EFFECT OF PESTICIDES ON THE DEVELOPMENT OF BOMBYXMORI

Transcription

1 CHAPTER - 6 EFFECT OF PESTICIDES ON THE DEVELOPMENT OF BOMBYXMORI 6.1 INTRODUCTION: Mulberry (Morus spp) is infested by several pests. These pests affect the growth of mulberry and cause considerable damage to the plant and loss in the yield. The insecticides applied for the control of mulberry pests have greater impact on silkworm. Pesticides leave residues in mulberry leaves which inturn affect the sensitive silk worm. To overcome this problem, safe waiting period should be followed for leaf harvest (Yokayama, 1962). Field observations in India have indicated loss of yield of cocoons from silk worms fed on mulberry leaves harvested from farms that were sprayed with insecticides (Narasimhanna, 1988). Exposure to the residue of insecticides in the mulberry leaves could affect growth, reproduction, the quality of economic characteristics of cocoons, eclosion and fecundity (Bhosale et. al., 1988). Perusal of literature in this aspect reveals that the loss of body weight was noticed in eri silk worm, Philosomia ricini when exposed to Malathion (Pant and Katiyar, (1983), Venkata Reddy et. al., (1989) have reported growth changes in terms of body weight of silk worm when exposed to carbaryl. Further Surendranath (1993) experiments with lethal and sub-lethal concentrations of organophosphorous pesticides had indicated a significant reduction in larval weight in pure Mysore and NB 18 races. 50

2 Subacute exposure to pesticides is reported to affect the reproduction (Kuribayashi, 1981, 1982; Yamonoi, 1981). Watanabe (1966) revealed that silk worms were more sensitive to chemical treatment just after moult and gained resistance there after.pesticide residues were also thought to be transmitted to the silk worm eggs, embryos and pupae affectd later generation (Watanabe and Takano, 1966 a, b; Kuwanna et. al., 1968; Gamo and Hirobe, 1977; Kuribayashi 1980, 1981; Yamonoi 1980, 1981, 1984). Along with chemical pesticides neem based insecticides are known to possess several adverse biological effects on insects like repellency, antifeedancy, growth and regulatory activity, antifecundity and prothoracicotropic hormone inhibitory activity (Schmutterer, 1990; Medina et. al., 2004). All the neem based insecticides had caused prolongation of nymphal period, ecdysial status and development of adultoids and imagoes with varied degree of deformities. (Tiwari et. al., 2006) All the insecticides initiated dose dependent changes, resulting in delayed metamorphosis with abnormal wing development no moulting and finally death with in hrs after treatment (Kodandaram et. al., 2008). The neem based pesticides were highly detrimental to first, second and third instar larvae of Bombyxmori causing complete mortality and most of the larvae died with out moulting (Jothi et. al., 1999). Growth and development of neonate larvae of Spilosoma oblique larvae on different dietary concentrations of Azadirachtin showed that performance of growth parameters decreased with increase of concentration. (Mandel and Bhattacharya, 2005). Toxicity of cartaphydrochloride, diflubenzuron and lufenuron were detrimental to the growth and development of Bombyxmori worms at the lowest concentration of 0.1 ppm leading to significantly higher mortality. (Abhay Kumar Singh, et. al., 2008) 51

3 The feeding behaviour of phytophagous insects may change when it feeds on insecticide treated plant as well as when it got exposed to sub lethal dose of insecticides. Alterations in feeding leading to changes in conversion of both ingested and digested food into their body matter which may eventually cause changes in their further development, metamorphosis and also fecundity of resultant adults (Sreenivasa Rao & Rao 2003). The larval and pupal critical weight which is an important factor for metamorphosis may be affected by the insecticide treatment. (Nagapasupathy, 2005). Lepidoptera were among the organisms most sensitive to neem extracts (Schmutterer & Singh, 1966). Sublethal concentrations of Azadirachtin incorporated into artificial diet and offered to third instar larvae of Spodoptera littoralis prolonged larval instars and reduced food intake. (Carvalho, 1996). These effects were observed after the treated larvae had been transferred to plain diet. The larval food intake was reduced due to secondary antifeedent effect. Azadirachtin did not influence digestion efficiency but diminished the ability of the larvae to convert both ingested and digested nutrients into growth, particularly immediately after treatment. Growth was more severely reduced than food intake, and the reduction in growth also occurred during period when food intake was not affected, possibly due to post ingestive effect. (Martinez and VanEmden, 1999). Food intake by larvae, as well as the quality of food ingested, affects growth rate, development time, final body weight and survival (Slansky & Scriber, 1985). Azadirachtin affect food intake by exerting strong antifeedant effects against a wide range of insect species (Warthen, 1989; Mordue (Luntz) & Black well, 1993), 52

