Effects of hermetic storage on adult Sitophilus oryzae L. (Coleoptera: Curculionidae) acoustic activity patterns and mortality

Authors: NJOROGE, A - Purdue University; Mankin, Richard; SMITH, B - Indiana University-Purdue University; BARIBUTSA, D - Purdue University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2017
Publication Date: 10/16/2017
Citation: Njoroge, A.W., Mankin, R.W., Smith, B.W., Baributsa, D. 2017. Effects of hermetic storage on adult Sitophilus oryzae L. (Coleoptera: Curculionidae) acoustic activity patterns and mortality. Journal of Economic Entomology. 110(6):2702-2715.
DOI: https://doi.org/10.1093/jee/tox260

Interpretive Summary: When insects are placed in an airtight (hermetically sealed) container of grain, they consume all the oxygen and die, reducing the economic damage. Hermetic storage 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. Acoustic methods can be used to determine the activity levels of insects as they suffer oxygen deprivation and perish. Students and scientists at Purdue University of Florida and scientists at the USDA, Agricultural Research Service, Center for Medical, Agricultural, and Veterinary Entomology, Gainesville, Florida, used acoustic sensors to monitor activity of adult rice weevils over time after they were placed in hermetically sealed containers. Oxygen depleted enough to reduce insect activity to negligible levels within 3 to 14 days depending on the number of insects and the initial amount of oxygen in the container. Such information is of value to farmers and warehouse managers attempting to reduce pest damage in stored crops.

Technical Abstract: Hermetic storage is of interest to farmers and warehouse managers as a method to control insect pests in small storage facilities. To develop improved understanding of effects of hermetic storage on insect pest activity and mortality over time, oxygen levels, acoustic signals, and observations of visual movement were recorded from three replicates each of 25, 50, and 100 adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae) hermetically sealed in 500- and 1000-ml glass jars. Recordings were done for 28 d; twice daily for the first 6 days and twice weekly thereafter. Insect sounds were identified by signal analysis software as short bursts (trains) of impulses with spectra that matched average spectra (profiles) of previously verified insect sound impulses. Oxygen consumption was highest in treatments of 100 insects / 500-ml-jar and lowest in 25 / 1000-ml-jars. The rates of bursts per insect, No. impulses per burst, and rates of burst impulses per insect decreased as the residual oxygen levels decreased in each treatment. Activity rates < 0.02 bursts s-1, the acoustic detection threshold, typically occurred as oxygen fell below 5%. Mortality was observed at 2% levels. The time to obtain these levels of insect activity and oxygen depletion ranged from 3 - 14 days. Acoustic detection made it possible to monitor insect activity during hermetic storage and estimate the duration required for reduction of activity to levels resulting in negligible damage to the stored product. Such information is of value to farmers and warehouse managers attempting to reduce pest damage in stored crops.