The combined use of spinosad with deltamethrin against adults of Sitophilus oryzae, Sitophilus granarius and Tribolium confusum was evaluated in a series of laboratory bioassays in two hard wheat varieties (Athos and Sifnos). Two groups of bioassays were carried out. In the first group of bioassays, spinosad or deltamethrin were applied alone at the tested wheat varieties at the doses of 0.01, 0.1 and 0.5 ppm for spinosad and 0.125 ppm for deltamethrin. In the second group of bioassays, the tested wheat varieties were treated with the combination of the above spinosad rates with 0.125 of deltamethrin. In both series of bioassays, mortality of the tested species was evaluated after 7 d of exposure on the treated wheat varieties at 25oC and 65% r.h. Mortality for all species was always significantly higher in Athos than Sifnos. The highest mortality of S. oryzae (73 and 40% for Athos and Sifnos respectively) or S. granarius (88% and 58% for Athos and Sifnos respectively) was recorded in the cases that spinosad was applied alone at 0.5 ppm. On the contrary, in the case of T. confusum, 0.125 ppm of deltamethrin was significantly more effective than any of the application rates of spinosad either when applied alone or in combination with deltamethrin. Despite the fact that the highest mortality of S. granarius adults was recorded after exposure on the wheat varieties treated with 0.1 ppm of spinosad x 0.125 ppm of deltamethrin, in light of the results of the present study, the combination of spinosad with deltmethrin requires further investigation since in most of the tested cases of the present study, single application of spinosad or deltamethrin was more effective or of equal effectiveness than the respective combination of spinosad with deltamethrin. Keywords: Spinosad, Deltamethrin, Tribolium, Sitophilus, Wheat, Variet

Athanassiou, C. G.

Kavallieratos, N. G.

Tatsi, G.

Vayias, B. J.

English

JKI Open Journal Systems (Julius Kühn-Institut)

