Effects of Diflubenzuron on Chaoborus astictopus and Nontarget Organisms and Persistence of Diflubenzuron in Lentic Habitats1

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Abstract
Diflubenzuron 1-(4-chlorophenyl)-3 (2, 6 difluorobenzoyl)-urea) applied to 3 farm ponds at rates of 10, 5, and 2.5 ppb, and a lake at 5 ppb, inhibited emergence of adult Chaoborus astictopus Dyar and Shannon 2–7 days following the treatments by 95–100%. Emergence reoccurred in some ponds 4.5–6 wk after treatment. Larval populations in the ponds declined by 98, 88, and 44% of pretreatment at 10, 5, and 2.5 ppb, respectively, and recovered to 30, 87, and 131% of pretreatment numbers, respectively. In the control pond, larvae declined by 53% during the same period but increased to 314% of initial numbers. In the lake, larvae decreased by 99% of the pretreatment level 3 wk posttreatment and remained at low levels. Suppression of crustacean zooplankton occurred at all treatment rates. Cladocerans were more susceptible than copepods and required longer recovery periods. Pond and lake rotifer and algal populations were not altered by the treatments. Bluegill sunfish, Lepomis macrochirus Rafinesque, collected from the lake fed predominantly on cladocerans and copepods but switched to chironomid midges and terrestrial insects after the treatment. Fish growth was not altered by the treatment. Residues in ponds treated at 10, 5, and 2.5 ppb averaged 9.8, 4.6, and 1.9 ppb, respectively, shortly after the applications, and declined steadily averaging 0.2, 0.3, and 0.5 ppb, respectively, 2 wk later. Diflubenzuron residues in the lake averaged 3.3 ppb following treatment, and after 35 days, averaged 0.4 ppb. No residues were found in lake sediment. Residues in white crappie, Pomoxis annularis Rafinesque, varied from 355.1 to 62.2 ppb at 4 and 21 days, respectively, following treatment. Fish residues did not persist at high levels and, by 14 days posttreatment, had begun to decline rapidly.