Response of Trichogramma chilonis to infochemicals: an SEM and electrophysiological investigation

Abstract

The external morphology and peripheral olfactory responses of antennal chemoreceptors of Trichogramma chilonis Ishii (Hymenoptera:Trichogrammatidae) to host related stimuli were examined by SEM and EAG technique respectively. The antennae of male and female T. chilonis reveal strong sexual dimorphism in structure as well as in types, density and distribution of individual sensillar types. The female antennae are characterized by the presence of a single uniporous sensilla on the apical tip of the dome and numerous multiporous pitted sensilla. Sensilla common to both males and females include the multiporous plate sensilla, the peg sensilla and trichoid sensilla. Differences between males and females occur with respect to their EAG profiles to 22 chemicals commonly found in plants viz.leaf extracts of three host plants of Helicoverpa armigera (cotton, chickpea and pigeon pea) and hexane scale extracts of adult males and females of H. armigera. Individually, the largest peak amplitudes in females were obtained with citronellal, phytol, caryophyllene, R-(+)-limonene, linalool, carvacrol and citronellol while in males citronellol, caryophyllene, linalool, R-(+)-limonene and amyl acetate caused the highest response. Among the different chemical classes, the largest peak amplitudes in females were obtained with oxygenated monoterpenes, while in males, fatty acid derivatives caused the highest response. In both males and females, the hydrocarbon monoterpenes caused the least response. Thus, the wide spectrum response of Trichogramma chilonis, to a wide group of chemicals belonging to different chemical classes, though varying, nevertheless suggests that using plant information enhances its parasitization efficiency.

Antennal Structures Used in Communication by Egg Parasitoids

“…3.6f, g). Sen et al (2005) discussed a similar hypothesis for this sensillum in Trichogramma chilonis (Ishii) females.…”

“…These sensilla are laterally flattened, ending with a sharp tip and they show numerous grooves running parallel on both sides up to the ventral margin, where they converge. For these sensilla, different functional hypothesis have been proposed; from bi-modal mechano-chemosensory units (Voegelé et al 1975) to olfactory organs (Sen et al 2005). TEM investigations on T. brassicae (Isidoro et al 1996) revealed the following ultrastructural features: (i) a multiporous area located along the ventral margin (Fig.…”

Electrophysiological responses of Dendroctonus armandi (Coleoptera: Curculionidae: Scolytinae) to volatiles of Chinese white pine as well as to pure enantiomers and racemates of some monoterpenes

“…No corrections were made for differences in volatility between the test compounds. Consequently, comparisons among responses were relative (Sen et al 2005). The threshold of response to each compound was taken as the minimum stimulus concentration at which, relative to the standard, the EAG percent to the stimulus was significantly greater (P = 0.05) than that to the corresponding solvent controls.…”

Plant Volatile Chemicals and Insect Responses

“…In parasitic or predatory insects, there is a conspicuous sexual dimorphism in antennal sensillary structures, probably functioning in identifi cation of ovipositional substrates in females and as mate locating organs in males. Sen et al ( 2005 ) studied the external morphology and peripheral olfactory responses of antennal chemoreceptors of the generalist parasitoid Trichogramma chilonis to host plant-related chemical stimuli using scanning electron microscope (SEM) and EAG techniques. Uniporous sensilla on the antennal tip and numerous multiporous pitted sensilla character-ise the female antennae.…”