Trapping Tribolium castaneum (Coleoptera: Tenebrionidae) and Other Beetles in Flourmills: Evaluating Fumigation Efficacy and Estimating Population Density

Abstract

This paper reports beetle pests common to flourmills targeted during a series of trapping studies over a two-year period in flourmill 1 and a one year period in flourmill 2. Objectives were (1) use pheromone-baited traps to detect T. castaneum (Herbst) and other pest species present for their distribution over space and time, (2) monitor T. castaneum activity before and after fumigations to assess efficacy of the treatment, and (3) correlate counts of T. castaneum via trap capture against direct T. castaneum counts from samples of the milled flour to assess the value of trap data to estimate relative size of the pest population. Traps were deployed in two different flourmills over two consecutive years. T. castaneum was the most commonly trapped beetle during both years in mill 1. In mill 2, Typhaea stercorea (L.) and Cryptolestes ferrugineus (Stephens) were both captured in higher numbers than T. castaneum. In mill 1, trap capture was higher overall during Year 2 for most of the species compared with capture during Year 1, likely due to a dust cover modification made for the pitfall trap used in Year 2. Trap capture was also evaluated by location within the mills and a significant difference was found in the capture of T. stercorea during both years in mill 1. T. castaneum captures were significantly reduced following most fumigations, which used methyl bromide in milling areas and phosphine in bulk-stored finished flour. However, in most cases trap catches showed that beetle populations were not eliminated. Trap captures after fumigation suggest either that the fumigations were not entirely effective, or that full grown adult beetles were entering the mill soon after fumigation. When captures of T. castaneum from traps in two spaces of mill 1 during Year 2 were compared with counts of beetles from samples of siftings collected in the finished flour, the correlation coefficients were nearly significant for both sets of traps.

Keywords: Cryptolestes ferrugineus; Typhaea stercorea; methyl bromide; pheromone; phosphine; red flour beetle; stored products; traps.

Figure 1

Layout of mills 1 & 2. Traps were deployed on floors three to eight of mill 1, in the rooms above and below the bulk flour bins, and in warehouse 1. Traps were deployed among all mill 2 floors (basement to fourth floor) and the corresponding warehouse areas of each floor (basement to third floor).

Figure 2

Capture of the three most commonly trapped beetle pests by locations within mill 1 during Year 1. Results are from 13 biweekly observations from 34 pitfall traps. Capture of Tribolium castaneum was not significantly different by location (F = 1.77; df = 9, 25; p = 0.1241). There was a significant difference in capture of Typhaea stercorea (F = 10.90; df = 9, 25; p = 0.0001). Capture of Cryptolestes ferrugineus was not significantly different by location (F = 1.57; df = 9, 25; p = 0.1791). Mean captures of T. stercorea with the same letter are not significantly different.

Figure 3

Capture of the three most commonly trapped beetle pests by location within mill 1 during Year 2. Results are from 18 weekly observations from 16 modified pitfall traps. Capture of T. castaneum was not significantly different by location (F = 2.59; df = 4, 11; p = 0.0952). There was a significant difference in capture of T. stercorea (F = 4.79; df = 4, 11; p = 0.0176). Capture of Oryzaephilus surinamensis was not significantly different by location (F = 0.66; df = 4, 11; p = 0.6315). Means with the same letter are not significantly different.

Figure 4

Capture of the three most commonly trapped beetle pests by location within mill 2 during Year 2. Results are from 18 weekly observations from 17 modified pitfall traps. Capture of T. stercorea was not significantly different by location (F = 2.28; df = 8, 8; p = 0.1326). There was not a significant difference in capture of C. ferrugineus (F = 0.84; df = 8, 8; p = 0.5917). Capture of T. castaneum was not significantly different by location (F = 1.25; df = 8, 8; p = 0.3804).

Figure 5

Trap capture throughout mill 1 (top graph) and counts of T. castaneum from six load-out system tailings during Year 1 (bottom graph). Results are from biweekly observations from 34 pitfall traps. Load-out counts are consolidated to correspond with trapping times and intervals. Arrows denote fumigations on 31 May and 30 August. Significantly fewer numbers of beetles were trapped following the 31 May methyl bromide fumigation (t = 2.13; df = 23; p = 0.0455, shown with a * in the top graph), but not after the 30 August fumigation. Significantly fewer beetles were sampled from tail-overs following the 30 August phosphine fumigation (t = 6.83; df = 5; p = 0.0010, shown with ** in the bottom graph), but not following the 31 May fumigation. Count data for t-tests were square root transformed.

Figure 6

Trap capture throughout mill 1 and counts of T. castaneum from six load-out system tailings during Year 2. Trapping results are from weekly observations from 16 modified pitfall traps. Load-out counts are consolidated to correspond with trapping times and intervals. Arrows denote fumigation on 4 July. Beetle trap capture was significantly lower following methyl bromide fumigation (t = 3.72; df = 11; p = 0.0047, shown with ** in the top graph). Beetles sampled from tail-over samples were significantly lower following phosphine fumigation (t = 4.10; df = 4; p = 0.0262, shown with * in the bottom graph). Count data for t-tests were square root transformed.

Figure 7

Correlations (r, with significance of the correlation analysis, p) of T. castaneum trapped in mill 1 to those sampled from bulk load-out tail-overs during Year 2. Results are from 18 weekly observations from 16 modified pitfall traps (mill-wide data, top graph) and 2 modified pitfall traps (below bulk flour bins data, bottom graph). Load-out data are from six load-out systems.

Figure 8

Capture of T. stercorea, C. ferrugineus, and T. castaneum throughout mill 2 during Year 2. Results are from weekly observations from 17 modified pitfall traps. Arrows denote methyl bromide fumigation on 1 August. Capture of T. castaneum was significantly lower following methyl bromide fumigation (t = 3.88; df = 16; p = 0.0015; a ** signifies statistical significance after 1 August). Count data for t-tests were square root transformed.