4 including S.littoralis (Meisner et. al., 1981 a, b; E1-Sayed, 1982; Simonds & Blaney; 1984; Ley et. al., 1989; Blaney et. al., 1990). Since Dichlorovos is widely used against a variety of agricultural pests, particularly mulberry pests which may attack silkmoth through their feeding on pesticide sprayed leaves during development. Neem pesticide also caused more than 80% larval mortality in many insects. Hence in the present investigation an attempt has been made to study the effect of Vijay neem and Dichlorovos on the development of mulberry silk worm, Bombyx mori.l. 6.2 MATERIAL AND METHODS: Eggs of the silk worm breed LXCSR2 were procured from Government sericulture grainage at Tenkasi, Tamilnadu and were raised up to 3 rd instar in a rearing house. Controlled temperature ( C) and humidity (75-80%) were maintained and appropriate measures were taken to prevent parasitization by uzifly. The silkworms were fed with mulberry leaves and standard rearing practices were followed (Krishnaswami, 1971). (Rearing procedure was followed as mentioned in the chapter4). Two pesticides (Dichlorovos, Vijay neem) were used for this experiment. III instars (soon after the second ecdysis) of uniform size from a pooled batch were divided into eleven groups of 100 larvae each. Sublethal concentrations of Dichlorovos (0.0001, , , and %) and Vijay neem (0.001, 0.002, 0.003, and 0.005%) were given to the III instar larvae by feeding with pesticide sprayed leaves one time on the first day. Larvae were transferred to rearing tray containing fresh mulberry leaves. 53

5 Simultaneously control was also maintained. Surviving larvae were kept for pupation and observations on various parameters like larval weight, pupal weight, larval duration, and larval, pupal and adult abnormalities were recorded. The recorded data were subjected to analysis to determine the significant difference between the various parameters of the treated and untreated insects. 6.3 RESULTS AND DISCUSSION: Silkworm larvae fed with pesticide treated foliage resulted in persistent growth inhibition at different levels during metamorphosis. The silkworm larvae fed with pesticides treated foliage caused growth disruption in pupal and adult morphogenesis in a dose dependent manner. When compared to Dichlorovos, Vijay neem showed much morphogenetic inhibition effect (Table 7.1). The present findings showed that pesticide is effective in inhibiting larval growth and inducing pupal and adult deformities in silk worm (Table 7.1). Such growth inhibitory effect of pesticide ranging from delay in moulting with the production of deformed insects, to the complete inhibition of growth at high doses had been reported in various insect species. (Schmutterer, 1990). Dose dependent inhibition of larval growth and morphogenesis in silkworm Bombyx mori could be accounted due to reduced physiological change brought about by reduced food intake and weight gains as reported in Heliothis virescens (Barnby and Klocke, 1989, Joseph, 2000). The present study revealed that 4.04% of larval mortality was due to % concentration of Dichlorovos. The mortality rate was 24.24% at a concentration of %. Similarly a reduction was noticed in the number of moths emerged. 54

