Steady rise in invasions by alien pests and outbreak of new plant diseases induced by global warming over the last two decades made the researchers as well as the Department of Agricultural Extension officials and researchers worried.
Researchers as well as DAE officials agree that minor pests that could be easily controlled in the past became strong plant attackers now that are proving difficult to keep under check.
At times these pests and plant diseases get highly difficult to control for which the authorities slashed the acreage of vulnerable crops and limited export of some other crops.
‘Never before in the past did Bangladesh encounter such a big threat from pests and plant diseases,’ Bangladesh Agricultural Research Institute’s principal scientific officer Mohammad Shahadat Hossain told New Age.
Shahadat said, ‘we identified at least a dozen invasive alien pests and plant diseases that entered Bangladesh after 2000.
Some of the alien invasive pests and plant diseases remained unidentified despite their strong presence in parts of Bangladesh, he said.
‘Due to limited capacity, we prioritise dealing with invasive alien pests and plant diseases with the potential to cause large-scale damage,’ he said.
Between 1970 and 2000, major pests and diseases in Bangladesh were known to the farmers as well as the researchers , said Shahadat whose career as a researcher began in 1995.
‘Influx of alien invasive pests or these plant diseases were unknown to Bangladesh between 1970 and 2000,’ he said.
The situation is changing fast, he said for rice, wheat, corn, potato, mango, papaya, coconut, tomato, brinjal, tea and other major crops as they are increasingly coming under attack from the invasive alien pests and plant diseases.
Razzab Ali, professor of Entomology at Sher-e-Bangla Agricultural University, said that increased pest attacks and plant diseases were occurring mainly due to global warming.
‘Insects are ectotherms, dependent on outside temperature for physiological activities, which means physiologically they become more active in warmer conditions,’ said Razab.
High humidity also an influencing factor for the growth of insects, he said.
‘Humidity is higher in warm air,’ said Razzab.
Dhaka University zoology professor Murshida Begum said that increased physiological activities means shorter life cycles.
‘The shorter the lifecycle the greater the generation of insects,’ she said.
Murshida said that it was almost universal knowledge that low temperature slowed down insect growth for which blue flies are seen in Bangladesh in large number in the summer.
She said that in a summer month blue flies complete four lifecycles but in a winter month they cannot complete even two lifecycles.
Global warming, she said, made winters shorter and longer summers facilitating faster growths in insect populations.
Similar conditions are applicable for many of the crops diseases caused by fungus, bacteria or virus.
The 5th assessment report of the Inter-Governmental Panel on Climate Change (IPCC) confirmed the links between global warming and increased pest and disease attacks.
The first ever research quantifying crop losses caused by increased pest attacks linked to climate change was done in August 2018 by US-based scientists.
According to them, even if climate change is restricted to the target 2C, increased pest attacks would still destroy 50 per cent more of the wheat crop than they do today, 30 per cent more corn and 20 per cent more rice.
The researchers said that warmer temperature increases insect reproduction rates and more insects mean a rise in their food demand.
It is predicted that the need for more food may force insects to change their food habit or make them travel far and wide. Warmer temperature would only expand their territory of migration.
Former BARI director Syed Nurul Alam said that the most dangerous of the new alien invasive pests that arrived in Bangladesh was identified as Fall Army Worm, a native in the Americas.
First detected in November last year, the pest was already spread across Bangladesh, infesting at least one per cent of the corn crop, he said.
The pest was first seen outside its native continent in Africa in 2016. In just two years it became pervasive in 44 of the 54 African countries, causing famine in five of them, destroying almost entire production of their staple crop corn.
Able to travel hundreds of kilometres overnight in favourable winds, the pest already invaded India, Thailand, Myanmar, Sri Lanka Nepal and also possibly China.
Although it prefers to feed on corn primarily, the voracious pest could survive on 80 other crops, including rice, said Nurul Alam.
Wheat and Maize Research Institute director Naresh Chandra Deb Barma said that outbreak of a fungal disease, blast, forced them to reduce the crop acreage over last four years.
Blast was restricted to the rice crop cultivated in South America only for centuries until it started infecting wheat in 1985.
In Asia, wheat blast, considered the most fearsome and intractable of the diseases that appeared in recent decades, was first detected in Bangladesh in 2016.
Wheat was cultivated in 4.45 lakh hectares the year the disease first broke out. This year wheat was cultivated in 3.30 lakh hectare.
‘We were looking for a cure to the disease before expanding wheat production,’ said Naresh.
In 2014, bug scare at Eden Women’s college in the capital made headlines, bringing leading entomologists in the country together to investigate into it.
The bug was identified as giant mealy bug, a mango pest which is believed to have come from Africa.
Entomologists believed that the pest entered Bangladesh through army peacekeepers who served UN missions in Africa.
They were not sure when the pest arrived in Bangladesh, but after they were seen at the Eden College they drew the attention of the scientists.
Now, mealy bug pest is seen throughout Bangladesh, especially at mango plantations.
Another major threat to mango cultivation comes from Mango Fruit Borer, believed to have entered Bangladesh in 2008.
Another major pest, coconut mite was first detected in Bangladesh in 2012, forcing the authorities to introduce coconut varieties resistant to the disease.
Initially a threat in the coastal district, the pest is spread all over Bangladesh, said BARI’s principal scientific officer Shahadat.
According to the DAE estimates, coconut cultivation was reduced to 46,384 hectares last year from 50,971 hectares in 2012.
Entomologists in Bangladesh are also worried over the infestation of pests like Papaya Mealy Bug, American Tomato Leaf Miner, Root Aphid, and Codding Moth.
Vegetable export to UK and the Middle East was limited since 2009 following detection of Thrits, a pest, in several vegetable crops, said Shahadat.
The pest is attacking brinjal, tomato, chilli and many other vegetable crops besides causing large-scale damage in tea plantations.
‘We have known Thrits for long but never before did we find it so devastating,’ said Bangladesh Tea Research Institute’s senior scientific office Shameem Al Mamun.
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