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Neem, Azadirachta indica, as a potentialbiopesticide for controlling the apple snail,Pomacea canaliculata

Siti Noor Hajjar Md Latip1 and Mohd Fahmi Keni2

1Faculty of Plantation and Agrotechnology, University Technology MARA, 40450 Shah Alam, Selangor, Malaysia. Email: noorhajar@salam.uitm.edu.my2Biology Division, Malaysian Palm Oil Board (MPOB), No. 6, Persiaran Institusi, Bandar Baru Bangi, 43000 Kajang, Selangor, Malaysia.

Abstract

Experiments were undertaken to assess the efficacy of methanol and water extractions of fresh neem (Azadirachta indica) seed against apple snails. Each assay included five neem treatments (10-50 % dilutions of concentrated extract), a control treatment and a chemical treatment using Niclosamide. Assays were replicated. Snail mortality was recorded at 24, 48, 72 and 96 h. There was little difference between the extracts obtained by methanol and water extractions. Mortality increased over time and with neem extract concentration. The highest concentration of neem extract (50 % dilution) resulted in similar mortality levels to the Niclosamide treatment. The study showed that fresh neem seed extract has potential as a botanical pesticide against apple snails.

Additional keywords: Ampullariidae, botanical pesticide, Malaysia, Mollusca, neem seed, pest, rice

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Introduction

The South American apple snail Pomacea canaliculata, listed among 100 of the world’s most invasive species (Lowe et al., 2000), was intentionally introduced and cultivated as a protein source in Taiwan, but rapidly spread to other parts of Asia (Ng & Tan, 2011). It now occurs in most Southeast Asian countries (Hayes et al., 2008), where it is a serious invasive agricultural pest, especially in paddy cultivation fields (Cowie, 2002). Several characteristics may facilitate the snails’ invasive potential including that it is a food generalist and has a very fast growth rate and reproduction capacity (Hayes et al., 2015).

Damage to rice plants occurs primarily as a result of the snails feeding on the young leaf tips within the first 14 days after transplanting or emergence of the seedlings (Ito, 2002). Older seedlings with hardened leaves are less vulnerable to attack. In cases of severe infestation, the snails can cause extensive crop losses and farmers may even lose their entire crop. The damage level in the field depends on the size and number of the snails (Morallo-Rejesus et al., 1989). Naylor (1996) reported that a density of eight snails/m2 can decrease rice yields by 90 %.

Various strategies are being used by farmers to eradicate or control the snails, including cultural and mechanical, biological, chemical and botanical control. Hand picking and crushing of adult snails and eggs is widely practiced in most rice growing regions in Asia, including Malaysia. Significant control can be achieved by hand picking if sufficient labour is available. The efficacy of hand picking can be improved by using attractants such as leaves of various plants (Teo, 1999). Other common cultural and mechanical practices that are still implemented widely include installing metal screens on irrigation inlets to prevent entry of apple snails from irrigation canals, maintaining a shallow water depth after transplanting to suppress snail activities, transplanting seedlings that are more than 30 days old, dry rotavation and keeping the fields dry during the off planting season to inhibit breeding (Teo, 1999).

Biological control using fish such as the common carp, Nile tilapia, black carp and hybrid fish have been experimentally used to control apple snails in rice fields in the Philippines and Vietnam with encouraging results. However, field trials of the use of hybrid catfish in Malaysia have thus far not been so successful (Jambari & Suryanto, 2000). The use of fish may not be practical because fish culture requires maintaining relatively deeper water in the fields (Cowie, 2002).

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Synthetic chemical molluscicides are used extensively in Asia to control these snails, but it may be costly to both the farmer and the environment. Niclosamide, metaldehyde, endosulfan, tea seed cake (residue) and copper sulphate have been used but they are lethal to non-target organisms and pollute water bodies (Joshi, 2005). For example, Niclosamide, which is the only compound recommended for control of aquatic snails by the World Health Organization (WHO), is effective against apple snails at 0.5-1.0 mg a.i./l, but the LC50 for carp is only 0.14 mg a.i./l (San Martin et al., 2008). The major environmental concern with these pesticides is their ability to leach down to the subsoil and contaminate the ground water, or they may persist on the top soil and become harmful to microorganisms, plants, animals and people (Tomašević & Gašić, 2012). Such concerns have led to a focus on isolation and characterization of natural products that are as effective as synthetic pesticides without posing the threats to the environment.

