Insect growth regulators for managing insect pests
Storage of cereals and their products is a vital part of post-harvest operations, through which food commodities passes from its way from farmer field to the ultimately consumer. Annual post-harvest losses of stored cereals due to various biological factors in the storages range from 10-20% of overall production. Insect pests are the main factor responsible for these losses as they reduce both quality and quantity of grains. Among various stored grain insect pests, khapra beetle and red flour beetle are pests of economic importance because they feed on a wide range of stored cereals and their products. There is a continuous need to protect the stored grains and their products against deterioration, especially loss of weight and quality during storage.
The Khapra Beetle (T. granarium Evarts) is a serious pest of stored grains and their products. Although the adults are harmless and short lived, the larval stage of this pest is very destructive and that results in huge economic loss of stored cereals and their products. An obvious feature of this pest infestation is masses of these hairy larvae and their cast skin. Losses caused by T. granarium have been reported to be 0.2-2.9% over a period of 1-10.5 months in Pakistan.
The red flour beetle (T. castaneum) is a malicious and cosmopolitan pest having an extensive association with stored food. Both the larvae and adults cause damage. In a case of heavy infestation, the flour becomes moldy and greyish with an unpleasant smell that affects baking quality of flour which results in the flour no longer fit for human consumption. Indeed considerable losses have been reported in storage due to its high fecundity. Economic losses caused by this pest have been estimated to be of 34 % in stored millet and 40% in wheat flour Stictly speaking, the overall loss in quantity and quality of the stored grains, and the health hazards attributed to the insect damage as waste products, translate to a monetary concern that could amount to millions of rupees further emphasizing the need to prevent infestation. Therefore, control of these storage insect pests is not only vital to ensure food safety and food security condition, but it is also a pre-requisite to export of surplus cereal grains.
The current management strategies for stored product insect pests mainly depends upon neurotoxic chemicals (i.e., organophosphates and pyrethroids), fumigants. These control practices have been effective in many cases, but there is increasing concern that these control tactics have limitations. These problems include the development of resistance in insecticides as consequence of their excessive use; the residual chemicals in products obtained from treated grains their toxicity to mammals and their potential negative impact on environment. Public awareness about these risks has urged scientists to develop more effective, sustainable and comparatively safer methods for the protection of stored commodities against the damage caused by insect pests.
At present there is an emphasis on the use of insecticides having bio-rational properties owing to many concerns about the use of neurotoxin insecticides. This concept also includes the use of reduced risk control tactics, such as insect growth regulators (IGRs). The IGRs include chemicals which mimic hormones that control molting and metamorphosis in insects and thus disrupt process of normal insect development. The use of IGRs as grain protectants has certain advantages over conventional neurotoxic pesticides. The IGRs are biodegradable in the environment and possess low mammalian toxicity to non-target organisms. The IGRs includes chemical classes with different mode of action, and can tentatively be divided into three categories;
1) Juvenile hormone agonists,
2) Ecdysteroid agonists (Antagonizing JH activity),
3) Chitin synthesis inhibitors (Interfering with cuticle formation).
Therefore, present investigation was designed to estimate the quantitative losses occurred in advance genotypes of wheat rice and maize and to investigate the insecticidal effect of seven insect growth regulators viz., lufenuron, flufenoxuron, pyriproxyfen, tebufenozide, methoxyfenozide, triflumuron and buprofezin against T. granarium and T. castaneum.estimation the quantitative storage losses in wheat, rice and maize and relative effectiveness of seven (7) Insect Growth Regulators (IGRs) for their anti-insect activity against T. granarium and T. castaneum.
From the results of our studies it is concluded that all the IGRs have proved to be very effective against both the species examined in the present study, and therefore, these compounds particularly CSIs (flufenoxuron, lufenuron and triflumeron) should be considered as potential components in IPM of stored grains insects pests. Following are the outcomes of all the experiments;
• In term of weight loss, wheat is the most susceptible than rice and maize.
• All the testes IGRs exhibited remarkable potential as grain protectant.
• Bioactivities of IGRs were found to be dose and exposure period dependent.
• JHAs (pyriproxyfen) are not best option because they may produce super larvae which cause more loss. Their application to the late instar larvae may results in pupal adult intermediates. They are not very effective against adult stage.
• Ecdysone agonists (methoxyfenozide and tebufenozoide) are on second place in term of their effectiveness after CSIs.
• Final recommendation are for CSIs (flufenoxuron, lufenuron and triflumeron), they are most effective against most of the stages of test insects.
• All the IGRs are more persistence and effective when applied on wheat, than on rice and maize
Furthermore, considering the effectiveness of insect growth regulators as nonhazardous and environmental friendly control agents, government should promote their use directly by providing financial support to the agro-chemical industries and research institutions to undertake investigations and synthesis of IGRs locally, so they are more widely available to the end users.
The author is Msc (Hons) Entomology, while his supervisor is Prof. Dr. Sohail Ahmed, Department of Entomology, University of Agriculture, Faisalabad-Pakistan.