Master of Science (MS)
Formosan subterranean termites, Coptotermes formosanus, are economically important structural pests of warm and humid regions. Different control measures have been developed to avoid the damage caused by them. Among the available measures, chemical treatments have predominated for the last five decades. In our study we tested the effect of spinosad, a biopesticide, on C. formosanus. Spinosad is composed of bacterial metabolites that have been widely used to control various agriculture pests. It has been tested on Kalotermitidae and Termitidae; however, not on Rhinotermitidae, the most destructive of termite families. Both no choice and choice tests were conducted using three concentrations, 1ppm, 25ppm and 50ppm, of spinosyn products Entrust, Tracer and Radiant. In the no choice test in sand, more than 85% mortality was observed at 25 and 50ppm after 1 day exposure followed by 100% mortality at 7 days. Similarly, after 7 days at 25 and 50ppm in soil and filter paper, 100% mortality was observed. In the two-choice test, observations before the onset of termite mortality showed that none of the products or concentrations was repellent. Likewise, in the multiple-choice test, the preference of termites among 1ppm, 25ppm, 50ppm, control and release chamber in all 3 concentrations was somewhat random. The tunnel area in control and treated choices was not significantly different which supports the non repellent attribute of spinosyns on C. formosanus. Ethogram analysis was conducted to observe the behavioral changes of termites using a sublethal dose of spinosad over 7 days. Behaviors including walking, antennal touching, moving, grooming, gnawing, shaking, digging and particle movement were observed in this test. Spinosad did change the duration and frequency of some major behaviors like walking, antennal touching, grooming and moving (other than walking). Treated termites allocated more time in grooming and moving behaviors. Results of ethogram analysis suggest that social behaviors like grooming could be exploited for toxin transfer. Horizontal transfer of spinosad was conducted in sand and soil at 1, 25 and 50ppm. Donor and recipient termites began to contact and groom each other immediately after releasing them together. Spinosad was more effectively transferred in sand than in soil. In sand at 25 and 50ppm, significantly high mortality of donors and recipients was observed after 7 days. Our laboratory study suggests that spinosad and spinetoram are effective against termites and further study is needed to address its effects against C. formosanus in field conditions.
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Bhatta, Dependra, "Effects of spinosad on Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae)" (2015). LSU Master's Theses. 4156.