Molluscicidal and Insecticidal Potential of Monoterpenes on the White Garden Snail, Theba Pisana (Muller) and the Cotton Leafworm, Spodoptera Littoralis (Boisduval)
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Appl. Entomol. Zool. 45 (3): 425–433 (2010) http://odokon.org/ Molluscicidal and insecticidal potential of monoterpenes on the white garden snail, Theba pisana (Muller) and the cotton leafworm, Spodoptera littoralis (Boisduval) Samir A. M. ABDELGALEIL* Department of Pesticide Chemistry, Faculty of Agriculture, 21545-El-Shatby, Alexandria University; Alexandria, Egypt (Received 8 February 2010; Accepted 27 April 2010) Abstract The present article reports the fumigant and contact toxicities of eleven monoterpenes against adults of Theba pisana and third instar larvae of Spodoptera littoralis. The majority of the tested compounds were found to be toxic to both pests with variable degrees of potency. Among the tested monoterpenes, (L)-fenchone showed the highest fumigant toxicity against T. pisana and S. littoralis with LC50 values of 2.51 and 2.27 mg/l, respectively. Myrcene and 1-8-cine- ole exhibited strong fumigant toxicity against T. pisana, while cuminaldehyde, geraniol and (Ϫ)-menthol were not ac- tive. On the other hand, 1-8-cineole and (ϩ)-camphor revealed potent fumigant toxicity against S. littoralis. In the contact assay, the tested monoterpenes were more toxic against T. pisana than S. littoralis. Cuminaldehyde ϭ (LD50 28.37 m g/snail) was significantly the most effective compound against T. pisana, followed by geraniol and (Ϫ)-limonene. Interestingly, eight of the tested monoterpenes were more toxic to adults of T. pisana than methiocarb. The results of the present study suggested that cuminaldehyde, geraniol, (Ϫ)-limonene and (ϩ)-camphor could be used as alternative control agents for T. pisana. In addition, (L)-fenchone and 1-8-cineole could be useful as fumigants for control T. pisana and S. littoralis. Key words: Monoterpenes; fumigant toxicity; contact toxicity; Theba pisana; Spodoptera littoralis several economic crops, including tree fruits, veg- INTRODUCTION etables and ornamental plants (El-Okda, 1983). White garden snails, Theba pisana Muller (Mol- The Egyptian cotton leafworm, Spodoptera lit- lusca: Gastropoda: Helicidae), feed on a wide vari- toralis Boisduval (Lepidoptera: Noctuidae), is a ety of plants, including cereals, vegetables, fruits, well-known polyphagous pest of various crops (e.g. herbs, and many ornamentals, destroying seeds and cotton, soybeans, alfalfa, pepper, eggplant, tomato, seedlings, stunting growth, and reducing yields. lettuce, strawberry), widely distributed in the Not only do they directly damage the plants they Mediterranean region, the Middle East, and North feed on but the wounds they create allow plant and East Africa (Hosny et al., 1986; Pineda et al., pathogenic fungi to infect plants. The snails can 2007). S. littoralis larvae feed mainly on leaves and also be vectors of various plant pathogens, and stems and can seriously retard growth or reduce their mucus trails can contaminate grains, vegeta- crop production. bles, fruits, and herbs. In large numbers, their bod- Monoterpenes make a class of natural products ies and shells can be contaminants of mechanically containing ten carbons, found in many different harvested crops (Godan, 1983; Barker, 2002). The higher-order plants. These compounds give plants white garden snail is currently a serious agricul- their unique odoriferous properties. They are de- tural pest in many areas of the world, including Eu- rived from the coupling of two isoprenoid units, rope, the USA, the Mediterranean region and Aus- which are made from isopentylpyrophosphate, a tralia, particularly in wet seasons. In Egypt, this precursor in the biosynthesis of cholesterol. These snail is a destructive agricultural animal pest of compounds are usually fragrant oils or low melting * E-mail: [email protected] DOI: 10.1303/aez.2010.425 425 426 S. A. M. ABDELGALEIL solids, are often found in perfumes and other cos- Chemicals. Eleven monoterpenes, camphene metics, and are commonly used as food additives (95%), (ϩ)-camphor (98%), (Ϫ)-carvone (98%), and therapeutic drugs (Tsao and Coats, 1995). The 1-8-cineole (99%), cuminaldehyde (98%), (L)-fen- natural pesticidal properties of some monoterpenes chone (98%), geraniol (98%), (Ϫ)-limonene make them useful as potential alternative pest con- (96%), (Ϫ)-linalool (95%), (Ϫ)-menthol (98%) trol agents as well as good lead compounds for the and myrcene (90%) were purchased from Sigma- development of safe, effective, and fully bio- Aldrich Chemical Co. (Steinheim, Germany). degradable pesticides. Monoterpenes have been Chemical structures of these monoterpenes are shown to possess remarkable pesticidal activities, shown in Fig. 1. Methiocarb (98.9%) was supplied including insecticidal (Isman, 2000; Grodnitzky by Bayer AG (Leverkusen, Germany). All chemi- and Coats, 2002), herbicidal (Duke et al., 2000; cals were of the highest grade and commercially Singh et al., 2002), fungicidal (Wuryatmo et al., available. 