الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 239 |  |  |
| | | from | 239 | | |
Abstract
Eleven chemicals were evaluated against egg and adult stages of the pulse beetle, Callosobruchus chinensis. Tested chemicals were evaluated from the point view of their acute toxicity and their latent effects on P1 development and F1 progeny . Behavioral effects of tested chemicals in choice tests having treated and untreated legume seeds were also a topic of the current study. Another three natural products (nootkatone, sulfur and boric acid) were also included in the current study when evaluating chemical persistence on legume seeds during the storage. Negative impact of the fourteen chemicals on the viability of treated legume seeds after six and twelve month storage periods was also taken in consideration. Five novel pesticides (thiocyclam hydrogène oxalate, abamectin, spinosad, imidacloprid and indoxacarb) have never been previously evaluated against this insect species, were compared with the conventional pyrethroid (lambda-cyhalothrin), two IGR’s (hexaflumuron and flufenoxuron) and two formulations of the neem oil extracts (Achook and Neemix), commonly named azadirachtin. The evaluation also included four eco-friendly natural products (2′-acetylnaphthalene, nootkatone, sulfur and boric acid). 2’-Acetonaphthone (2′-acetylnaphthalene) and nootkatone are commonly used in the industry of perfumes and soaps and more recently found to be a termite repellent and toxicant. The obtained data are summarized as follows:
5.1. Acute toxicity of tested chemicals on Callosobruchus chinensis adults
1- Of the eleven chemicals tested in this section; abamectin, lambda-cyhalothrin, azadirachtin (Achook), and thiocyclam hydrogène oxalate were the most effective as adulticides. More than ninety percent of adults died after 4days exposure to those pesticides at 0.5, 12.5, 13.5 and 25ppm (mg a.i. /kg seeds), respectively.
2- Spinosad was a slow acting pesticide, adults did not respond to any of tested concentrations during the first two days after treatment. However, it was effective after four days to be (based on the 96h LC50) in the same toxicity order of indoxacarb and imidacloprid (96h LC50s = 28.2, 36.6 and 39.4ppm, respectively) and statistically was more toxic than indoxacarb and imidacloprid (based on the 96h LC90 = 85.5, 169.7 and 1007.4ppm, respectively).
3- Azadirachtin, in the formulation commercially named Achook was 44.0-fold more toxic than its formulation commercially named Neemix. The 96h LC90s were 13.5 and 594.4ppm, respectively.
4- 2’-Acetonaphthone, exhibited moderate toxicity and statistically came in the next order (based on the 96h LC90) after the greatest toxic chemicals (abamectin, lambda-cyhalothrin, thiocyclam hydrogène oxalate, azadirachtin commercially named Achook and the bacterial based insecticide, spinosad). It was in the same toxicity order of indoxacarb and azadirachtin commercially named Neemix. However, it was more toxic than the two IGR’s tested and imidacloprid.
5- The toxicity line of imidacloprid was very flat exhibiting the lowest slope. This pushed imidacloprid down into the inferior order when the comparisons based on the 96h LC90.
6- When toxicity lines of tested chemicals are not parallel which indicate different mode and speed of actions, the comparison between such chemicals based on the median effective concentrations is inaccurate.
5.2. Effect of tested chemicals on egg laying
1- After four days of exposing 0-24h old adults to the residues of tested chemicals on lentil seeds, lambda-cyhalothrin and abamectin were superiors in reducing egg-laying. Mean number of eggs was reduced by 90% at relatively low concentrations of lambda-cyhalothrin and abamectin (17.8 and 20.8ppm, respectively) followed by Achook (50.1ppm) = thiocyclam hydrogène oxalate (61.6ppm) followed by spinosad (169.1ppm) followed by flufenxuron (541.2ppm)
2- The inferior treatments that required very high concentrations (1349.2 to 29313.3ppm) to induce similar response were 2’-acetylnaphthalene (1349.2ppm) = hexaflumuron (1636.1) = indoxacarb (2026.2) > imidacloprid (29313.3ppm).
3- In general, based on the EC50s, tested chemicals could be arranged numerically and statistically in the following orders ”lambda-cyhalothrin (2.4ppm = 0.00024% W/W-E), abamectin (6.0 = 0.0006-DE), thiocyclam hydrogène oxalate (8.9 = 0.00089-D), Achook (21.7 = 0.0022), spinosad (28.2 = 0.0028-C), imidacloprid (66.6 = 0.0067-C), flufenxuron (132.9 = 0.0133-B), indoxacarb (143.1 = 0.0143-AB), hexaflumuron (160.5 = 0.0161-AB), 2′-acetylnaphthalene (198.3 = 0.0198-A) and Neemix (200.3 = 0.02-A).
