Studies On Persistence And Toxicity Of Two Organophosphorus Insecticides And Plant Extracts To Stored Product Insect:
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M. E. Hassan |
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Ph.D
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Benha University
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2004
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Plant diseases.
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Studies on persistence and toxicity of two organophosphorus insecticides and plant extracts to stored product insects 1- Toxicity of two organophosphorus insecticides and certain plant extracts against three insect species of stored products:The toxic effect of two organophosphorus insecticides i.e., malathion and pirimphos-methyl as well as the acetone and petroleum ether extracts of four plants namely (Cubeb fruits Piper cubeba, Thyme flowering buds Thymus vulgaris, Damsissa leaves Ambrosia maritima and Marjoram leaves Majorana hortensis was studied in the laboratory at 26 ± 2°C and 60 ± 5 RH against the adults of three insect species of stored products i.e., the rice weevil Sitophilus oryzae (L.), the lesser grain borer Rhizopertha dominica (F.) and the red flour beetle Tribolium castaneum (Herbst.)The obtained results showed the follows: 1.1- Malathion and pirimiphos-methyl (Actellic):The toxicity of malathion and pirimiphos-methyl to the adults of the three insect species was concentration and exposure - period — dependent.The toxic effect increased with increasing the concentration of the insecticide and the period of exposure.SUMMARY -122-The susceptibility of the insects varied from insect species to another S. oryzae adults were the most sensitive species followed by T.castaneum and R. dominica to the two insecticides. However, it was evident that the recommended concentration (8 ppm)` of malathion for controlling stored product insects was not sufficient to achieve complete kill for the adults of R.dominica and T castaneum even after longer exposure periods (3-7 days).Pirimiphos—methyl was more toxic to the various insect species than malathion. Results of the calculated lethal concentrations indicated that the LC50 of malathion at 3 days exposure period was 0.93, 19.50 and 2.98 ppm for the adults of S. oryzae, R. dominica and T castaneum, respectively. These values were 0.52, 11.22 and 2.20 ppm at 7 days exposure period for the three insect species, respectively. The LC50 of pirimiphos—methyl were 0.09,6.80 and 2.05 ppm after 3 days exposure period and 0.05, 4.98 and 1.36 ppm at 7 days exposure period for the various insect species, respectively .Meanwhile, the LC99 of malathion at 3 days exposure period was 8.06, 556.30 and 50.22 ppm. These values were 2.86, 106.72 and 16.79 ppm at 7 days exposure period for S. oryzae, R. dominica and T. castaneum, respectively. The LC99 values of pirimiphos — methyl were 0.42, 150.83 and 14.65 ppm at 3 days and 0.36, 24.98 and 5.76 ppm at 7 days for the three insect species, respectively. This result showed clearly that R. dominica adults were highly resistant to malathion and pirimiphos—methyl. Also, T. castaneum adults were highly tolerant to malathion and showedlow tolerance ratio to pirimiphos—methyl. While, S. oryzae adults were sensitive to the two tested insecticides. 1.2- Plant extracts :The results revealed that the toxic effect of the various plant extracts was also concentration and exposure period—dependent. Susceptibility of the adults of the three insect species varied also from insect species to another .The adults of S. oryzae was the most sensitive species under study. Meanwhile, the toxic effect of the tested plant extracts varied from plant to another. The acetone extracts of the plants showed generally higher toxic effect than the petroleum ether extracts except the petroleum ether extract of Thyme flowering buds. For example, after 5 days exposure period the highest tested concentration (2% w/w) of the acetone extract of Cubab fruits caused 100, 100 and 36.7 % for the adults of S. oryzae, R. dominica and T castaneum, respectively.The corresponding mortality values using the petroleum ether extract of the same plant were very low (8.9, 7.8 and 5.4%) for the three insect species, respectively.In case of the acetone extract of Thyme flowering buds at 2% (w/w) concentration and 5 days exposure period, mortalities were low (27.8, 11.1 and 4.4%) for the three insect species, respectively. Petroleum ether extract of this plant gave higher values (100, 100 and 16.5%).For Damsissa leaves acetone extract, mortalities were (36.7, 26.7 and 6.7%) with the three insect species, respectively. While, the petroleum ether extract of this plant gave also lower mortality values (20.0, 10.3 