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Abstract
SUMMARY The efficacy of Bactericides (Bacillus thuringiensis), and viral insecticide (NPV) against the newly hatching, 2nd and 4th larval instars of S. littoralis were studied under both laboratory and field conditions. The results are summarized as follow:
I. Laboratory studies:
1. Residual toxicity of different tested commercial microbial products on larvae of Spodoptera littoralis:
Data show the effect of the B.t. compounds (Protecto, Dipel-2X and Ecotech-bio) and one Virus NPV (Viroset) with five concentrations of 0.01, 0.05,0.1,0.5 and 1.0 gm. on mortality percentages on newly hatched, 2nd and 4th larval instars of S. littoralis. Increasing form 0.01 to 1.0 gm. Led to increase of mortality. The % reduction in the population increased gradually after 1 day of treatment till 9 days with different concentration, depending on LC50, LC90 and slop values. The newly hatched larvae were the most susceptible to the microbial insecticides.
2. Latent effect of the tested compounds on percentages of larval failed to pupate:
2.1. Effect of the 2nd larval instar:
Results cleared that the highest percentages of the 2nd instar larvae failed to pupate after treating with three tested B.t. compounds Protecto, Dipel-2X and Ecotech-bio were (24,20 and 22%) respectively, whereas it decreased to (18%) when larvae treated with Viroset. The corresponding value in the check groups was (6%) only.
2.2. Effect of the 4th larval instar:
The obtained results indicated that there was a reduction in pupation percentages in all tested concentrations compared with that resulted from untreated larvae. The highest percentages of the 4th instar larvae failed to pupate were (30, 18 and 22%) at the 1.0 % concentration for Protecto, Dipel-2 x and Ecotech-bio respectively. These percentages decreased to (22, 18 and 18 %) when the concentration decreased to (0.01 %). The percentages of larvae which were not able to continue their development after treating with Viroset ranged between (30 to 2) when concentration increased from 0.01 to 1.0 % gm..
3. Latent effect of the tested compounds on some biological aspects of cotton leafworm:
3.a. Effect on percentages of pupation, emergence and malformation of moths:
The cumulative mortality at the end of the larval stage after the indicated days of treating 2nd instars larvae; revealed that of malformed moths. At the highest concentration (1.0 gm) the number of pupae obtained from larvae treated with Protecto , Dipel-2x and Ecotech-bio were 28.6, 54.5 and 65.2 %respectively, Viroset gave highest effect 82.9% pupation followed by Dipel-2x (77.8%) and Protecto (63.00%) on the other hand, Viroset gave 50.00% pupation. The percentages of produced pupae in the check were 93.6 %. Records in case of treating the 4th instar larvae gave the same trend of pupation of the different formulations, with fewer percentages.
3.b. Influence of different tested bio-compounds on fecundity of S. littoralis females and hatchability of eggs:
3.b.1. Fecundity of females resulting from treated 2nd
instar larvae:
It was found that the total number of eggs/female was correlated with the used compound and the concentration. When larvae treated with Protecto it reached between 180-245 eggs /female for the three conc. (0.1, 0.05 and 0.01 gm), while in other two conc. (0.5 and 1.0 gm.) no eggs were deposited. On the other hand, the total number of hatchability eggs / female reached between 116-165 with the above three concentrations. In the same trend it was found the total number of batched eggs /female reached between 230-336 eggs / female indifferent concentrations. In all conc. Of Ecotech-bio % reduction on number of eggs per female ranged between 36.90-53.50. the total no. of eggs/female when treating with Dipel-2x reached between 425-163 eggs/female in case of the four conc. (0.5,0.1,0.05 and 0.01 gm.), while in the conc. (1.0 gm.) no eggs were deposited. The average no. of eggs/female in the control was 487.5 on the other hand, the total on. Of hatched eggs/female when treating with Dipel-2x reached between 223-113 for the above four conc., respectively, also in other conc. (1 gm.) no eggs were hatched. No eggs were deposited in Viroset treatments at all concentrations.
3.b.2.Fecundity of females resulting from treated 4th instar
larvae:
Results obtained indicated that the average no. of eggs/female influenced by the tested biological agents. In Protecto treatments, no eggs were deposited at the two highest concentrations (1.0 and 0.5%). Numbers of deposited eggs/female at the three other concentrations. averaged between 260-285, while the check treatment recorded on average of 324 eggs/female. For the two formulations Ecotech–bio and Dipel-2x, the mean no. of eggs /female not affected by the different concentrations. The maximum number of deposited eggs/female reached 458(1.0%) and 502 (0.5 %) for Ecotech-bio and Dipel-2x treatments, respectively. In spite of the high no. of eggs laid per females in all bacteria, comparing with that in the control, the fertility of the egg-masses were lower than that obtained in the check. The percentage of reduction in hatchability ranged between (44.06-70.2), (41.3-68.6) and (26.3-42.3 for Protecto, Ecotech-bio and Dipel-2X treatments, respectively. The corresponding value in the control was 23.4%.
4. Latent effect of tested bio-compounds on no. of emerged adults and sex ratio after treatment:
4.1. Effect of different compounds on sex ratio and emergence of the 2nd larval instar of S. littoralis:
The results indicated that there was a reduction in adults’ emergence from developed pupae due to the latent effect of the different compounds. An adversing correlation was existed between the concentration and no of obtained adults. The lowest emergence percentage (1%) was recorded at the conc. 1.0 gm of Protecto treatment, while the highest percentage (24%) was at the conc. 0.01 g of Dipel-2X compared with 41% for the check. No moths were obtained at the two highest conc. 1.0 and 0.5 g of Viroset. On the other hand, no significant effect on the sex ration.
II. Field evaluation:
Field experiments were carried out during two successive seasons 2000 and 2001 to evaluate the efficiency of the three biocides Protecto, Ecotech-bio and Dipel-2X and one NPV virus (Viroset) with three concentrations against different instars larvae of the cotton leafworm, Spodoptera littoralis.
Generally, Viroset showed high mortality percentage after 7 days of treatment in the two seasons 2000 and 2001 followed by both of Dipel-2X in the season 2000 and Protecto in the season 2001, percent reduction in larval population caused by Viroset ranged between 92-74.9% and 93-93.2% for the different concentration during the two seasons 2000 and 2001, respectively.
The maximum percentage of reduction in larval population due to applying Protecto was 90.5% at 1.0 g conc. While the minimum one was 59.5% in the season 2000. These percentages decreased to 81.5% and 72.9% in the season 2001.
Reduction percentages in cotton leafworm larvae in case of Ecotech-bio and Dipel-2X ranged between (71.3-63.0) and (82.9-65.3) for the season 2000 and between (78.3-51.3) and (60.0-54.8) for the second season 2001, respectively.