Detection of stored‐wheat beetle species and estimation of population density using unbaited probe traps and grain trier samples

Abstract

Field studies were conducted in order to compare the effectiveness of unbaited probe traps and grain trier samples in the detection of several beetle species. On June 15, 1997, fourteen probe traps were placed in three steel bins containing wheat in Central Greece. Two of them were inserted in the central zone of the bulk, five in the half of the bin radius (median zone) and seven near the bin wall (distal zone). From June 30 up to and including January 1998, the traps were checked for adult beetles every fifteen days (15 sampling dates in total). On each date, samples were also taken from spots adjacent to trap locations, using a grain trier. The mean temperatures recorded near the bulk surface decreased by an average of 1.16 • C per sampling date. Twenty-four species, belonging to 14 families of Coleoptera were found. The most abundant species in the traps were Cryptolestes ferrugineus and Tribolium castaneum, while Sitophilus oryzae was the most abundant in the samples. Significantly greater numbers of adults were found in traps than in samples, during the whole sampling period; traps also detected adults in most locations while in the corresponding samples no adults were found. Significantly higher numbers of adults were found in the central sampling zone, using both devices. Taylor's power law parameters showed that in both sampling methods the most abundant species showed aggregated spatial patterns. Although the correlation coefficient values between trap catches and number of adults per trier sample differ significantly from zero (P < 0.01) in a high number of sampling dates, it can be concluded that traps are poor indicators of population density. The accuracy provided as a percentage of the mean, decreases exponentially with the increase of the mean value. Based on traps, the desired accuracy level (35%) is not achievable even in higher mean values or even with high numbers of traps. On the contrary, with trier samples it is possible to estimate population density with a relatively low number of sampling units. Significant differences in the required number of sampling units (sample size) were noted among species.

Kernel-kernel interactions and behavioral responses of Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

“…However, in storage facilities where newly-harvested and aged maize is present at the same time, all kernel categories examined here are likely to coexist and, based on our results, fresh and stored maize has the same possibility of being infested by S. zeamais. Newly harvested grains are less likely to be heavily infested (Hagstrum, 1987;Athanassiou and Buchelos, 2001), but this is also because insect populations at that time are low.…”

Three-dimensional distribution and sampling indices of insects and mites in horizontally-stored wheat

“…and moth larvae. For the statistical analysis, only the number of live individuals found was used, as only these correspond to actual population densities (Hagstrum et al, 1998;Athanassiou and Buchelos, 2001). For mite extraction from the samples, the Berlese-Tullgren method was used (Haarlov, 1947).…”

“…This multispecies "patchiness" is likely to increase the required number of sampling units exponentially (Subramanyam and Harein, 1990;Athanassiou and Buchelos, 2001), and hence, the reliability of sampling is negatively affected. In addition, insect and mite distributions are likely to be dissimilar, which means additional complications when estimating their presence ).…”

Factors affecting the insecticidal efficacy of the diatomaceous earth formulation SilicoSec® against adults of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

“…Exposure studies were conducted at three temperatures, 22, 27 and 30°C and two levels of rh, 55 and 65%. The above temperature values were selected since they belong to the most common thermal range (22-32°C), which prevails inside wheat storage facilities, in relation to beetle infestation in Greece (Athanassiou and Buchelos, 2001). In particular, the temperatures 27 and 30°C also belong to the optimum thermal range (27-31°C) for the development of S. oryzae (Howe, 1965;Fields, 1992).…”