and 3.3%).The obtained mortalities with the acetone extract of Marjoram leaves were 33.3, 15.6 and 4.4 % at 2 % (w/w) concentration and 5 days exposure period for the three insect species, respectively. Petroleum ether extract of this plant gave 30.0, 10.0 and 4.5% indicating that the two extracts of this plant had low toxic effect on the insects. It was evident that only the acetone extract of Cubab fruits and petroleum ether extract of Thyme flowering buds were the most effective extracts. While, the petroleum ether extract of Cubab fruits was the least effective extract under study.Meanwhile, the reduction rates in the Fi-progeny of the insect species resulted from various concentrations [0.125-2% (w/w)] of the most effective plant extracts under study were between 16.8-100%, 30.2-100% and 21.8-100% with the acetone extract of Cubeb fruits for S. oryzae, R. dominica and T. castaneum, respectively.For the petroleum ether extract of this plant, these values were 8.2-63.8%, 5.0 - 34.8% and 4.6 - 24.2% for the three insect species, respectively.The corresponding values caused by the acetone extract of Thyme flowering buds were 14.8-55.1%, 3.9-49.9% and 19.7-49.2.% and for the petroleum ether extract of this plant were 20.3-100%, 14.4-100% and 4.9-79.8% for S. oryzae, R. dominica and T. castaneum, respectively.It was evident, that reduction rates in the Fi-progeny of T castaneum caused by various plant extracts were generally higher than that of mortality.2- Residual toxicity of the two organophosphorus insecticides and the plant extracts : The residual toxicity of the two organophosphorus insecticides i.e. malathion and pirimiphos-methyl was determined using two methods namely the GLC and a bio-test using the adults of S. oryzae, the most sensitive insect species under study. This bio-method was used only for determining the residual toxicity of the various plant extracts. The obtained results showed that pirimiphos-methyl had longer persistence than malathion and gave a greater protection extended to one year to the adults of S. oryzae. On the other hand, the tested plant extracts gave shorter protection to the adults of S. oryzae indicating that they have lower persistence than the two organophosphorus insecticides. Furthermore, results of the GLC indicated that pirimiphos-methyl persistened relatively longer in the tested grains and seeds than malathion. On the other hand, the persistence of the two insecticides was markedly greater. for cowpea seeds compared with maize and wheat grains. Also, loss rates of the two insecticides by washing of wheat and maize samples were around 50% of deposits of the unwashed grains at the initial time, while these were only around 35 % for the two insecticides in case of cowpea seeds. It was also evident, that the persistence of various the plant extracts was obviously lower than that of the two organophosphorus insecticides3- Effect of two plant extracts at 1% (w/w) alone and under MA of CO2 on the populations of S. oryzae and R. dominica at various storage periods:Experiments were performed inside metal drums which were situated inside a breeding room at 26 ± 2°C and 60 ± 5 RH. _ 200g wheat grains were treated with 1% (w/w) of Cubeb fruits (P. cubeba) acetone and/or petroleum ether extract of Thyme flowering buds (T vulgaris) alone and under MA of 25% CO2 against S. oryzae and R. dominica. Grains were infested with 32 adult insects of each species. Three replicates were used in each treatment. The results indicated that, all treatments caused a complete inhibition of S. oryzae adult populations in the wheat grains during the storage periods of 12 months.The number of R. dominica adults in wheat grains treated with P. cubeba fruits acetone extract, T. vulgaris flowering buds petroleum ether extract, MA of 25% CO2 alone and untreated grains was 185.5, 173.0, 0.3 and 1922.0 after 2 months, respectively. While the combined treatments of each extract under MA gave a total inhibition of the two insect species populations during the whole storage periods. Thus, the combined treatment of the plant extract under MA of CO2 was high effective against the tested insects and could be considered as an alternative method for methyl bromide to control stored product insects.4- Effect of two plant extracts at 1% (w/w) alone and under MA of 25% CO on the wei ht loss of stored wheat grains : The weight loss of wheat grains was determined for one year in 200 g wheat grains treated with 1% (w/w) of Cubeba fruits P. cubeba acetone extract and Thyme flowering buds T vulgaris petroleum ether extract alone and under MA of 25% CO2 as well as MA of 25% CO2 alone compared with untreated grains. Grains were infested with thirty two adults (0-15 days old) of S. oryzae or R. dominica. Results showed that the