4- Based the comparisons on the EC90s, some chemicals kept their order (lambda-cyhalothrin and abamectin), the flat line chemicals (such as imidacloprid) pushed down to the inferior order and some chemicals (such as 2′-acetylnaphthalene) pushed up. The orders based on the EC90s are as follows ”lambda-cyhalothrin (17.8ppm-F), abamectin (20.8-F), Achook (50.1), thiocyclam hydrogène oxalate (61.6-E), spinosad (169.1-D), flufenxuron (541.2-C), Neemix (1038.5-AB), 2′-acetylnaphthalene (1349.2-B), hexaflumuron (1636.1-B), indoxacarb (2026.2-B) and imidacloprid (29313.3-A).
5.3- Factors affecting the performance of tested chemicals
To study the effect of insect age and type of treated pulse on pesticides performance against the pulse beetle, Callosobruchus chinensis; tested chemicals were evaluated at the biologically active concentrations for 50%reduction in egg laying (EC50s). Some chemicals when evaluated at these concentrations completely inhibited egg hatching. For this reason, the discriminating concentrations were reduced to half the EC50s when studying the effect of cultured pulse and temperature during application. The choice of different concentrations, however all were giving similar response because tested chemicals were varied in their toxicity. In addition, the major objective of this study was to evaluate the effect of each factor (adult age, egg age, treated pulse, culture pulse and temperature during application) on the performance of each chemical alone. An additional objective was the comparison among chemical treatments after combining the data for the sub-treatments of each chemical treatment.
5.3.1- Adult age
Regardless the age of treated adults, alls died after 96h exposure to lambda-cyhalothrin (2.4ppm), abamectin (6.0ppm), thiocyclam hydrogène oxalate (8.9ppm) and Achook (21.7ppm). For the rest of chemical treatments, younger adults (0-48h old) were more sensitive and the 96h mortality data were greater when testing chemicals during the first two days of adult age. The 48-72h old adults seemed to be the greatest tolerant age. These variations in adult sensitivity were also documented in ethanol treatment, however with less value. Combining the 96h mortality of all tested ages, revealed great mortality in the treatments of indoxacarb (143.1ppm induced 90.8%), imidacloprid (66.6ppm induced 89.8%), Neemix (200.3ppm induced 88.3%) and spinosad (28.2ppm induced 87.3%). 2′-Acetylnaphthalene (198.3ppm induced 78.8%) was in the same statistical order of Neemix, flufenxuron and hexaflumuron (132.9 and 160.5ppm induced 73.8 and 75.5, respectively).
5.3.2- Egg age
1 Of the eleven chemicals assayed at their EC50s, three of them (lambda-cyhalothrin, imidacloprid and Achook) completely disrupted egg hatching regardless the age of eggs when treated. The rest of chemical treatments (thiocyclam hydrogène oxalate, abamectin, spinosad, indoxacarb, flufenxuron, hexaflumuron, azadirachtin (Neemix) and 2′-acetylnaphthalene) performed well as ovicides against older eggs of 72-96h old. Younger eggs of 0-48h old seemed to be the least sensitive age toward those treatments.
2- Treatments that exhibited the greatest ovicidal activity, offered the least percentages of emerged F1 and this referred that inhibition of emergence was a major function of the ovicidal activity of tested chemicals.
3- With the exception of spinosad treatment, most of hatched eggs were developed to adult stage. This confirms that tested chemicals could not be reached larvae inside the seeds which increase the safety of using them as legume and grain protectants.
4- Five chemicals (lambda-cyhalothrin, abamectin, spinosad, imidacloprid and azadirachtin commercially named Achook) offered ≥90%IE when eggs of different ages were treated. For the rest, their performance in inhibiting emerged F1 ranged from 8.76 to 60.09%, according to tested chemical and egg age; however, they performed better on older eggs of 72-96h old.
5- Three chemicals [(lambda-cyhalothrin, imidacloprid and azadirachtin (Achook)], at their EC50s offered complete protection when eggs of different ages were treated. For the rest except hexaflumuron and indoxacarb, their performance was better against older eggs
6- For indoxacarb and hexaflumuron treatments, Percentages of inhibition of emerged F1 was not in strong positive correlation with percentages of reduction of seed damage. Unhatched eggs outside and dead immature stages inside, in addition to the moisture factor may add false weight to treated seeds. For that reason, it is more accurate to calculate the damage based on the mean number of holes not based on the loss in seed weight.
5.3.3-Type of treated pulse
For each chemical treatment, seeds from the four types of pulses) lentil, chickpea, broad bean and cowpea) were admixed with a discriminating concentration corresponding to the EC50 and used against 0-24h old adults. The obtained results are summarized as follows:
1- Based on adult mortality after four days exposure, tested chemicals (except thiocyclam hydrogène oxalate) exhibited similar performance on all types of treated pulses. Thiocyclam hydrogène oxalate performed well on chickpea.
