Lethal and sublethal effects of Azadirachta indica-based products on Tetranychus neocaledonicus (Acari: Tetranychidae)

The objective of this study is to evaluate the toxicity, repellency, and the ovicidal, residual, and sublethal effects of different neem-based commercial formulations on the red mite Tetranychus neocaledonicus André (1933) reared in the laboratory on lima bean (Phaseolus lunatus L.). To evaluate the toxicity on adult females of T. neocaledonicus, different concentrations of Natural Neem® (NN), Off-Neem® (ON), Nim-I-GO® (NG), and Azamax® (AZ) were defined from preliminary tests. The mortality and toxicity ratio were evaluated 48 h after application of the lethal concentrations (LC₅₀ₛ and LC₉₅ₛ). The repellent effect was verified through a two-choice test. The concentration used was the LC₅₀ of the products calculated in the toxicity test. The number of mites attracted, the repellency index (RI), and the percentage of repellency of each product were calculated. The ovicidal effect after application of the LC₅₀ₛ and LC₉₅ₛ of each product and egg viability were observed. To evaluate the residual efficiency, the plants were sprayed with LC₅₀ and LC₉₅ of the products and the leaves were subsequently harvested at 24, 48, and 96h after the application of the products to evaluate mortality and oviposition reduction (PR - percentage of reduction). The sublethal effects were evaluated by applying the LC₃₀ of the products (AZ, NG) to newly emerged females, whose survival and oviposition were evaluated daily. The determined LC₅₀ₛ were 0.39; 0.48; 0.68; and 1.39% for AZ, ON, NN, and NG, respectively. Considering the LC₅₀, AZ was the most toxic product followed by ON, whereas the established LC₉₅ₛ were 2.20; 3.74; 6.10; and 7.98% for NN, ON, AZ, and NG, respectively. All tested products were classified as repellents for adult females of T. neocaledonicus. The eggs of T. neocaledonicus treated with the LC₉₅ₛ of the products had their viabilities inhibited. However, when using the LC₅₀ₛ, NN provided the lowest viability (8.0%), being considered the most toxic for eggs. The products presented reduced residual effect probably due to their rapid degradation. The mites treated with sublethal concentrations showed an average survival in days of 25.43, 28.35, and 29.20 for the treatments with Azamax®, control (untreated), and Nim-I-GO®, respectively. Relatively high oviposition rates in the first weeks decreased until the end of their life cycle. The life history of T. neocaledonicus is affected by sublethal concentrations of neem-based products. It was concluded that the tested products demonstrated acaricidal potential in the control of T. neocaledonicus on P. lunatus, presenting toxicity and repellent and ovicidal effect, although residual and sublethal effects were less significant.