MOLLUSCICIDAL EFFICACY AND TOXICITY OF SOME PESTICIDES UNDER LABORATORY AND FIELD CONDITIONS

Laboratory and field trials were carried out at Koom Hamada district and Etay El-baroud research station during 2004/ 2005 season to clarify the molluscicidal activities of the following: indoxacarb, lufenuron, Bacillus thurringiensis, kurestaci (Bt.) and methomyl against glassy clover snails Monacha cartusiana (Müler). Results indicated that all tested pesticides decreased snails population compared with control. Under the field conditions, the efficiency of the tested compounds were 98.0, 93.4, 93 and 71.58% for methomyl, lufenuron, indoxacarb and Bt. after 5, 6, 13, and 28 days of treatment, respectively. Moreover the effect of LC50 and 0.5 LC50 of these compounds were investigated on some biochemical parameters in vivo. The activities of acetylcholinestrase (AChE), alanine aminotransferases (ALT) , aspartate aminotransferases (AST) and protein contents at different time intervals were evaluated. The specific activity of AChE reached 0.009, 0.002, 0.006 and 0.001 mole/ mg protein/ min for indoxacarb, lufenuron, Bt. and methomyl, respectively, after one day of treatment with (LC50 for each compound). In general, Bt. and indoxacarb caused slight inhibition on AChE enzyme. All treatments decreased ALT and AST enzyme activity in the tested animals. However, Bt. Showed slight effect on the activity of aminotransferases enzymes.


INTRODUCTION
Mollusks are a large and diverse group of animals distributed worldwide (El-Okda, 1980;Godan, 1983 andNakhla et al 1993). Terrestrial gastropods (mollusks: snails and slugs) are being abundantly distributed in the North coast, new rec-laimed lands and addition to delta region of Egypt (Kasaab and Daoud, 1964); (El-Okda and Khalil, 1981) and (Abou-Baker, 1997). Also, snails are becoming serious agricultural animal pests in Egypt, especially in the Northern coastal areas. Their damage to ornamental plants resembles that done by caterpillars or Abdel-Halim; Abou-El Khear and Hussein Arab Univ. J. Agric. Sci., 14(2), 2006 862 wireworms. The brown garden snail (Helix aspersa), is the common snail causing problems in California gardens; it was introduced from France during the 1850s for use as food. Snails and slugs move by gliding along on a muscular "foot". Snails and slugs feed on a variety of living plants as well as on decaying plant matter. On plants, they chew irregular holes with smooth edges in leaves and can clip succulent plant parts (Flint, 1998). They can also chew fruit and young plant bark. A good snail and slug management program relies on a combination of methods. The first step is eliminate, all places where snails or slugs can hide during the day. Boards, stones, debris, weedy areas around tree trunks, leafy branches growing close to the ground, and dense ground covers such as ivy are ideal sheltering spots safe (Salagado, 1990). Synthetic molluscicides are still considered the most effective measures for the control of snails. Lufenuron is a new insecticide being effective against resistant pests to organophosphates and pyrthroides. It was soft on adult beneficial and predatory mites, safe on a wide range of crops and suitable for integrated pest management (Harder et al 1996). One of the most promising biological control approach that has received attention of many scientists is the development of Bacillus thuringiensis (Bt.) toxins as insecticides (Belfore et al 1994). Diple -2X is one of the biological insecticides containing proteins that are highly toxic to insects. Indoxacarb is the common name proposed for the S-isomer of oxadiazine derivative, which is insecticidal active isomer. This compound represents a new class of compounds has broadspectrum insecticidal activity and yet be environmentally safe (Salagado, 1990).
The present study was aimed to evaluate the efficacy of some safe pesticides such as indoxacarb, Bacillus thuringiengsis (Bt.) and lufenuron as molluscicides compared with methomyl under field conditions, and examined their effects on some biochemical parameters in the laboratory.