produced progenies differed from one treatment to another and the loss caused consequently differed according to the resulted progenies. The weight loss of wheat grains caused by S. oryzae adults at 6 months were 11.3, 4.8, 10.1, 5.4, 5.6 and 29.4% for the acetone extract of Cubeb fruits, Cubeb fruits acetone extract under MA of CO2, Thyme flowering buds petroleum ether extract, Thyme extract under MA of CO2, MA of 25% CO2 alone and untreated grains, respectively. The corresponding values caused by R. dominica were 31.3, 1.3, 70.4, 0.8, 4.5 and 74.8% at 6 months storage for aforementioned treatments, respectively.Reduction rates in grains weight loss resulted from various treatments were 64.3, 84.6, 68.9, 83.5 and 81.0% and 42.9, 98.0, 0.5, 98.9 and 93.9% at 12 months storage period for S. oryzae and R. dominica adults, respectively. Data also indicated that the treatment of wheat grains with each plant extracts at 1% (w/w) under MA of 25% CO2 reduced markedly the grain losses caused by the two insect species infestation.5- Effect of certain treatments on germination of wheat grains and chlorophyll content of the seedlings : Results of tests performed to investigate the effects of four plant extracts at 4,2 and 1 % (w/w) and two insecticides i.e. malathion at 16, 8, 4 ppm as well as pirimiphos-methyl at 20, 10, 5 ppm on wheat grains germination and chlorophyll content of the seedlings showed significant decrease in germination rates of wheat grains treated with the acetone and petroleum ether extracts of P. cubaba fruits and T. vulgaris flowering buds acetone extract at all tested concentrations, as well as, at the two highest concentrations of the petroleum ether extract of T. vulgaris and A. maritima leaves. Meanwhile, similar result was achieved at the highest concentration [4% (w/w)] of A. maritima acetone extract. On the other hand, no significant differences in the germination of wheat grains were found for two extracts of M hortensis leaves and two insecticides at all tested concentrations compared with untreated grains.At the same time, no obvious differences between the chlorophyll content of the treated seedlings and control were found. 6- Effect of sublethal concentrations of two plant extracts, malathion and pirimiphos-methyl on some biological aspects of T. castanewn : Results of various treatments to T. castaneuin adults, which treated with the sublethal concentrations (causing 50-60% adults mortality) of Cubeb fruits acetone extract, acetone and petroleum ether extracts of Thyme flowering buds, malathion and pirimiphos-methyl indicated significant reduction in the number of eggs laid daily per female during an observation period of two weeks for all tested treatments compared with the control. Percentages of decrease in egg numbers were 64.6, 51.2, 32.5, 39.0 and 27.8% for Cubeb acetone extract, Thyme acetone extract, Thyme petroleum ether extract, malathion and pirimiphos-methyl, respectively. On the other hand, no significant differences were achieved between all treatments and control for hatchability rates of eggs, duration of pupal stage and sex ratio. The mortality rates of larval instars were 33.3, 16.7, 16.7, 0.0 and 0.0% for aforementioned treatments, respectively.Treatment of T castaneum adults with the sublethal concentration of Cubeb fruits acetone extract prolonged significantly pre-oviposition period, incubation period of eggs and durations of second and fourth larval instars in comparison to control. But, no significant differences were observed between the treatment and the control for duration of the larval stage and total developmental period of immature stages. The sublethal concentration of Thyme flowering buds _acetone extract indicated significant decrease in the pre-oviposition period, durations of second and third larval instars, larval stage period and total developmental period of immature stages of T castaneum compared with control. While, no significant differences were obtained between the treatment and control for incubation period of eggs.Also, significant decline in incubation period of eggs and the durations of third and fourth larval instars was achieved using sublethal concentration of petroleum ether extract of Thymeplant. But, no significant differences was found for pre-oviposition period, larval stage period and total developmental . period of immature stages. Results indicated also that treatment of adults with the sublethal concentration of m pirimiphos-methyl decreased significantly larva and the total developmental period of immature sta significant differences were found between tr control for pre-oviposition period and incubation pT. castaneum lathion and stage period :es. While, no atments and riod of eggs. |
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