Polymorphism in the ant Pogonomyrmex badius was studied using morphometric analysis. Head shape in P. badius was compared to 14 closely related monomorphic Pogonomyrmex believed to differ in worker morphology due to character displacement. Head shape in P. badius and two polymorphic Solenopsis species, one known to have a seed-milling caste (S. geminata) and the other continuously polymorphic (S. invicta), was also compared. Monomorphic species of Pogonomyrmex differed from P. badius in the rules of transformation that accompany changes in worker head size. Although workers of the Pogonomyrmex species studied changed in size primarily by increases in the area of the occipital region and the width of the head, polymorphic P. badius workers showed a significantly greater allometric increase in the occipital region. The comparative morphometrics of P. badius, monomorphic Pogonomyrmex and two polymorphic Solenopsis species did not support the hypothesis that size-related changes in head shape are due to competitive displacement, because head shapes in P. badius were not similar to head shapes in the monomorphic Pogonomyrmex. In contrast, results suggest that a dietary change may have led to the evolution of polymorphism in P. badius through selection for a seed-milling caste. This conclusion is supported by additional analyses that indicate the existence of two distinct modal head shapes in the caste distribution of P. badius and S. geminata, suggesting that bimodal shape variation might be a common evolutionary response to seed processing.
Two formulations of spinosad (NAF-85 and NAF-371) were evaluated to determine the effect of concentration, deposit condition (dried, wet, or topical), and exposure time (0.1-10 h) for toxicant transfer among nestmates in the drywood termite Incisitermes snyderi (Light). Spinosad treatments were compared with two formulations of disodium octaborate tetrahydrate (DOT) (10% aqueous dilution, 98% dust) and with 35% calcium arsenate dust. Termites were dyed and individually exposed to different treatments for 0.1, 1.5,1.0, 5.0, 10.0 h, or 0.1 and 1.0 h (DOT and calcium arsenate dust) and then placed with 10 unmarked, untreated nestmates in a petri dish. Spinosad formulations also were evaluated by topical application to dyed termites. Transfer of lethal doses of toxicants between termites was indicated by significant mortality of untreated termites in 25 of 28 treatments by 28 d after introduction of dyed, treated termites. Only three treatments, one spinosad treatment (NAF-371, wet, 1 h) and both DOT 10% solution treatments, resulted in mortality of untreated termites that was not significantly different than that of water-treated controls. Two spinosad treatments and both calcium arsenate dust treatments resulted in >90% (94-98%) mortality of untreated termites by 28 d after introduction. Mortality of untreated termites was significantly different from controls for the two spinosad formulations, depending on condition of deposit and duration of dyed termite exposure to treatments.
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