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Abstract This work was carried out at the Institute of stored products protection of the Federal Biological Research Centre for Agri. and Pbrestry in Berlin Dahlem (Fed. Rep. of l}ermany). The main objective- of these investieations was to study the effect of the inert gas carbon dioxide on the effecaoy of phosphine against some stored product insects. Larvae and pupae of Sitotroga cerealella and adults of Sitophilus oryzae and Tribolium castaneum were used in the Experiments. A recirculatory multi-flask apparatus was designed to prOVide a fumigation chamber for test insects. Phosphine was generated from PHOSTIXI~-Pelletts. Biological studies were carried out to determine the appearance times of larval and pupal stages of Sitotroga cerealella and adult emergence of Sitophilus oryzae and Tribolium .castaneum • It esults obtained were recorded. Data achieved could be summarized under the following topioar I. Effect of phosphine on the tested insects: I.l. Larvae and pupae of Sitotroga cerealella: Probit analyses for toxicological data, obtained to find the relative toxicity of phosphine to larval and pupal stages of Sitotrolljacerealella exposed to varying phosphine concentrations for 2, 4, 8, 24, 48 and 72 hr. at 20°C and 28°C, showed that the LC50 of phosphine decreased from average, 1609~g/L at 2 hr. to 4.59~g/L at 72 hr. for larvae at 200C and from 1397 ~g/L to 4.36 ~5/Lat ~80C. In case of pupae the LC50 of phosphine declined from 3056 ~g/L to 8.17 ~g/L at 20°C and from 2297 ~g/L to 8.00 ~g/L at 280C. from these results we find that there was inver- sible relationship between the concentration and exposure period. Pupae of Sitotroga cerealella were more tolerant to phosphine than larvae. PHOSTOXI~ at 280C was more effective than at 200C. I.2. Adults of Tribolium castaneum and S1tophllus oryzae: The toxicological data obtained to find the relative toxicity of phosphine to adults of Tribolium castaneum ~nd Sitophilus oryzae exposed to different concentrattons and for 2, 4, 8, 24. 48 and 72 hr. exposure prriods at 28°C showed that the LC50 of phosphine decr-eased from 70.4 /lg/L at 2 hr. to 2.) ~/L at 72 hr. for Tribolium castaneum and from 128 ~/L at 2 hr. to 1.8/lg/L at 72 hr. for SitophiluS oryzae. There was also inversible relationship between the concentration and the exposure period. II. Effect of carbon dioxide alone on the tested insects: The results indil~ated that carboh dioxide at short exposure periods of 2, 4 and 6 hr. had a negligible effect on the mortality of larval and pupal stages of .§. cerealella. At longer exposure periods of 24. 48 and 72 hr. the effect of CO2 on the mortality of larvae and pupae of .§. cerealella was noticeable. especially at 50 and 78% concentrations. With respect to adults of Tribolium castaneum and Sitophilus oryzae the effect of CO2 on the mortality was very low at 2. 4 and 8 hr. at all carbon dioxide concentrations but was high at 24, 48 and 72 hr. at 50 and 78% concentrations of CO2• III. Ettect of mixtures ot phosphine and CO2: Results obtained trom using mixtures ot LC50 of phosphine and carbon dioxide concentrations showed high increase in the mortalities ot larvae ot -S. cereal ella at all exposure periods than of phosphine or carbon dioxide alone. In case of pupae the resu.1ts revealed an increase in the mortalities at all exposure periods but this increase was lower than for larval stage. The morta1ities at 28°C were higher than at 200C. Complete mortalities were recorded at all exposure periods by using the mixtures ot carbon dioxide concentrations and LC50 ot phosphine against adults ot T. castaneum and §. oryzae at 280C. Accordingly, llIixturesot vaI’3fingconcentrations ot CO2 + LC50 ot PHJ induced higher insect-mortalities. Therefore we could re~l1ce the phosphine dose requiered in the tumigation , besides the potentiation ot the action ot the gas. |