| Red imported fire ant(Solenopsis invicta Buren) is a dangerous invasive pest in the world, the current status of domestic and international prevention, chemical control is still the main prevention measures to control its the spread and expansion. Different castes of the red imported fire ant(Solenopsis invicta Buren) play different roles in the colony. However, the contact activity of different castes of this ant to insecticides is still not clear. In this study, the contact toxicities of indoxacarb, compared with fipronil and beta-cypermethrin, to different castes of the red imported fire ant were measured by topical application. In addition, this paper measured the knockdown and lethal activity of sublethal doses of indoxacarb to worker ants in red imported fire ants. And discussed foraging habits and transferring insecticidal activity of indoxacarb baits preliminarily at the same time. The major results are summarized as follows:1. There were significant differences in the contact activity of ants to the different insecticides; Ants were strongest contact insecticidal activity to fipronil, then to the beta-cypermethrin, and weakest contact insecticidal activity to indoxacarb. The insecticide contact activity of different castes has similar rule in three different insecticides. Winged adults and queens were highly strongest, soldiers were less contact activity than winged ants and queens. Workers were less contact activity than soldiers. Fourth-instar larvae were the least contact activity to the three insecticides tested; The LD50 values of which were 428.77 mg/kg, 699.77 mg/kg and 1159.95 mg/kg, respectively. The contact toxicity of indoxacarb was significantly weaker than the control insecticides, more suitable as active ingredient of baits.2. Regression analysis shows that contact activity to different insecticides differed significantly among individuals in same caste. This was especially true for soldier and worker ants. For example, with respect to fipronil, the slope values for these castes were 1.1 and 1.8, respectively. However, individuals showed little variation in their contact activity of indoxacarb, with slope values > 4.7 and reaching 7.8 in worker ants. Though we didn't observe a general pattern in contact activity of different insecticides among individuals of the same caste, individual differences were basically low, especially in fourth-instar larvae, winged male ants and queens, all of which had slope values > 4.0. These results provide theoretical guidance for the use of insecticides to control fire ants in the field.3. From the measurement results of the knockdown and lethal activity of sublethal doses of indoxacarb to worker ants in red imported fire ants,the indoxacarb, compared with fipronil and beta-cypermethrin, causes knocked down and death of worker ants, the order of time is indoxacarb > fipronil > beta-cypermethrin. Indoxacarb has a certain range of doses of delayed contact toxicity, while its sub-lethal doses can interfere with the normal foraging behavior of worker ants, and affect the food supply in the nest and reduce the energy supply in the nest, therefore reduce the number of ant colony, which has important guiding significance to guide for practice in the prevention and control of red imported fire ants.4. The preliminary study on the foraging characteristics of red imported fire ants found that Solenopsis invicta both have a foraging peak during the day and night, the insecticidal activity of pesticide can significantly weaken the foraging peak and make it shifted while reducing the lure rate of food to worker ants. The poison speed and transferring insecticidal activity of indoxacarb baits to the worker ants of the red imported fire ant(Solenopsis invicta Buren) were measured with the co-cup method in a laboratory. The indoxacarb in bait was able to be transferred by the feeding behavior and trophallaxis behavior of worker ants. Indoxacarb was one of suitable insecticides for bait preparation. |
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