Elsevier

Biochemical Systematics and Ecology

Volume 40, February 2012, Pages 201-207
Biochemical Systematics and Ecology

Optimum extraction method for volatile attractant compounds in cabbage to Pieris rapae

https://doi.org/10.1016/j.bse.2011.09.015Get rights and content

Abstract

As an initial step in developing attractant traps for Pieris rapae, we identified the attractant significantly preferred by P. rapae and the best extraction methods for obtaining the extract from cabbage. Cabbage extracts obtained by the diethylether solvent extraction method (DEM), countercurrent-distribution method and Porapak Q column concentration method were analyzed for volatile compounds attractive to P. rapae. Cabbage extracts were also identified and quantified by gas chromatography-mass spectrometry. P. rapae showed the highest preference toward the cabbage extract obtained by DEM when compared to the extracts obtained by the other methods. A total of 21 compounds were detected from the highly preferred extract: 4-methyloctane, 2-methylbutanenitrile, propylthiocyanate, d-limonene, methallylcyanide, allyl 2-ethylbutyrate, 1-hexanol, (Z)-3-hexen-1-ol, 3-methoxy-3-methylbutanol, acetic acid, 2-ethyl-1-hexanol, 1,2,4-trithiolane, heptadecane, tridecanol, benzothiazole, 1-undecanol, octadecanal, 2-phenethyl isothiocyanate, 2-nonadecanone 1-heptadecanol, 5,9-dimethyl-3-decanol. Moreover, five compounds from the cabbage extract—dimethyltrisulfide, acetic acid, dimethylsulfoxide, 4-(methylthio) butanenitrile and benzenepropanenitrile—had the highest concentration when obtained by DEM, suggesting that these compounds are the primary attractants to P. rapae.

Highlights

Pieris rapae preferred the cabbage extract by diethylether solvent extraction method. ► A total of 21 compounds were detected from the highly preferred cabbage extract. ► The primary attractants to P. rapae are characteristic in Brassicaeae plants.

Introduction

Consumer interest in the safety of food and agricultural products has risen in recent years, and producers are increasingly focusing on pesticide-free and organic farming that take human health and the environment into account. However, in these farming systems, there is a risk of increased disease and insect damage to crops. This has led to a demand for alternative pest management systems which use less or no agricultural chemicals harmful to the environment or human health. In this paper we focus on the knowledge needed to develop a control method against a destructive insect, the small cabbage butterfly (Pieris rapae crucivora Boisduval), which is a major pest of the Brassicaceae family that includes many economically important vegetable crops.

Volatile chemical compounds are known to play a significant role in insect–plant interactions (Visser, 1986). Plant chemicals, serving as attractants or repellents, have been studied extensively in moths (Fenemore, 1988; Ramaswamy, 1988; Tingle et al., 1990; Mitchell et al., 1991; Tingle et al., 1991), but there have been few studies in butterflies.

More than 99% of butterflies, moths and other Lepidoptera are herbivorous insects and their larvae damage plants mainly by feeding on them. Most butterflies are either oligophagous (feeding on a relatively narrow range of host plants) or monophagous (feeding on only one kind of host plant) (Honda, 1995). Butterflies also have egg-laying preferences and lay eggs only on specific plant species. It is believed that these insects search for plants suitable for egg-laying by detecting characteristic chemical substances in the host plant and then laying their eggs after landing on the plant (Renwick and Chew, 1994; Honda, 1995).

Moths are known to use the volatile compounds released by plants as indicators when searching for and landing on host plants (Renwick and Radke, 1983, Renwick and Radke, 1988, Feeny et al., 1989; Honda, 1995: Omura et al., 1999). Saxena and Goyal (1978) showed that Papilo demoleus was specifically attracted to the ether-soluble volatile components of host plants. Although gravid female butterflies are known to seek out host plants among many other plants and can accurately discriminate host plants (Renwick and Chew, 1994; Honda, 1995.), there have been few similar studies on other butterfly species.

After adult females of P. rapae have copulated, they search for host plants over a range of several kilometers in order to lay eggs (Ohsaki et al., 1980). The resulting larvae damage the host by feeding on plant leaves (Verschaffelt, 1911). Our previous study indicated that after mating, adult females of P. rapae search for plants for egg laying. These females visually judge whether or not an object is a plant and identify host plants through olfactory detection of host plant volatile components (Ikeura et al., 2010). However, the volatile components serving as attractants to P. rapae have not been identified to date. Since it is reported that the concentration and composition of volatile compounds are different when obtained with different extraction methods (Richter and Schellenberg, 2007), there is a need to identify the best extraction method for the extract containing abundant attractants of P. rapae.

As a first step to developing a biological pesticide for P. rapae such as a pheromone trap, this study was conducted with the following objectives: 1) to assess the preference of P. rapae for cabbage extracts obtained by different extraction methods; 2) to analyze by gas chromatography-mass spectrometry (GC–MS) the cabbage extracts obtained by the different extraction methods; and 3) to determine and estimate the amount of compounds serving as attractants to P. rapae.

Section snippets

Test plants

Seedlings of the Brassicaceae test plant, cabbage (Brassica oleracea var. capitata L.), and an Asteraceae control plant, lettuce (Lactuca sativa L.), were grown in a Meiji University greenhouse from May 2 to July 31, 2007.

Insect collection and rearing

Gravid adult females of P. rapae crucivora Boisduval were collected from cabbage patches in Kawasaki City. They were released in a cage (1.6 m × 1.6 m × 1.8 m) covered with a white shading net in the greenhouse at Meiji University and allowed to oviposit on potted cabbages

Results and discussion

The preference of P. rapae to lettuce treated with control (diethylether) vs. cabbage volatile extracts by different extraction methods is shown in Fig. 1. The preference of P. rapae to cabbage extracts by the diethylether solvent extraction method (DEM), PQM and countercurrent-distribution method (CDM) was 75.7% (χ2 = 34.4, P < 0.01), 67.4% (χ2 = 14.2, P < 0.01) and 68.2% (χ2 = 14.7, P < 0.01), respectively, and the preference of P. rapae to all extraction methods was significantly higher

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