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Systenotelus stockwelli in focus


This morning I had an opportunity to revisit an interaction that was part of my graduate thesis research; i.e. the reproductive association of Carludovica “Panama hat palms” and acalyptine weevils in the genus Systenotelus.

Carludovica plants are members of the Cyclanthaceae and are common along roads and trails in and around Gamboa, Panama. The development of the flowering process is short (essentially lasting 24 hours) and highly predictable – one can observe an inflorescence’s spathes opening and detaching during the night prior to the main flowering event. Having spotted one such plant yesterday night at the “Frog Pond”, I arrived at the fully opened and extended inflorescence of C. palmata at 5:30 am on the following morning.

Sometimes, especially in open habitats where Carloduvica plants receive high sun exposure, leaf-cutter ants and stingless bees will find the inflorescences early and cut off the staminodes, thereby reducing the attractiveness of the inflorescence and intensity of the weevil-attracting scents. This was not the case with this inflorescence, however. Likely more than 300-500 weevils pertaining to four acalyptine species arrived during this morning. I managed to record about 2.5 hours of close-up weevil feeding and reproductive behavior under very good conditions. A short 1-minute video (shot with a point-and-shoot camera) is posted here.

Of primary interests to me was filming the behavior of Systenotelus stockwelli – possibly for the first time. Presently three species are recognized in the genus Systenotelus, of which S. stockwelli is the smallest and also that which most closely resembles weevils in the related genus Perelleschus in terms of general shape. However, unlike Perelleschus, Systenotelus weevils a not pollinators of Carludovica, and instead of primarily feeding on the fleshy red pulp, the larvae are seed predators. Hence the evolution of Perelleschus and Systenotelus marks a transition from weevils being largely beneficial to being detrimental to the plant’s reproductive success.

Only about 15-20 individuals of S. stockwelli arrived at the inflorescence, at least 30 minutes after other species of Azotoctla, Ganglionus, and Perelleschus had arrived. Both females and males of S. stockwelli are quite active in the first 1-2 hours following arrival. I was able to observe and film multiple instances of feeding, probing and drilling oviposition sites, mating attempts, copulatory courtship, mate guarding, male-to-male conflicts, male-to-female conflicts, and oviposition.

In the next few days we hope to find more inflorescences of C. palmata around Gamboa, and also dissect fruits which contain the weevil larvae (mostly of Perelleschus, according to initial samples). We are also looking for other weevils that can be observed feeding and reproducing at sites that can be carefully observed and recorded on video.

Evening update. I revisited the inflorescence after 8 pm today. The staminodes were on the ground and in a state of rotting. Only Ganglionus, Perelleschus, and very small species pertaining to an undescribed genus (though often identified as Phyllotrox – which is not typically on cyclanths) were present, in lower numbers, and not on the surface layer.

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