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Susceptibility of some legume varieties to the infestation with cowpea beetle, C. maculatusOnly 14 pages are availabe for public view
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Abstract
The present study was carried out to evaluate some safe alternative pesticides against the cowpea beetle, C. maculatus.
Investigations included determination the relative susceptibility of some legume varieties to infestation by cowpea beetle, and evaluation of some materials such as plant essential oils, plant extracts, plant powders, inorganic salts and growth regulators against the beetle.
Evaluation was based on direct toxicity, effect on oviposition, adult emergence, infestation rate, and loss in cowpea seed weights.
The obtained results could be summarized in the following:
1- Susceptibility of some legume varieties to infestation with the cowpea beetle, C. maculatus:
1- In choice infestation test, and after three generations of the beetle, results indicated that the two varieties of lentil were the least infested by the pest and showed the least loss in weight of cowpea seeds. The two varieties of cowpea (Dokki 331 and Karim 7) showed the highest in infestation rate and in the loss in seeds weight. The varieties of faba bean and chickpea were inbetween.
2- Positive significant correlation was recorded between percentage of infestation and seeds weight loss.
3- In no-choice infestation test, and after 3 generations of the pest, results of infestation rate and seed loss weight showed the same trend of choice infestation test data, but it were much lower. Varieties of cowpea (Dokki 331 and Karim 7) showed the highest in percentages of infestation and the loss in seed weight. Whereas, the varieties of lentil (Giza 9 and Giza 370) exhibited the lowest percentage in infestation and in seed weight loss. Other varieties of legume showed moderate infestation rate and loss in seed weight. Significant correlation between infestation rate and loss in seed weight was recorded.
4- In choice and no-choice infestation tests, cowpea variety Dokki 331 showed the highest significant in beetle eggs laid, followed by Karim 7 variety. The two varieties of lentil (Giza 9 and Giza 370) received the lowest number of adult beetle eggs, other varieties were of inbetween.
5- The susceptible varieties of legume showed relatively high content of protein, low content of carbohydrate and high content of moisture, whereas the tolerant varieties showed low content of protein and moisture, high content of carbohydrate.
2- Evaluation of five plant oils against the cowpea beetle, C. maculatus:
Five plant oils viz., cinnamon, jojoba, mustard, soybean and black cumin were tested against cowpea beetle, results showed that:
2.1- Direct toxicity:
At all concentrations tested of black cumin, complete kill of adult beetle was achieved at all periods of exposure (24 to 96 hrs).
According to LC50 and LC90 values recorded at all periods of exposure, the plant oils tested may be arranged as follows cinnamon > jojoba > mustard > soybean.
2.2- LT50 and LT90:
At 2.5 ml/kg seeds of the five plant oils applied against cowpea beetle, black cumin gave 100% kill to cowpea adult beetle, as for the rest of oils and according to LT50 and LT90 values, cinnamon was the highest effective oil, and soybean was the least efficient oil. At a dose of 5.0 ml/kg seeds, the plant oils may be arranged according to their efficiency as follows black cumin > soybean > cinnamon > jojoba > mustard. The order at dose of 7.5 ml/kg seeds applied was black cumin > jojoba > cinnamon > soybean > mustard.
According to direct toxicity LC50 and LC90, and LT50 and LT90, black cumin was the highest efficient oil against the cowpea beetle.
2.3- Oviposition:
Significant variation in number of cowpea beetle eggs laid was found between treated and untreated seeds, also between concentrations of oils tested. Oviposition decreased as the concentrations increased for all oils tested.
Black cumin and cinnamon oils reduced significantly the eggs laid on cowpea seeds at 2.5 and 5.0 ml/kg seeds, and no eggs laid were recorded at 7.5 ml/kg seeds. Mustard oil was the least effective oil in reducing oviposition, whereas jojoba and soybean oils were inbetween. The three plant oils at 10.0 ml/kg seeds reduced oviposition completely.
