Feeding and life history of Spodoptera litura (Lepidoptera: Noctuidae) on different cotton varieties

Abstract

Feeding and life history of Spodoptera litura were studied with cotton varieties viz. CB9, CB10 and SROS. The cotton varieties varied with their morphological characteristics. The biochemical analysis showed that the variety CB10 and CB9 possessed significantly higher percentage of protein (30.6%) and starch (21.3%), respectively. The morphological and biochemical characteristics of the cotton varieties influenced on the feeding behaviour of larvae, and the larvae produced significantly varied amount of excreta. The mating behaviour of S. litura feeding on different cotton varieties showed that premating period of male and female ranged from 2.6 to 2.7 and 2.0 to 2.3 day: respectively which were statistically indifferent. However, the mating periods were statistically different with food sources of moths and ranged from 102.6 + 20.5 to 123.4 + 26.8 minute. The longest mating period was recorded when reared on SROS. The moths showed significantly higher percentage (71.4%) of mating success when they were reared on CB10 variety. Males revealed significantly lower number (7 times) of matings and remating success (62.5%) when they were reared on SRO05 variety. Females reared on different cotton varieties showed 50 % remating success and their number of matings were recorded 2 to 3 times which were statistically indifferent. The results of the reproductive performances showed that preoviposition and oviposition periods were dependent on the food sources. Females fed on CB10 variety revealed significantly lower preoviposition period (19.4 = 1.8 hour).

The oviposition period varied from 1.2 + 0.6 to 2.1 + 0.6 hour and the females showed longest period when they were reared on SROS5 variety. The cotton varieties have significant effect on the fecundity, incubation, total larval and pupal period, hatching, pupation and adult eclosion rates. The highest fecundity (1656.3 = 715.5) and incubation period (4.8 + 0.5 day) was found when the moths were provided with SROS. The highest larval (33.4 + 3.1 day) and pupal (17.3 + 1.5 day) periods were observed when the larave fed CB10 and CB9 variety, respectively. The highest hatching (63.0 + 15.4%), pupation (93.2 + 15.2%) and adult eclosion (79.1 + 8.4%) rates were found when the larvae were provided with CB10 variety. Longevity of male and female moths ranged from 9.6 + 0.9 to 10.4 + 0.9 and 8.2 + 0.8 to 8.6 + 0.9 day, respectively, and cotton varieties did not show significant effect on the life span of adult moth. The morphometric parameters of the study showed that the cotton variety SROS5 revealed significantly the highest diameter of egg mass (7.4 + 0.4 mm). The cotton varieties also showed significant effect on the length of different larval instars. Food sources did not affect pupal length but showed significant variation of the breadth. The highest breadth (6.5 + 0.6 mm) was observed when the pupae were reared on SROS5 variety. The length and breadth of adults were found statistically indifferent but the weight of different larval instars, cocoons and adults differed significantly with food sources. The sex ratio of male: female varied from 1: 0.85 to 1: 0.92 and cotton varieties showed significant effect.