Lethal efficacy of the chitin synthesis inhibitors flufenoxuron (cas-101463) and lufenuron (cga-184699) on Schistocerca gregaria (orthoptera: acrididae)

Abstract

The present work was carried out aiming to assess the lethal activity of the chitin synthesis inhibitors (CSIs): Flufenoxuron (CAS-101463) and Lufenuron (CGA-184699) on the desert locust Schistocerca gregaria. Five concentration levels of each CSI: 1000, 500, 250, 125 and 62.5 ppm, were given through fresh clover leaves as a food to the newly moulted (4 th or 5th) instar nymphs or the late-aged 5th instar nymphs. All observations and results were recorded after 24 hours of feeding. During few days after feeding of the newly moulted penultimate instar nymphs on Flufenoxuron treated food, the mortality increased (40%) at the highest concentration level but decreased (10%) at the lowest concentration level. The lethal action of Flufenoxuron appeared also along the later days of penultimate instar at the lower concentration levels . With few exceptions, the mortality of the last instar nymphs increased proportionally to the ascending concentration level. At the highest concentration level, the lethal action was lately exhibited in the adult stage at the lower concentration levels. Lufenuron exerted its mortal activity on the penultimate instar nymphs proportionally to the concentration level. No certain trend of the mortality of last instar nymphs could be appreciated by Lufenuron. Also, some deaths were observed among adults varying between 40% (at 250 ppm) and 14.2% (at 62.5 ppm). After treatment of the newly moulted last instar nymphs, the available results show no certain trend of mortality, whether nymphal instar or adult stage. After treatment with the highest concentration level, the lethal effect was easily detected which spread along the nymphal instar. With regard to the adult stage, the greatest mortality was observed at 250 ppm. Among the newly moulted last instar nymphs, the mortality ascended as the conc. level of Lufenuron was increased but estimated in 49% at both 250 and 500 ppm. Several adult mortalities were recorded but in no certain trend. After treatment of the late-aged last instar nymphs, the lethal activity of Flufenoxuron, to some extent, increased consecutively to the ascending concentration level in both nymphs and adults. The highest lethal effect of Lufenuron on late-aged last instar nymphs (30%) was observed at the higher two conc. levels. However, the lethal effect of Lufenuron on nymphs was lately recorded. Also, increasing adult mortality paralleled to the ascending concentration level with an exception.