2.4- Adult emergence:
All oils significantly reduced adult emergence of cowpea beetle with variable degrees. Black cumin oil completely inhibit the adult emergence at all concentrations tested, cinnamon oil completely prevent the emergence at 5.0 ml/kg seeds, whereas, the other oils inhibit emergence at 7.5 ml/kg seeds.
2.5- Infestation rate:
The effect of the plant oils tested on the infestation rate by cowpea beetle took the same trend of effect on adult emergence. No infestation was recorded at all concentrations tested of black cumin oil, and at 5.0 ml/kg seeds for cinnamon oil, and at 7.5 ml/kg seeds for jojoba, mustard and soybean oils. Significant variation in infestation was found between treatments and also between treated and untreated seeds.
2.6- Loss in seed weight:
As for the effect of plant oils on the loss of seed weight, significant variation in loss was recorded between treated and untreated seeds. Also, there was significant variation between treatments. Black cumin and cinnamon oils at 2.5 ml/kg seeds reduced significantly the loss and no loss was recorded at 5.0 ml/kg seeds. The three other oils completely reduced the loss in seed weight at concentrations of 7.5 ml/kg seeds.
Comparing the efficiency of the five plant oils tested against C. maculatus on the basis of direct toxicity, oviposition, adult emergence, infestation rate and the loss of seed weight, black cumin and cinnamon oils gave the best result so it may be recommend in the control programme of cowpea beetle.
3- Evaluation of five plant extracts against the cowpea beetle, C. maculatus:
3.1- Direct toxicity:
According to LC50 and LC90 values and percentage of mortality recorded after 24, 48 and 72 hrs exposure, camphor extract showed the highest efficient extract against cowpea adult beetle, complete kill was achieved at all concentrations tested after 72 hrs exposure. Black pepper extract exhibited the least toxic extract against the adult beetle, whereas neem, garlic and cumin extracts showed moderate toxic effect.
3.2- LT50 and LT90:
At 25 mg/100g seeds, camphor and neem extracts showed great toxicity against adult beetle (LT50 14.14 and 21.24 hrs, and LT90 50.08 and 95.92 hrs, respectively).
Black pepper extract showed the least values of LT50 43.63 and LT90 191.90 hrs. Other extracts were inbetween.
At 50 mg/100g seeds, camphor and neem extracts caused 100% mortality to adult beetle. Garlic, cumin and black pepper extracts showed moderate toxicity.
According to LC50, LC90, LT50 and LT90 values, camphor extract exhibited the highest efficient extract against the cowpea adult beetle.
3.3- Oviposition:
Significant variation in the number of eggs oviposited between untreated and treated seeds. For all treatments, the number of eggs laid decreased significantly as concentrations increase. Despite concentrations, camphor and neem exhibited the highest efficient extracts to reduce oviposition. Other extracts showed moderate effect.
3.4- Adult emergence:
The number of cowpea adult beetle emerged was significantly higher in untreated than treated seeds. Regardless of concentration tested, camphor and neem were the highest efficient extracts to inhibit adult emergence, camphor at 50 mg/100g seeds, completely inhibited emergence, whereas neem gave the same result at 75 mg/100g seeds. All extracts at 100 mg/100g seeds caused 100% inhibition to the beetle adult emergence.
3.5- Infestation rate:
The five plant extracts at all concentrations tested significantly reduced the infestation rate as compared with untreated seeds. The percentages of infestation decreased significantly by increasing concentrations for all extracts. Despite concentrations, camphor extract showed the highest effective extract in reducing infestation rate, followed by neem extract, no infestation was recorded for the two extracts at concentration of 50 mg/100g seeds. However, all extracts at 100 mg/100g seeds completely reduced the infestation by cowpea adult beetle.
3.6- Loss in cowpea seed weight:
The five plant extracts at all concentration tested, significantly reduced the loss in cowpea seed weight as compared with untreated seeds. Significant variation in weight loss was recorded between treatments. Camphor and neem extracts exhibited the highest efficient extracts. Black pepper was the least active extract, whereas garlic and cumin extracts were inbetween. All extracts at 100 mg/100g seeds completely reduced the loss in seed weight.
