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Fill It Full: A Simple Way to Reduce Weevil Damage in Maize Seed Stored in Airtight Containers

Introduction

Postharvest losses inflicted by insect pests in stored grains represent major challenge smallholder famers face in the global South. The maize weevil (Sitophilus zeamais) is one of the most important postharvest pests in maize. With dry maize stored in woven polypropylene bags, Likhayo et al. (2018) found that insect pests (maize weevils and another maize pest called the lesser grain borer [Prostephanus truncatus]) reduced grain weight by 36%. Such losses threaten farmers’ food security and overall financial stability.

Extensive research has investigated postharvest control of insect pests (including maize weevil). Practices that have been studied include the use of resistant varieties (Abebe et al., 2009), airtight storage bags (Likhayo et al., 2018) and maize cob powder (Nwosu et Nwosu, 2012). ECHO has also explored the use of sealed containers using the following techniques/strategies:

All these techniques aim at reducing the amount of oxygen available to the pests within the empty spaces in a container, thus increasing their chances of suffocation. However, some equipment used to remove or replace oxygen may be out of reach to farmers and grinding maize cobs may be time consuming and/or costly. That is why we decided to investigate the control of S. zeamais by simply increasing the volume (of a sealed storage container) occupied by the seeds, which reduces the volume of air (oxygen) available to the weevils. We hypothesized that reducing air space within sealed containers will help control maize weevil in stored maize seeds by depriving them the access to oxygen. This approach works if the container is hermetically sealed, meaning that there are no leaks that would allow the movement of outside air into the container.

Methodology

To conduct the experiment, we used 12 jars that we filled with maize seeds (Figure 1) as follows:

  • 4 jars with 100% of their volume occupied with seeds = Full.
  • 4 jars with 50% of their volume occupied with seeds = Half
  • 4 jars with 25% of their volume occupied with seeds = Quarter

Twenty live maize weevils were added to each container before hermetically sealing (by screwing the lid on tight) and placed in a screened-in porch for six months at ambient conditions. Two sets of data were collected for a total of eight response variables:

  1. The first dataset consisted of data collected for the whole container where the following response variables were measured:
    a. Total live weevils.
    b. Total dead weevils.
    c. Maize powder weight

  2. For the second dataset, a subset of a hundred kernels were randomly sampled from each container and the following data were collected:
    a. Number of damaged kernels/100 kernels
    b. Number of holes/100 kernels
    c. Number of live weevils/100 kernels
    d. Number of dead weevils/100 kernels
    e. Weight of 100 kernels


    Figure 1: Overview of the weevil control experiment laid out as a RCBD with 4 reps and 3 treatments (F=Full; H=Half and Q=Quarter)

Findings

Results for the parameters investigated, though not all statistically significant, met our expectations of less weevil damage with full than partially filled (25% to 50%) containers (Figures 2 and 3). Our findings met our expectations for most of the parameters investigated where maize seeds in the containers filled at 25% of their volume were more greatly affected by the maize weevil infestation while those that were full of seeds suffered the least damages (Figures 2 and 3).


Figure 2: Bar plots of a) total powder weight generated by maize weevils’ feeding activity; b) total live maize weevils per treatment; c) total dead maize weevils per treatment.


Figure 3: Bar plots of a) damaged kernels within a 100 kernels sample per treatment; b) Dead maize weevils within 100 kernels sample per treatment; c) live maize weevils within 100 kernels sample per treatment; d) number of holes within 100 kernels sample per treatment.

Conclusion

In conclusion, these results fell in line with our hypothesis that the emptier the space within the sealed containers, the more oxygen available for the weevils, thus, the longer they will survive/proliferate and negatively impact maize kernels over time. Our findings suggest that filling up containers completely full of seeds, and keeping them hermetically sealed, can help control maize weevils in stored maize seeds by limiting their access to oxygen but may not complete control the pest population. This quite simple method of controlling weevils can help farmers reduce postharvest loss. This method can be coupled with some of the other strategies mentioned earlier to increase the weevils’ control in maize. Findings have implications for storing seeds for consumption or future planting.

Have you ever tried this method? What were your findings? Have you ever coupled it with some other techniques? Share your thoughts with us

References

  1. Abebe, F., Tefera, T., Mugo, S., Beyene, Y., and Vidal, S. 2009. Resistance of maize varieties to the maize weevil Sitophilus zeamais (Motsch.) (Coleoptera: Curculionidae). African Journal of Biotechnology, 8:21.

  2. Likhayo, P., A. Y. Bruce, T. Tefera, and J. Mueke. 2018. Maize Grain Stored in Hermetic Bags: Effect of Moisture and Pest Infestation on Grain Quality. Journal of Food Quality. 3:1-9. DOI:10.1155/2018/2515698

  3. Nwosu, L. C., and Nwosu, U. I. (2012). Assessment of maize cob powder for the control of weevils in stored maize grain in Nigeria. Journal of Entomological Research, 36(3), 195-199.

Diatomaceous earth, a powder, seems like a potential solution. It can be very inexpensive and even nutritionally beneficial but sourcing might be difficult. This stuff would kill the weevils by tearing them to death with microscopic sharp edges.

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