Tackling emerging threat to rice in Pakistan

Pest has been found in rice consignments exported to different countries

LAHORE: Exports of Pakistan are mainly based on agriculture and rice (Oryza sativa) is our main export, contributing about 0.7% to the country’s GDP.

Being the third largest exporter of Basmati and Irri varieties (Ministry of Commerce 2016), Pakistan exports more than 50% of its produce.

Fine varieties are exported to the US, Australia, the UK and other sensitive countries while Irri varieties are exported to China and some other countries. In recent years, the export share of Pakistan has declined, going down from $2.2 billion in 2014 to $2.1 billion in 2018.

Among a number of factors contributing to the decline is the notorious stored grain pest ‘Khapra beetle’. Khapra has been known to be a pest of stored wheat, however, now it has been observed feeding rice. The pest is also found in consignments of rice exported to other countries and can cause losses of up to 30%.

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This has opened a new area for researchers to monitor the activity of this pest in stored rice. The larvae of this pest were detected twice in rice shipments to the US and later in 2014 it was once again detected at the US entry point. As a result, 43,000 pounds of rice was shipped back.

In 2013, Mexico rejected a rice consignment from Pakistan weighing 3,000 tons due to infestation of this pest and imposed a ban on Pakistani rice, which exists to date.

Continued rejection by trading partners from 2011 to 2014 led to an estimated loss of $1 billion. Now, recently in 2019, the same pest has been detected in rice exported to Russia despite the fact that it was treated with Methyl Bromide (CH3 Br). Due to this, the Russian authority imposed a temporary ban not only on rice but on all food grain commodities shipped from Pakistan.

The eradication of this pest is difficult due to the resistance developed against synthetic insecticides. It has been ranked among top 100 most-invasive species worldwide.

Origin of Khapra beetle

Trogoderma granarium may have originated from the Indian subcontinent and is still present in some areas of Asia, the Middle East, Africa and a few countries in Europe. It is one of the very few stored product pests with limited distribution. T granarium has very limited ability to spread without human aid because it is unable to fly, so international movement of host commodities appears to be the only means of spreading the pest.

It is very important to distinguish between records that relate to interception of the pest in imported commodities (ie its finding in the commodity during the border phytosanitary control without further spread) and those of established infestation.

Geographical range

The pest can be found in areas outside its known geographical range as long as good climatic conditions prevail. T granarium is established within an area broadly limited north by the 35° parallel, south by the Equator, west by West Africa and east by Myanmar.

It is reported in some countries of Africa, however, others are still free of the pest and require protection as well to limit the spread of the pest.

Risk

The pest could be associated with maize or wheat grain (as pathway) moving in international trade or food aid and once imported, it could establish owing to the following:

Ability to survive lengthy periods of cold, drought or starvation of up to 13 months as resting larvae, ability to reduce pesticide uptake and translocation due to its low metabolic rate, therefore very difficult to kill, short life span for adults making them less vulnerable target of fumigation, and low respiration rate of facultative diapausing larval stage also leading to tolerance of fumigation.

Identification

Adults are oblong-oval beetles, approximately 1.6 to 3mm long and 0.9 to 1.7mm wide. Males are brown to black with indistinct reddish brown markings on their elytra.

Females are slightly larger than males and are lighter in colour. The head is small and deflexed with short 11-segmented antennae. The antennae have a club of three to five segments, which fit into a groove in the side of the pronotum. The adults are covered with hairs.

Adult Khapra beetles have wings, but apparently do not fly and feed very little. Mated females live from four to seven days, unmated females from 20 to 30 days, and males from seven to 12 days.

Established infestations are difficult to control because of the beetle’s ability to live without food for long periods of time and to survive on foods of low moisture content.

These beetles tend to crawl into tiny cracks and crevices and remain there for long periods, making them relatively tolerant to many surface insecticides and fumigants. Therefore, it is important to prevent Khapra beetle’s introduction in uninfected areas.

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Detection and management

Detection methods include examination of cracks and crevices and inspecting behind panelling on walls and under timbers, tanks, shelves, etc. Larvae are most likely to be seen just before dusk, since they tend to be more active at that time.

Some fumigants give control at high dosages, even though this beetle is more resistant to fumigants than most stored product pests. High concentrations of fumigants must be maintained over the fumigation period to allow penetration into all cracks and crevices.

In an eradication programme, both fumigants and surface sprays are used in combination with preventive measures, eg good sanitation practices and exclusion.

Keeping in view the above constraints, there is a dire need to develop Khapra beetle-free rice supply chain in Pakistan by adopting system approaches and natural factors.

Published in The Express Tribune, July 22nd, 2019.

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