Abstract
Acoustic monitoring was applied to consider hermetic exposure durations and oxygen levels required to stop adult Callosobruchus maculatus activity and economic damage on cowpea. A 15-d study was conducted with six treatments of 25, 50, and 100 C. maculatus adults in 500 and 1000 mL jars using acoustic probes inserted through stoppers sealing the jars. Acoustic activity as a result of locomotion, mating, and egg-laying was measured by identifying sound impulses with frequency spectra representative of known insect sounds, and counting trains (bursts) of impulses separated by intervals of <200 ms, that typically are produced only by insects. By the end of the first week of storage in all treatments, oxygen levels declined to levels below 4%, which has been demonstrated to cause mortality in previous studies. Concomitantly, insect sound burst rates dropped below an acoustic detection threshold of 0.02 bursts s−1, indicating that the insects had ceased feeding. Statistically significant relationships were obtained between two different measures of the acoustic activity and the residual oxygen level. Based on the experimental results, a simple equation can be used to estimate the time needed for oxygen to decline to levels that limit insect feeding damage and thus grain losses in hermetic storage containers of different insect population levels and various volumes.
Highlights
Cowpea (Vigna unguiculata (L.) Walp.) is an economically important indigenous protein source in the semi-arid tropical and subtropical world, namely Asia, Africa, southern Europe, and Central and South America [1]
The acoustic activity was minimal when the residual oxygen was less than 4%
Our results demonstrated that insects in all treatments ceased acoustic activity and became quiescent, i.e., ceased feeding, ovipositing, and other movements when O2 decreased below 4% during hermetic storage
Summary
Cowpea (Vigna unguiculata (L.) Walp.) is an economically important indigenous protein source in the semi-arid tropical and subtropical world, namely Asia, Africa, southern Europe, and Central and South America [1]. It is important in Sub-Saharan Africa compared to other regions, with consumption growing at the rate of 3.2% per annum between 1980 and 2009 [1]. Callosobruchus maculatus is an important pest of stored legume grains including cowpea and widely distributed all over the continent [4] It spreads with grain trade and greatly lowers the value of dried pulses in markets, especially in Sub Saharan Africa. Infestation usually starts in the field before harvest and proliferates to devastating levels during storage, depending on the methods of storage used
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