Abstract: CAMB Bt. based and fungus based biopesticides, commercial Bt. formulation from mycogen and a new chemical pesticide Methoxyfenozide (RH2485-240SC) were tested on cauliflower field against cabbage butterfly (Pieris brassicae). All pesticides successfully controlled the population of cabbage butterfly in cauliflower crop. The efficacy against I to V instar larvae and field stability of CAMB Bt. biopesticide was better than chemical and other biopesticides. So, CAMB Bt. can be safely recommended for pest management strategies against Lepidopteral pests on vegetables with no harmful effects on its predators as in case with chemical pesticides.
Introduction
Cabbage butterfly (Pieris brassicae) is a serious and widespread pest of cauliflower, cabbage, turnip, nasturtium (Tropoeolum), rarely red cabbage, radish and Resadaceae (Guan-Soon and Yuan-Ba, 1990). The butterfly is active when the sun shines and the temperature is sufficiently high, otherwise, it remains under leaves or other shelters. The butterflies mate during their mass migration. They deposited eggs in clusters of 20 to 100 on the underside of the leaves of host plants. Eggs are elongated in shape, 1.5 mm high and 0.6 mm at their base, ribbed, yellow in colour and placed one besides the other (Subramanian, 1987; Hashmi, 1994). Embryonic development lasts 6 to 10 days. First instar larvae live in colonies, narrowly grouped one against the other. After the second moult, they scatter into groups of 4 to 5 individuals. Then they are extremely voracious and perforate the foliage. The large caterpillars made more damage to the leaves, often leaving only the large veins (Hashmi, 1994). In Pakistan, the control of Pieris brassicae on vegetables is usually carried out with the use of conventional chemical insecticides. The health hazard problems, associated with the use of such chemical pesticides on vegetables urged the need to generate opportunities for the development of alternative control tactics of vegetable pests. One control tactic is the use of biopesticides, which are safe and environmentally acceptable for controlling agronomically important pests (Dent, 1993; Karim and Riazuddin, 1997). Present findings are the continuation of our research and development work using CAMB biopesticides (Zafar et al., 2000; Karim et al., 2000; Rehman et al., 2002). The present study describes the evaluation of the field performance of CAMB biopesticides in comparison with imported commercial biopesticides and chemicals against Pieris brassicae.
Materials and Methods
Cauliflower field: The trial was conducted on cauliflower (variety Shahzadi) at National Center of Excellence in Molecular Biology, Lahore during February-April 2001. One-acre plot area was divided into four replicates with eight treatments per replicate, according to randomized complete block design (RCBD).
Pesticides: CAMB Bt. biopesticide developed by propagating local Bt. isolate in the pilot plant fermentors at CAMB Bt. Formulation lab (Zafar et al., 2001; Zafar et al., 2003), CAMB-fungal biopesticide, however, was prepared by CAMB-fungus lab by propagating Metarhizium anisopliae. Imported Bt. biopesticide from Mycogen and chemical pesticide RH-2485-240SC (Methoxyfenozide) (a new chemistry from FMC united (Pvt.) Ltd.) were run in parallel to determine the performance evaluation of chemical and biopesticides in the field.
Treatments: Timing of biopesticide application and larval behaviour are very important for the effective control of target pests (Ghidiu and Zehnder, 1993). For best results, it was recommended to apply biopesticide treatments in the evening hours (Karim et al., 1999). For each treatment separate backpack hand sprayers were used and treatments were applied one hour before sunset.
| T1 | = | CAMB Bt. (biopesticide) | @250 g/100 L /Acre |
| T2 | = | CAMB fungus (biopesticide) | @250 g/100 L /Acre |
| T3 | = | CAMB Bt. + CAMB Fungus (biopesticide) | @ 250 g+250 g / 100 L / Acre |
| T4 | = | RH-2485-240SC (chemical) | @ 100 ml/100 L / Acre |
| T5 | = | RH-2485-240SC (chemical) | @200 ml/100 / Acre |
| T6 | = | Lepinox (biopesticide) | @740 g/100 L / Acre |
| T7 | = | Lepinox (biopesticide) | @1480 g/100 L / Acre |
| T8 | = | Control |
Pests scouting: To evaluate the comparative effect of biopesticides and chemical pesticide, number of eggs and pest scouting were performed 24 h pre and 24 h post spray. Post spray pest scouting were also performed on 3rd and 7th day. For number of eggs and pest scouting, four plants/replicate, i.e., 16 plants from each treatment were randomly selected. Data was analyzed through t-test with the least significant difference at 5%.
Results
During the study in February to April 2001, the weather was often cool and dry with high temperature ranging from 20-32°C and low temperature ranging from 6-14°C. No rainfall occurred during the spray applications. Average number of eggs was decreased at 3 days post spray; however, no eggs were observed at 7 days after the application (Table 1). A decrease of I, II and III instar larvae population were observed in all treatments except in control at 3 days post spray (Table 2), where as, in case of IV and V instar larvae, a significant decrease in comparison with the control was observed at 24 h post spray (Table 3).