II-Biochemical Studies
The glassy clover snails Monacha cartusiana (Müller) were collected from clover fields in 2004/2005 season from Koom Hamada district and transferred to laboratories at Etay El-Broud Research Station, El-Behera governorate. The shell diameter of adult snails was measured at average 1.6 cm. They were acclimatized for a week under laboratory conditions and fed on lettuce (Lactuca sativa) ad lib. Toxic white bran baits were prepared containing each LC 50 or 0.5 LC 50 values of tested pesticides. The bait consisted of grain bran: molasses: blue dye with the ratio 8: 1: 1, respectively, (WHO, 1961). Baits were distributed in three replicates and 15 healthy animals were used in each replicate. In the case of control, pesticides were substituted with distilled water. Replicates were kept under laboratory conditions and suitable humidity required for snail activity. The dead animals were discarded, while the healthy adults were taken at different time intervals, i.e. 1, 3, 5, and 7 days of treatment. The soft tissues were weighed at average (0.86 gm), pooled, and homogenized as 1: 10 (w/v) in buffer phosphate (0.1 M) PH 7.0. The homogenate was centrifuged at 5000 rpm for 20 min under cooling. The supernatant was decanted and frozen at -20 °C until used as enzymes source. Activities of some enzymes were measured such as alanine aminotransferases (ALT), aspartate aminotransferases (AST) according to Retman and Frankel method (1957). Additionally, acetylcholiesterase (AChE) activity was measured according to Ellman et al (1961) and its specific activity was expressed as μmole substrate hydrolyzed/mg protein/min. Total protein was measured according to Lowry et al (1951).

Statistical Analysis
In filed treatments, analysis of variance was used to compare means among treatment. The least square means were compared for significant differences between treatments using student-New man-Keals test (Sokel and Rohlf, 1969). While, in biochemical studies all data were calculated as X  S.E. and comparison between two groups was performed by student t-test (Motulesky, 1987). Pvalue of 0.05 was considered significant.

Molluscicidal activities of tested insecticides
The Survey and observation of the studied area showed that, glassy clover snails Helix aspersa (Müller) is the common species snails on winter crops. The Concerning the amounts of consumed baits, it was found that, Bt. bait exhibited the highest consumption by snails (7.6 Kg /feddan). While, the low consumptions were 2.5, 4.0, and 5.5 Kg/feddan for methomyl, lufenuron, and indoxacarb, respectively. On the other hand, the periods required to achieve successful control of the snails were 5, 12, 14, and 28 days for methomyl , lufenuron, indoxacarb and Diple-2X, respectively.
Generally, lufenuron and indoxacarb showed high molluscicidal effect against clover snails, which considered an important pest on most field crops, under field conditions compared with methomyl, in addition to other positive properties of the compounds low toxicity to non-target organisms and short persistence in the environment (Salagado, 1990;Harder, et

al 1996 and Pluschkell et al 1998). Abou-El Khear et al (2005)
found the same results under laboratory conditions. These results agree with the findings by Hussien (2003) who indicated that, methomyl was more effective as mollusci-cidal compound using topical application and poisoned food techniques than indoxacarb. Abou-Baker (1997) illustrated that, the chemical control is the most powerful tool available for controlling snails. Zedan et al (1999) found that, bacterial formulation was the most effective against land snails compared with methomyl.

Toxicolgical activities of tested insecticides
Data on the Aspartate aminotransferases (AST), alanine aminotransferases (ALT), acetylcholinesteras activities and protein concentration in animals treated with 0.5 LC 50 and LC 50 of the tested pesticides at different time intervals are shown in Tables (2 and 3). AST activity was reduced by 85.4 and 80.6% (Diple-2X); 69.6 and 53.3% (indoxacarb); 79.8 and 72.6% (lufenuron) and 63.6 and 67.7%( methomyl) for animals treated with 0.5 LC 50 and LC 50 , respectively, after three days of treatment. Alanine aminotransferase was also significantly reduced compared with control animals. The inhibitory effects by 0.5 LC 50 and LC 50 for methomyl, lufenuron, indoxacarb, and Diple-2X on the AChE activity of snails are shown in Table (3). The results indicated that, the highest inhibitory effect against AChE enzyme activity of treated animals was occurred with LC 50 of methomyl. The specific activity of AChE was expressed as μmole/mg protein/min which accounted for 0.004, 0.004, 0.002, and 0.001 μmole/mg protein/min for Diple-2X, indoxacarb, lufenuron, and methomyl, respectively. Slight inhibition in AChE enzyme activity was done with lufenuron and Diple-2X treatments. In addition, the protein