Differential response to sex pheromone of the shoot and fruit borer Conogethes punctiferalis reared on castor and cardamom

Abstract

Conogethes punctiferalis (Crambidae: Lepidoptera) is an important pest of castor, Ricinus communis. The Conogethes species population infesting cardamom, Elettaria cardamomum in India was earlier thought to be C. punctiferalis. This is because moths of both populations appear similar in morphology, particularly wing patterns and colour. The moths too showed a differential response to the sex pheromone components viz. (E)-10-hexadecenal (E10–16: Ald), (Z)-10-hexadecenal (Z10–16: Ald) and hexadecenal (16: Ald) when exposed in castor and cardamom fields. This elicited a doubt that the pheromone composition of castor and cardamom populations might be different. Therefore investigations using Electroantennogram (EAG) and wind tunnel bioassays of populations on castor and cardamom were conducted. Conogethes reared on castor (CBR) had greater EAG response than the one reared on cardamom (CBE) to E10–16: Ald+ Z10–16: Ald mixed in 1: 1 (0.96±0.025 mV). However, CBE elicited highest response to E10–16: Ald+ Z10–16: Ald at 100: 8 (1.10±0.25 mV). In comparative EAG studies both populations gave higher responses to respective female abdominal gland extracts. Wind tunnel bioassay of synthetic pheromone blend E10-6: Ald+ Z10–16: Ald+ 16: Ald (100: 8: 16) showed source contact when tested against males of CBR, contradictory to CBE. The experimental results revealed that the major pheromone component of both the populations was E10–16: Ald but differed in minor components and their proportions. Supportive data on other aspects of the two populations suggested that these are different and could be different species.