According to result of direct toxicity, oviposition adult emergence, percentage of infestation and loss in seed weight, camphor exhibited the highest efficient extract against the cowpea beetle, so it may recommended in the pest management programme.
4- Evaluation of five plant powders against the cowpea beetle, C. maculatus:
Five plant powders viz., basil, chilli, jatropha, turmeric and clove were evaluated against cowpea beetle adults and the results showed that:
4.1- Direct toxicity:
The clove powder exhibit the highest toxic powder against adult beetle, complete kill was achieved at all concentrations tested for 24, 48, 72, 97 and 120 hrs. As for the other powders and according to LC50 and LC90 values obtained after 120 hrs the powders may be arranged as follows, turmeric > jatropha > basil > chilli.
4.2- LT50 and LT90:
The clove powder at concentration of 1.0, 2.0, 3.0 and 4.0% gave complete kill to the adult beetles. According to LT50 and LT90 values obtained at concentrations of 1.0, 2.0, 3.0 and 4.0%, jatropha and turmeric powders exhibited the highest efficient against the adult beetles, whereas basil and chilli powders showed moderate effect.
On the basis of direct toxicity (LC50 and LC90), and LT50 and LT90, and percentage of mortality, clove, jatropha and turmeric powders showed high efficiency against cowpea adult beetle, so it may be recommended for control strategy programme.
4.3- Oviposition:
The mean number of eggs deposited on untreated seeds were significantly higher than that obtained on treated seeds. At all concentrations tested, seeds treated with clove powder showed significant low number of beetle eggs laid. Turmeric and jatropha powders followed clove powder in reducing egg laid. However, basil and chilli powders exhibited moderate effect on oviposition.
4.4- Adult emergence:
The plant powders applied on cowpea beetle significantly reduced the adult emergence of the insect as compared with untreated. Clove powder completely inhibited adult emergence at all concentrations tested. The number of adult emergence decreased as the concentrations of powders increased. Chilli powder was the least efficient one, jatropha, turmeric and basil powders showed moderate effect on adult emergence of cowpea beetle.
4.5- Infestation rate:
All plant powders tested showed significant effect on infestation by cowpea beetle as compared with untreated seeds. Significant variation in infestation rate was recorded between treatments, and also between concentrations. Clove powder completely prevent infestation by the pest, no infestation was observed at all concentrations tested. Chilli powder exhibited the least efficient powder on infestation rate. Jatropha, turmeric and basil powders showed moderate effect. The infestation rate decreased by the increase in the concentrations.
4.6- Loss in cowpea seed weight:
The plant powders tested significantly reduced the loss in seed weight as compared with untreated seeds. Significant variation in the seed weight loss was found between treatments. Clove powder was the highest efficient one, no loss in seed weight was recorded at 2.0% concentration. Chilli powder exhibited the least effective one in reducing the loss. Other powders tested showed moderate effect in loss weight. Increasing concentration of all powders decreased the loss in loss seed weight.
Results of plant powders showed that clove powder exhibited the highest efficient one on mortality of cowpea beetle since all concentrations caused complete kill at all periods of exposure.
The powder also decreased oviposition significantly, and completely reduced the adult emergence, infestation rate and the loss in seed weight. So, it may be recommend to control the cowpea beetle.
5- Evaluation of five inorganic salts against the cowpea beetle, C. maculatus:
5.1- Direct toxicity:
Five inorganic salts were applied on cowpea adult beetle at four concentrations, for 144 hrs. According to LC50 and LC90 values recorded at 24, 48, 72, 96 and 120 hrs, sodium fluoride, potassium phosphate and sodium chloride showed relative high toxicity against adult beetle after 144 hrs exposure. All concentration of sodium fluoride and potassium phosphate caused 100% mortality to adult beetle. The efficiency of all inorganic salts applied increased by increasing concentrations or the exposure period.
5.2- LT50 and LT90:
The LT50 and LT90 values recorded when the inorganic salts applied at concentration of 0.5, 1.0, 1.5 and 2.0% emphasized that sodium fluoride and potassium phosphate were the most efficient salts against cowpea beetle. The two salts had the lowest LT50 and LT90 values. Sodium phosphate and potassium chloride showed less toxicity against the insect.