On 3 days post spray, the mortality percentage of I, II and III instar larvae of treatments T1, T2, T3, T4, T5, T6, T7, and T8 were 91.9, 95.2, 90.6 80.5, 80.3, 94.6, 98.7 and 0.0% respectively (Fig. 1), whereas on 7 days post spray the mortality percentage of I, II and III instar larvae, of T1, T2, T3, T4, T5, T6, T7 and T8 were 97.7, 93.7, 91.1, 95.8, 92.0 50.9, 79.6 and 0.0% respectively (Fig. 1). There was 100% mortality of IV and V instar larvae on 3 days post spray, in all treatments except T3 and T8, which were 70.0 and 0.0% respectively (Fig. 2). On 7 days post spray, however, mortality of IV and V instar larvae were 100% in all treatments except T2 and T8, i.e., 70.2 and 0.0% respectively (Fig. 2).
| Fig. 1: | Mortality of I, II and III instar larvae of Pieris brassicae |
| Fig. 1: | Mortality of IV and V instar larvae of Pieris brassicae |
| Table 1: | Average number of eggs/plant |
| Table 2: | Average number of I, II and III instar larvae/plant |
| Table 3: | Average number of IV and V instar larvae/plant |
Figures followed by the same letters are not significantly different from each other according to LSD at 5% level of significance. | |
Discussion
The negative after effects of the use of chemical insecticides have been pronounced. A microbial pesticide offers a potential complementary alternative to chemical insecticides (Dent, 1993). In this study, we evaluated the performance of local CAMB Bt. biopesticide (Zafar et al., 2001) and CAMB fungus biopesticide against Pieris brassicae with the comparison of imported chemical insecticide and imported Bt. based biopesticide. All pesticides have a dose response that is sensitive to the body weight of the pest, whereas for biopesticides, Bt. is particularly sensitive to the effect of larval size on mortality (Savin et al., 1982).
In a pest population that is developing synchronously, careful eggs and larval scouting can help for the time of application. Pest population with staggered hatch has large and small larvae present at the same time. Twenty four hours after application, the eggs population of Pieris brassicae was found to be higher than twenty four hours before application (Table 1). It may be due to the fresh egg laying by adult moths because biopesticides have no direct effect on adult moths. Three days after application the egg population was low due to hatching of larvae from eggs and 7 days after application, there was no fresh egg laying, which was due to the effective control of larvae in the field by the application of pesticides. Potter et al. (1982) reported that Bt. was capable of reducing pest populations under field conditions.
Three days post spray, biopesticides showed high mortality of I, II and III instar larvae (Fig. 1). Bartels and Hutchison (1995) reported the high mortality of lepidopteron neonates when Bt. was applied before neonates hatch. Activity of CAMB Bt. (T1) persisted up to seven days post spray, whereas rate of mortality decreased in imported Bt. (T6 and T7) at seven days post spray (Fig. 1). This indicates that CAMB Bt. pesticide has longer stability as compared with imported biopesticide. Karim et al. (1999) has shown the effective control of Helicoverpa armigera by applying CAMB Bt. preparation in potato field. Yaman and Demirbag (2000) control the population of large butterfly larvae by employing bacterial biopesticide. Different Bt. isolates can have a large variation in their biological activity against same species of pests and a given isolate may be very active against one species and inactive against others (Jarrett and Burges, 1982). High diversity of Bt. isolates is due to the presence of multiple cry genes encoding a variety of different protoxins (Jarrett, 1985). Possible explaination of the effective performance of CAMB Bt. pesticide could be that the indigenous isolate have different expression levels of cry toxin proteins in their crystal complex as in the imported Bt. isolate. Another reason of low activity of imported Bt. pesticide may be the constituents of formulation, which may not be more stable in our environmental conditions and required high dose for pest mortality. The effective performance of indigenous isolate of CAMB Bt. pesticide over the other commercial formulations has already been reported (Karim et al., 1999; Karim et al., 2000; Zafar et al., 2000).
Hundred percent mortality of IV and V instar larvae was observed in all treatments except control and CAMB fungus pesticides T2 and T3 on 7 and 3 days post spray respectively (Fig. 2). Unlike Bt. toxins, which infect orally, fungi generally infect insects by penetrating directly through the body wall or through spiracle openings. The development of fungal infections in pests is influenced by environmental conditions. High humidity and optimum growth temperature is vital for the germination of fungal spores and transmission of pathogen from one insect to another (MaGuire, 1993). It was observed that the activity of CAMB Bt. pesticide was decreased with the combination of fungus pesticide (T3) (Figs. 1 and 2). Other commercial companies like Zagro was also not recommended to mix their bioproduct “Larvo Bt.” with any fungus pesticides (Larvo, 2001). CAMB Bt. biopesticide (T1) showed high performance to effectively control all larval stages of Pieris brassicae (Tables 2, 3) by employing one standard dose of indigenous Bt. formulation @ 250 g/100L spray whereas high dose (T7) is required for imported Bt. formulation for the mortality of I, II and III instar larvae (Fig. 1). For I, II and III instar larvae, CAMB Bt. (T1) showed better results against low and high doses of chemical pesticides (T4 and T5) (Fig. 1). This indicates that the level of indigenous Bt. toxin in CAMB formulation is highly effective to control small instar as well as large instar larvae of cabbage butterfly.
Our previous (Karim et al., 1999; Zafar et al., 2000; Karim et al., 2000) and recent studies demonstrated that using Bt. biopesticides could greatly reduce the indiscriminate use of chemical pesticides on vegetables. Bt. based products can provide environmentally safe alternative to many global pest control problems.
Acknowledgment
We thank Dr. M. A. Qadeer for his critical comments. Mr. Sajjad Haider and Mr. Rana M. Zahid for their technical assistance. Pakistan Science Foundation supported research work under the project P-CEMB/IND-21.