Plodia interpunctella Cryptolestes ferrugineus Field Evaluation of Three Diatomaceous Earth Application Treatments for Controlling Stored Wheat Insects Edmond L. Bonjour1, Siwei Liu1, Thomas W. Phillips1, and Frank H. Arthur2 1Oklahoma State University, Department of Entomology and Plant Pathology, 127 Noble Research Center, Stillwater, OK 74078 2USDA-ARS Grain Marketing and Production Research Center, 1515 College Avenue, Manhattan, KS 66502 E-mail addresses: ELB4119@okstate.edu; lsiwei@okstate.edu; tomp@okstate.edu; arthur@gmprc.ksu.edu E.L. Bonjour Rhyzopertha dominica Lesser Grain Borer Plodia interpunctella Indianmeal Moth Tribolium castaneum Red Flour Beetle Cryptolestes ferrugineus Rusty Grain Beetle Sitophilus oryzae Rice Weevil Background Diatomaceous earth (DE) is an alternative to chemical control for the protection of stored grains. DE absorbs insect cuticular waxes resulting in death by desiccation. Factors limiting its acceptance for replacing chemical controls are that DE lowers the grain test weight when applied to the entire mass of grain and it is listed as a foreign substance when the grain is graded. The most effective treatments of DE are those made to the entire grain mass, but these reduce grain quality. It may be possible to protect grain by creating barriers with DE to prevent insect infestations. Barriers of DE would cost less than an entire treatment and may not affect test weight when the grain is mixed during unloading. Objectives Compare the efficacy of three diatomaceous earth applications to hard red winter wheat stored in steel grain bins in Oklahoma and challenged with introduced insect infestations. Assess the residual activity of these applications in a laboratory bioassay on pests of stored wheat at the end of the storage period. Determine if test weight of the grain is affected by various DE treatments at time of unloading bins. ab a b NS c Mean number of beetles Fig. 6. Mean number of T. castaneum adults collected from grain trier samples Mean number of beetles b a ab NS Fig. 7. Mean number of R. dominica adults collected from grain trier samples NS b a Mean number of beetles Fig. 8. Mean number of C. ferrugineus adults collected from grain trier samples b a c NS 5500 Fig. 9. Mean number of T. castaneum adults collected in probe traps Mean number of beetles Fig. 10. Mean number of R. dominica adults collected in probe traps Mean number of beetles a b NS Mean number of beetles b a ab NS Fig. 11. Mean number of C. ferrugineus adults collected in probe traps Experimental Protocol Three DE applications of Dryacide® and an untreated control were applied to wheat at bin filling in July 2004 (3 bins per treatment) in bins containing 170 bushels of hard red winter wheat (Fig. 1) DE applications were as follows: 1) top-layer application to the top 50 cm of grain (500 ppm) 2) layered application – top and bottom 50 cm of grain (500 ppm) in combination with an empty bin application 3) total grain mass application (300 ppm) All bins were challenged with insect infestations by the addition of 100 adults each of R. dominica, T. castaneum, and C. ferrugineus into the tops of each bin at the time of bin filling and for the next three consecutive weeks Field Sampling Grain samples were collected from the bins by combining two grain trier samples per bin at 4, 8, 12, 16, 20, and 36 weeks post-treatment and insects were sifted from the samples and counted (Fig. 2) One probe trap sample per bin was collected for a duration of one week at each of the above post-treatment periods and the insects trapped were identified and counted (Fig. 3) Fig. 1. Experimental grain bins. Fig. 2. Grain trier. Adult (P1) Mortality (%) a b NS ab Fig. 12. Mean adult beetle mortality in bioassays at end of study – 28 April 2005 Mean Number of F1 Progeny c b NS a Fig. 13. Mean number of F1 beetle progeny in bioassays at end of study – 28 April 2005 Percent Adult Emergence ab b c a Fig. 14. Mean adult emergence of P. interpunctella adults in bioassays at end of study – 28 April 2005 Fig. 3. Probe trap. Results For most sampling dates, fewer insects were captured in bins where DE was applied to the entire mass (Figs. 6-11) In general, there was no difference in the number of insects captured in bins where DE was applied to the top layer only or to the top and bottom layers (Figs. 6-11) Mortality was highest for R. dominica and S. oryzae adults in grain treated entirely with DE than the other treatments in the bioassays at the end of the study but there was only partial control (Fig. 12) T. castaneum were unaffected by any treatments in the bioassay for adult mortality (Fig. 12) Fewer LGB progeny were produced on all DE applications than the control with the entire treatment having fewer progeny than either of the layer treatments (Fig. 13) Fewer RW progeny were produced on the entire DE treatment and the layer treatments were not significantly different from the untreated control (Fig. 13) No significant difference was observed in RFB progeny production (Fig. 13) Only the entire grain mass application significantly reduced emergence of IMM adults in bioassays (Fig. 14) Test weights were significantly lower in bins where the DE was applied to the entire mass than all other treatments at the end of the study, and the layer treatments were significantly lower than the control bins (Table 1) July 2004 May 2005 Treatment Grade TW1 Grade TW2 Control 1 61.6 1 62.8 1 61.6 a 1 62.9 a 1 61.7 1 62.7 Top SG 56.5 1 60.4 SG 56.7 c SG 61.1 b SG 57.1 SG 59.7 Layered SG 57.3 SG 60.3 SG 57.2 b SG 58.3 b SG 57.6 1 60.1 Entire Mass SG 56.0 SG 56.4 SG 55.9 SG 55.8 TW = test weight in pounds SG = sample grade (not fit for human consumption) 1 test weight from samples taken with grain trier in bin after treatments were applied 2 test weight from samples taken with grain trier after unloading and mixing of entire grain mass Table 1. Official grades and test weights at beginning and end of study d c Laboratory Bioassays At the end of the 36-week storage period, approximately 100 grams of grain from trier samples were placed in each of 3 jars (0.24 liter) for each bin (3 reps per treatment per species) A total of 50 R. dominica, T. castaneum, or S. oryzae adults that were 2-3 weeks old was added to each jar for a specific species Bioassays for adult beetle mortality (7 day exposure) and F1 progeny production (after 7 weeks) were conducted at 28.0 °C and ~65% relative humidity (Fig. 4) P. interpunctella were evaluated at 36 weeks by placing 20 eggs on sticky black paper strips placed on 40 grams of half-crushed wheat in 0.12 liter jars and emerged adults were counted (Fig. 5) Fig. 4. Bioassay for beetles. Fig. 5. Bioassay for moths. Conclusions Dryacide® is not effective in controlling stored grain insects when applied as a layered treatment to small bins Even with mixing of the grain at the end of the study, layered treatments still had reduced test weights