10th International Working Conference on Stored Product Protection Julius-Kühn-Archiv, 425, 2010  919 Insecticidal action of the combined use of spinosad and deltamethrin against three stored-product pests in two stored hard-wheat varieties. Vayias, B.J.*#1, Kavallieratos, N.G.2, Athanassiou, C.G.3, Tatsi, G.1 1 Laboratory of Agricultural Zoology and Entomology, Agricultural University of Athens, 75 Iera Odos str., 11855, Athens, Greece. Email: bvayias@gmail.com 2 Laboratory of Agricultural Entomology, Department of Entomology and Agricultural Zoology, Benaki Phytopathological Institute, 8 Stefanou Delta str., Kifissia, Attica, Greece 3 Laboratory of Entomology and AgriculturalZoology, Department of Agriculture, Crop Production and Rural Environment, University of Thessaly, Phytokou str., 38443, N. Ionia, Mangisia, Greece * Corresponding author # Presenting author DOI: 10.5073/jka.2010.425.223 Abstract The combined use of spinosad with deltamethrin against adults of Sitophilus oryzae, Sitophilus granarius and Tribolium confusum was evaluated in a series of laboratory bioassays in two hard wheat varieties (Athos and Sifnos). Two groups of bioassays were carried out. In the first group of bioassays, spinosad or deltamethrin were applied alone at the tested wheat varieties at the doses of 0.01, 0.1 and 0.5 ppm for spinosad and 0.125 ppm for deltamethrin. In the second group of bioassays, the tested wheat varieties were treated with the combination of the above spinosad rates with 0.125 of deltamethrin. In both series of bioassays, mortality of the tested species was evaluated after 7 d of exposure on the treated wheat varieties at 25oC and 65% r.h. Mortality for all species was always significantly higher in Athos than Sifnos. The highest mortality of S. oryzae (73 and 40% for Athos and Sifnos respectively) or S. granarius (88% and 58% for Athos and Sifnos respectively) was recorded in the cases that spinosad was applied alone at 0.5 ppm. On the contrary, in the case of T. confusum, 0.125 ppm of deltamethrin was significantly more effective than any of the application rates of spinosad either when applied alone or in combination with deltamethrin. Despite the fact that the highest mortality of S. granarius adults was recorded after exposure on the wheat varieties treated with 0.1 ppm of spinosad x 0.125 ppm of deltamethrin, in light of the results of the present study, the combination of spinosad with deltmethrin requires further investigation since in most of the tested cases of the present study, single application of spinosad or deltamethrin was more effective or of equal effectiveness than the respective combination of spinosad with deltamethrin. Keywords: Spinosad, Deltamethrin, Tribolium, Sitophilus, Wheat, Variety 1. Introduction The consumers’ growing demand for residue-free goods as well as the fact that many species have now developed resistance to the most commonly used grain protectants (Arthur, 1996) have made essential the evaluation of new insecticides for the control of stored-product pests. Spinosad can be considered as one promising alternative to the currently used grain protectants, as it has low mammalian toxicity (Sparks et al., 2001; Subramanyam et al., 2003) and also it is effective against many of the most important stored-product pests (Fang et al., 2002; Athanassiou et al., 2008; Vayias et al., 2009). Deltamethrin is a pyrethroid insecticide, registered in many parts of the world for stored grain protection. This insecticide is also effective against stored-product pests and can provide a long-term protection that lasts four months or more (Athanassiou et al., 2004).  Insecticides vary regarding efficacy against different target species. For instance, spinosad is moderately effective against Tribolium spp. (Fang et al., 2002, Vayias et al., 2009), while deltamethrin is generally more effective against these species (Athanassiou et al., 2004). Hence, the combined use of more than one pesticide is likely to moderate these differences, and provide a grain protectant with satisfactory protection against a wider range of species. In a recent study, Athanassiou et al. (2009) found that the combined use of deltamethrin with chlorpyriphos-methyl successfully controlled stored-grain psocids, which could not be controlled with spinosad or natural pyrethrum. In the present study, the combined use of low spinosad combined with low deltamethrin application rates was evaluated on two hard wheat varieties originating from Greece. This combination was assessed against three stored-product pests  10th International Working Conference on Stored Product Protection 920  Julius-Kühn-Archiv, 425, 2010 which are very common to in bulk grains stored in Greece; two primary colonizers, the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae), and the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae), and one secondary colonizer, the confused flour beetle Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae). 