Biphasic control of Argulus bengalensis Ramakrishna (1951) (Crustacea: Branchiura) with plant derivatives

Efficacy of treatment with some plant parts containing ingredients viz. rotenone, azadirachtin, and nicotine for control of a piscine ectoparasite Argulus bengalensis has been tested in laboratory experiments. Among those plant preparations, tobacco leaf dust (TLD) containing nicotine is found potentially active against the adult parasitic morphs at a lethal concentration of 8 ppm which is sublethal and tolerable to the host fish. However, nicotine is not effective on the embryonic life stages of the parasite and thus the gene pool is retained in the form of egg investment. Embryonic development and subsequent hatching of the eggs occurs normally in the post treatment period which results in recurrence of parasitaemia (F1 generation) within 12 to 16 days in summer and 15 to 18 days in winter in a temperature dependant manner. Considering maturation of F1 generation and subsequent investment of their first clutch of eggs at the age of 21 days onwards, one vulnerable time window of 17 to 19 days for summer experiment and another of 19 to 21 days for winter experiment have been identified. Since the time windows are brief and exist only for three days and those windows overlap at day 19, the day 19 has been targeted for application of a second phase of treatment in both seasons. The study recommends a new approach of biphasic treatment for complete eradication of A. bengalensis infestation.