Technique for Mexican Bush Katydid Egg Laying

Today we have finally found a good way to get our fertilized Mexican Bush Katydid females (Scudderia mexicana) to oviposit!

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For weeks now since our first Mexican Bush Katydid female (Scudderia mexicana) got mated we have been struggling to find a way to get them to lay eggs. Yesterday, we made a post about how we actually found a group of six eggs layed by our first female in a slit created by a piece of tape and a paper towel in our glass aquarium tank. While it was surely a great discovery for us, what puzzled us is why the katydid insisted on ovipositing only in the tank and not anywhere in the actual breeding enclosure that we provided it -- a 2 x 2 x 4 feet screened box with a live potted passionflower vine (Passiflora) in it. The leaves of the passionflower vine looked as excellent as any leaf for ovipositing; they were large and thick, easily enough room for the katydid to insert her scimitar shaped ovipositer in.

It has been weeks now and not a single egg that we know have in the enclosure. While, SINA recommends depriving the female for a few days of suitable ovipositing sites, this is quite ironic. We had put the female who laid the six eggs into the tank in an attempt to deprive of proper sites (obviously that unexpectedly failed, in a good way) and yet she chooses not to lay in the enclosure where there should be plenty of places.

Starting from yesterday, we noticed two of our females, presumably fertile, struggling with all of their might to oviposit in a small tag sticking out from the top of the enclosure. The tag was basically a thin strip of plastic (only one layer) so there was no possible way that the females could oviposit in it, but they kept obsessing over it, biting at the edges with their jaws and stabbing it with their ovipositers as if their life depended on it. Why, oh why were they so interested by this tag when there is a live plant in there? 

Well, the make a long explanation short, the only thing we could come up with is that the females require a very specific position for laying eggs. Actually, specific ovipositing position is something that can be seen in a lot of insects. Simply put, the female can't lay unless her ovipositor (whatever shape it may be) is not in a convenient angle or location on the substrate to do so. In the case of these katydids, we noticed that unlike the leaves on the passionflower, the tag was sticking in just the right way such that the female could crawl directly onto the edge and position her ovipositer comfortably, without falling off. In nature, they probably search all day for suitable places, which isn't terribly difficult with the enormous diversity of the plants growing around but in our enclosure the passionflower vine probably just didn't cut it.

To test our prediction, we took one of the females inside and put her on an orchid flower (the ornamental plants kind you can find in most grocery stores). Like mentioned before, being able to crawl directly along the edge of the substrate is critical. An orchid flower is unique in that the petals are very flat, rigid, and thick (roomy for ovipositing) like a disc which allows the katydid to have a firm grip crawling on it without wobbling (like on a flimsy leaf or flower). The clincher is the orientation: the orchid flower was growing vertically and not somewhat horizontally like most flowers (the latter, I imagine, would be awkward to crawl on the edge of). But even with the convenient morphology of the orchid flower, we had to help her a bit sometimes, allowing her to crawl on our hand while ovipositing on the edge.

Within a few minutes, she had laid four eggs, methodically feeling around with her mouth-parts for the edge and then nibbling at it when she found it so she could insert her ovipositer into it. Once in, there is a short pause as she prepares to lay. The egg is actually laid when she slowly withdraws the ovipositer; it is left within is slit created by the ovipositer. The entire process only takes a few minutes (shown in the videos below). After each egg, she would thoroughly clean her ovipositer with her mouth.  

Eventually, we brought in the three other females to lay. One of them, our first fertilized katydid (who also laid the eggs in the tank) seemed even more enthusiastic and laid immediately. However, the other two seemed to have no reaction whatsoever; one of them even started to eat the orchid. We assumed that they weren't fertile and took them away. By the time the two fertile females were done, we had collected 20 or so. At last, we have found a successful technique to get them to lay the eggs!

​Mexican Bush Katydid (Scudderia mexicana) Ovipositing (1)*

​Mexican Bush Katydid (Scudderia mexicana) Ovipositing  (2)*

​Mexican Bush Katydid (Scudderia mexicana) Ovipositing  (3)*

* Shown in 4x speed

- Brian