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Bioefficacy of Bifenthrin as a Prophylactic Against Four Major Stored Grain Pests

Y. Siva sankara reddy and S.V.S. Gopala Swamy
I T for Agriculture, Division of Entomology,
International Institute of Information Technology,
Hyderabad, India - 500 032

ABSTRACT Prophylactic spraying of storage surfaces with insecticides is the most safe and efficient method to protect grain. The studies were conducted to know the efficacy of bifenthrin when used for disinfecting ware houses and jute sacks against four different stored grain pests i.e., Sitophilus oryzae, Tribolium castaneum, Trogoderma granarium, and Rhizopertha dominica at Indian Grain Storage Management and Research Institute, Hyderabad during 2004. The toxicology studies under laboratory conditions revealed that the LD50 values of bifenthrin against S. oryzae, T. castaneum, T. granarium and R. dominica were 3.389, 46.65, 4.509 and 5.573 respectively when treated on concrete slabs and 4.629, 48.0, 5.056 and 6.042 respectively when treated on jute strips. The investigations revealed that bifenthrin when used for prophylactic control is effective only against S. oryzae, T. granarium and R. dominica but not against T. castaneum.

KEYWORDS Bifenthrin, bioefficacy, stored grain pests.

INTRODUCTION Insects cause considerable losses both in quality and quantity of stored food grains. For controlling these storage pests, malathion, DDVP, pirimiphosmethyl, chlorpyriphos methyl, fenitrothion, alluminium phosphide, bioresmethrin, fenvalarate, deltamethrin, ethylene dibromide, methoprene etc are being employed as prophylactic and curative measures. However, prophylactic spraying of storage surfaces with insecticides is the most safest and efficient method to protect grain. Several insect species of stored grain have already developed significant levels of resistance to most of the available grain protectants (Zettler and Cuperus, 1990; Collins et al., 1993; Guedes et al., 1996; Lorini and Galley, 1999) and there are also concerns over organophosphate residues in grain even after several months of storage. Hence, a grain protectant that gives adequate control of a range of stored grain insects, while resulting in lower levels of residues and minimal effect on non target organisms can solve much of the storage problems. Recently bifenthrin, a third generation pyrethroid with high insecticidal activity was developed and demonstrated as great promise in grain protection against several stored pests (Daglish and Wallbank, 2003; Wilkin et al., 1994). The present studies were conducted to know the efficacy of bifenthrin when used for disinfecting ware houses and jute sacks against four different stored grain pests i.e., rice weevil Sitophilus oryzae (L.), rust red flour beetle Tribolium castaneum (Herbst), khapra beetle Trogoderma granarium (Everts), and lesser grain borer Rhizopertha dominica (F.) at Indian Grain Storage Management and Research Institute (IGMRI), Hyderabad during 2004.

MATERIALS AND METHODS The present studies were conducted at Indian Grain Storage Management and Research Institute, Hyderabad during 2004. Technical grade bifenthrin was supplied by M/s FMC Corporation Pvt Ltd, Australia.

Maintenance of insect culture: Except T. granarium, adult stages of insects were taken for the study. Since T. granarium adult longevity is only few days and harmless, larvae were taken for the study. The test insects i.e S. oryzae, T. castaneum, T granarium, and R. dominica were reared in separate plastic containers on sterilized whole sorghum grain in an environmental chamber at 30±1 ºC and 65±5% RH. For this, each individual container was infested with 50 full grown larvae of test insects separately to get adults of same age. To obtain T. granarium larvae, 50 pupae were kept in a container and after adult emergence, they were separated and released into another container for egg laying. After one week eggs were collected by sieving through a 1 mm sieve and transferred to fresh grain. Seven day old larvae were used for the study.

Treatments: The experimental procedure followed the general guidelines standardized by IGMRI, Hapur, India. The experimental treatments were imposed on concrete slabs and jute strips simulating the warehouse storage conditions. There were six treatments in each, replicated thrice in a randomized block design. To conduct the experiment, raised concrete slabs (0.25 m²) were disinfected with formaldehyde and later cleaned with distilled water. The slabs were secluded with acrylic sheets. The technical grade was diluted with distilled water so that the experimental area will receive 20, 30, 40, 50 and 60 mg a.i/m² (doses within the range recommended by the manufacturers). The automizer was calibrated in a preliminary test, and found that 7.5 ml of spray fluid is required to cover 0.25 m² surface area of concrete slab/jute strip. After ensuring complete drying of concrete slabs, 7.5 ml of distilled water was sprayed on control slabs from a height of 20 cm on the surface using an automizer with the spray nozzle turned downwards. Starting from the least concentration, all the treatments were imposed on the respective concrete slabs and allowed for 30 minutes drying. Then 20 insects of each test species were released on to the respective treated slabs using camel hair brush and the surface was firmly covered with PVC plastic film to prevent insect escape and entry of outside insects into treated area. The insects were allowed for half an hour to get insecticidal exposure. Then the treated insects were transferred into plastic vials with sterilized whole sorghum grain. The insects were maintained in an environmental chamber and mortality was assessed, 72 hours after treatment. Similar experiment was done separately on jute strips of 0.25 m² with above concentrations. The data was subjected to probit analysis after correcting the percent mortalities using Abbott's formula:

The percent mortalities were plotted against log concentration of insecticide and LD₅₀ values of bifenthrin for each insect were obtained.

