Influence of grain type on the insecticidal efficacy of two diatomaceous earth formulations against Rhyzopertha dominica (F) (Coleoptera: Bostrychidae)

Abstract

Laboratory bioassays were carried out in order to evaluate the effectiveness of two diatomaceous earth (DE) formulations, Insecto and SilicoSec, against adults of Rhyzopertha dominica (F) in eight different grain commodities. The adherence of the two DEs to each grain was also measured. The eight grains tested were wheat, whole barley, peeled barley, oats, rye, triticale, rice and maize. These commodities were treated with the DEs at three rates, 0.75, 1.0 and 1.5 g DE kg(-1) grain. The mortality of R dominica adults was measured after 24 h, 48 h, 7 days and 14 days of exposure in the treated grains at 26 degrees C and 55% RH. After the 14-day mortality count, all adults were removed and the treated grains retained under the same conditions for a further 60 days. The treated grains were subsequently examined for F1 progeny. Significant differences were recorded among the eight grain types as well as between the DE formulations tested. After 14 days of exposure, even at the lowest DE rate for both formulations, adult mortality was high (>90%) in wheat and triticale. In contrast, adult mortality was significantly lower in peeled barley. Increasing the rate improved the efficacy of the DEs significantly in only some of the grains tested. Reproductive capacity in all the treated grains was significantly suppressed when compared with untreated grains. Generally, more F1 individuals of R dominica were noted in the treated peeled barley than in the other commodities. Significant differences in the percentage of DE retention were noted among the eight grains. The highest retention level was noted in rice (>87%) and the lowest in maize (<6%). However, the degree of DE adherence to a given grain was not always indicative of the effectiveness of DE against R dominica.

Bioactivity of raw diatomaceous earth against Rhyzopertha dominica Fab. (Coleoptera: Bostrichidae): Effects of grain type, dose rate and exposure period

“…Our results are in agreement with the findings of La Hue [24], Wakil et al [25 ] and Athanassiou et al [26] who also reported that adult mortality increased with increase in dose rate and exposure period, and efficacy varied between grain types. Variations in efficacy of DEs among different grain types has been noted in a series of recent studies, involving tests with different DE products on different grain types [14,15,27,28]. The significant interaction effect (P<0.001) between dose rate and grain type on mortality of R. dominica noted in this study, confirms the aforementioned statements that DE efficacy is influenced by grain type.…”

Direct and admixture toxicity of diatomaceous earth and monoterpenoids against the storage pests Callosobruchus maculatus (F.) and Sitophilus oryzae (L.)

“…One of the most promising alternatives to synthetic contact insecticides in stored product protection is the application of diatomaceous earth (DE) (Fields and Korunic 2000;Vayias and Athanassiou 2004;Athanassiou et al 2005;Kavallieratos et al 2005). Although several modes of action have been proposed (Subramanyam and Roesli 2000), it is today generally accepted that damage occurs to the protective wax layer in the insect's cuticle, resulting in water loss and desiccation (Mewis and Ulrichs 1999;Subramanyam and Roesli 2000).…”

Relative Susceptibility of Four Coleopteran Stored-product Insects to Diatomaceous Earth SilicoSec®

“…It is not known whether the results obtained in this study would hold true under different conditions. Perhaps different results may be obtained if the DE were to be tested on grains other than wheat or maize because DE efficacy is known to vary among grain types [4,5,16,32]. The susceptibility of a given species to DE might be influenced by the insect strain [33].…”

“…temperature [2,[14][15][16], moisture content or relative humidity [15,[17][18][19], and type of grain commodity [4,20,21]. Laboratory experiments have also revealed significant effect of insect species [15], insect strain [22,23], stage [19,24].…”