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Abstract SUMMARY The present study was carried out to evaluate the efficiency of six toxicants from different groups against the prepupae of the peach fruit fly, Bactrocera zonata. 1. Effectiveness of six toxicants against prepupae, pupae and adults of the peach fruit fly, Bactrocera zonata: The toxicity of the organophosphorus insecticides; Malathion, Dimethoate, Actellic, the miscellaneous toxicant, Abamectin, the entomopathogenic fungi, Bio-power and the entomopathogenic Nematodes to the prepupae (full grown larvae) ,pupae and adults of the peach fruit fly, B. zonata was studied. 1.1. Effect of organophosphorus insecticides ( Actellic, Malathion and Dimethoate): Exposure of prepupae and pupae of the peach fruit fly, B. zonata to sandy soil treated with reasonable concentrations of Malathion, Dimethoate, and Actellic caused obvious mortality of the pupae. The two insecticides; Dimethoate and Actellic showed no effect against prepupae; whereas, Malathion showed slight effect against the prepupae at the concentrations of 5000 and 6000 ppm.The two toxicants; Malathion and Dimethoate had slight latent effect against the emerged adults; while Actellic showed no latent effect against the emerged adults. Generally, Actellic was more toxic against the adults of B. zonata than Malathion and Dimethoate. SUMMARY - 134 - 1.2. Effect of the Miscellaneous insecticide; Abamectin, entomopathogenic fungi and entomopathogenic Nematodes: The toxicity of the miscellaneous toxicant, Abamectin and the entomopathogenic agents; fungi, Bio-power, Beauvaria bassiana and Nematodes, Sternernema feltiae against prepupae, pupae and adults of the peach fruit fly, Bactrocera zonata was studied. Exposure of the prepupae and pupae of the peach fruit fly, B. zonata to sandy soil treated with reasonable concentrations of the miscellaneous toxicant, Abamectin was effective against the pupae and has no effect against the prepupae. Also, the toxicant had no latent effect on the adults emerged from treated prepupae. Data of the present study showed that the Bio-power was highly effective against the pupae and had no effect on the prepupae. Also, the toxicant had no latent effect against the emerged adults. Results showed that S. feltiae was effective against the pupae and had no effect on perpupae. S. feltiae had no latent effect on the emerged adults from treated perpupae of B. zonata. 2. Total toxicity of the six toxicants: The total toxicity of the different concentrations of each toxicant was determined on the basis of the dead individuals of three stages ; prepupae, pupae and adults. The total mortality rates were used in drawing the toxicity lines . the toxicants were evaluated according to the following basis: SUMMARY - 135 - 2.1. Comparison on basis of LC50 and LC90 values: The obtained results show that the miscellaneous toxicant; i.e. Abamectin was the most pronounced toxicant against prepupae of the peach fruit fly, B. zonata at LC50 and LC90 values. 2.2. Comparison on basis of toxicity index and potency levels: In this study, the toxicity index was used as a mean for comparing the relative toxicity of insecticides against the prepupae of the peach fruit fly, B. zonata . The miscellaneous toxicant; Abamectin was taken as the standard insecticide and given arbitrary index value 100 units to study the toxicity index of the other five toxicants as compared with this standard toxicant. Also, relative potency level can be used as a convenient method in comparing the degree of toxicity of different toxicants to any pest. The potency levels of tested toxicants are expressed as the number of folds, at the required toxicity level, compared with the least effective toxicant included in the evaluation against the tested insect. Bio-power was considered the standard toxicant.. 2.3. Comparison on the slope of toxicity lines: The present study showed that Abamectin had the steepest toxicity line followed by Actellic and the entomopathogenic Nematodes, whereas Bio-power had the flattest toxicity line when the six toxicants were tested against the prepupae of B. zonata. On the other hand, Malathion and Dimethoate occupied medium situation of the toxicity lines among the six toxicants used in this study. Hence, the six toxicants had three trends of slopes, the steepest being that of Abamectin, Actellic and Nematodes followed by Malathion and Dimethoate then Bio-power having flattest toxicity lines. SUMMARY - 136 - The above mentioned conclusion is correct whether it is the slope values or LC90 /LC50 ratios, since the later method simply expresses the steepness of the LC-P lines in a reversal way to the slope values. Therefore, an increase in the slope value or a decrease in the LC90 /LC50 ratio indicates an increase in steepness of the toxicity line. 2.4. Persistence of the six tested toxicants: The exposure of the prepupae to treated soil with different concentrations of the six toxicants and determination of their efficiency after 0,3,6,9,12,15and18 days by measuring the total toxicity have been studied. The practical proposed concentrations for field application against B. zonata of Malathion, Dimethoate, and Actellic are 5000, 7500 and 10000 ppm, respectivily. Also, the recommended concentrations of miscellaneous toxicant; Abamectin, the entomopathogenic fungi; Beauvaria bassiana and the entomopathogenic nematodes; Steinernema feltiae are 1000 ppm, 40000 ppm and 5000 infective juveniles, respectively. Monitoring insecticidal resistance in the field colony of B. zonata flies collected from different Governorates to Malathion toxicity by using discriminating concentration technique: Four strains were selected from natural populations; i. e. fields located in Menoufia, Qalubia, Behira, and Ismailia Governorates to determine the resistance levels of B. zonata flies to the recommended organophosphorus insecticide, Malathion. Moreover, the effect of the LC50 of the tested toxicants used in this study on some biotic potential in the flies emerged from the prepupae was implemented. The laboratory strain was used as a baseline in insecticidal toxicity and biochemical assays. SUMMARY - 137 - The response of the peach fruit fly, B. zonata flies collected from different Governorates to discriminating concentration of Malathion (LC99) was investigated. Data revealed that Ismailia field strain exhibited the highest resistance value to Malathion toxicity followed by Behira field strain. On the hand, Menoufia and Qalubia field colony strains showed the lowest resistance value to Malathion. 