RESULTS AND DISCUSSION The toxicology studies under laboratory conditions revealed that the LD₅₀ values of bifenthrin against S. oryzae, T. castaneum, T. granarium and R. dominica were 3.389, 46.65, 4.509 and 5.573 respectively when treated on concrete slabs (Table 1). Where as, the LD₅₀ values of bifenthrin for the same insects when treated on jute strips were 4.629, 48.0, 5.056 and 6.042 respectively (Table 2). Chi-square values also indicated that there was no heterogeneity between observed and expected mortalities of all the four insect pests. In each case, the LD₅₀ values recorded on concrete slabs were lower than the values recorded on jute strips indicating that the concrete slabs offered uniform coverage of insecticide and more contact surface to the insects. In both the experiments, bifenthrin was found to be highly effective against S. oryzae even at low concentrations followed by T. granarium and R. dominica in sequence. However, T. castaneum adults were not affected much by bifenthrin which required 46.65 and 48.0 mg a.i./m ² on concrete slabs and jute strips respectively, to cause 50 percent mortality. From this it is evident that T. castaneum has already developed tolerance to this product. The results observed here are consistent with the earlier findings of Wilkin et al, (1994) who found bifenthrin was very active against R. dominica and S. oryzae, but not against T. castaneum. In addition, Collins (1990) detected high levels of pyrethroid resistance in T. castaneum. Further, Reddy and Srivastava (2003) showed better persistent toxicity of deltamethrin WP than bifenthrin WP on jute against T. castaneum. Though S. oryzae and R. dominica were found susceptible to bifenthrin, reports of high level resistance to pyrethroids by Heather (1986) and Collins et al, (1993) suggest that these insects also have the potential to evolve resistance to bifenthrin. Since there is no single protectant that can control all species that attack stored grain, synergized combination of two products is inevitable. Successful control of R. dominica (Ali et al., 2003); Sitophilus granarius (L.) and T. granarium (Sokolov, 2004) was achieved with a combination of bifenthrin and malathion. While, piperonyl butoxide synergised bifenthrin plus chlorpyriphos methyl prevented R. dominica, T. castaneum, Oryzaephilus surinamensis (L.) and Cryptolestes ferrugineus (Steph.) from producing live progeny for upto 7 months (Daglish et al., 2003). From the investigations it is clear that bifenthrin when used for prophylactic control is effective only against S. oryzae, T. granarium and R. dominica. Insensitivity of T. castaneum to bifenthrin suggests that a combination with an organophoshate compound would be a better option to control a range of stored pests.

ACKNOWLEDGEMENTS Authors are thankful to Sri. K.M. Nimje, Director Officer- in-charge, IGMRI and Sri U.C.Gupta, Technical Officer, IGMRI for providing technical assistance and facilities for successful completion of the study.

REFERENCES

Ali, N. S., Munir, M., Ali, S. S. and Shakoori, A. R. 2003. Efficacy of mixtures of an organophosphate malathion and a synthetic pyrethroid Talstar against lesser grain borer, Rhyzopertha dominica. Pakistan Journal of Zoology. 35: 2, 163-167;

Collins, P.J., Lambkin, T.M., Bridgeman, B.W. and Pulvirenti, C. 1993. Resistance to grain - protectant insecticides in coleopterous pests of stored cereals in Queensland, Australia. Journal of Economic Entomology. 86: 239 - 245

Collins, P.J.1990. New resistance to pyrethroids in Tribolium castaneum (Herbst). Pesticide Science. 28: 101 - 115.

Daglish, G.J. and Wallbank, B.E. 2003. An update on development of Bifenthrin as a grain protectant. Proceedings of the Australian post harvest Techinical conference, Canberra, 25 -27.

Daglish G.J and Wallbank, B.E. and Nayak, M.K. 2003. Synergised bifenthrin plus chlorpyriphos-methyl for control of beetles and psocids in sorgum in Australia. Journal of Economic Entomology, 96: 525 - 532.

Guedes, R.N.C., Dover, B.A. and Kambhampati, S. 1996. Resistance to chlorpyriphos- methyl, pirimiphosmethyl and malathion in Brazilian and US populatios of Rhizopertha dominica (Coleoptera: Bostrichidae). Journal of Economic Entomology. 89: 27 - 32.

Heather,N.W. 1986. Sex-linked resistance to pyrethroids in Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Journal of Stored Products Research. 22:15-20

Lorini, I. and Galley, D.J. 1999. Deltamethrin resistance in Rhizopertha dominica (F.) (Coleoptera: Bostrichidae), a pest of stored grain in Brazil. Journal of Stored Products Research. 35 - 37.

Reddy, S. D. and Srivastava, C. 2003. Persistent toxicity of deltamethrin (WP) and Bifenthrin (WP) on jute surface against Tribolium castaneum. Indian Journal of Entomology. 65(4) : 561-565.

Sokolov, E. A. 2004; Prostor against pests of stored products. Zashchita-i-Karantin-Rastenii. (8): 46

Wilkin, D.R., Binns, T., Haubruge, E. and Shires, S. 1994. The development of a grain protectant, containing the pyrethroid bifenthrin, which has the potential for lower terminal residues. Proceedings of the sixth International working conference on stored product protection, Canberra, Australia, 2: 863 - 866.

Zettler, J.L., and.Cuperus G.W 1990. Pesticide Resistance in Tribolium castaneum (Coleoptera: Tenebrionidae) and Rhyzopertha dominica (Coleoptera: Bostrichidae) in Wheat. Journal of Economic Entomology. 83(5): 1677-1681.

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