Effects Of Series Of Concentrations Of Several Insecticides On The Oviposition Of Nilaparvata Lugens (St(?)l) (Homoptera: Delphacidae) On Two Rice Varieties

The brown planthopper (BPH) Nilaparvata lugens (St?l) (Hemiptera:Delphacidae) is an important pest that impacts rice development and grain quality. Outbreaks of the pest frequently occur in Asia. Chemical control is the main method to reduce the damage of N. lugens, and the use of pesticide was considered an important factor for resurgence occurrence, especially, the effect of insecticide on reproduction of N. lugens. The present study tested the toxicity of imidacloprid, buprofezin, deltamethrin and triazophos to third instar nymphs of N. lugens, and established the toxicity regression equations of four insecticides; The present study investigated effects of series of concentrations of four insecticides on laid-eggs female ratio (LFR), preoviposition and oviposition durations (POD and OD), longevity of female (LOF), number of laid-eggs (NLE), number of egg-masses (NEM), grade of egg-production (GEP) and egg hatchability of N. lugens on two rice varieties, TN1 and Xieyou 963. The quadratic regression equations with significant correlation coefficients between each index and insecticide concentrations could be established for four insecticides on both rice varieties. The results showed as follow:The toxicity of imidacloprid to third instar nymphs of N. lugens was maximum, LC50 was 0.0848 mg·L-1, followed by buprofezin. The toxicity of deltamethrin and triazophos was less than buprofezin, LC50 was 33.71 mg·L-1 and 42.59 mg·L-1, respectively. The susceptibility of N. lugens to imidacloprid and buprofezin was more than deltamethrin and triazophos.The indices of N. lugens, LFR, POD, OD, LOF, NLE, NEM, GEP and hatchability varied with insecticides, their concentrations, spray times and rice varieties. For imidacloprid and buprofezin, LFR, NLE, NEM and hatchability decreased, POD elongated, and OD and LOF shortened with increase of concentrations significantly, and the GEP was mainly in gradeⅢ. In contrast, for deltamethrin and triazophos, POD shortened, LFR, OD, LOF, NLE, NEM and hatchability increased with increase of concentrations significantly, and the GEP was mainly in gradeⅣ.Rice variety also showed a significant influence on the indices. For example, NLE on TN1 significantly increased compared to on Xieyou 963 under the same concentrations and spray times. Regression equations with significant correlation coefficients between each index and insecticide concentrations could be established for four insecticides on both rice varieties except for hatchability for single spray of buprofezin on TN1 and for LOF for single of deltamethrin on TN1. In addition, increase of spray times for the four insecticides amplified effects on these indices. For example, three sprays of deltamethrin significantly increased NLE compared to single spray under the same concentrations and rice variety.The present study demonstrated that deltamethrin and triazophos stimulated fecundity of N. lugens. The type of insecticide, applicathion time and method were key fators for control of the pest. The present findings have very important significance for the understanding of mechanisms of N. lugens resurgence and for management of the pest in commercial rice production.