BIOECOLOGICAL STUDIES ON MALADA BONINENSIS OKAMOTO, A NEW CHRYSOPID PREDATOR OF WHITE FLIES, BEMISIA TABACI GENNADIUS
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Date
1988
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AAU, Anand
Abstract
The studies on bioecology of Mallada boninensis Okamoto (Neuroptera : Chrysopidae) were carried out at Anand Campus of Gujarat Agricultural University during 1987-88. The studies revealed that, the predator lays characteristically stalked eggs in groups of 11 to 20, which hatch out in 4 to 5 days. The tiny larva, after eclosion runs fast in search of food and feeds on all kinds of soft bodied insects such as white flies, mites, aphids, scales, eggs and young larvae of lepidopterans. The larva has habit of carrying on its back the remains of the dead prey after sucking the internal content. In the laboratory when fed on eggs of Corcyra cephalonica (Lepidoptera Pyrallidae) the larvae pass through three instars to complete their development. The average durations of first, second and third instar were 4.11, 4.11 and 4.63 days at constant temperature 25.26°c + 2.2°C and 59.90% relative humidity) respectively. At varying temperature during October (average maximum and minimum temperature and relative humidity was 28.89°C, 25.37°C and 56.83% respectively) the larval duration of first, second and third instar was 3.36, 3.57 and 3.0 days respectively. Similarly during February-March, (average maximum ana minimum temperature and relative humidity was 26.57 C, 23.06°C and 62.33% respectively) the average larval duration of three instars was 5,00, 4.17 and 4.25 days respectively. The total larval period averaged 10,43, 13.42 and 12.85 days during October, February-March and at controlled temperatures respectively. The full grown larvae undergo a short prepupal stage (5 to 8 hours) before undergoing pupation. The pupal stage averaged 9.71, 14.72 and 13.79 days during October, February-March and xittder constant temperature respectively. The adults are bright green with membranous transparent wings and eyes are metalic golden. In the field they can easily be identified by characteristic fluttering flight, when a plant is shaken. The sexes can easily be differentiated. The female is slightly bigger than the male.The male female ratio was 1:1.5 and the percentage emergence was 81,4U, Preoviposition, oviposition and post-oviposition periodsof the predator averaged 9.90 + 1,60, 36.90 + 4.41 and 18,00 + 12.24 days respectively. The average fecundity was 431.3 + 39.41 eggs* the maximum being 473 eggs, with an average daily rate of oviposition of 11.B6 eggs. The average longevity of female and male v/as 64.8 + 15.97 and 27,36 + 8.03 days respectively. The entire life span from egg to death of the adult averaged 76.74 and 49.99 days in females and males respectively at varying room temperatures, whereas uhder controlled conditions, it averaged 96.38 and 59,18 days in females and males respectively. The larvae are voracious feeders and consume on an average 628.75 eggs of Corcyra cephalonica Staint or 453 nymphs of white flies before reaching maturity. The newly hatched larvae can survive for aiaverage period of 2.29 + 0.49 days without food in the laboratory. Cannibalism is common among the larvae of the predator, when reared in group. The extent of wnicn was worked out to be 14.5 percent.The activity of predator was found on various crops such as oicra, Indian bean, wheat, cotton, groundnut, lucerne, mango and citrus. The activity of the predator v/as almost synchronous with that of its prey. The predator was found to have a. positive prey dependent relationship. Heavy rains appear to have deleterious effect on the natural populations of the predator. Under congenial conditions the predator was found to regulate the prey infestation in cotton. Telenomus sp., spiders and Minochilus sexmaculatus were recorded as natural enemies of the predator, though, the extent parasitism/predation was negligible. In laboratory experiment, the fungal pathogens viz Metarhizium anisopliae and Beauveria bronqiartii were found to be non-pathogenic to the larvae of the predator. Six insecticides viz phosphamidon 0.03%, cypermethrin 0.009%, monocrotophos 0,04%, fenvalerate 0,015% decamethrin 0.0028% and endosulfan 0.07% were tested for their ovicidal action, but found to have no significant effect. It is concluded that the M. boninensis is an important predator of white flies. Considering its several attributes, its mass propagation and field testing against white flies in cotton is suggested. Its introduction in different parts of the country where it is not known to occur and white fly is a pest is also suggested.
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AGRICULTURAL ENTOMOLOGY, A STUDY