2- Based the comparisons on %reduction of egg-laying on the four types of treated pulses. Spinosad and imidacloprid offered similar effect on the four types of treated pulses. Indoxacarb, IGRs, azadirachtin and 2′-acetylnaphthalene performed well on treated broad bean. Lambda-cyhalothrin, thiocyclam hydrogène oxalate and abamectin performed well on chickpea.
3- Ovicidal activity was similar for eggs laid on different types of treated pulses with any of lambda-cyhalothrin, Achook, thiocyclam hydrogène oxalate, indoxacarb and flufenxuron. For the rest of chemical treatments, ovicidal activity was a combined effect of both tested chemical and treated pulse. The lowest percentages of egg hatching were calculated from eggs laid on treated chickpea and cowpea with abamectin and spinosad, treated lentil and cowpea with imidacloprid, treated cowpea with hexaflumuron, treated lentil with Neemix and treated broad bean with 2′-acetylnaphthalene.
4- Most of hatched eggs developed to adult stages and tested chemicals may be unable to reach neonates inside any type of treated pulses or may reach them at sub-lethal concentrations.
5- 2′-Acetylnaphthalene was the unique treatment that differently acts on different types of treated pulses. The lowest percentages of emerged F1 were from eggs laid on treated broad bean and lentil seeds (30.8 and 52.5, respectively) that were significantly less compared to those from eggs laid on treated chickpea and cowpea seeds (82.3 and 81.8, respectively).
6- Percentages of inhibition of emerged F1 (%IE) were significantly different among the four types of treated pulses for only two chemical treatments (thiocyclam hydrogène oxalate and 2′-acetylnaphthalene). For thiocyclam hydrogène oxalate, %IE was significantly greater for treated chickpea than that for treated broad bean. For 2′-acetylnaphthalene treated chickpea and cowpea, %IE was significantly less compared to that for treated broad bean.
7- Six chemicals (Lambda-cyhalothrin, abamectin, spinosad, imidacloprid, indoxacarb and Achook at their EC50s) offered complete protection for the four types of treated pulses. Five chemicals (thiocyclam hydrogène oxalate, flufenoxuron, hexaflumuron, Neemix and 2′-acetylnaphthalene) performed well on broad bean, offering the greatest protection to this pulse type. %Reduction of seed damage was not always in strong positive correlation with %IE.
8- It could be concluded that variations among chemicals in their ability to protect treated seeds are essentially related to their chemical properties. However, for each chemical at the same tested concentration, variations among different types of treated pulses may be related to the physical properties for both chemical and pulse surfaces that allow different pulses to adsorb different amounts of the active substances.
5.3.4-Type of cultured pulse
Half of the EC50s of tested chemicals were selected when conducting this and next study. Obtained data are summarized as follows:
1- Based on the 24h mortality data, adult beetles cultured on four different types of pulses were insignificantly different in their sensitivity toward tested chemicals except toward thiocyclam hydrogène oxalate and indoxacarb treatments. For both chemical treatments, lentil culture was the most tolerant and chickpea seemed to be the greatest sensitive culture.
2- Based on the 96h mortality, the four cultures responded similarly toward each of lambda-cyhalothrin, thiocyclam hydrogène oxalate, abamectin, imidacloprid, Achook and 2′-acetylnaphthalene. For each of spinosad, indoxacarb, flufenoxuron, hexaflumuron and Neemix; lentil culture seemed to be the greatest tolerant culture.
3- Although lentil culture was suffering the least mortality; however laid less eggs in abamectin and indoxacarb treatments with the greatest reduction in eggs laid by this culture in the each of the two treatments. The rest of chemical treatments similarly performed against all cultures.
4- Eggs laid by chickpea culture had the greatest sensitivity toward indoxacarb, flufenoxuron, hexaflumuron and 2′-acetylnaphthalene treatments and also toward ethanol treatment. On the other hand eggs laid by broad bean culture were mostly the greatest tolerant.
5 Percentages of emerged F1 in relation to number of hatched eggs confirmed that tested chemicals did not affect neonates inside treated seeds either because they do not reach them inside or because they reach them in sub-lethal concentrations.
6- Based on %IE as a criterion for the combined effects of tested chemicals on adult survivorship, egg laying and egg hatching, it seemed that the variations among cultures were only significant in only four chemical treatments (thiocyclam hydrogène oxalate, indoxacarb, flufenoxuron and azadirachtin commercially named Neemix). Lentil culture seemed to be the greatest tolerant culture toward TCHO and Neemix. However, broad bean culture seemed to be the greatest tolerant toward indoxacarb and flufenxuron.
