Pure Camphor and a Thujone-Camphor Mixture as Eco-Friendly Antifeedants against Larvae and Adults of the Colorado Potato Beetle.

The Colorado potato beetle (CPB) is a serious pest of economically important Solanaceae species. The use of essential oil compounds in pest management has been proposed as an alternative to harmful chemical insecticides that disturb human health and ecosystem functioning. We examined the antifeedant activity of three concentrations (0.125%, 0.25% and 0.5%) of pure camphor and a thujone-camphor mixture against 3rd instar larvae and adults. Their efficacy was evaluated according to the degree of leaf damage and avoidance of treated leaves by the CPB. Treatment of potato leaves significantly reduced leaf damage compared to the control. Leaf protection increased at higher concentrations of the examined compounds. Camphor was more effective against larvae and the thujone-camphor mixture was more effective against adults. Additionally, adults moved faster towards the control leaf disc in the two-choice olfactometer assay if an alternative disc was treated with a thujone-camphor mixture, whereas larvae responded similarly to the two potential repellents. However, after contact with the leaf disc treated with the highest compound concentration, the larvae escaped faster from the thujone-camphor mixture than from pure camphor. In conclusion, both examined compounds are promising eco-friendly antifeedants, but their efficacy depends on the developmental stage of the beetle, compound type and applied concentration.

Assessment of Sex-Specific Toxicity and Physiological Responses to Thymol in a Common Bean Pest Acanthoscelides obtectus Say.

Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae), is one of the most important pests of the common bean Phaseolus vulgaris L. Without appropriate management it may cause significant seed loss in storages. In search for means of environmentally safe and effective protection of beans we assessed biological activity of thymol, an oxygenated monoterpene present in essential oils of many aromatic plants. We studied contact toxicity of thymol on bean seeds and its effects on adult longevity and emergence in F1 generation. Furthermore, we determined acetylcholinesterase (AChE), superoxide dismutase (SOD), catalase (CAT), mixed-function oxidase (MFO), carboxylesterases (CarE) and glutathione S-transferase (GST) activities in response to 24 h exposure of beetles to sublethal and lethal thymol concentrations. Our results showed that thymol decreased adult survival, longevity and percentage of adult emergence. Higher median lethal concentration (LC50) was recorded in females indicating their higher tolerance comparing to males. Overall, activities of SOD, CAT and CarE increased at sublethal and MFO increased at both sublethal and lethal thymol concentrations. On the other hand, GST and AChE activities decreased along with the increase in thymol concentrations from sublethal (1/5 of LC50, 1/2 of LC50) to lethal (LC50). Enzyme responses to the presence of thymol on bean seed were sex-specific. In the control group females had lower CarE and higher SOD, CAT and GST activity than males. In treatment groups, females had much higher CAT activity and much lower CarE activity than males. Our results contribute to deeper understanding of physiological mechanisms underlying thymol toxicity and tolerance which should be taken into account in future formulation of a thymol-based insecticide.

Potential of Essential Oils from Anise, Dill and Fennel Seeds for the Gypsy Moth Control.

The gypsy moth (Lymantria dispar L. (Lepidoptera: Erebidae)) is a serious pest of hardwood forests. In the search for an environmentally safe means of its control, we assessed the impact of different concentrations of essential oils (EOs) from the seeds of three Apiaceae plants (anise Pimpinella anisum, dill Anethum graveolens, and fennel Foeniculum vulgare) on behavior, mortality, molting and nutritional physiology of gypsy moth larvae (GML). EOs efficacy was compared with commercial insecticide NeemAzal®-T/S (neem). The main compounds in the Eos were trans-anethole in anise; carvone, limonene, and α-phellandrene in dill; and trans-anethole and fenchone in fennel seed. At 1% EOs concentration, anise and fennel were better antifeedants and all three EOs were more toxic than neem. Neem was superior in delaying 2nd to 3rd larval molting. In the 4th instar, 0.5%, anise and fennel EOs decreased relative consumption rate more than neem, whereas all three EOs were more effective in reducing growth rate, approximate digestibility and efficiency of conversion of food into body mass leading to higher metabolic costs to GML. Decrease in consumption and metabolic parameters compared to control GML confirmed that adverse effects of the EOs stem from both pre- and post-ingestive mechanisms. The results indicate the potential of three EOs to be used for gypsy moth control.

