Oxygen consumption and acoustic activity of adult Callosobruchus maculatus F. (Coleoptera: Chrysomelidae: Bruchinae) during hermetic storage

Authors: NJOROGE, ANASTASIA - Purdue University; Mankin, Richard; SMITH, BRRADLEY - Purdue University; BARIBUTSA, DIEUDONNE - Purdue University

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2018
Publication Date: 4/20/2018
Citation: Njoroge, A.W., Mankin, R.W., Smith, B.W., Baributsa, D. 2018. Oxygen consumption and acoustic activity of adult Callosobruchus maculatus F. (Coleoptera: Chrysomelidae: Bruchinae) during hermetic storage. Insects. 9(2):45. https://doi.org/10.3390/insects9020045.
DOI: https://doi.org/10.3390/insects9020045

Interpretive Summary: Post-harvest loss of stored grain to insect damage is a major concern for farmers, millers and warehouses thought the U.S. and the world. The loss of fumigants as a control measure has required the implementation of new methods to control these stored grain pests. Hermetic grain storage, containment in an airtight (hermetically sealed) container that results in consumption of the oxygen and death, has been used successfully to control pests in small storage facilities in sub-Saharan Africa. However, the time course of oxygen depletion and death is not well-understood. Students and scientists at Purdue University and scientists at the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, FL, used acoustic monitoring to assess the activity of adult cowpea insect pests over time after they were placed in hermetically sealed containers. Oxygen depleted enough to reduce insect activity to negligible levels within 7 days. The information was used to estimate how long typical cowpea infestations would survive in commonly used 50-kg bags. This information can be used by farmers, millers and warehouse managers to develop protocols to reduce insect pest damage in stored crops and processed products.

Technical Abstract: Acoustic monitoring was applied to consider hermetic exposure durations and oxygen levels required to stop Callosobruchus maculatus feeding 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 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 and economic damage in hermetic storage containers of different volumes and different insect populations.