Biosystematics of rice brown planthopper and rice green leafhoppers
The Brown planthopper,Nilaparvata lugens (Stal) is causing serious damage to rice cultivation in tropical countries of Asia for the last 10–15 years. Green leafhoppers,Nephotettix spp. are also assuming serious proportions in different parts. This has been attributed to improved rice production technology, especially with the introduction of high yielding varieties. Damage is not only through loss of sap as a result of feeding but also by transmitting diseases in this process. Various reasons have been attributed like breaking of resistance, migration, insecticidal treatment etc. One such reason, which led to the biosystematic studies of these pests is the assumption that this is due to evolution of new forms referred to as biotypes. Of late biotypes have also been reported inNephotettix virescens. This term is basically used with reference to differential ability of the insect to infest particular rice cultivars having resistant genes. This phenomena is attributed by some scientists, not to the breaking of resistance, but to the evolution of new forms which are different from the original population. As per the conventional taxonomy, this new form is similar to the original form, and hence biosystematists attempted various methods like chemical and honeydew analyses, cytology, acoustic behaviour, morphometrics, etc in order to help the breeders in differentiating and identifying these and also to find out the mechanism and causes evolving such biotypes.