2. Materials and methods Unsexed, <2 week-old adults of S. oryzae, S. granarius and T. confusum, obtained from laboratory cultures reared on hard wheat at 27 ± 1oC and 60 ± 5% relative humidity (r.h.) were used in the study. The tested wheat varieties were Athos and Sifnos obtained from Greek crops. The moisture content of the tested varieties at the beginning of the tests ranged between 10.9 and 11.5%. The grain characteristics of the tested varieties are given in Table 1. In the first group of tests four 1-kg lots of each variety were separately treated with three spinosad application rates (0.01, 0.1 and 0.5 ppm) and one deltamethrin rate (0.125 ppm). In the second group of experiments three 1-kg lots of each variety were separately treated with the combination of each spinosad rate x 0.125 ppm deltamethrin (e.g. 0.01 ppm spinosad x 0.125 ppm deltamethrin; 0.1 ppm spinosad x 0.125 ppm deltamethrin; 0.5 ppm spinosad x 0.125 ppm deltamethrin). In addition, a 1-kg lot of each grain was sprayed only with distilled water and served as the untreated control. From each treated (or untreated) 1-kg lot of grain, of a specific variety, three 30 g samples were obtained and used as a bioassay substrate with the above insect species at 25oC and 65% r.h. Mortality was assessed after 7 d of exposure of the tested species on the treated or untreated grains. The total procedure was repeated three times (3 x 3 vials per treatment) by preparing new 1-kg lots from each wheat variety each time. Data were analyzed separately for each species by a two way ANOVA with mortality as the response variable with grain variety and treatment as the main effects. For the separation of means the Tukey and Kramer HSD test was used at P<0.05 (Sokal and Rholf, 1995). Table 1 Grain characteristics of the tested wheat varieties. Wheat variety Specifications Αthos Sifnos Brush length Short short Kernel shape Ovoid semi elongate Mean (± SE) weight of 100 kernels (g) 4.3 ± 0.1 5.2 ± 0.1 Mean (± SE) kernel size of 100 kernels (ml) 5.7 ± 0.1 6.9 ± 0.2 Protein content (%N x 5.7) 16.5 14.5 Gluten index 22.14 64.4 Mean (± SE) bulk density (g/lt) 742.5 ± 0.2 744.5 ± 0.6  3. Results Mortality of the tested species on the untreated wheat varieties was negligible and did not exceed 2.5% in any of the tested cases. Irrespective of the treatment, susceptibility of all of the tested species was overall higher in treated Athos in comparison with treated Sifnos with the sole exception of the combination of 0.1 ppm spinosad x 0.125 ppm deltamethrin against S. oryzae, while the reverse was noted (Table 2). Among the tested species, T. confusum was the most tolerant to spinosad, deltamethrin or their combination. Sitophilus granarius was more susceptible than S. oryzae in all of the tested cases. Generally, the combination of spinosad with deltamethrin did not appear to be compatible for S. oryzae or T. confusum since the highest mortality ratio for those species was with 0.5 ppm of spinosad for the former and 0.125 ppm for the latter when these substances were applied alone rather than in combination. For instance, although 73% of the exposed S. oryzae adults were dead after exposure on Athos variety treated with 0.5 ppm of spinosad, mortality was only 39% on the same variety treated with 0.5 ppm spinosad x 0.125 ppm (Table 2). With T. confusum, mortality from exposure to spinosad was generally low and did not exceed 15% on both varieties, while it was slightly increased to 22% when 0.125 ppm of deltamethrin was applied to Athos prior to application of 0.5 ppm  spinosad. The combination of deltamethrin with spinosad also gave low mortality levels with T. confusum. Mortality was only 28% on wheat treated with 0.125 ppm of deltamethrin alone, and was significantly higher or of equal effectiveness with the tested spinosad combinations (Table 2). An additive effect of deltamethrin with spinosad was observed only when S. granarius was exposed to 0.1 ppm spinosad x 0.125 ppm 10th International Working Conference on Stored Product Protection Julius-Kühn-Archiv, 425, 2010  921 deltamethrin. In the latter case, efficacy of 0.1 ppm spinosad x 0.125 ppm deltamethrin increased to 90% in Athos and 62% in Sifnos while efficacy of the respective spinosad or deltamethrin doses when applied alone did not exceed 54% in Athos or 26% in Sifnos. The combination of 0.5 ppm of spinosad x 0.125 ppm deltamethrin, slightly improved the performance of the respective spinosad dose in Athos against S. granarius, but did not demonstrate an additive effect in Sifnos against the same species (Table 2). Table 2 Mean (±SE) mortality of adults of S. oryzae, S. granarius and T. confusum after 7 d exposure on two hard wheat varieties treated with spinosad alone, deltamethrin  alone as well as with the combination of spinosad and deltamethrin. Within a given species, means followed by the same letter are not significantly different (lowercase letters for treatments; uppercase letters for varieties). For treatments df=6, 62; For varieties df=1, 17; Tukey and Kramer HSD test at P<0.05.    Mortality (%) Dose (ppm) Wheat variety Species Spinosad Deltamethrin Athos Sifnos S. oryzae 0 125 47.4 ± 3.1 Abc 25.9 ± 3.0 Bbc  0.01 0 42.6 ± 3.9 Abc 20.0 ± 1.0 Bc  0.1 0 53.3 ± 4.4 Ab 29.3 ± 3.1 Bb  0.5 0 73.0 ± 3.7 Aa 39.6 ± 3.7 Ba  0.01 0.125  15.2 ± 3.6 Ad 19.3 ± 2.9 Ac  0.1 0.125  17.8 ± 3.1 Ad 24.4 ± 3.1 Abc   0.5 0.125  35.9 ± 2.3 Ac 32.6 ± 2.7 Aab S. granarius 0 125 66.3 ± 5.1 Ab 25.2 ± 1.4 Bc  0.01 0 53.3 ± 2.4 Ab 17.8 ± 1.8 Bc  0.1 0 57.4 ± 2.3 Ab 25.2 ± 2.2 Bc  0.5 0 88.1 ± 2.1 Ab 58.1 ± 3.0 Bab  0.01 0.125  61.1 ± 3.6 Aa 28.1 ± 1.9 Bc  0.1 0.125  90.0 ±2.5 Aa 62.2 ± 3.3 Ba  0.5 0.125  91.1 ± 3.0 Aa 49.6 ± 3.9 Bb T. confusum 0 125 28.1 ± 2.2 Aa 23.3 ± 3.0 Aa  0.01 0 1.9 ± 0.8 Ac 0.7 ± 0.5 Ac  0.1 0 4.8 ± 1.0 Ac 3.0 ± 1.5 Ac  0.5 0 14.4 ± 3.7 Ab 8.9 ± 1.6 Ab  0.01 0.125  2.6 ± 1.3 Ac 1.9 ± 0.6 Ac  0.1 0.125  3.7 ± 0.9 Ac 4.4 ± 1.4 Ac   0.5 0.125  21.5 ± 5.4 Aa 18.6 ± 3.3 Aa  4. Discussion In our study, the combined use of spinosad with deltamethrin at low application rates was not successful against S. oryzae or T. confusum, but was effective against S. granarius. With S. granarius only the specific combination of 0.1 ppm spinosad x 0.125 deltamethrin was highly effective since effectiveness of the remainding combinations against the same species was lower than or at least equal to the effectiveness of a single spinosad or deltamethrin application. It is possible that spinosad could