Effect of some Essential Oils Against Green Leafhopper, Empoasca decipiens Paoli (Hemiptera: Cicadellidae)

The journal of Toxicology and pest control is one of the series issued twice by the Egyptian Academic Journal of Biological Sciences, and is devoted to publication of original papers related to the interaction between insects and their environment. The goal of the journal is to advance the scientific understanding of mechanisms of toxicity. Emphasis will be placed on toxic effects observed at relevant exposures, which have direct impact on safety evaluation and risk assessment. The journal therefore welcomes papers on biology ranging from molecular and cell biology, biochemistry and physiology to ecology and environment, also systematics, microbiology, toxicology, hydrobiology, radiobiology and biotechnology. www.eajbs.eg.net Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.


INTRODUCTION
The green leafhopper, E. decipiens is one of the most important economic hemipterans pests infest a wide range host of plants caused serious damage whether directly or indirectly.They feed by piercing plant tissue and penetrating the phloem with needle-like mouthparts.Both nymphs and adults of E. decipiens cause damage by removing sap from vital cells and plant tissues, which adversely affect to leaves and stems beside damage caused by egg punctures of the larger spots where, E. decipiens females lay their eggs within the host plant tissue (Raupach et al., 2002;Backus et al., 2005 andAbou-Yousef et al., 2010) and they are not visible to the naked eye (Schöpke, 1996).The insect injects toxic substances in plant tissues, that interfere with plant physiology (Sakthivel et al., 2011).This species is an efficient vector of several important virus diseases.Several investigators recorded the role of some leafhopper species in transmitting the pathogens of plant diseases (Nielson, 1968).The fauna of this species was studied in Egypt in the field of vegetable crops and fruit trees (Awadalla et al., 2011;Shalaby et al., 2012;Awadalla et al., 2013 and2014).
Controlling the insect pests using chemical pesticides has resulted in several problems to the environment and human health.Thus, it has been crucial to avoid or reduce the applications of these chemicals.Shaaya et al. (1997) recommended using plant bioactive chemicals to avoid environmental pollution and not damage populations of natural enemies where plants offer an alternative source for insect control because many plants contain a wide range of bioactive chemicals, many of which are selective and less harmful on non-target organisms and environment.In the same direction, Pavela (2005) reported that botanical insecticides may represent attractive alternatives to currently used synthetic chemical insecticides for pest management.
Ben Jemaa (2014) evaluated essential oils as a source of bioactive constituents for the control of some important insect pests.Some species of camphor, Eucalyptus have a vast range of insecticidal activities including fumigant contact and repellent effects, the most important active ingredients are 1.8 cineole and αpinene.Camphor oil is a natural product derived from the wood of the camphor laurel (Cinnamomum camphora L.) trees through steam distillation and purification by sublimination; the trees used should be at least 50 years old (Bin Jantan, 2006).Menthol oil a natural product derived from the Mint plants were grown in a greenhouse in pots (Mentha piperita L.) (Scavroni et al, 2005).Khan et al. (2017) indicated that some oil extracts obtained from plants in family Lamiaceae could be exploited and further developed as potential plant-based insecticides against some sucking insect pests.
The aim of this study was to determine the effect of menthol oil, camphor oil and their mixture against the green leafhopper, E. decipiens in the laboratory and application of LC 90 on it under semi-field conditions.Camphor formula (Lincoln and Lawrence, 1984).A Mixture of both oils made by adding a proportion of 1:1 of each oil.

E. decipiens
Convenient stock concentrations of each oil were prepared on the basis of the tested plant oil weight and the volume of the distilled water (w/v) in the presence of tween 80 (0.1%) as the emulsifier.Then, concentrations were prepared according to Abd-Allah and Marouf (2015) and kept in glass-stoppered bottles under refrigeration.Such stock solutions were prepared periodically.

Laboratory Experiments:
Three treatments (menthol oil, camphor oil and their mixture) were examined to evaluate their toxicity on the adults of E. decipiens.Five concentrations (100, 200, 300, 400 and 500 ppm) of each plant oil and their mixture were made to be tested against the target insect pest.The five diluted concentrations were used to draw the LC-P lines.Four replicates were used for each treatment concentration and the same for the untreated.
Twenty individuals of the green leafhoppers for each replicate were introduced into plastic units (9 cm in diameter and 5 cm high) and applied with the different current treatments concentrations which were sprayed directly on the target insect pest to estimate the mortality line, as well as twenty adults of E. decipiens in the untreated which was sprayed only by distilled water and tween.
The mortality percentage was estimated and corrected according to Abbott's formula, 1925.LC 50 values were determined by using probit statistical analysis method (Finney, 1971).

