Evidence of male pheromone in Conogethus punctiferalis (Lepidoptera: Pyralidae).

Abstract

Conogethes punctiferalis Guenee is a polyphagous insect pest that is difficult to manage because it feeds within plant tissue. Management by mass trapping using semiochemicals, especially pheromones, represents a viable option to control such borers. Herein, pheromonal compounds were extracted from male and female moths and assessed using headspace sampling and electroantennogram response. One-d-old C. punctiferalis showed a higher response to volatile solvents than 4-d-old ones, irrespective of sex. The male antenna was found more sensitive than the female for volatile compounds. However, the female response to male headspace extract and abdominal tip extract was very high (i.e., 4.006 mV and 2.217 mV, respectively), which revealed the presence of males producing a female-attracting olfactory cue in C. punctiferalis. This was also confirmed by males calling the female before mating by extruding the hair pencils in their abdominal tip. The male pheromone extract when analyzed in gas chromatography–mass spectrometry indicated the presence of methyl acetophenone or 3-ethyl acetophenone.

Conogethes punctiferalis Guenee (Lepidoptera: Pyralidae) is a polyphagous pest that infests 30 crop plants belonging to 23 families (Thyagaraj et al. 2003). It is an important pest not only in South and South East Asia and Australia (Pena et al. 2002) but also as a newly introduced pest in Europe. Although its management is normally attained by the use of chemical pesticides (Renuka et al. 2002, Stanley et al. 2010, Regupathy and Ayyasamy 2014), proper management is achieved only by repeated applications of high concentrations because of the concealed nature of the larvae that feed within the plant tissues. Pest management using pheromones for mass trapping or mating disruption offers a viable alternative for such borers (Breth and Tee 2007). The use of a pheromone is more effective in detecting the infestation and, thus, determines timing of pesticide application (Cruz et al. 2012), leading to a reduction in insecticide usage.

The isolation, identification, and use of sex pheromones of C. punctiferalis have been previously reported. The pheromone component of C. punctiferalis was first reported by Konno et al. (1982) as (E)-10-hexadecenal. Traps containing 250 μg of C. punctiferalis pheromone were reported to significantly reduce the pest in citrus orchards in China (Cai and Mu 1993). The compounds were later identified as (E)-10-hexadecenal and (Z)-10-hexadecenal as the major compounds (Liu et al. 1994). But, the synthetic sex pheromone consisting of (E)-10-hexadecenol and (Z)-10-hexadecenal was not as effective as the crude pheromone extracts (Xiao and Honda 2010). Three compounds, (E)-10-hexadecenal (E10-16:Ald), (Z)-10-hexadecenal (Z10-16:Ald), and hexadecanal (16:Ald), were identified in the female gland extract of C. punctiferalis by Jung et al. (2000). Among the various combinations E10-16:Ald and Z10-16:Ald at 70:30 to 80:20 were the most attractive to males in wind tunnel experiments and field trapping experiments in orchards (Jung et al. 2000). The third compound 16:Ald did not show an electroantennogram (EAG) response in a Korean population but elicited response in the C. punctiferalis from China (Liu et al. 1994). Apparently, variation in sex pheromonal compositions appears to be far more widespread than previously thought and the composition differs from population to population. The sex pheromone attraction of the Korean population of C. punctiferalis varies with that of Chinese and Japanese populations (Boo and Park 2005). In India, E10:16Ald used in pheromone traps resulted in moth catches in castor fields but not in cardamom plantations (Chakravarthy et al. 2013). The (Z)-10 hexadecenol and 16-hexadecenal blend did not attract and trap any male moths (Chakravarthy et al. 2015). Thus, there is a need to isolate and identify the pheromone compound of the C. punctiferalis populations in India. Furthermore, a complex combination of the pheromone system of the C. punctiferalis consists of E10-16:Ald, Z10-16:Ald for long-range attraction and Z9-27:CH,Z3Z6Z9-23:CH for short-range attraction and final recognition of females by males (Xiao and Honda 2010, Chakravarthy et al. 2015). In addition, E-2-methyl-2-butenoic acid (tiglic acid), a compound extracted from the hair pencils of males, was reported to have a significant role in mate recognition, coupling, and mating success. The present study was designed to extract pheromones of both male and female C. punctiferalis by gland excision/solvent extraction and headspace extraction and to determine the biological activity, detect EAG response, and identify the active compounds by using gas chromatography–mass spectrometry (GC-MS) techniques.