6 Reduction was also found to be dose dependent. Moths emergence percentage was reduced to 4.34 at a concentration of % Dichlorovos and 36.46% at a concentration of % Dichlorovos. In the neem pesticide sprayed leaves fed larvae the mortality rate was 9.09% for a concentration of 0.001% and 35.35% for a concentration of Similarly a dose dependent reduction was noticed in the moth emergence. Moth s emergence rate was reduced to 11.45% for a concentration of 0.001% and a reduction of 57.29% was noticed for a concentration of 0.005%. From the present study it was found out that among the two pesticides, neem pesticide has a more lethal effect than Dichlorovos (Table 6.1). The two pesticides had an impact on the development of normal pupae also. The reduction in the development was found to be dose dependent. The development rate was reduced to 4.25% for a concentration of % Dichlorovos and 28.57% for a concentration of % Dichlorovos. The development of normal pupae was more affected in the case of larvae fed with neem sprayed leaves. A maximum of 42.85% reduction in the development rate was noticed for a concentration of neem pesticide (Table 6.1). EFFECT OF PESTICIDES ON LARVAL WEIGHT OF SILK WORM BOMBYX MORI In the present study the larval weight of silk worm Bombyx mori fed with Dichlorovos and Vijay neem sprayed leaves were recorded. It was found out that there was change in the body weight due to the consumption of pesticide sprayed leaves. After the treatment in sublethal dose, the body weight had decreased gradually from third to fifth instars. The mean weight of third instars in the control worm was 55

7 1.37±0.12 g where as it was reduced to 1.19 ± 0.01 g at higher concentration of Dichlorovos (0.0005% concentration) and 1.30 ± 0.09 g at lower concentration of Vijay neem (0.001% concentration). Vijay neem had affected the silk worm (third instar) weight in a higher percentage than Dichlorovos. i.e percentage changeover control due to the application of 0.001% Vijay neem was 27% whereas it was 13.14% in the case of larvae fed with % concentration of Dichlorovos sprayed leaves (Table 6.2). The mean weight of IV instar in the control was 5.17 ± 0.16 g where as it was reduced to 4.89 ± 0.14 g due to Dichlorovos and 3.50 ± 0.34 g due to neem at higher concentrations. The percentage change over control was 32.30% due to Vijay neem and 5.49% due to Dichlorovos at higher concentrations. The mean weight of V instar at first and fourth and sixth day was found out. The weight was maximum in control and it was reduced to 13.35%, 33.19% and 13.30% due to higher concentration of Vijay neem in first day and fourth day and sixth day of fifth instars and it was 7.43%, 25.53% and 13.12% due to higher concentration of Dichlorovos in first, third and sixth day of fifth instars (Table 6.2). The ANOVA showed significant changes in larval weight of Bombyx mori in response to concentration of pesticides. The F value between pesticide is 2.16 and between larvae is (Table 6.2). It is seen that the larval weights reduced progressively as the concentration of pesticide is increased. It is obvious that the quality of mulberry leaves has predominating influence on the development of the worms. This contension is supported by the literature on the influence of quality of mulberry leaves on the growth and development of silk worm, (Ito and Arai 1963; Radha et. al., 1978; Pillai and Jolly, 1985) It is therefore concluded that feeding of larvae with pesticides treated leaves had a negative response 56

8 on silk worm in respect of growth. The impact of pesticide was greater at the beginning of larval stage (Table 6.2). EFFECT OF PESTICIDE ON SILK WORM LARVAL DURATION : A significant increase in larval duration was observed at different dietary concentrations of pesticides (Dichlorovos and Vijay neem) as compared to control diet. Larval period was also extended with increase in concentration of pesticides in the feed. Larval period from control 19.10± 0.52days was extended to ± 0.86days due to Dichlorovos at higher concentration0.0005% and ± 0.65days due to Vijay neem at higher concentration 0.005%. (Table 6.3). A similar condition was noticed in the development of pupae also. The pupal period of control larvae (10.28±0.64days) was extended to 11.34±0.70days and 13.42±0.78days at higher concentrations of Dichlorovos and Vijay neem respectively. The total development period of control worms was days whereas it was days in the case of larvae fed with Dichlorovos at a concentration of % sprayed leaves and days in the case of larvae fed with neem at a concentration of 0.005% sprayed leaves, Among the two pesticides Vijay neem had a more negative effect on the development of silk worm larvae (Table 6.1, Fig 6.1 to 6.4). ANOVA showed significant changes in larval and pupal period of Bombyx mori in response to concentration of pesticides. The F value between pesticides is and between larvae is (Table 6.3). 57