7- When the comparisons based on %reduction of seed damage, nine chemicals offered similar performance in protecting the seeds from the damage caused by the four cultures. For indoxacarb and Neemix, lentil culture seemed to be the greatest tolerant culture, causing the greatest loss in seed weight.
8- Results confirmed that lentil and broad bean cultures were mostly the greatest tolerant cultures, however, chickpea culture was mostly the greatest sensitive cultures. Results, particularly in the treatments of indoxacarb, confirm that %IE was not always in strong positive correlation with %reduction of seed damage and better in the future to measure the damage based on the number of holes, not on the weight of seeds.
5.3.5-Temperature during the application
Newly emerged adults of C. chinensis that were reared on lentil pulse seeds were released on treated lentil seeds with half of the corresponding concentrations for 50%reduction in egg laying and then incubated at four constant temperatures (15, 20, 25 and 30oC) till the emergence of F1. Data obtained are summarized as follows:
1- In six chemical treatments (lambda-cyhalothrin, thiocyclam hydrogène oxalate, imidacloprid, indoxacarb, and the two formulations of azadirachtin), the 96h mortality increased as temperature decreased. For the rest (abamectin, spinosad, flufenxuron, hexaflumuron and 2′-acetylnaphthalene), mortality did not significantly differ at the four constant temperatures. Abamectin was the unique treatment that offered 100% mortality at all constant temperatures. In contrast IGR’s and 2′-acetylnaphthalene were inferiors in this respect.
2- Five chemical treatments (thiocyclam hydrogène oxalate, abamectin, the two formulations of azadirachtin and 2′-acetylnaphthalene) offered their greatest performance in reducing egg-laying at 15oC. For the rest of chemical treatments (l-cyhalothrin, spinosad, imidacloprid, indoxacarb and IGR’s), percentages of reduction in egg-laying did not significantly differ among the four constant temperatures.
3- The ovicidal activity of thiocyclam hydrogène oxalate, indoxacarb, the two IGRs, azadirachtin commercially named, Neemix, and 2′-acetylnaphthalene significantly decreased as temperature increased. The rest of chemical treatments (l-cyhalothrin, abamectin, spinosad, imidacloprid, and azadirachtin commercially named Achook) are excellent ovicides regardless the incubated temperature.
4- Lambda-cyhalothrin, abamectin and Achook completely inhibited adult emergence from insects incubated at the four constant temperatures. For the rest of chemical treatments (TCHO, spinosad, imidacloprid, indoxacarb, 2-IGRs, Neemix and 2′-acetylnaphthalene), ovicidal activity increased as temperature decreased.
5- lambda-cyhalothrin, abamectin, and azadirachtin commercially named Achook offered complete protection for treated seeds at all tested temperatures. The rest of chemical treatments were more potent in protecting legume seeds from the damage of Callosobruchus chinensis when incubated at the lowest tested temperatures (15 and 20oC).
5.4-Latent effects of tested chemicals on insect development and its progeny
Lentil seeds bearing single eggs were treated with the EC25s of tested chemicals. Then incubated at 30 ± 2oC and observed for egg hatching and adult emergence. Emerged adults were coupled and released on untreated lentil seeds and observed for oviposition and egg hatching. The obtained data are summarized as follows:
1- Incubation period of treated eggs did not significantly differ among all treatments including the two controls.
2- Seven chemicals significantly elongated larval and pupal stages duration; those treatments are thiocyclam hydrogène oxalate, indoxacarb, the two IGRs, the two formulations of azadirachtin and 2′-acetylnaphthalene.
3- Fecundity of emerged adults was significantly reduced in the treatments of lambda-cyhalothrin, thiocyclam hydrogène oxalate, abamectin, spinosad, imidacloprid, indoxacarb and Achook.
4- Fertility of eggs laid by emerged females was significantly reduced in the treatments of thiocyclam hydrogène oxalate, abamectin, imidacloprid, spinosad, indoxacarb and Achook. Hatchability of eggs in those treatments ranged from 50% in imidacloprid treatment to 79% in abamectin treatment compared to 100% hatching in the two controls.
5- It could be concluded that treatments of thiocyclam hydrogène oxalate, indoxacarb, Achook at their EC25s, significantly elongated insect life span and also reduced the reproductive capacity of emerged adults. On the other hand, tested IGRs, 2′-acetylnaphthalene and Neemix significantly elongated P1 life span, however, did not significantly affect the reproductive capacity of emerged adults. In contrast, abamectin, spinosad, imidacloprid and lambda-cyhalothrin significantly reduced the reproductive capacity of emerged adults, however, did not significantly affect insect life span.