Botanical pesticides are of great interest because they occur naturally. Historically, plant materials have been in use longer than any other type of pesticide. The flowers, leaves, bark, seeds and roots are finely ground and used in this form, or the toxic ingredients are extracted and used alone or in combination with other toxicants. Neem (Azadirachta indica) has been recognised for its pest control properties and is regarded as the most reliable source of eco-friendly botanical pesticide. In Thailand, Benchawattananon & Boonkong (2006) compared the toxicity of crude extracts of neem leaf and garlic (Allium sativum L.); 1000 mg/l of neem killed 96 % of apple snails in 96 hours, while 1000 mg/l of garlic killed 92 % in 96 hours. In Malaysia, showed that neem leaf extracts killed 93 % of small snails (10-20 mm) and 84 % of large snails (20-40 mm) after 96 hours in the laboratory (Massaguni & Latip, 2012).

A major reason for the interest in neem is the widely held view that neem has numerous valuable attributes, including that it is safe to both the environment and non-target organisms, and it is degraded rapidly in the environment. The present study assessed the efficacy of water and methanol extractions of fresh neem seeds against apple snails.

Material and methods

Apple snails and neem seed were collected at the Federal Land Consolidation and Rehabilitation Authority (FELCRA), Seberang, which is located in the Kampung Gajah Sub-district, Perak, Malaysia. Ten apple snails in the 20-25 mm size range were selected for the laboratory study. Neem seed extract was obtained from fresh neem seeds by

neem, azadirachta Indica, As A Potential BioPesticide For Controlling The APPle Snail,Pomacea Canaliculata

346 BIology and ManageMent of InvasIve apple snaIls

extraction with either methanol or water as the solvent. For the methanol extraction, the protocol of Parekh et al. (2005) was used, and for the water extraction that of Polaquini et al. (2006) was used, both with some modification. In both cases the neem extract was diluted to concentrations of 100,000 ppm, 200,000 ppm, 300,000 ppm, 400,000 ppm and 500,000 ppm by volume. 1 ml of Tween 20 was added as an emulsifier in the water dilutions.

Each assay included five neem treatments (100,000 ppm (T1), 200,000 ppm (T2), 300,000 (T3), 400,000 ppm (T4) and 500,000 ppm (T5), a control treatment and a chemical treatment using Niclosamide. Each assay was replicated eight times for each of the water and methanol extractions. Snail mortality was recorded at 24, 48, 72 and 96 h. Snails were considered dead when the body was contracted within the shell and no response to a needle probe could be elicited (Singh et al., 1996). Dead snails were removed as soon as they were found.

The data were analyzed using Minitab 16 and POLO PLUS software. Analysis of variance (ANOVA) followed by Tukey Simultaneous tests were performed to assess differences among treatments in overall mortality after 96 h within each of the assays for methanol and water extractions. Probit analysis also performed to determine LC50 values (the concentration at which 50 % mortality would occur after 96 h exposure).

Results and discussion

The total percentage mortality differed significantly among treatments for both extraction protocols (ANOVA: methanol, F = 386.42, P

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Fig.1. Percentage mortality of apple snails treated with different concentrations of neem extracted in methanol over 96 hours.

Fig.2. Percentage mortality of apple snails treated with different concentrations of neem extracted in waterover 96 hours.

Das et al. (2010) showed that the duration of each larval stage of the red slug caterpillar, Eterusia magnifica, lengthened with increase of neem kernel aqueous extract concentration. And Pinheiro et al. (2009) reported increased mortality of nymphs of the silverleaf or sweet potato whitefly, Bemicia tabaci, between three and five days after application of neem oil and in particular that neem oil caused mortality to third and fourth instar nymphs after two days application of treatment.

neem, azadirachta Indica, As A Potential BioPesticide For Controlling The APPle Snail,Pomacea Canaliculata

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Probit analysis gave LC50 values for neem extract dilution at 96 h of 26.8 % (95 % confidence interval 22.5-31.8 %) for the methanol extraction and 24.9 % (95 % confidence interval 20.5-29.8 %) for the water extraction.

There was little difference in the results for the two extraction methods with the highest neem seed extract concentration (50 % dilution) resulting in the highest mortality due to neem, similar to the level of mortality due to Niclosamide. This study showed that fresh neem seed extract has potential as a botanical pesticide against apple snails.

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