2003; Cärdenas-Ortega et al., 2005), and bacterici- Fumigant toxicity assay on T. pisana. Glass dal (Cristani et al., 2007; Cantore et al., 2009) jars of one liter capacity were used as exposure properties. chambers to test the toxicity of monoterpene va- Several studies have described the fumigant and pors against adults of T. pisana. The monoterpenes contact toxicities of monoterpenes against stored were applied to Whatman no. 1 filter paper pieces product insects (Park et al., 2003; Lee et al., 2004; (3ϫ3 cm) attached to the undersurface of the screw Papachristos et al., 2004; Abdelgaleil et al., 2009); caps of the glass jars. The tested concentrations however, no studies have reported the fumigant were 0.25, 0.5, 1, 2.5, 5, 10, 20, 40, 60, 80 and 100 toxicity of monoterpenes against T. pisana and S. mg/l. Liquid monoterpenes were applied without littoralis as well as the contact toxicity against S. dilution while solid monoterpenes (camphene, (ϩ)- littoralis. El-Zemity (2001) stated that some camphor and (Ϫ)-menthol) were dissolved in ace- monoterpenes, such as α-terpineol, pulegone, anisole, thymol and eugenol, revealed contact toxi- city against T. pisana. Taking into account the lack of literature on the activity of monoterpenes against T. pisana and S. littoralis and the urgent need for new snail control agents due to the few commercially available molluscicides, this study aimed to evaluate the fumigant and contact toxici- ties of 11 monoterpenes belonging to different classes against T. pisana and S. littoralis. MATERIALS AND METHODS Test organisms. Adult terrestrial snails (16Ϯ 0.5 mm shell diam.), Theba pisana (Muller), were collected from the Faculty of Agriculture Garden, Alexandria, Egypt in April, 2008. The snails were kept under laboratory conditions at 26Ϯ2°C in ventilated glass jars for two weeks before bioassay and were fed a diet of fresh lettuce leaves (Lactuca sativa L.). A susceptible strain of Spodoptera lit- toralis (Boisd) was obtained from the Bioassay Laboratory, Faculty of Agriculture, Alexandria University. The colony was reared under laboratory conditions on caster bean leaves, Ricinus commu- nis L. (Euphorbiaceae), at 26Ϯ2°C and 70Ϯ5% r.h. (El-Defrawi et al., 1964). Fig. 1. The chemical structures of monoterpenes. Pesticidal Activity of Monoterpenes 427 tone before treating the filter papers. After the ad- of concentrations ranging from 0.2 to 100 mg/l. At dition of volatile monoterpenes and the complete least six concentrations for each monoterpene were evaporation of acetone (2 min), the jars were tested and each concentration was in triplicate. The sealed. A similar set-up but without volatile larvae were fed on fresh castor bean leaves. The monoterpenes served as a control. For each treat- mortality percentages were recorded after 24-h ment, four replicates with 5 snails on each one treatment. LC50 values were calculated as previ- were maintained. The snails were fed on fresh let- ously described. tuce leaves during the experiment. Mortality was Contact toxicity assay on S. littoralis. Topical determined after 24-h exposure. Test snails were application assay was used to evaluate the larvici- considered dead if no response was observed after dal activity of the monoterpenes against third instar being touched with a thin needle (WHO, 1965). larvae of S. littoralis. Concentrations of the mono- LC50 (lethal concentration to kill 50% of the popu- terpenes were prepared in acetone. One microliter lation relative to control) values were calculated by of test solution was applied to the dorsum of larvae probit analysis (Finney, 1971). by a microapplicator. The larvae were treated with Contact toxicity assay on T. pisana. The effi- a single dose of 1 mg/larva. Three replicates of 10 ciency of monoterpenes was evaluated on adult larvae each were maintained for each monoterpene snails of T. pisana as described by Hussein et al. and control treatment. Treated larvae were then (1994) and El-Zemity and Radwan (1999) with placed in glass cups and supplied with fresh castor some modifications. Stock solutions of monoter- bean leaves. The percentages of mortality were penes and methiocarb, a standard molluscicide, recorded after 24-h treatment. were prepared in dimethyl sulfoxide (DMSO). The Statistical analysis. The mortality of each dose snails were treated with doses of 5, 10, 20, 40, 60, and⁄or concentration was calculated after 24-h 80, 100, 200, 400, 600, 800 and 1,000 mg/snail. treatment as the mean of three replicates. The mor- These doses contained in 5 ml DMSO solution tality data were subjected to probit analysis were gently applied to the surface of the snail body (Finney, 1971) to obtain the LD50 and LC50 values, inside the shell using a micropipette. Three repli- using SPSS 12.0 (SPSS, Chicago, IL, USA). The cates (five snails in each) of each concentration values of LD50 and LC50 were considered signifi- were used. Control snails were treated with the cantly different if the 95% confidence limits did same volumes of DMSO. The treated snails were not overlap. The contact toxicity data of S. littoralis placed in 0.3 l glass jars. The jars were covered larvae were analyzed by one-way analysis of vari- with cheesecloth fastened by rubber bands to pre- ance.