3. Biochemical studies on the peach fruit fly, B. zonata: Hydrolyzing enzymes activity( alkaline and acid phophatases, nonspecific esterases and acetylcholinesterase) glutathione S-transferase, mixed function oxidases and total protein content were determined in flies of B. zonata collected from four Governorates. The obtained results were compared with the baseline laboratory strain that was not subjected to any insecticides. The results indicated that B. zonata flies of the different field strains showed remarked higher levels of the enzymatic activity that were mentioned previously than the laboratory strain. The flies of B. zonata selected from Ismailia Governorate showed the highest levels of the hydrolases, and glutathione S-transferase activity as well as total protein content. On the other hand, flies collected from Qalubia horticultural orchards exhibited the lowest levels of hydrolases, mixed function oxidases, Glutathione S-transferase activity and total protein contents. It could be concluded that the enzymatic activity as well as the total protein content play an important role in resistance of the B. zonata flies to Malathion toxicity, where there was positive correlation between resistance levels in the different field strains and the levels of the enzymatic activity in these strains. SUMMARY - 138 - 4. Development of resistance in the flies of the peach fruit fly, B. zonata to the toxic action of Malathion: The pressure of Malathion against the flies of B. zonata showed an increase of 20.05 folds than the laboratory strain after six generations. Results revealed that, there was a correlation between the response of the different generations and selection pressure with Malathion. The LC50values increased by succession of generations irrespective of the tested toxicant by using LC20 of Malathion as compared with the laboratory strain. Tolerance in the selected adults to the toxicant was noticed in the first four generations, i.e. G1 –G4, whereas G5 and G6 exhibited resistance in the selected adults. 5. Effect of the six toxicants on the biotic potential of B. zonata: It is important to clarify the possible relationship between adult emerged by prior treatment of the prepupae with the LC50 values of the six toxicants used in this study and the reproductive potency of these adults. 5.1. Effect on pre-and oviposition periods: It is quite clear from the obtained results that there is a significant increase in the pre-oviposition periods at all toxicants as compared to the control group. The lowest pre-oviposition period was observed with the tested organophosphorus insecticides in case of copulations between untreated males and treated females as compared with the other toxicants . On the other hand, lower periods of oviposition were recorded in case of copulations between flies emerged from prepupae treated with the LC50 values of the organophosphorus insecticides than those emerged from SUMMARY - 139 - treatment with LC50 values of the miscellaneous toxicant, Abamectin, entomopathogenic fungi and entomopathogenic Nematodes. The lowest periods of oviposition were attained in case of copulations between treated males with treated females. There is a significant decrease in the oviposition periods at all tested toxicants as compared with the correspondent untreated males with untreated females. 5.2. Effect on fecundity (the number of eggs laid/ female): It is quite clear from the obtained results that there is highly significant decrease in the number of eggs laid/ female at all toxicants as compared with the control group. The lowest number of eggs deposited per female was attained for the tested organophosphorus insecticides (Malathion, Dimethoate and Actellic) in case of copulations between treated males and treated females. Maximum fecundity was noticed in the other copulations between treated males and untreated females associated to the organophosphorus insecticides. Moderate effect of the LC50valuess of the six tested toxicants on the number of eggs laid/ female was attained in case of the copulation between treated females and untreated males. The lowest fecundity was observed in case of treatments with Malathion and the highest fecundity was observed in case of treatments with Nematodes. 5.3. Effect on fertility (percent of hatchability): It is clear that the fertility of eggs (percent of hatchability) deposited by females emerged from the treatments of prepupae of B. zonata with the LC50 values of the six toxicants in this study showed a significant decrease in all tests as compared with the untreated flies. It is obvious that Malathion and Dimethoate have pronounced latent effect on the egg viability. The lowest latent effect of the six toxicants was attained when the treated females mated with untreated males. SUMMARY - 140 - The highest latent effect of the six tested toxicants on the viability of eggs deposited by females of B. zonata emerged from treated prepupae was attained when the treated females mated with treated males followed by the copulation between untreated females and treated males, whereas the lowest latent effect was observed when treated females mated with untreated males. 5.4. Effect on sterility: It was obvious that, the highest sterility value was noticed when the copulations occurred between males and females emerged from the treatments of prepupae of B. zonata with the LC50 values of all toxicants with the exception of Bio-power. On the other hand, the lowest sterility percentages were attained in case of mating between treated females with untreated males. Whereas the copulation between untreated females with treated males occupied the middle situation among the two copulations that mentioned previously. The decline of sterility may be related to sperm ability of treated males as well as inhibition of ovarian development of treated females of the peach fruit fly, B. zonata. |