Dr. Debasish Sarker and Dr. Nirmal Kumar Dutta :
There had been widespread concern recently whether invasive insect pest "desert locust" would attack Bangladesh since two of our neighbors- India and Pakistan already started losing crops due to locust invasion. Moreover, recent localized outbreak of a "locust-like insect" in our country in Uttar Lambari village of Cox's Bazar's Teknaf upazila added fuel to the confusion over locust attack amid the corona virus situation. The insect was first observed on April 18, 2020 in about 25 decimal of homestead forest of that village. This outbreak created panic among the locals since the insect was confused with invasive desert locust. As par directives of the Ministry of Agriculture, GOB, Entomologists of different NARS (National Agricultural Research System) institutes along with DAE (Department of Agricultural Extension) officials visited the spot and identified the species as spotted coffee grasshopper, Aularches miliaris Linn. belonging to order Orthoptera and family Pyrgomorphidae. Scientists noted that there was no risk of serious crop loss by the insect since it was considered a minor pest of agricultural crops. The insect was not new in Bangladesh, it was previously recorded in Bangladesh in 1967 by noted Entomologist Dr. M. Z. Alam. However, the insect infestation of that area was successfully controlled by spraying insecticides through local DAE initiatives. So, this local problem was not related to the recent outbreak of destructive desert locust in some parts of India and Pakistan.
The desert locust, Schistocerca gregaria is a species of locust, a swarming short-horned grasshopper in the family Acrididae. The insect is considered to be the most dangerous of all migratory pest species in the world since it has the ability to reproduce rapidly, migrate long distances, and devastate crops. A desert locust lives about three to five months, although this is extremely variable and depends mostly on weather and ecological conditions. The life cycle comprises of three stages: egg, nymph (hopper) and adult. Eggs hatch in about two weeks. Hoppers shed their skins five or six times, each time growing in size. This process is called moulting and the stage between moults is referred to as an instar. Hoppers develop over a period of about 30-40 days. Adults mature in about three weeks to nine months but more frequently from two to four months, depending on environmental conditions, mainly temperature. Desert locusts have two phases: the solitary phase and the gregarious phase. During the solitary phase, locust populations are low and present no economic threat. After periods of drought, when vegetation flushes occur in major desert locust breeding areas (e.g. India/Pakistan border), rapid population build ups and competition for food occasionally result in a transformation from solitary behavior to gregarious behavior on a regional scale. Following this transformation, which can occur over two or three generations locusts often form dense bands of flightless nymphs and swarms of winged adults that can devastate agricultural areas. Desert locusts are highly polyphagous, target crops and vegetation used as pastoralists' herds and can consume the approximate equivalent of their body weight (2 g) each day. Locust swarms fly during the day; carried in the same direction of wind, they can travel as far as 150 Km/day. A swarm of one square kilometer in size contains about 40 million locusts, which can eat the same amount of food in one day as about 35,000 people.
FAO is the lead agency in Desert Locust monitoring and control and runs the Desert Locust Information Service (DLIS) throughout the world. FAO provides information on the general locust situation to the global community and gives timely warnings and forecasts to those countries about probable invasion. According to recent FAO Desert Locust situation update published on 20 June 2020, Sudan, Ethiopia, South Sudan, Pakistan and India should remain on high alert during the next four weeks. In Southwest Asia, locust swarms continue to appear along the Indo-Pakistan border, many of which have continued further east in to several states of Northern India. Control operations are going on in both countries.
Now the question, whether Bangladesh is at risk of locust invasion? FAO Senior Locust Forecasting Officer Keith Cressman recently gave an online presentation organized jointly by the Ministry of Agriculture, FAO, and the International Maize and Wheat Improvement Center (CIMMYT). Cressman pointed out that there are three main reasons why there is very little chance of its invasion in Bangladesh. These include: Bangladesh is far away from where the locust swarms are now; they can't travel against the wind and most important one is that our soil, habitat and climate is not conducive for its breeding. Bangladesh has no desert. The country is too wet with green vegetation. Cressman also noted that the moonson and India's good national locust control program would also help protect Bangladesh.
Although desert locust is very less likely to invade our country, but we should keep constant watch on probable locust attack, we should have preparation to face the emergency. Under Ministry of Agriculture, a National Task Force may be formed comprising relevant stakeholders to oversee the issues related to locust and other invasive migrant pests. Regular surveillance and monitoring of desert locust by all NARS institutes and DAE is very much important. A national strategy for its prevention and management should be formulated. At present the effective method of controlling desert locust is with mainly organophosphate/synthetic pyrethroid insecticides applied by vehicle-mounted and aerial sprayers. Bio-pesticide, Metarhizium anisopliae var. acridium is also proved to be very effective against desert locust. The chemical pesticides are available in our country, but we lack the bio-pesticide. We have also shortage of vehicle mounted sprayer. So, we should have arrangement for several vehicle mounted sprayers to face the emergency. Necessary steps could be taken for registration of Metarhizium anisopliae var. acridium in our country since this is also very effective against many other insect pests of crops.
Our present agriculture-friendly government has taken all out steps for boosting the crop production amid the corona virus outbreak. Due to climate change and other factors newly emerging insect pests might continue to create problem in our crop production. We have the expertise and skills to handle this issue. But we should be very careful so that any fake news or rumor cannot create panic among our farmers. Recently, we have been able to very successfully manage the attack of destructive pest Fall Armyworm in maize though well coordinated approach from our Ministry of Agriculture. Hopefully, in future we will be able to continue the increasing trend of our agricultural production facing all limitations through the active participation of our farmers and relevant stake holders.
(Dr. Debasish Sarker is Chief Scientific Officer & Head and Dr. Nirmal Kumar Dutta is Principal Scientific Officer, Entomology Division, Bangladesh Agricultural Research Institute).