Purdue Improved Crop Storage (PICS) bags (formerly Purdue Improved Cowpea Storage bags)[1] are a hermetic storage technology developed by Purdue University.[2] PICS bags are used to reduce post-harvest cowpea (Vigna unguiculata) losses due to bruchid infestations in West and Central Africa.[3]
A PICS bag consists of two layers of polyethylene liners and a third layer of woven polypropylene.[4] When each layer is tied and closed separately, it creates a hermetically sealed environment for storing harvested grain. This oxygen-deprived environment proves fatal for Bruchidius atrolineatus,[5] Callosobruchus maculatus,[6] and other post-harvest insects.[7][8]
Cowpea is an important crop for Western and Central African countries.[9] Cowpeas are highly nutritious for humans and are a source of fodder for animals, and are regularly used by rural women to generate their own income, thereby providing an important source of liquidity for farmers.[5]
Stored cowpea grain can face a reduction in shelf-life due to the potential threat posed by insect pests. Species such as Bruchidius atrolineatus[5] and Callosobruchus maculatus[10] (commonly known as cowpea weevils, or bruchids) carry out their life cycle within grain,[5] and their presence makes the crop unfit for consumption. These insects reproduce rapidly; thus, the presence of a few insects in a collection of cowpeas can cause significant damage within a month.[11]
In 1987, Professor Larry Murdock of Purdue University, in partnership with Bean/Cowpea CRSP, USAID,[5] and BIFAD, led a team of researchers working to combat bruchid infestations of cowpea harvests in Cameroon.[11] The outcome of this initiative were PICS bags.[12]
Since 2007, more than 1.75 million PICS bags have been sold in West and Central Africa,[11] and demonstrations of their effectiveness have been conducted in 31,000 villages.[11] As of 2023, the project has been funded with $11.4 million (USD) by the Bill and Melinda Gates Foundation.[13]
The PICS project has evolved since its original conception. As such, the project's target objectives have also evolved to meet the needs of its mission of delivering safe, cheap, and effective post-harvest storage solutions to smallholders.
Active from 2007-2011, the specific objectives of this project involve determining the best design for a triple-layer, hermetically sealed, commercially available cowpea storage bag.[14] Another goal is to increase the knowledge of farmers and rural-development groups on non-chemical cowpea storage methods, and to demonstrate the most effective cowpea storage methods for these groups. It is also important to the project to develop a local supply chain for PICS bags that makes them available for rural farmers, while additionally providing development opportunities for local businesses.[9] Funding was $11.4 million over 5 years.[15]
Active from 2011-2014, PICS2 sought to expand the original scope of the PICS program. Its goals were to identify other agricultural commodities that suffer losses to insects during storage, test the PICS bags through collaborative projects with scientists in developing nations in primarily sub-Saharan Africa, implement economic analyses to estimate the potential benefits of optimizing the PICS technology for a specific commodity and develop plans to disseminate the technologies for those commodities where it would provide the greatest benefit.[14] Funding was $1.1 million over 30 months.[15]
The third phase of the program began in April 2014, and is ongoing as of 2023. The program is currently funded by the Bill and Melinda Gates Foundation.[2] PICS 3 seeks to improve market access, cash incomes, and food security among smallholders in Sub-Saharan Africa by reducing post-harvest storage losses through expansion of the PICS bag technology.[16]
This project was first developed in Cameroon, but it has since spread to 23 nations in Africa and Asia.[13] To date, PICS bags have been introduced and are in use in the following nations: Afghanistan, Benin, Burkina Faso, Burundi, Cameroon, Chad, the Democratic Republic of the Congo, Ethiopia, Ghana, India, Kenya, Malawi, Mali, Mozambique, Niger, Nigeria, Rwanda, Senegal, Tanzania, Togo, Uganda, and Zambia.[13]
After harvesting and thoroughly drying the grain, farmers place grain into a polyethylene bag capable of holding either 50kg or 100kg.[9] The bag is then tightly sealed, preventing air from entering.[11] The first polyethylene bag is surrounded by a second identical bag, which is also sealed, making it airtight.[11] The double-bagged grain is then sealed inside a third woven polypropylene bag, which provides the mechanical strength for PICS bags.[10]
This method of triple bagging creates an airtight environment, and seals any insects present in the crop inside the bag. These insects briefly continue to consume oxygen, but as oxygen levels in the bags drop, and CO2 concentrations rise,[5] the insects stop feeding and quickly die, thereby protecting the crop from further damage.[11]
Recent studies have shown that bruchids sealed in PICS bags do not die from asphyxiation, but rather from thirst. This subfamily of Chrysomelidae has the ability to produce water through their own metabolism.[11] This process requires oxygen, so when oxygen levels in PICS bags decrease the bruchids lose the ability to produce water and die of dehydration.[11] It is reasonable to assume that this same adaptation exists in other post-harvest insects.
