Contact toxicity on glass

The bioassay evaluated the effect of direct contact of insecticides to insect body on S. exigua and P. maculiventris mortality. This bioassay was conducted in 20 mL glass vials treated with a 0.5 mL solution of each insecticide according to the treatment. The vials were stirred until the water evaporated and the insecticides covered the inner vial surface [26]. The control had vials treated with distilled water. The bioassay was designed according a completely randomized design between five to eight concentrations and six replications per insecticide. Dilution ratios of insecticide solutions between 1:1 to 1:10⁵ were tested. Each insecticide was diluted in distilled water to obtain the desired concentration.

Per each replication, three larvae of 3^rd instar S. exigua or three nymphs of 3^rd instar P. maculiventris were individualized in the glass vial treated with each treatment and were kept at 25 ± 2°C, 70 ± 5% RH and 12L:12D photoperiod. Spodoptera exigua and P. maculiventris mortality was determined 24 h after exposure; larvae (pest) and nymphs (predator) unable to walk up to 10 mm when released were considered dead [27].