (not determined by day length) and can take up for five years to hatch in a system called "bet-hedging". By having eggs hatch at random times after they are laid, it makes the chances higher that at least some of them will hatch during the "right" time. Still, other species in environments with mild winters such as ours, there may really be two generations in which there are two distinct times during the year when eggs are laid where photoperiod cues not when the eggs will hatch but when the adults should oviposit. With all of these different factors in play, it may be impossible to trace the origins of our little second instar katydid. Though there is still a very good chance that we were right and it is just a second brooder.

- Brian