Repellent activity of Tanacetum parthenium (L.) and Tanacetum vulgare (L.) essential oils against Leptinotarsa decemlineata (Say).

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is one of the most destructive pest species to have developed resistance to most chemical insecticides. We determined the composition and evaluated the potential of Tanacetum parthenium L. and Tanacetum vulgare L. (Asteraceae family) essential oil (EO) application as an alternative eco-friendly control strategy against L. decemlineata. We assessed the antifeedant activity for L. decemlineata larvae and adults by estimating the damage to potato leaves treated with three concentrations of EOs dissolved in ethanol (0.125, 0.25 and 0.5%). Results showed that T. parthenium EO was more effective against larvae, and T. vulgare was more effective against adults. In an olfactometer assay, the time required to choose an untreated leaf disc did not depend on the Tanacetum species, or life stage examined. However, the concentration of EO exhibited a significant effect on the behaviour of both developmental stages. At higher EO concentrations, both third instar larvae and adults require less time to choose an untreated leaf disc. Additionally, T. parthenium EO provoked more rapid movement away from the treated leaf disc than T. vulgare, especially at the highest concentration. Successful modification of L. decemlineata behaviour by the two Tanacetum oils suggests that they possess the potential for use in potato protection.

Toxic, Oviposition Deterrent and Oxidative Stress Effects of Thymus vulgaris Essential Oil against Acanthoscelides obtectus.

The bean weevil Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae) can cause significant losses in production of its primary host common bean Phaseolus vulgaris L. To avoid bean protection with environmentally risky chemical insecticides and provide sustainable and safe production of food, new pest management methods based on natural compounds are investigated. In the present study, we evaluated protective potential of the essential oil (EO) from the common thyme Thymus vulgaris L. applied on bean seeds. We assessed residual contact toxicity of thyme EO and its effects on A. obtectus longevity, oviposition and adult emergence. Furthermore, to elucidate the role of oxidative stress in thyme EO toxicity, we estimated the levels of oxidatively damaged proteins and lipids, as well as the level of thiols which have important role for antioxidant capacity. We found that thyme oil significantly reduced adult survival and longevity, induced oxidative damage to lipids and proteins and depleted protein and non-protein thiols in a concentration-dependent manner. Females appeared to be more tolerant to thyme oil treatment than males. Sublethal EO concentrations affected oxidative stress indices, deterred oviposition and strongly inhibited adult emergence. The results suggest that thyme oil has the potential to be used as an ecofriendly insecticide for A. obtectus control.

Toxicity of twenty-two plant essential oils against pathogenic bacteria of vegetables and mushrooms.

ASBTRACT Toxicity of twenty-two essential oils to three bacterial pathogens in different horticultural systems: Xanthomonas campestris pv. phaseoli (causing blight of bean), Clavibacter michiganensis subsp. michiganensis (bacterial wilt and canker of tomato), and Pseudomonas tolaasii (causal agent of bacterial brown blotch on cultivated mushrooms) was tested. Control of bacterial diseases is very difficult due to antibiotic resistance and ineffectiveness of chemical products, to that essential oils offer a promising alternative. Minimal inhibitory and bactericidal concentrations are determined by applying a single drop of oil onto the inner side of each plate cover in macrodilution assays. Among all tested substances, the strongest and broadest activity was shown by the oils of wintergreen (Gaultheria procumbens), oregano (Origanum vulgare), and lemongrass (Cymbopogon flexuosus. Carvacrol (64.0-75.8%) was the dominant component of oregano oils, while geranial (40.7%) and neral (26.7%) were the major constituents of lemongrass oil. Xanthomonas campestris pv. phaseoli was the most sensitive to plant essential oils, being susceptible to 19 oils, while 11 oils were bactericidal to the pathogen. Sixteen oils inhibited the growth of Clavibacter michiganensis subsp. michiganensis and seven oils showed bactericidal effects to the pathogen. The least sensitive species was Pseudomonas tolaasii as five oils inhibited bacterial growth and two oils were bactericidal. Wintergreen, oregano, and lemongrass oils should be formulated as potential biochemical bactericides against different horticultural pathogens.

