Development of Water-resistant Baits for the Control of Solenopsis invicta (Hymenoptera: Formicidae) Based on Its Foraging Activity
Date Issued
2010
Date
2010
Author(s)
Kafle, Lekhnath
Abstract
An efficient bioassay for the screening of local materials to find a potential water -resistant fire ant bait carrier was developed. To develop an efficient bioassay, the effect of Solenopsis invicta Buren (red imported fire ant, RIFA) worker population size, size of the foraging area, the number of foods, duration of experiments and the effect of the queen’s presence on foraging activity of RIFA workers were investigated under laboratory conditions. The results showed that 600 workers with 120 broods was the most efficient combination for the RIFA workers preference study. The foraging activities of RIFA were significantly decreased by the presence of queen in the nest. The optimal duration for RIFA preference study was 2.5 h with 4 foods placement.
The effects of different ground surfaces on the foraging efficiency of RIFA workers were also investigated. The RIFA workers were more efficient when they foraged on hard and smooth plastic surfaces than on soil surfaces. Similarly, obstacles reduced the foraging efficiency of RIFA workers. The RIFA workers from wild colonies were more efficient than the workers from one-year-old laboratory colonies.
A commercial fire ant bait (Esteem®, 0.5% pyriproxyfen) was microencapsulated and evaluated under both laboratory and field conditions for the RIFA’s preference and water resistance abilities. A positive correlation between microencapsulation rate and water resistance ability of bait was observed; a bait coated with 5% poly-ε-caprolactone was more resistant to water by ~20% than normal bait. However, the microencapsulated and wet baits were less preferred than normal baits by the RIFA workers.
In another study, preference of RIFA for distiller''s dried grains with solubles (DDGS) was investigated under the laboratory conditions. The DDGS was mixed with soybean oil and shrimp shell powder (SSP), and then evaluated. The DDGS only attracted significantly larger number of RIFA workers than the commercial bait (Advion, 0.045% indoxacarb) (C-bait). The DDGS containing 15% oil and 20% SSP attracted largest number of RIFA workers than rests of combinations. The wetted DDGS with 15% oil and 20% SSP attracted ~10 times more RIFA workers than the wetted C-bait.
Accordingly, a new fire ant bait (T-bait) was prepared by using DDGS with 15% soybean oil and 20% SSP as phagostimulants, and cypermethrin (0.128%) as toxicant. The 100% RIFA workers were killed within 4 days by a normal T-bait (cypermethrin 0.128%) or C-bait (Advion®, indoxacarb 0.045%) in the laboratory; however wetted T-bait or wetted C-bait killed only 70.62% and 39.68%, respectively. Similarly, efficacy of T-bait was also higher than the C-bait against RIFA workers when exposed to the field. However, under field conditions, normal T-bait and normal C-bait had almost the same efficacy. And, when T-bait and C-bait were wetted, efficacy of T-bait to inactivate RIFA mounds was somewhat reduced, while C-bait lost most of its efficacy to inactivate RIFA mounds in the field. DDGS was compatible with other insecticides, such as d-allethrin, permethrin and pyrethrin.
The DDGS was also mixed with Beuveria bassiana F256, a native strain, and was evaluated the effect on the killing of RIFA under the laboratory and field conditions. The B. bassiana delivery methods had significant effects on the mortality of RIFA. The direct application of B. bassiana into the mound had higher efficacy to inactivate RIFA mounds than its bait application. Twenty eight days after treatment, the direct application of B. bassiana and Advion® (indoxacarb 0.045%) inactivated ~90% of RIFA mounds in the field. The Advion® and Esteem® (0.5% pyriproxyfen) inactivated RIFA mounds ~3 times faster and ~3.5 times slower than the direct application of B. bassiana in the field conditions, respectively.
Based on its abilities to resist water and field exposure, its RIFA killing capability under both laboratory and field condition, as well as its compatibility with phagostimulants, toxicants and B. bassiana F256, we conclude that DDGS based fire ant bait (T-bait) is an efficient fire ant bait suitable for humid conditions.
Subjects
Solenopsis invicta
foraging efficiency
water-resistant bait
soybean oil
shrimp shell powder
Beuveria bassiana
Type
thesis
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