Bioefficacy of New Ready Mixed Insecticide Novaluron 5.25% + Emamctin 0.9% SC against Diamond Back Moth ( Plutella xylostella L . ) in Cabbage in West Bengal

Field experiments were conducted during the rabi season of 2012 and 2013 in experimental plots of Bidhan Chandra Krishi Viswavidyalaya, West Bengal to evaluate the efficacy of ready mixed insecticide Novaluron 5.25% + Emamectin 0.9% SC @ 750, 825 and 875 ml ha -1 against Plutella xylostella in cabbage. Efficacy of different treatment schedules of novaluron 5.25% + emamectin 0.9% SC against DBM showed that all the treated plots with chemicals were significantly superior in their performance over that of control plots during both the year. Novaluron 5.25% + emamectin 0.9% SC @ 825 and 875 ml ha -1 gave superlative control of diamond back moth larvae up to harvesting period than the other insecticidal treatments. Novaluron 5.25% + emamectin 0.9% SC @ 875 ml ha -1 gave 100 per cent control from 5 th day after second spray during both experimental year. The maximum yield was obtained from the plots treated with novaluron 5.25% + emamectin 0.9% SC @ 875 ml ha -1 closely followed by @ 825 ml ha -1 .

Cabbage (Brassica oleracea var. capitata L.) the widely cultivated popular crucifer vegetable crop in many countries, including India. Cabbage occupies 5.4 per cent share in whole vegetable production with an area of 369 thousand ha and a production of 7949 thousand metric tons with an average productivity of 21.5 metric tons ha-1 during 2010-11 in India and West Bengal is the largest producer of cabbage with 27 per cent share in national cabbage production (Indian Horticulture Database, 2011) . It is grown during rabi season in different parts of West Bengal. In India wide numbers of insect pests have been reported to infest cabbage. Srivastava and Butani (1998) reported four major and 31 minor insects pests of crucifers. Diamond back moth, Plutella xylostella (L.) (Plutellidae:Lepidoptera) is the most destructive insect pest of cruciferous plants throughout the world and the annual cost for managing it is estimated to be US $ 1 billion (Talekar and Shelton, 1993). Among cruciferous crops cauliflower and cabbage are the most preferred hosts for DBM (Uthamasamy et al., 2011). This notorious pest has developed resistance to almost all the recommended insecticides belonging to major groups in many parts of the world (Talekar and Shelton, 1993) and becoming increasingly difficult to control. In India, resistance to different insecticides was reported from several states like Punjab, Haryana, Tamilnadu, Karnataka and Andhra Pradesh (Mehrotra and Phokela, 2000). The problem *Corresponding author email : abhijishu@gmail.com is acute in areas where vegetables are grown extensively throughout the year (Joia et al., 2005). Control of this pest with any single potent toxicant for a long time is quite difficult and rather impossible. The present investigation was, therefore, oriented to find out the bio-efficacy of novaluron 5.25% + emamectin 0.9% SC in controlling the DBM of cabbage in field condition.

Materials and Methods
Field experiment was conducted to evaluate the efficacy of novaluron 5.25% + emamectin 0.9% SC against DBM in cabbage and to study the adverse effect, if any, of the chemical on important larval and pupal parasitoid found in association with cabbage at University Instructional Farm of Bidhan Chandra Krishi Viswavidyalaya, West Bengal during the year 2012 and 2013. Healthy seedlings of cabbage (var. Green Express) were transplanted in 20 m2 plot during September at 30 cm x 30 cm spacing with recommended fertilizer dose. The whole experiment was laid out in randomized block design with seven treatments; replicated thrice along with control. Three sprays at 10 days interval were given when pest population reached ETL level (in general one larvae plant-1, Jayaratnam, 1977 reported that four or more medium sized larvae (3rd or 4th instar) could render a seedling un-transplantable and ten larvae per plant up to one month and twenty larvae per plant between one and two months after planting necessited insecticide application) with knapsack sprayer at high volume @ 500 l ha-1. Observation was recorded on before spray as well as 1, 5 and 10 days after each spray from ten randomly selected plants. To observe the effect of the insecticides used on natural enemies; ten plants were selected randomly and two leaves were again chosen at random from each of the ten plants. Each leaf was examined on 7th day after each spraying to collect pupal stages of DBM. These were kept in a growth chamber (280C ± 100C and 80% R.H.) to follow the course of development. The emergence hold and the presence of parasitoids in the glass chamber were used as an index of parasitisation. The DBM larvae were also collected from the leaves to note the rate of larval parasitisation. The data were presented in percentage and were subjected to analysis of variance after making necessary transformation.
To observe the phytotoxic effect of the used insecticides on cabbage, if any; observations on 1, 3, 7 and 10 days after spraying were recorded from five leaves per plant each from ten pre selected plants per plot regarding leaf injury on tips and leaf surface, wilting, necrosis, vein clearing, epinasty etc. and the following scale was used to assessing phytotoxicity as per the protocol of Central Insecticidal Board Registration Committee (C.I.B and R.C).