Growth and development of Colorado potato beetle larvae, Leptinotarsa decemlineata, on potato plants expressing the oryzacystatin II proteinase inhibitor.

Plant proteinase inhibitors (PIs) are attractive tools for crop improvement and their heterologous expression can enhance insect resistance in transgenic plants. PI oryzacystatin II (OCII), isolated from rice, showed potential in controlling pests that utilize cysteine proteinases for protein digestion. To evaluate the applicability of the OCII gene in enhancing plant defence, OCII-transformed potatoes were bioassayed for resistance to Colorado potato beetle (Leptinotarsa decemlineata Say). Feeding on transformed leaves of potato cultivars Desiree and Jelica significantly affected larval growth and development, but did not change mortality rates. During the L2 and L3 developmental stages larvae consumed the OCII-transformed foliage faster as compared to the nontransformed control. Also these larvae reached the prepupal stage (end of L4 stage) 2 days earlier than those fed on control leaves. However, the total amounts of consumed OCII-transformed leaves were up to 23% lower than of control, and the maximal weights of prepupal larvae were reduced by up to 18% as compared to larvae fed on nontransformed leaves. The reduction in insect fitness reported in this study in combination with other control measures, could lead to improved CPB resistance management in potato.

Ecologically acceptable usage of derivatives of essential oil of sweet basil, Ocimum basilicum, as antifeedants against larvae of the gypsy moth, Lymantria dispar.

Abstract Ethanol solutions of five fractions obtained from essential oil of sweet basil Ocimum basilicum L. (Lamiales: Lamiaceae) (F1-F5) were tested for their antifeedant properties against 2(nd) instar gypsy moth larvae, Lymantria dispar L. (Lepidoptera: Lymantriidae), in laboratory non-choice and feeding-choice experiments. Prior to bioassays, the chemical composition of each fraction was determined by gas chromatography analyses. Significant larval deterrence from feeding was achieved by application of tested solutions to fresh leaves of the host plant. The most effective were were F1 (0.5%), F4 (0.05, 0.1, and 0.5%), and F5 (0.1 and 0.5%), which provided an antifeedant index > 80% after five days. A low rate of larval mortality was observed in no-choice bioassay. In situ screening of chlorophyll fluorescence as an indicator of plant stress level (assessed by the induced fluorometry) confirmed that the tested compounds did not cause alternations in the photosynthetic efficiency of treated leaves.

Larvicidal and antifeedant activity of some plant-derived compounds to Lymantria dispar L. (Lepidoptera: Limantriidae).

Ethanol solutions of essential oil of Ocimum basilicum and its main component, linalool (both isomer forms), all in three concentrations, as well as botanical standard Bioneem (0.5%), were tested for their toxicity and antifeedant activity against the second instar gypsy moth larvae in the laboratory bioassay. The essential oil of O. basilicum was subjected to gas chromatography analysis, and totally 37 compounds were detected, of which linalool was predominantly present. All tested solutions showed low to moderate larvicidal effect in both residual toxicity test and in chronic larval mortality bioassay. Chronic mortality tests showed that obtained mortality was a consequence of starving rather than ingestion of treated leaves. However, antifeedant index achieved by application of tested solutions in feeding choice assay was remarkable. Foliar application of all tested compounds deterred feeding by L2 in the same percent as Bioneem. Antifeedant index was relatively high at all tested treatments (85-94%); moreover, the larval desensitization to repelling volatiles has not occurred after five days of observation. Low toxic and high antifeedant properties make these plant-derived compounds suitable for incorporation in integrated pest management programs, especially in urban environments.