Absorbacide™ Efficacy as a grain protectant and insecticide
15 July, 2015
Efficacy of Absorbacide™ as a grain protectant and insecticidal surface treatment for control of insect pests of stored grain.
Patrick J. Collins and Tina M. Lambkin
Queensland Department of Primary Industries
80 Meiers Road , Indooroopilly, QLD 4068
Introduction
Diatomaceous earths (DEs), such as Absorbacide™, have insecticidal properties that can be exploited to control insect pests of stored products (Subramanyam and Roesli 2000). The advantage of these materials is that they are non-toxic replacements for the residual chemicals used as surface treatments and grain protectants.
The diatomaceous earth, Dryacide®, is registered in Australia for control of insect pests of stored grain, both as a surface treatment and as a grain protectant. As this material was the first to be registered and has had wide acceptance in the grain industry, we have used it as the standard with which to compare Absorbacide™.
The aim of these experiments was to compare the efficacy of Absorbacide™ with two other DEs, Dryacide®, and a second material from the Hell Hole mine west of Brisbane.
Materials and Methods
Diatomaceous earths
Samples of Absorbacide™, and Hell Hole were supplied by Steve Graham (Absorba-stone and Wondergrow Products). Dryacide® was obtained commercially.
Insect species tested
Efficacy of the three DEs was tested against the major coleopterous pests of stored grain including:
Lesser grain borer, Rhyzopertha dominica
Granary weevil, Sitophilus granarius
Rice weevil, Sitophilus oryzae
Sawtoothed grain beetle, Oryzaephilus surinamensis
Rust-red flour beetle, Tribolium castaneum.
Efficacy as a grain protectant
50 adult test insects were added to organic wheat (500g) either untreated (control) or treated with one of the test DEs at a rate of 1 kg/tonne grain. Each treatment was replicated 3 times. Grain bioassays were stored in constant conditions of 25 oC and 55% relative humidity. Total number of insects (parents and progeny) surviving each treatment were counted 8 weeks later.
Efficacy was quantified as the number of living adult insects in each treatment compared with the total number of living adults in the parallel control.
Efficacy as a surface treatment
20 adult test insects were confined to concrete surfaces (56.74 cm 2 discs) treated with one of the test DEs at the intended label rate of 2 g/m 2 or to untreated concrete surface (control). The mortality of test insects was recorded each day for a period of up to 17 days. The insects were provided with food during the exposure period and the experiments were maintained in constant conditions of 25 oC and 55% relative humidity. Each treatment was replicated 5 times. Results are reported as mean % mortality of the 5 replicates at each observation.
Results
Efficacy as a grain protectant (Table 1)
All of the DEs tested completely suppressed populations of O. surinamensis and were very effective against S. granarius suppressing >98% of population growth. Both Dryacide® and Absorba-cide® were almost as effective against S. oryzae but Hell Hole was less effective. R. dominica was the most difficult species to control with DEs. Dryacide® and Absorba-cide® each produced about 84% suppression but the Hell Hole treatment resulted in only about 58% control of this species.
Efficacy as a surface treatment
All DEs tested were most effective against S. granarius (Fig. 1) and S. oryzae (Fig. 2). For example, S. oryzae was completely controlled by Dryacide® in 6 days and by both Absorbacide™ and Hell Hole in 5 days. Absorbacide™ was the most effective material against O. surinamensis providing complete control in 10 days followed by Hell Hole and Dryacide which gave 100% mortality in 12 days (Fig. 3). Hell Hole performed relatively poorly against R. dominica (Fig. 4) and T. castaneum (Fig. 5) providing 100% mortality after 17 and 15 days, respectively. These species were completely controlled by Dryacide® in 8 (R. dominca) and 10 (T. castaneum) days, with Absorbacide™ taking a little longer for complete mortality at 10 and 13 days, respectively.
Time taken, in days, for each of the test DEs to provide complete mortality are listed in Table 2.
Conclusions
These experiments revealed no significance difference between the activities of Dryacide® and Absorbacide™ as grain protectants. Hell Hole, however, was not as effective as the other two treatments.
In general, each of the three DEs tested could yield complete control of test insects on surfaces given enough time (Table 2).
If the criterion of efficacy for a surface treatment is speed of action to 100% mortality, then the most effective treatment was Dryacide® as it controlled 3 of the test species faster than Absorbacide™. However, in the field, there is probably no significant difference between getting complete mortality at, for example, 10 days compared with complete mortality at 12 days. In addition, if the criterion of efficacy is time taken to achieve a lower % control, say 75-80%, then there is little difference in the performance of Absorbacide™ and Dryacide® (Fig. 4 and 5).
Reference cited
Subramanyam, B. and Roesli, R. (2000). Inert Dusts In Subramanyam, B. and Hagstrum, D.W. (Eds). Alternatives to pesticides in stored product IPM. Kluwer, Boston .
Table 1.
Percent suppression of insect populations in grain either untreated (Control) or treated with diatomaceous earths at a rate of 1 mg/kg. Insects were held for 8 weeks at 25 oC, 55% r.h. after treatment
Table 2.
Summary of times (days) to complete mortality of insect pests of grain exposed to surfaces treated with various diatomaceous earths