According to direct toxicity (LC50 and LC90 values), and LT50 and LT90 values, sodium fluoride and potassium phosphate showed high efficiency against cowpea adults beetle.
5.3- Oviposition:
At all concentrations applied, the five inorganic salts significantly reduced the number of adult beetle eggs laid on cowpea seeds, as compared with untreated seeds. Significant variation in number of eggs laid was recorded between treatments. The salts may be arranged according to their efficiency on oviposition as follows, potassium phosphate > sodium fluoride > potassium chloride > sodium chloride > sodium phosphate. For all inorganic salts tested, the efficiency on oviposition increased by the increase in concentrations.
5.4- Adult emergence:
All inorganic salts tested at all concentration reduced the adult emergence of cowpea beetle significantly, when compared with untreated seeds. The adult emergence varied significantly between treatments. Potassium phosphate and sodium fluoride exhibited the highest efficient salts, no adult emergence from seeds treated with potassium phosphate at 1.5% and sodium fluoride and chloride at 2.0%. For all salts, the percentage of adult emergence decreased by the increase of concentrations.
5.5- Infestation rate:
The five inorganic salts tested significantly reduced the infestation rate, as compared with untreated seeds. Significant variation in infestation rate was recorded between treatments. Potassium phosphate exhibited high significant effect on infestation rate, no infestation was observed at 1.0% concentration. It was followed by sodium fluoride and potassium chloride. Sodium phosphate showed the least efficient salt to reduce infestation rate, whereas, sodium chloride showed moderate efficiency on infestation rate. All salts at concentration of 2.0% completely prevent infestation by cowpea beetle.
5.6- Loss in cowpea seed weight:
Application of inorganic salts on cowpea seeds, significantly reduced the loss in seeds weight due to the infestation with beetle, as compared with untreated seeds. The inorganic salts tested may be arranged according to their efficiency in reducing seed weight loss as follows, potassium phosphate > sodium fluoride > potassium chloride > sodium chloride > sodium phosphate. All inorganic salts applied at 2.0% completely reduced the loss in seeds weight except sodium phosphate.
6- Evaluation of IGR’s, buprofezin and methoxyfenozide on the cowpea beetle, C. maculatus:
Two insect growth regulator’s, buprofezin and methoxyfenozide were applied on cowpea beetle, and the effect on oviposition, adult emergence development period and loss in seed weight was evaluated and the result showed that.
6.1- Oviposition:
The two compounds at all concentration decreased the number of cowpea beetle eggs laid significantly, as compared with the number of eggs laid on untreated seeds. The number of eggs laid decreased significantly as the concentrations of the two compounds increased. Comparing the reduction in eggs deposited in the two treatments, it seems that buprofezin is more efficient than methoxyfenozide.
6.2- Adult emergence:
The two insect growth regulators tested decreased the adult emergence of cowpea beetle significantly as compared with untreated seeds. Increasing concentrations of the two compounds significantly decreased the number of adult emergence. Buprofezin compound showed relative efficiency on adult emergence of cowpea beetle, as compared with methoxyfenozide compound.
6.3- Developmental period:
The developmental periods of cowpea beetle in days was slightly shorter at all concentrations of the two compounds as compared with untreated. There was negative relation between concentrations and developmental period.
6.4- Loss in weight of cowpea seeds:
The two compounds used reduced the loss in weight of cowpea seed significantly as compared with untreated seeds. The efficiency of buprofezin in reducing loss in seeds weight was relatively higher than that recorded with methoxyfenozide.
Generally, the present study proved that the two varieties of cowpea Dokki 331 and Karim 7 were susceptible to infestation with cowpea beetle, so it needs to develop new resistant varieties.
According to direct toxicity, effect on oviposition, adult emergence and loss in seed weight, the higher efficient materials were, the plant oils black cumin and cinnamon, the plant extracts camphor and neem, the plant powder clove and the inorganic salts sodium fluoride and potassium phosphate, so it may be recommended to use these material singly or in combination to control cowpea beetle, C. maculatus.