Crop response/crop injury Grade
No Phytotoxicity 0 Phytotoxicity ratings were recorded based on the following visual scale. The per cent leaf injury was calculated using the formula,

Per cent = Total grade points leaf injury
Max. grade x no. of leaf x 100 observed
Novaluron 5.25% + emamectin 0.9% SC is recently developed ready mixed formulated insecticide having two different mode of action and they are important insecticides having excellent action on insects with abnormal symptoms such as deformed moulting with feeding cessation and caused a gradual contraction of the insect body thickening and shortening without convulsions and the symptoms were obviously different from those of conventional insecticides. As this is newly developed insecticide and not yet launched therefore the effect of novaluron and emamectin benzoate against DBM may be correlated with the present findings. Harish et al . (2003) reported 90 per cent larval mortality. High efficacy of novaluron against the pest in our experiment is also in conformity with Wavare et al . (2008). Kumar and Devappa (2006) reported that emamectin benzoate was very effective on suppressing the larval population of the pest and increased yield of cabbage. This above report made by different worker give the conformity of the effect of this ready mixed insecticide novaluron5.25% + emamectin 0.9% SC against DBM.

Effect on some important parasitoids of DBM
The identities of larval and pupal parasitoids were established as Cotesia (Apanteles) plutellae and Brachymeria sp., respectively. The pooled data on adverse effect on novaluron 5.25% + emamectin 0.9% SC against two important parasitoids namely Apanteles plutellae and Brachymeria spp. of DBM has been presented in Table 4 which shows non significant effect among the different treatments. It may conclude that novaluron 5.25% + emamectin 0.9% SC had practically no adverse effect on the two parasitoids. At the highest dose of the product i.e. 875 ml ha-1, 20.67% in larval parasitisation and 2.33% in case of pupal parasitisation was recorded. While 21.33 % larval parasitisation and 3.00% pupal parasitisation was recorded in untreated check. Similar result was recorded in next year also. Our result is in line with the findings of Nandihalli (2009). Sontakke et al. (2007 reported that emamectin have no phytotoxic effect on plants and no harmful effect on natural enemies. Dhanalakshmi and Mallapur (2008) reported that emamectin was safe as the untreated control to natural enemies (coccinellid larvae, spiders and Chrysoperla larvae). Chitin synthesis inhibitor lufenuron has no adverse effect on Cotesia plutellae (Senguttuvan and Kuttalam, 2013), which can be correlated with this present findings as novaluron also a chitin synthesis inhibitor. Safety of emamectin benzoate is in line with Suganyakanna et al. (2005), who reported its safety to natural enemies.

Phytotoxic effects
The observations (1, 3, 7 and 10 days after spraying) clearly indicated that there was no phytotoxicity symptoms like leaf injury, wilting, epinasty and hyponasty, necrosis and vein clearing etc., were observed in all the three doses of novaluron5.25% + emamectin 0.9% SC @ 875, 1750 and 3500 ml/ha. Therefore, it may be considered as safe to cabbage. Clarke and Fleischer (2003) reported that the lepidopteran pests of vegetables needed safer insecticides like emamectin benzoate with least phytotoxic effects with efficient control of the insect pests, which supports our experimental result. Senguttuvan and Kuttalam (2013) reported that chitin synthesis inhibitor have no phytotoxic effect on cabbage.

Conclusion
It is evident from the present investigation that novaluron5.25% + emamectin 0.9% SC was effective against DBM of cabbage @ 825 to 875 ml ha-1 and very safe to two most important parasitoids of diamond back moth infesting cabbage in West Bengal.