synergize deltamethrin under specific conditions and for specific insect species; therefore more extensive research on this combination is needed. The fact that effectiveness of deltamethrin or spinosad varied between the tested varieties could be attributed to differences in physical or chemical characteristics of the grain, variations in insect behavior after contact with the treated kernels of a specific variety, or a combination of the above factors. Sifnos had more elongated, heavier and larger kernels compared to Athos. Also, gluten index was higher in Sifnos than in Αthos. The above characteristics may have affected the efficacy of the tested formulations, as the treated species were overall less susceptible on Sifnos than in Athos, although in the case of T. confusum the differences were not significant. Kernel size is likely to play an important role in efficacy of insecticides, since better distribution of the toxicant is achieved on smaller kernels compared to larger ones (Huang and Subramanyam, 2007). As a result, insects may be able to more easily avoid the treated areas of larger kernels and consequently, avoid contact with the toxic substance (Athanassiou et al., 2003).Since distribution of deltamethrin or spinosad was better in the  10th International Working Conference on Stored Product Protection 922  Julius-Kühn-Archiv, 425, 2010 smaller kernels of Athos compared to Sifnos, this could partially explain the higher mortality that occurred in Athos compared to Sifnos. Nevertheless, correlation of grain characteristics with efficacy of grain-insecticides is not always feasible. Fang et al. (2002), found that a significant variation in the performance of spinosad against several stored-product pests occurred among different wheat classes. The authors however, could not correlate this differential spinosad performance to grain kernel diameter, kernel weight, kernel hardness, protein content, dockage, or fiber. Hence, differential performance of insecticides among commodities or even varieties of a given commodity is a very complicated issue, and requires further experimental work. Generally, pyrethroids provide quick mortality against insects, and this fact may influence their combination with other slow-acting insecticides. Le Patourel and Singh (1984) found that the combination of silica, which is a slow acting insecticide, with high doses of permethrin, cypermethrin and deltamethrin, did not exhibit any additive effect against the red flour beetle, Tribolium castaneum (Herbst) due to rapid knock down caused by the pyrethroids. In our study, additive effect was evident only in the case of the low doses of the insecticides tested, and this could be attributed to the delayed mortality, allowing both insecticides to act. Additional measurements at shorter intervals (e.g. 24 or 48 h) are necessary to clarify the basis of this hypothesis.  References Arthur, F.H. 1996. Grain protectants: current status and prospects for the future. Journal of Stored Products Research 32, 293-302. Athanassiou C.G., Kavallieratos, N.G., Tsaganou, F.C., Vayias, B.J., Dimizas, C.B., Buchelos, C.Th. 2003. Effect of grain type on the insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Crop Protection 22, 1141-1147. Athanassiou, C. G., Kavallieratos, N. G., Vayias, B. J., Papagregoriou, A.S., Dimizas, C. B. , Buchelos, C. Th. 2004. Residual toxicity of beta cyflurthrin, alpha cypermethrin and deltamethrin against Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) on stored wheat. Applied Entomology and Zoology 39, 195-202. Athanassiou, C.G., Kavallieratos, N.G., Yiatilis, A.E., Vayias, B.J., Mavrotas, C.S., Tomanović, Ž., 2008. Influence of temperature and humidity on the efficacy of spinosad against four stored grain beetle species. Journal of Insect Science 8, 60. Athanasiou, C.G., Arthur, F.H., Throne, J.E., 2009 Efficacy of grain protectants against four psocid species on maize, rice, and wheat. Pest Management Science 65, 1140-1146 Fang, L., Subramanyam, Bh., Arthur, F.H., 2002. Effectiveness of spinosad on four classes of wheat against five stored product insects. Journal of Economic Entomology 95, 640-650. Huang F., Subramanyam, Bh., 2007. Effectiveness of spinosad against seven major stored grain insects on corn. Insect Science 14, 225-230 Le Patourel G.N.J., Singh, J., 1984. Toxicity of amorphous silicas and silica-pyrethroid mixtures to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Journal of Stored Products Research 20, 183-190. Sokal, R.R., Rohlf F.J., 1995. Biometry, 3rd edition, Freedman and Company Sparks, T.C., Crouse, G.D., Durst G., 2001. Natural products as insecticides: the biology, biochemistry and quantitative structure-activity relationships of spinosyns and spinosoids. Pest Management Science 57, 896-905. Subramanyam Bh., Toews, M.D., Fang, L., 2003. Spinosad: an effective replacement for organophosphate grain protectants. In: Credland, P.F.A., Armitage, D.M., Bell, C.H., Cogan, P.M., Highley, E. (Eds), Proceedings of the Eighth, International Working Conference on Stored-product Protection, 22-26 July 2002, York, UK, CAB International, Wallingford, UK, pp. 916-924. Vayias B.J., Athanassiou, C.G., Mylonas, D.N., Mavrotas, C., 2009 Activity of spinosad against three stored-product beetle species on four grain commodities. Crop Protection 28, 561-566.   

Insecticidal action of the combined use of spinosad and deltamethrin against three storedproduct pests in two stored hard-wheat varieties.

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Insecticidal action of the combined use of spinosad and deltamethrin against three storedproduct pests in two stored hard-wheat varieties.

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