Evaluation of halofenozide against prey mosquito larvae Culex pipiens and the predator fish Gambusia affinis: impact on growth and enzymatic activities.Commun Agric Appl Biol Sci. 2008; 73(3):659-66.CA
Culex pipiens (Diptera: Culicidae) is the most widely distributed mosquito species in Algeria and many other countries in the world. Mosquitoes are generally controlled by conventional insecticides but these may pose strong secondary effects on the environment. In this context, the insect growth regulators (IGRs) have shown promise in controlling pest insects. Halofenozide (23% EC) is a novel IGRs belonging to the class of non-steroidal ecdysone agonists, and it was found toxic for larvae of C. pipiens. In addition biological methods constitute an alternative to chemical control. Several fish species have been tested against mosquitoes, and Gambusia affinis was found very efficient. In the present study we evaluated the impact of this new potent insecticide (halofenozide) on growth and metric indexes in the larvivorous fish G. affinis under laboratory conditions. In addition, the effects were evaluated on the enzymatic activities of acetyl cholinesterase (AChE) and glutathione S-transferase (GST). The insecticide was added in water at two concentrations (12.6 and 28.6 microg/L) corresponding to the LC50 and LC90 obtained against fourth instar larvae of C. pipiens, and adult females of G. affinis were exposed to halofenozide for 30 days. At different exposure times we measured the length and weight of fishes, the index of condition (K), the gonado-somatic ratio (GSR) and the hepato-somatic ratio (HSR). The results showed that halofenozide had no significant (p>0.05) effects on growth, metric indexes and AChE activities. However, treatment caused a significant induction (p<0.05) in GST activities at days 15 and 30 with the highest dose. Our results indicate that this ecdysteroid agonist presented only minor secondary effects on the non-target fish species, and so it has potential for controlling of mosquitoes in an integrated manner.