Mil­lions of farm­ers across Africa can now pre­vent their cowpeas from de­struct­ive weevils using a low-cost in­nov­at­ive way of stor­ing the legumes.

Sci­ent­ists have been study­ing how farm­ers store cowpeas and learnt that a long-stand­ing method of killing cowpea weevils in­volved stor­ing the har­vest in­side three-layered and in­di­vidu­ally sealed plastic bags. It was as­sumed the pests died of suf­foc­a­tion something which was not to be.

Now re­search­ers in Africa and the US have pub­lished a study of the method say­ing that while lack of oxy­gen re­duces the weevils’ feed­ing activ­ity, what ac­tu­ally kills them is lack of water, and that the drier the har­vest at the time of stor­age the harder it is for the weevils to sur­vive and mul­tiply.

Har­ves­ted beans are vul­ner­able to cowpea weevils, Cal­lo­sobruchus mac­u­latus, which can mul­tiply rap­idly. Even a small in­fest­a­tion can des­troy an en­tire stored crop in a few months.

“The weevils use oxy­gen to pro­duce water and so are de­prived of their main water source. But some of their water, maybe 15–20 per cent, comes from the seed,” said Larry Mur­dock, an en­to­mo­lo­gist at US-based Purdue Uni­versity and lead au­thor of the study.

Mil­lions of triple plastic bags have already been dis­trib­uted across West and Cent­ral Africa through the Purdue Im­proved Cowpea Stor­age (PICS) bags pro­ject that tar­gets West, Cent­ral and East Africa. “The simple re­com­mend­a­tion is to store, in a PICS bag or via other meth­ods, your grain when it is drier, if you can, be­cause you’re re­du­cing the sup­ply of water and pla­cing the weevils under even greater water stress,” Mur­dock said.

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The team are now in­vest­ig­at­ing whether the dry, air­tight en­vir­on­ment in­hib­its other cowpea pests in the same way.

Sci­ent­ists and re­search­ers in Kenya have wel­comed the study at a time when Kenyan farm­ers are strug­gling with post-har­vest losses in cowpeas. “I strongly feel that av­er­age prices can in­crease 60–100 per­cent between har­vest and the next plant­ing sea­son. So any im­prove­ment in stor­age has the po­ten­tial to in­crease rev­enue by that much,” said Mucheke Mu­gene from the Tege­meo In­sti­tute of Ag­ri­cul­ture.

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