PICS bags provide benefits to smallholders. They are an effective insecticide-free, low-cost method of storing cowpeas and other grain,[11] and they are easy to explain to farmers.[5] The PICS bags can be stored in family homes, making this an effective way for smallholders to protect their harvests.[5]
In addition, the bags can be opened at any time. When they are unsealed, the cowpeas are ready to be consumed.[5] The PICS bags can then be reused, provided they are free of holes and tears.[17] Studies have demonstrated that PICS can be used multiple times across several years without any loss in quality.[18]
Delaying the sale of grain until it attains a higher market value enables consumers to maximize their profits. Additionally, the storage serves as a means to create food reserves for communities during the post-harvest season.[5] Even after several months of storing in PICS bags, the quality of the grain does not decline.[17]
The PICS project aims to increase the incomes of smallholder producers.[5] By 2012, Purdue University researchers expected each household that used the PICS bags to increase their annual income by an average of $150 USD.[19] With widespread adoption of PICS bags, global savings of cowpea harvests were predicted to be worth $500 million USD annually.[11]
The additional income provided through the use of PICS bags is expected to allow smallholder producers to invest in their own farming practices and local communities, thereby encouraging local development.[5]
Some problems with this technology are that PICS bags are prone to theft, and therefore need to be protected.[5] In areas where grain has always been sold immediately after harvest, storage areas may not exist for PICS bags. Therefore, the bags' introduction to some communities may also require the construction of new storage facilities.[5] In addition, it is essential that grain intended to be stored in PICS bags be thoroughly dried prior to storage in order to prevent mold growth and grain rot.[20] And while PICS bags protect cowpeas against damage caused by insects, they do not provide a barrier against mice, rats, or other animals.[5] Finally, the environmental impact of PICS bags remains largely unstudied.[9]
In order to increase the effectiveness of PICS bag technology, the following suggestions should be considered:
As studies show, PICS bags work not only by depriving bruchids of oxygen, but also by dehydrating their environment. Therefore, this technology could be improved by finding additional methods of quickly lowering the moisture content within sealed bags.[11] Since PICS bags do not provide protection from mice, rats, or other animals, any NGO aiming to increase their use should ensure that farmers are taught to keep their stored cowpea harvest in an environment free of these exterior threats. There is potential for PICS bags to be improved through the use of an additional barrier that cannot be punctured by animals. Due to low levels of local literacy, this project aims to communicate PICS bag technology to communities through verbal demonstrations and also through information communicated via radio.[5] In order to ensure full community participation in effective cowpea storage, women, men, and children must all participate in PICS bag demonstrations.[5]
Solutions competing with PICS bags to prevent insect-induced post-harvest grain losses are other forms of hermetically sealed containers, such as the GrainPro bag. A similar method of protecting the crop is to store grain inside sealed steel drums.[17] Furthermore, the same basic principles of disabling insects within hermetically stored containers could potentially be applied to other crops in the region.