Microbial Control Of The Cotton Leafworm By Bacteria And Its Preparation:

Naglaa Fikry Abd Ei-hameed

Laboratory experiments were carried out to estimate the efficacy of three bacterial commercial insecticides of Bacillus thuringiensis (Berliner ) on each of the six larval instars of Spodoptera littoralis ( Bosid . ) and the survivors of subsequent stages . Recorded data included mortalities , malformations , egg — laying activity of resultant adults and hatchability percentages among the deposited eggs . Studies extended also to evaluate the efficacy of Dipel 2X ( which showed best results ) when sprayed on cotton plants artificially infested with the egg — masses . Also , trials were made to determine the role of each of 3 materials used as photoprotectants for B. t. kurstaki from the detrimental effect of U.V. ( in the laboratory ) and the effect of UV emmited through sunlight( in the field ) . Studies included also estimations for the efficacy of a new bioinsecticide ( MVP n. ) , depending on B. t. kurstaki S endototin bioencapsulated in killed Pseudomonas flouresens , on S. littoralis 1st and 3rd instar larvae and the survivors , and also the effect of UV ( in laboratory and field ) on the biological activity of this product against S. littoralis larvae . Studies covered also the effect of Dipel 2X treatments by LC20 and LC50 to S. littoralis 2nd and 4th instar larvae on the larval haemolymph and also the effect of the same product at LC50 and LC90 to 1St and 3rd instar larvae of S. littoralis on the histology of mid — gut .The obtained results may be summarized as follows :— Effect on different larval instars of S littoralis:1 -1- Effect on larval mortality :By two days feeding of different of each of the six S. littoralis larval instars on leaves treated with different concentrations of Dipel 2X195, Dipel EC and Ecotech , the following percentages were recorded among treated larvae :•Newly hatched larvae ; 26.7 - 100 , 26.7 -100 and 26.7 - 100 % .•24 h. old 1st larval instar ; 23.3 - 96.7, 26.7 - 96.7 and 26.7 - 93.3%.•2nd larval instar ; 20.0 - 100 ,26.7- 100 and 26.7 - 93.3 % .•3rd larval instar ; 26.7 - 96.7 ,20- 96.7 and 20.0 - 90.0 % .•4th larval instar ; 26.7 - 96.7, 13.3- 96.7 and 13.3 - 100 % .•5th larval instar ; 13.3 - 93.3, 13.3- 90.0 and 16.7 - 93.3 % .•6th larval instar ; 10.0 - 90.0, 6.7- 86.7 and 10.0 - 90.0 % .After 5 days of starting treatment by Dipel 2X , Dipel EC and Ecotech , the LC 50’s were 0.464 x 103, 0.899 x 103 and 0.810 x 103 I. U. / mg for treatment of newly hatched larvae ; 0.998 x 103 , 1.266 and 1.188 x 103 I. U. / mg for 24 h. old 1st instar larvae , 1.06 x 103, 1.528 x 103 and 1.352 x 103 I.U./ mg for 2nd instar larvae , 1.622 x 103, 2.11 x 103 and 2.077 x 1031. U./ mg for 3rd instar larvae , 1.843 x 103 , 2.267 x 103 and 3.654 x 103 I. U./ mg for 4th instar larvae , 4.144 x 103, 4.691 x 103 and 4694 x 1031. U. / mg for 5th instar larvae 4.288 x 103, 6.133 x 103 and5.409 x 103 I. U. /mg for the 6th instar larvae fed on castor - bean leaves treated by Dipel 2X , Dipel EC and Ecotech , respectively .1.2. Effect of larval feeding on castor - bean leaves treated by the LC 50’ s on the survivors :By different instar larval feeding on LC50 of Dipel 2X , Dipel EC and Ecotech , the following biological data were obtained :•Malformations among pupae & subsequent moths :196Newly hatched larvae ; 13.64 & 15.0 ,8.33 & 18.18 and 10.25 &8.57 % .< 1st larval instar ; 21.57&17.65,15.91 &16.22 and 13.15&15.15%2nd larval instar ;13.16 &27.2, 18.96 & 25.0 and 11.43 &16.13% .< 3rd larval instar ; 11.11 &25 , 18.92 & 22.13 and 11.76 &13.33% .4th larval instar ; 25.0&12.5 , 17.14& 10.34 and 14.28&13.33% .5th larval instar ; 12.9&14.28 , 6.68 & 22.22 and 16.67 &14.28.< 6th larval instal ;13.33&19.23 , 10.18 & 18.18 and 8.0 &16.67% .These percentages of malformations were obtained among the developing pupae & moths after treatments by the LC50 of Dipel 2X , Dipel EC and Ecotech , respectively .Each of the six larval instars of S. littoralis was fed for 48 h. on castor — bean leaves treated with Dipel 2X , Dipel EC and Ecotech at the LC50 , then on untreated leaves . The following biological data were recorded on the larvae and subsequent stages .•Larval and pupal period :Treatment of all larval instars caused significant prolongations in the larval periods , but the differences than control were more pronounced by larval treatments at earlier instarsThe pupal durations of those from treated larvae were also longer than that recorded from the control pupae , but the differences were significant by treatments of newly hatched larvae and those of 24 h. 1st , 2nd , 3rd and 4th instars t , but insignificant than control among those developed from the 5th and 6th instars .•Adults’ longevity :The life spans of males and females were found to be reduced due to treatment of either of the six larval instars by the LC50 of Dipel2X , Dipel EC or Ecotech . These periods averaged 4.2 — 6.2 for males and 4.6 — 6.6 days for females from treated larvae , opposed to 8.6 — 8.8 and 9 — 9.4 days for control males and females , respectively .•Oviposition period :This period was also reduced significantly due to larval treatment . The obtained averages of this period ranged from 4.9 — 7.1 days , while it averaged 8.3 — 9 days for the control females .•Eggs’ reproductivity :The resultant females showed , significant , reductions in their total numbers of eggs laid / female , due to feeding of different larval instars on castor — bean leaves treated with either of the three bioinsecticides . The obtained values for moth females from larval treatments by the LC50 of Dipel 2X , Dipel EC , Ecotech and control were , respectively , as follows :