9 Table: 6.1 EFFECT OF PESTICIDES ON METAMORPHOSIS OF SILKWORM BOMBYX MORI (% change over control given in parenthesis) Pesticide Concentration Surviving larvae (at 5 th day) Normal pupae Larval Pupal intermediates No. of emerged moths Deformed moth Control Dichlorovos Vijay neem (4.04) 90 (6.06) 81 (18.18) 78 (21.2) 75 (24.24) 90 (9.09) 86 (13.13) 77 (22.22) 70 (29.29) 64 (35.35) 94 (4.25) 83 (15.30) 79 (19.38) 73 (25.51) 70 (28.57) 87 (11.22) 83 (15.30) 73 (25.51) 61 (37.75) 56 (42.85) (4.34) 84 (12.5) 73 (23.95) 67 (30.21) 61 (36.46) 85 (11.45) 75 (19.79) 65 (32.29) 48 (50) 41 (57.29)

10 Pesticide Table: 6.2 EFFECT OF PESTICIDES ON LARVAL WEIGHT OF -SILKWORM BOMBYX MORI Concentration of pesticide (%) Mean weight of III instar larvae % change over control (Values per 10 larvae in gram) Mean weight of IV instar larvae % change over control Larval weight Mean Weight of V instar larvae I day % change over control Mean Weight of V instar larvae IV day % change over control Mean Weight of V instar larvae VI day Control ± ± ± ± ± DICHLOROVOS ± ± ± ± ± % change over control ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Vijay neem ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

11 ANOVA III larvae IV larvae V larvae Control DICHLOROVOS VIJAY NEEM Source of Sum of Mean F-value Variance Squares df Squares Calculated Table Result Rows (Between Pesticides) Column (Between Larvaes) N.S Sig. Residual (Error) Total F-table value with df (2,4) at 0.05 level is 6.94 F-table value with df (2,4) at 0.01 level is

12 Pesticide Table: 6.3 EFFECT OF PESTICIDE ON LARVAL AND PUPAL PERIOD OF Concentra tion of pesticide (%) SILKWORM BOMBYX MORI (Mean ± SD) (n=100) Larval Period (days) % Change over control Pupal Period (days) % Change over control Total Developm ental period (days) Control ± ± Larval Pupal index DICHLO ROVOS ±0.25 (-0.15) 10.49±0.29 (-2.04) ±0.36 (-4.65) 10.58±0.16 (-2.91) ±0.47 (-5.34) 10.94±0.80 (-6.42) ±0.56 (-5.96) 11.26±0.53 (-9.53) ±0.86 (-6.70) 11.34±0. 70 (-10.31) VIJAY NEEM ±0.68 (-2.11) 10.94±0.72 (-6.42) ±0.57 (-4.18) 11.90±0.66 (-15.75) ±0.66 (-8.06) 12.12±0.16 (-17.89) ±0.40 (-11.67) 12.98±0.73 (-26.26) ±0.65 (-15.91) 13.44±0.78 (-35.60)

13 ANOVA Larval Period Pupal Period Control DICHLOROVOS VIJAY NEEM III larvae IV larvae Control DICHLOROVOS VIJAY NEEM Source of Sum of Mean F-value Variance Squares df Squares Calculated Table Result Rows (Between Pesticides) N.S. Column (Between Periods) Sig. Residual (Error) Total F-table value with df (2,2) at 0.05 level is F-table value with df (1,2) at 0.05 level is F-table value with df (2,2) at 0.01 level is F-table value with df (1,2) at 0.01 level is

14 The present findings demonstrate that the pesticides have the potency to interrupt development and metamorphosis of Bombyx mori and thereby produce striking disorders in the external morphology. The different categories of resultant forms, developed after the consumption of pesticides sprayed leaves were, Abnormal larvae : (larval imaginal intermediates) (Antennae, labrum, maxillae and labial palps incompletely differentialed into imaginal organs preserving many larval features) Abnormal Adults : (Deformed moths) Wings twisted or curly, short, less pigmentation, mouth parts attained imaginal status but were defective.(fig 6.3.1) Unlike the abnormal adult the normal adults are with larvae expanded wings and functional mouth parts. (Fig 6.3.2) Defective pupae: Externally normal pupae but inside adultoids. Larvae began to lose weight on the 2 nd day of III instar, larvae gradually began to shrink and became smaller in size. Some of the larvae failed to spin cocoons and many larvae died on the mountages during spinning. Larvae built normal cocoons but did not pupate, built thin shelled cocoons with out pupation, larval death in side the cocoons and pupal death inside the cocoons were observed. Regarding Eclosion, pupae inside the cocoons did not develop into adult moths, but pupae became smaller in size and died. Moths were deformed and died before emergence and some moths died after emergence. 63

