Soil Exposures

Altriset® (18.4% chlorantraniliprole AI, Du-Pont Professional Products), was applied to sand (natural play sand, Sakrete, Bonsai America, Charlotte, North Carolina) in aqueous solutions and thoroughly mixed by hand for final dry concentrations (wt AI/wt sand) of 100 ppm, 50 ppm, and 0 ppm water only). The 50 ppm concentration is approximately the conventional soil application rate. For each treatment, 9 g of the dry treated sand was poured into an 8.2 cm ID plastic Petri dish bottom to which 6 mL of water was added. Twenty five (25) workers of N. corniger were then placed on top of the damp sand and a matching lid was used to close each bioassay unit. Each treatment was replicated 8 times. Termites were taken from a single large colony collected in Dania Beach, FL, in Dec 2011 and maintained in the laboratory under ambient conditions in a 148-liter aquarium. Termites were fed dead Schinus wood and damp cellulose sponges. The 24 units were placed in a laboratory incubator at 22 ± 0.5 ^°C and 90% RH. Termite mortality and moribundity were recorded once or twice per day for 7 days.

Spray Applications

A 4.6-cm-diam, 1-mm-thick cellulose pad (Gelman Inc.) was placed inside a 5.5 cm plastic Petri dish bottom and moistened with 1.25 mL of water. Twenty-five workers of N. corniger, as obtained above, were placed on top of the pad. The termites were taken from a whole field-collected colony that was maintained in the laboratory in a 40 gallon (148 L) aquarium tank. Eight replicates were sprayed with 500 ppm aqueous Altriset® and eight control replicates were sprayed with water. The liquid spray concentration of 500 ppm (0.05%) is the current label application rate for the commercial product. The sprays were deposited from a distance of 35 cm using a hand sprayer set to deliver medium/fine droplets. For each treatment (Altriset® or water) 4 pumps (6 mL total) were applied. About 2 mL actually landed inside all the replicates of each treatment. Within five minutes, the sprayed termites were transferred to identical clean, unsprayed, Petri dishes containing damp pads. Lids were placed on the pads and the 16 dishes were placed in a laboratory incubator at 22 ^°C and 90% RH. Termite mortality and moribundity were recorded once or twice per day, as time allowed, for 7 days.

Table 1 and Fig. 1 summarize time versus mortality for the five treatments prepared for this study. In all Altriset® exposures, locomotion of N. corniger workers slowed markedly, followed by moribundity. Moribundity preceded mortality by about 0.5-2 days. The 500 ppm Altriset® spray treatment yielded 44% mortality by 65 hours and reached 100% mortality in 161 hours post-exposure compared to 4% mortality for the water-only spray treatment. The 100 ppm Altriset® sand treatment produced 100% mortality by 25 h while the 50 ppm treatment yielded 1% mortality over this time period. However by 73 h, the 50 ppm sand exposure produced 45% mortality and by 161 h, mortality rose to 99%. At 161 h, the mortality in the water-only sand treatment was less than 4%.

This laboratory study attempts to represent typical routes of field exposure to N. corniger. During a commercial application of liquid termiticide (surface spray and injection), most termites will be exposed to the liquid termiticide through direct contact which is represented here by the topical direct spray bioassay. Additional contact by termites to treated carton (nest material) or foraging substrata is fairly represented by the sand exposure bioassay. Field trials must still be conducted to address the variables that could affect efficacy in the outdoor environment.

TABLE 1.

MEAN PERCENT MORTALITY (±SD) OF NASUTITERMES CORNIGER WORKERS AFTER 6 TO 161 HOURS EXPOSURE TO FIVE ALTRISET (CHLORANTRANILIPROLE) TREATMENTS.

Fig. 1.

Nasutitermes corniger worker mortality over time for Altriset spray and sand exposure bioassays and water controls.