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Title: Using a lethality index to assess susceptibility of Tribolium confusum and Oryzaephilus surinamensis to insecticides

item AGRAFIOTI, PARASKEVI - University Of Thessaly
item ATHANASSIOU, CHRISTOS - University Of Thessaly
item VASSILAKOS, THOMAS - University Of Thessaly
item VLONTZOS, GEORGIOS - University Of Thessaly
item Arthur, Franklin

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2015
Publication Date: 11/11/2015
Publication URL:
Citation: Agrafioti, P., Athanassiou, C.G., Vassilakos, T.N., Vlontzos, G., Arthur, F.H. 2015. Using a lethality index to assess susceptibility of Tribolium confusum and Oryzaephilus surinamensis to insecticides. Journal of Stored Products Research. 10(11): e0142044. doi: 10.1371/journal.pone.0142044.

Interpretive Summary: Insects that are exposed on a surface treated with an insecticide can be temporarily incapacitated but can potentially recover from this condition. We tested four different insecticides at two application rates and exposed adult stored product beetles on concrete and metal surfaces treated with those insecticides, and developed an index to assess mortality. Higher index values are correlated with greater mortality. Index values were lower for some insecticides than others, indicating that recovery from incapacitation had occurred. Index values for three of the four insecticides were also higher on metal compared to concrete, indicating lower effectiveness of the insecticide on concrete. Management personnel can use the results to select the appropriate insecticide for use as a treatment to a particular surface to control stored product beetles in storage and processing facilities containing grain and grain-based products.

Technical Abstract: We evaluated the knockdown effect caused by four insecticides: alpha-cypermethrin, chlorfenapyr, pirimiphos-methyl and fipronil against Tribolium confusum and Oryzaephilus surinamensis adults. Furthermore, for the same species and insecticides, we developed a “lethality index”, to assess knockdown patterns. For this purpose, bioassays were conducted on concrete and metal surfaces. Adults of the tested species were exposed on both surfaces treated with the above insecticides at two doses (low and high). Knockdown assessment was done after 15, 30 and 60 min of adult exposure on the treated surfaces. Also, after 1, 3, 5, 7 and 14 d of exposure, a lethality index was calculated with an equation resulting in values from 0 to 100, where 100 indicated complete mortality and 0 complete survival. For the lethality index calculation, each adult exposed on the surface was ranked from 0 to 4, based on a scale as follows; 0: adults moved normally, 1: adults were knocked down, but were able to walk for short intervals, 2: adults were knocked down and unable to walk, but with visible movement of antennae etc., 3: adults were knocked down, with very minimal movement of the tarsi and the antennae and 4: adults were dead (no movement). Knockdown of adults immediately after exposure (15-60 min) was higher for pirimiphos-methyl followed by alpha-cypermethrin, for both dose rates tested and species, but only on the metal surface. The lethality index was high and near 100 for all insecticides after 5d of exposure for O. surinamensis, while for T. confusum adults the lethality index was consistently low for alpha-cypermethrin, suggesting that that recovery occurred. Among the insecticides examined here, chlorfenapyr was the only one that was more effective on concrete than on metal, while the reverse was noted for the other three insecticides.