15 Emerged adults found to be difficult to copulate and the paired moths decouple often. They laid more sterile eggs than fertilized eggs, Irregular hatching of larvae occurred. The present finding was in acceptance with earlier findings.earlier studies have shown that the silk worm is sensitive to various insecticides (Kuwana et. al., 1967; Kashi 1972; Naseema Begum and Shivanandappa, 1996 a,b) Some earlier studies have also shown that pesticide residues affect growth, reproduction and development (Yamonoi, 1980, 1981, 1984; Kuribayashi 1981, 1982) In the present study, pesticides caused a lower percentage of pupation and adult emergence in treated insects in conjunction with increased pupal and adult abnormalities. This was in acceptance with the findings of Nagapasupathy et. al., (2005) on thiocarb treated larvae of Spodotera litura and Sreenivas Rao and Rao (2003) on chorphriphos and cypermethrin treated larvae. Neem based insecticides disrupt endocrine function and give chemical stress. (Tiwari et. al., 2006). The neem based insecticides caused physiological disturbances leading to the developmental abnormalities like prolongation of nymphal stage, ecdysial stasis, adultoid and deformed nymphs and adults. All these could be due to disturbance in the endocrine functions of treated insects (Schmutterer, 1990) Higher concentrations of azadirachtin could cause moulting disruption in Spodoptera littoralis (Carvalho, 1996). According to him interference of hormonal system could be the reason for moulting disruption. Azadirachtin in neem pesticide act as antifeedent growth regulator and sterilants in insects (Schmutterer, 1988) Juvenile hormone analogue treatment in Philosomia ricini Hutt indicated a number of morphological abnormalities such as pupal death with out metamorphosis, larvae failed to spin cocoons, naked pupae, thin cocoons, pupae retained larval characters, moth failed to fold their wings and 64

16 malformed wings. The treated larvae also excreted a large amount of watery fluid continuously for about 10 days, some larvae failed to pupate, survived for 24 days as larvae or pre pupae and then died (Aswathi, 1985). Foliar application of neem oil cause disturbance in the moulting process and extension of nymphal period (Heyde et. al., 1984), in the egg laying process (Coudriet et. al., 1985) Larval feeding of NSKE treated foliage resulted in persistent feeding deterrence and growth inhibition at different levels during metamorphosis. The results are consistent with the earlier reports on various lepidopterous species. (Fagoonee, 1984; Singh, 1993; Sahayaraj, 1998, Joseph, 2000). During incubation of the eggs, embryos died in the blue eye stage suggesting embryonic toxicity. The larvae that hatched from the eggs also died immediately after hatching. Similar observations had already been made (Kuribayashi, 1981, Naseema Begum 2003) Disruption of the silk worm reproduction and development due to insecticides, suggest altered hormonal status.generally Organophosphorous insecticides are known to alter juvenile hormone levels by inhibiting the enzyme, JH esterase (Monconduit and Mauchamp, 1999) Organochlorides, on the other hand, are neurotoxic compounds that may affect the neuroendocrine secretions which led to perturbations in regulation of hormone secretions (Dedos and Fugo, 1996). The changes in total body weight of III, IV & V instars larvae of B.mori treated with sublethal doses of demecron were reported to be inversely related to the doses of dimecron (Sivakumar, 1993). After the treatment of sublethal doses, the body weight was decreased gradually in III, IV and V instars.disruption of the silk worm development due to insecticides, suggests an altered hormonal status. Organophosphorous and carbamate insecticides are known to alter juvenile hormone levels by inhibiting the enzyme, JH esterase Monconduit and Mauchamp,