Efficiency of Two Phytochemical Compounds and a Biopreparation on the Common Prevailing Land Snail Species in Alexandria Governorate, Egypt.

Mollusks are the second biggest phylum in the animal kingdom, accounting for a significant portion of the world's fauna. Only the Gastropoda have successfully invaded land among all classes of mollusks (Sandeep et al. 2012). Mollusks are a varied category of invertebrate animals having soft, unsegmented bodies. (O’Connor and Crowe 2005). Terrestrial gastropods are classified as agricultural pests because they damage crops and cause financial loss by eating the leaves, roots and fruits of plants, as well as numerous horticultural plants ornamental plants, wood trees, and newly sown lawn grasses. They also decrease crop quality and contaminate agricultural products with their bodies, feces, or slime (Barker, 2002; Eshra, 2004; Awad et al., 2012; Puizina et al., 2013; Awad, 2014; Ali, 2017; Hussein and Sabry, 2019). As a following result, an unpleasant odor develops, preventing both humans and animals from eating these contaminated plants (Shetaia et al., 2009).

Today's gastropods in Egypt are significantly more harmful than they were in the past (Mortada, 2002). In many Egyptian governorates, the land snails Eobania vermiculata, Theba pisana, Helicella vestalis, Monacha obstructa, and Cochlicella acuta have been observed attacking various plantations (Kassab and Daoud, 1964; El-Okda, 1979; El-Deeb et al., 1996; Abu-Bakr, 1997; Eshra, 2004). Both E. vermiculata and T. pisana are significant agricultural pests that inflict significant damage in agriculture and horticulture. They are particularly destructive in locations where they may find the right circumstances for fast growth (Puizina et al. 2013).

Methomyl and other oxime-carbamates insecticides, which are used to control snails, are moderately poisonous to land snails but extremely hazardous to mammals and beneficial insects (Hussein et al., 1994; Radwan and El-Zemity, 2007; Salama et al., 2005; Abdelgaleil, 2010). Because of the aforementioned drawbacks of conventional pesticides, the request for safe and environmentally friendly alternative molluscicides is critical in order to protect human health and the environment.

Essential oils are green insecticides that are non-toxic to mammals and other species (Ferreira et al., 2009; Stroh et al., 1998), No residue-related problems exist (Misra and Pavlostathis, 1997). Essential oils and their constituents are gaining popularity as safe alternatives to pesticides for controlling a wide range of pests, including gastropods, acting as insecticides (Isman et al., 2001; Hussein, 2005; Radwan et al., 2008; Pavela, 2015; Klein et al., 2020; Owolabi et al., 2020).

The biological management of land snails or slugs utilizing microbial agents, i.e., bacteria, is an alternative strategy that gained more attention a few years ago and offers efficient control against land snails. Bacillus thuringiensis (Bt) is a soil gram-negative bacteria that generates pest-toxic compounds. Recently, it has emerged as one of the biological control agents for a number of insect pests (Dean, 1984). Numerous studies have examined this bacterium's toxicity toward a some land snails in Egypt (Zedan et al., 1999; Azzam and Belal, 2003; Kramarz et al., 2007).

The main aim of this work is to evaluate the molluscicidal effect of A. indica, M. piperita, essential oils and a Biopesticide formulation Biotect^® 9.4%W.P, a commercial formulation of                       B. thuringiensis, by dipping technique application and different concentrations under laboratory conditions against the most common land snails infesting various fruit orchards: E. vermiculata, and T. pisana.

2. MATERIALS AND METHODS

2.1. MATERIALS

a. Biotect 9.4%W.Pa Commercial formulation of Bacillus thuringiensis.

b. Neem oil (Azadirachta indica) and peppermint (Mentha piperita) essential oil were purchased as pure oil from National Research Center, Dokki, Cairo, Egypt.   

c. Acetone (pure) was purchased from Al-Nasr Pharmaceutical Chemicals Co. (ADWIC) (Egypt).