Semi-field Experiments:
Sixteen pots were planted by cowpea which is one of the important plants which infested by leafhopper (Ebadah, 2002;El-Kady et al., 2016 andEl-Khayat et al., 2017).The experiment was carried out in cages covering the plants where each plant was covered by special cylinder cage (14 cm in diameter and 30 cm high) which was coated by muslin.After approximately two weeks of the plantation, twenty individuals of the green leafhopper were transferred on the cowpea plants under cages in each pot.Four replicates were used for each essential plant oil treatment and also the untreated.
The LC 90 of all treatments was sprayed while untreated was sprayed by distilled water and tween.Death corrected ratio was computed one, three, five and seven days after treatment according to Abbott's formula (1925):

Laboratory Experiment:
Data in Table (1) showed the efficiency of treated essential plant oils against E. decipiens adults.It demonstrated that all concentrations of the mixture of menthol and camphor oils were highly effective and more toxic to the insect pest than either oil alone.This result was in agreement with Abd-Allah and Marouf (2015) who proved that the effectiveness of the mixture of menthol and camphor oils was higher than each oil alone against the pupae of cotton leafworm, Spodoptera littoralis (Boisd.).

P: Probability R: Regression
The slope values in Fig.
(1) indicated that the mixture of both ingredients had the lowest value 1.18 followed by 1.7 and 1.92 for menthol oil and camphor oil, respectively.The red flour beetle, Tribolium castaneum Herbst could be managed using oil extract of mint, M. longifolia (Khani and Asghari 2012).Osman et al. (2012) proved that camphor oil extract had a significant effect on larval mortality of cotton leaf worm.Abd-Allah and Marouf (2015) proved the effectiveness of camphor and menthol mixture on pupae of cotton leafworm.Mohamed et al. (2018) and Kwadwo et al. (2018) obtained similar results concerning the effectiveness of plant extracts against leafhoppers.decipiens.

Semi-field Experiment:
Results in Table (3) showed that LC 90 of the mixture of menthol and camphor oils was more effective in controlling green leafhopper, E. decipiens than each oil alone.Where, the mortality percentage of the target insect pest was 50% compared with 41.03% and 35.90% mortality for menthol and camphor oils, respectively.This result is in agreement with the result of Kwadwo et al. (2018).
From the current results, it could be concluded that applying oil extracts of menthol, camphor and their mixture could be effective in controlling the green leafhopper, E. decipiens.
Culture: Individuals of green leafhoppers were collected from infested cowpea plants at the unsprayed experimental farm of Faculty of Agriculture, Mansoura University and transported to the laboratory in paper bags.Nymphs were transferred for rearing on leaves and kept in jars covered with muslin at 27±2 O C and 65±5% RH for development to adults.Fresh leaves were provided to nymphs every two days.Then, newly emerged adults were collected to start the experiments.The Plant Oils: Both menthol and camphor oil extracts were bought from Essential oil Extracts Center, National Research Center.-Menthol oil is extracted from leaves of Mentha piperita L. (Family: Lamiaceae) and the chemical formula is C 10 H 20 O. (O'Neil, 2013) -Camphor oil, the chemical formula is C 10 H 16 O and it is found in the wood of the camphor laurel, Cinnamomum camphora L. (Family: Lauraceae).

Fig
Fig. (1) LC-P lines for some plant essential oils against green leafhopper, E.decipiens.

Table ( 1
) Corrected mortality percentages of the adults of green leafhopper, E. decipiens treated with essential plant oils under laboratory conditions (27±2 O C and 65±5% RH).Results in Table (2) revealed that LC 50 and LC 90 values of the mixture of both essential oils were lowest (37.86 ppm and 463.12 ppm) compared with each menthol oil (182.34ppm and 962.36 ppm) and camphor oil (242.80 ppm and 1128.05ppm) alone.This means that the mixture of both oils was more effective on E. decipiens control than either oil.

Table ( 2
) Efficiency of some plant essential oils against green leafhopper, E. decipiens.

Table ( 3
) Corrected mortality percentages of E. decipiens sprayed by LC 90 of menthol, camphor oils and their mixture under semi-field conditions.