By Professor Rohan Rajapakse, Senior Professor of Agricultural Biology Dr. Wolly Wijayaratne Senior Lecturer in Pest Management Rajarata University of Sri Lanka

Tea consignments from Sri Lanka to Russia were found to have a Khapra beetle a few days ago. Consequently, Russia restricted the importation of agricultural products from Sri Lanka. Sri Lankan tea, which accounts for about 23% of the Russian tea market, has earned a substantial amount of foreign exchange this year. The current situation, therefore, has affected not only the country’s foreign exchange reserves but also its image as a tea exporter.

Khapra beetle, scientifically named as Trogoderma granarium Everts (Coleoptera: Dermestidae), is a beetle species and a serious pest of nearly 100 food materials. It prefers grain and cereal products but infestations are also reported in dried plant/animal matter, pulses, vegetable seeds, herbs, spices, nuts, copra, dried fruits, and dried products of animal origin (milk powder, skins, dried dog food, dried animal carcasses), certain oil seeds, cocoa. Finally, it has been found in processed tea.

Khapra beetle is ranked among the 100 most destructive invasive insect species in the world. Its danger as a pest is accompanied by its rapid rate of population increase; high level of quantitative and qualitative loss in the infested stored products; ability to survive without food for years, live with low moisture content and undergo adverse environmental conditions in diapause and resistance to many insecticides. Khapra beetle thrives at higher temperatures 32-36ºC and can tolerate heat, desiccation and cold (tolerate up to 50⁰C, 2% moisture content and 2-4⁰C for one year!).

The adult beetle is oblong-oval shaped, 1.6- 3.0 mm long and 0.9-1.7 mm wide. Males are brown to black with indistinct reddish brown markings on the front wings. Females are lighter in colour than males and slightly larger. The adults are covered with hairs. The larvae are about 1.6-1.8 mm long, more than half the body has a tail made of hairs. Larval body is yellowish white, and body hairs are brown. As the larva grows, more body hairs develop and the body colour changes to golden/reddish brown. Mature larva is about 6 mm long and 1.5 mm wide. Khapra beetle can complete up to ten generations in one year depending on the availability of food, favourable tropical (warm) temperature and humidity. A complete life cycle can be as short as 26 days (around 32-35ºC) or as long as 220 days under suboptimal environmental factors.

The detection of khapra beetle includes visual inspections, sampling, use of food baits and pheromone traps. However, the detection of adults is considered difficult as they seek out cracks and crevices in packing materials, conveyances and storage facilities. In contrast, the larva can comparatively be detected easily during inspections; the presence of accumulated cast larval skins makes it easy.

Khapra beetle is considered native to India and was first reported in 1894. By now it is present in more than 40 countries in the Asia, the Middle East, Africa and Europe, especially near the equator where dry and hot environment exists. Khapra beetle has been sighted on several occasions in Sri Lanka. Jonathan Banks (1977) has reported its presence in Sri Lanka. Vayssiere and Lepesme (1938), Cotton (1954, 1955), Erturk (1956), Kiritani and Utida (1956) have reported this species to be present in Sri Lanka whereas Fernando (1963) denies that. Hinton (1945) has reported the presence of this species in Ceylon. Currently, the US has listed Sri Lanka as a country which harbours khapra beetle. European and Mediterranean Plant Protection Organization (EPPO) also had declared Sri Lanka as a country affected by Khapra beetle Trogoderma granarium but no records have been found as updated in 2006 (http://pqr.eppo.org/datas/TROGGA/TROGGA.pdf). CABI Crop Protection Compendium (2007 edition) also revealed this species is present in Sri Lanka. However, there are no records of its exact presence in made tea in Sri Lanka except the fact that it could be present in packing materials or discarded tea more importantly, khapra beetle is present in our neighbourhood India, Pakistan and also in many African countries. This geographical distribution pattern coincides with the ability of this insect species to establish well under warm climatic conditions. The pest could thrive on the packing materials used as the larvae are known to diapause effectively until it finds a suitable host.

Digressing to the control methods, it is obvious that they need to be sought with care to prevent their unacceptable negative impacts on consumers. Residual chemical insecticides are not recommended for commodities such as tea due to the possibility of leaving insecticide residues in made tea. Surface treatments also have limited success as the diapausing larvae of khapra beetle hide in cracks and crevices, limiting its exposure to the mortality factors. Fumigation has been very successful against khapra beetle. Methyl bromide is very effective against stored-product insects but its use is now restricted due to ozone depleting effect. Phosphine has demonstrated mixed results as the resistance by khapra beetle to this fumigant is also reported despite its successful control. Sulfuryl fluoride is a new fumigant used in North America for the disinfestations of stored products against pests but unfortunately not yet registered in Sri Lanka. This fumigant has been very effective against khapra beetle. Also, exposure to a mixture of carbon dioxide and another fumigant increases the susceptibility of insects to a fumigant. In Sri Lanka, the use of botanical Neem powder has desirable effect of controlling the larvae

Insect growth regulators affect insects and have minimum effects on human and other vertebrates. Methoprene is very effective against many stored-product insects and is registered in North America for agricultural pest management.

Advanced technology is available and used in the developed world for the management of khapra beetle. Vacuum-hermetic technology is one of the latest methods which completely kill the eggs and thus a good quarantine method. Heat treatment is also a good alternative for the use of chemical but accompanies limitations such as infrastructure prerequisites, cost factor and experiments are needed to ascertain its full potential. In the past, khapra beetle was controlled when the infested commodity (grain) was pneumatically conveyed several times but this method has not been attempted recently.

Irradiation by gamma or other rays is also effective against khapra beetle and is used in certain developed countries in stored-product protection but its use is hindered by factors such as the consumer concerns.

It is very difficult and expensive to eradicate this pest. It is up to experienced entomologists to find workable solutions to exclude the presence of khapra beetle in tea so as to help preserve Sri Lanka’s image as an exporter of high quality tea. Unfortunately, there has been no systemic survey for the past 35 years or so, to detect the presence and possible entry of khapra beetle here. Lack of attention to this insect species in Sri Lanka has caused considerable damage to the Sri Lankan export market. Immediate action is called for to overcome this serious pest damage. Entomologists with experience on stored-product pests in the country along with TRI entomologists have to take the lead in handling this national issue.