IMBECU   20882
INSTITUTO DE MEDICINA Y BIOLOGIA EXPERIMENTAL DE CUYO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Insecticidal Activity of a Novel Insecticide, Nanostructured Alumina, on the Stored Grain Pest Sitophilus oryzae (L.) (Coleoptera: Curculionidae)
Autor/es:
MICAELA BUTELER, TEODORO STADLER, DAVID K. WEAVER
Lugar:
San Diego
Reunión:
Encuentro; The 58th Annual Meeting of the Entomological Society of America; 2010
Institución organizadora:
ESA
Resumen:
Insecticidal Activity of a Novel Insecticide, Nanostructured Alumina, on the Stored Grain Pest Sitophilus oryzae (L.) (Coleoptera: Curculionidae)     INTRODUCTION               There is much interest in alternatives to conventional insecticides for controlling stored-product insects because of the loss of registered insecticides due to stringent regulations, exponentially increasing costs, and the increased occurrence of insecticide resistance, as well due to consumer demand for product that is free of insects and insecticide residues. Inorganic insecticidal dusts (inert dusts) are environmentally friendly alternatives for insect pests of field crops, stored products, and animals. They are chemically stable, highly persistent and have low mammalian toxicity. The action of these insecticidal dusts is inversely related to the size of the particles and ambient humidity, given that their mode of action is associated with the absorption of cuticle waxes leading to desiccation. Recently, a novel type of particulate material, nanostructured alumina (NSA), characterized by particles of 40-60çm, has been found to induce mortality in insects exposed to treated wheat, at rates comparable to those recommended for commercially available dusts.  More detailed studies are needed to determine the efficacy of NSA under varying ambient conditions, to further understand its mode of action and how it compares with that of other inert dusts. Moreover, studies are needed to determine its potential as an insect pest management tool.   OBJECTIVE   This study aimed to study the toxicity of nanostructured alumina on adults of Sitophilus oryzae (L.), major pests of stored grain, as well as its effect on progeny production, at different ambient humidities.   MATERIALS AND METHODS   Insecticide: Nanostructured alumina was obtained by combustion synthesis technique using a redox mixture, with glycine as fuel and aluminium nitrate as oxidizer.   Test insects: The species tested were adults of a grain pest, the rice weevil Sitophylus oryzae reared at Montana State University, Bozeman, MT.   Bioassay: Toxicity was assessed using dry dust applications and evaluated at five different concentrations of the product: 1000, 500, 250, 125, 62.5 mg kg−1 and three different humidity levels: 43%, 57%, and 75% RH. The target grain moisture levels for the low, medium and high humidity treatment were 10.7, 12.6, and 14.7 respectively. Adult mortality was assessed 3, 6, 9, 12, and 15 days after continuous exposure to the treated wheat. After 15 days, all the remaining live insects were removed; the wheat was returned to the Petri dishes, and held for 45 days at 27°C. After this time, the wheat was sifted and the numbers of F1 adults were recorded.   Statistics: The data were analyzed using a mixed-model approach, with mortality as the response variable and concentration and date of observation as main effects. Date of observation was the repeated measure. The progeny data was analyzed using a mixed models approach (Proc Mixed, SAS) with number of emerged F1 adults as the response variable and dose and Petri dish replicate as main effects. The variance–covariance structure was modeled as compound symmetry. Control mortality was rare, and, where corrections for mortality were necessary, these were accomplished using Abbott’s formula. Each level of humidity was analyzed separately and the Abbot correction was used to correct for control mortality.   RESULTS Toxicity to adults: Exposure of the insects to wheat treated with NSA significantly reduced survival in both species (Fig 2). There was a significant exposure time as well as a concentration effect on mortality at all humidity levels tested. Mortality increased as exposure interval and product concentration increased (Fig 2).       Progeny: There was a significant effect of NSA dose in the number of F1 adults emerged (High humidity: F= 16.21, d.f.= 5, 25, P < 0.0001; medium humidity: F= 24.05, d.f.= 5, 25, P < 0.0001; low humidity: F= 3.72, d.f.= 5, 25, P = 0.01). Treated Petri dishes had fewer adults than control ones, for all humidity levels tested (Fig 3).     DISCUSSION   These results are encouraging, and suggest nanostructured alumina may be as or more effective than other inert dusts. The results suggest this product may also have a similar mode of action than inert dusts, given that we observed a decrease in toxicity at greater humidity levels. The nanostructured characteristic of nanostructured alumina confers this dust a greater surface area per unit volume, probably increasing the effective disruption of cuticular waxes. Also, emergent electrochemical and physical properties from such small particle sizes should be investigated. In addition, further comparative studies are needed to determine the efficacy of nanostructured alumina relative to other commercially available insecticidal dusts. Nanostructured alumina can be synthesized easily, under controlled conditions, and may become cheaper than other commercially available inert dusts when mass produced. Thus, this inorganic nanomaterial may provide a cheap, reliable, and safe alternative for insect pest control.     I have not included this probit analysis in the poster. Here it is for your knowledge: PROBIT: Humidity Exposure time LD50 (ppm) LD95 (ppm) 43% RH Day 6 95.86 (86.02,106.48) 191.52 (162.95,245.32) Day 9 46.61 (28.98,58.02) 129.74 (105.26,202.14) 57% RH Day 6 123.66 (111.98, 136.73) 230.87 (198.83, 288.52) Day 9 69.43 (57.88,79.35) 169.46 (139.60, 236.14) 75% RH Day 12 (88.69, 77.68, 99.79) 205.60 (171.33, 272.64)