Khapra Beetle: A Review of Recent Control Methods

Research work revealed that stored grain pests pose serious threats to stored food commodities and cause economic losses. Khapra beetle (Trogoderma granarium) considered one of the most destructive pests that has great economic importance because of starvation capability for three years and has best survival rate at low humidity. T. granarium cause heavy losses in stored commodities and decrease the quality and quantity of grains. Development of resistance in T. granarium against insecticides like malathion, phosphine and pyrethroids has further increased its economic importance. There is no review available in the literature for the stored products policy makers and managers to control this pest. Following study reveals the economic losses cause by Khapra beetle in storage structures and its control by using integrated pest management strategies


Introduction
The Trogoderma granarium Everts belongs to family Dermestidae and order Coleopteran and is a world's most destructive stored grain pest. 115 species of Trogoderma genus reported by [1] in the world out of which twelve (Table 1) are stored grain pests. In fact, T. granarium ranked as one of the 100 worst invasive species worldwide and has been recognized as an A2 quarantine organism [2]. Larval stage of this pest considered most destructive stage that causes heavy economic losses to stored grains and other food commodities. Depending upon temperature, complete development (egg to adult) occur from 26 to 220 days and 35°C is the optimum temperature for its best survival. For an impressive timeframe or if hatchlings are extremely swarmed, if temperature falls beneath 25°C they may enter diapause. In diapause conditions, hatchlings may stay for a long time in this condition [3].
Due to its continued occurrence on commodities status of T. granarium is of highly economic importance and become potential for spread by use of roll-on roll-off road transport and dry cargo containers that make it a potential threat to global food security. has been reported. Such restrictions reinforced by facts that feeding by Khapra beetle larvae reduces quality of grain and weight loss. In Pakistan estimates of storage losses of food grains due to insects have been reported to vary widely; 4-10% [4], about 5.08% [5], 5% [6], 3.5 -25.5% [7]. Rahman et al. [8] reported average damage levels in India ranged from 6% to 33% of the grain in a single storage season, with maximum damage at 73%. Wheat lost 24% of its viability and 2.6% of its weight at optimal conditions of 36°C and 15% infestation [9]. Trogoderma sternale plagifer (Casey, 1916) Trogoderma sternale maderae (Beal, 1954) Trogoderma parabile (Beal, 1954) Trogoderma grassmani (Beal, 1954) Treatment may result in less profit for wholesalers due to loss of grain. Severe infestations may make stored unpalatable or unmarketable. Due to depletion of specific nutrients, quality may decrease. In wheat, Sorghum and maize grains, there was a decrease in crude fat, sugars, total carbohydrates, protein nitrogen, starch contents, vitamins thiamin, riboflavin, niacin, total lipids, phospholipids, glycolipids, polar and non-polar lipids; increases in the levels of uric acid, moisture, crude fiber, total protein and anti-nutrient polyphenol were observed [10,11]. Trogoderma have assigned a pest status due to quality deteriorating characteristics as technical barrier to trade. Use of chemicals, botanicals and physical strategies control the khapra beetle to some extent because they develop resistance against insecticides and botanicals and have best survival at low humidity and temperature. Biological control is effective against khapra beetle because naturel enemies only feed their host rather putting any damage to stored commodities.
As a stored grain pest Khapra Beetle T. granarium was first time reported from India in 1894 by Cotes. The latest literature reveals that the pest is present in more than 35 countries of the world [12].
This is a local pest of India yet favors hot and dry atmospheres of Asia, Africa and Eurasia [13] additionally reported in the USA [14,15]. It has achieved a status of extremely basic essential vermin of stored wheat, rice, and maize in the Indo-Pak subcontinent.  [17].

Damage in Pakistan
Annual storage losses in public sector and at farm level recorded as 7 and 4% respectively [18]. Different control measures for Khapra beetle shown in Table 2.

Plant Extracts (Botanicals)
The most extensive research on control methods against the khapra beetle that has been carried out during the last 10 years deals with the use of plant extracts (essential oils, botanical powders etc.). Repellence toxicity of a plethora of plant species against T.
granarium have been evaluated [58][59][60][61][62][63][64][65]. Characteristically, the use of neem (Azadirachta indica) essential oil as a fumigant and oras seed powder seemed to be a cheap and effective method to manage insect pest especially in developing countries [63]. Despite the promising results, plant oils and powders remain mainly experimental because of certain limitations with their production, quality standardization, formulation, and commercialization.  [71] have been found to parasitize or prey on the khapra beetle.

Conclusion
From the above study, 120 plants, their products and different chemicals have been used to control stored product pests [72]. Due to threat of insecticide resistance development in them, integrated pest management (IPM) practices should be followed. Chemicals, botanicals [73][74][75][76][77][78][79], physical and biological control measures should be used in a compatible manner to manage stored product pests below their infestation level and minimize the chances of resistance development in them [80].