2.2. Experimental snails:

 Adults of the brown garden snail, E. vermeculata (Müller), and the white garden snail, T. pisana (Müller), having approximately the same age and size were collected for laboratory experiments from El-Maamoura locality, Alexandria. These snails were transferred to plastic cups covered with cloth netting and maintained under laboratory conditions of 27 °C and 65% R.H. The snails were fed on lettuce leaves daily up to the initiation of tests. The snails were allowed to acclimatize to these conditions for two weeks. Dead snails were excluded as soon as possible, whenever needed.

2.3. Laboratory bioassay (Dipping leaves method)

The essential oils of each of A. indica and M. piperita, as well as the biopesticide formulation of B. thuringiensis, were tested for toxicity against E. vermiculata and T. pisana. Homogenous disks of lettuce leaves were dipped in a series of each of A. indica, M. piperita, and B. thuringiensis prepared concentrations for 5 min and left for dryness. The treated lettuce disks were transferred into plastic cups, and 10 adult snails were placed in each cup. Each treatment concentration had three replicates; results were detected along three different periods; after 24, 48, and 72 h., untreated lettuce disks were used as a check treatment. Mortality percentages were recorded after 24, 48, and 72 h post-treatment.

3. Statistical analysis.

Lethal effect was evaluated as percentages of cumulative daily mortality, corrected for mortality in the control variant according to Abbott's formula (Abbott, 1925) as follows:

Corrected Mortality =

The statistical toxicity indices,  LC₅₀ and LC_95, were estimated as described by Finney (1952), via the LdP line program (Ehab Soft, Cairo, Egypt).

3. RESULTS AND DISCUSSION

3.1. Efficiency of neem; peppermint essential oilsand Biotect^® (commercial formulation  B. thuringiensis)against T. pisana and E. vermiculata snails.

The toxicity of (neem oil) against T. pisana and E. vermiculata was evaluated. The calculated LC₅₀ values for T. pisana were 2.66, 1.29, and 0.87% after 24, 48, and 72hrs post treatment, respectively (Table, 1). Also, the extracted LC₅₀ values for E. vermiculata were 5.35, 4.02, and 2.26% after 24, 48, and 72 h post treatment, respectively. Noticeably, the toxicity of neem oil increased as the time of exposure increased for both snails  T. pisana and E. vermiculata. The obtained results indicated that neem oil was the high toxic against T. pisana than E. vermiculata snails.

The exhibited data in Table (2) show that tested peppermint oil was more toxic upon adults of T. pisana than E. vermiculata snails, with LC₅₀ values of 6.24, 3.19, and 2.37 % after 24, 48, and 72 hours, respectively. While, its deduced LC₅₀ values against E. vermiculata were 15.29, 11.07, and 9.523% after 24, 48, and 72hrs respectively. These results elucidate that the extracted LC₅₀ values of peppermint oil decreased with increasing the exposure time and indicated its higher toxicity against T. pisana than E. vermiculata snails.

Table (1): The calculated LC₅₀ values of neem oil on adults of T. pisana and                 E. vermiculata snails under laboratory conditions.

Table (2): The estimated LC₅₀ values of peppermint oilon adults of T. pisana and  E. vermiculata under laboratory conditions.

The included data in Table (3) represents the extracted LC₅₀ values for the tested commercial formulation of B. thuringiensis (Biotect®)  against E. vermiculata and T. pisana snails; their confidence limits, slope, and X² values. The estimated LC₅₀ values of Biotect® against T. pisana were 9.59, 15.7, and 8.81% after 24, 48, and 72hrs post treatment; while for E. vermiculata these values comprised 9.98, 16.3 and 2.16% after 24, 48, and 72hrs post treatment. The lower LC₅₀ values were obtained with increasing exposure. The toxic efficiency of Biotect® was higher against E. vermiculata than T. pisana snails.

Table (3): The calculated LC₅₀ values of experimental commercial formulation of B. thuringiensis   (Biotect^®) on adults of T. pisana and E. vermiculata snails under laboratory conditions.

الملخص العربي

فعالية مركبين كيميائيين نباتيين ومستحضر حيوي على القواقع الأرضية السائدة في محافظة الإسكندرية ، مصر.

حسن على عبدالحميد مصباح ¹ أحمد كمال خليل مراد ¹ السيد حسن عشره ² و مسعودة رمضان الزروق¹