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Abstract - The present investigation was carried out to estimate the ~ortalities amongst the pink bollworm, Pectinophora gossypiella (Saund.) larvae at different districts of four Egyptian governorates, and the role played by bacteria, virus, other mortality factors and natural mortality in causing mortalities amongst dead larvae, and to study the effect of the bacterium, Bacillu~ thuringiensis Ber. (in commercial preparations) on larvae of !. insulana and P. gossypie1la; the effect of field application of Eactospeine (a commercial preparation of ~. thuringiensis) on the larval popula- <~tion of P. gossypiella and the fecundity of resultant adults. The obtained data can be summarized as follows: A. Natural infection of E. gossypiella larvae with diseases and other mortality factors : Larvae of P. gossypiella that were counted in fortnightly samples, of 100 cotton bolls each, collected during September and October, 1980 and 1981, at different districts of four Egy;tian governorates (FaJ<Toum,QalUbia, ShaI’k:,’”ia and Gharbyia). Collected larvae were reared in the laboratory until pupation - 121 and adults en:.ergence. where li””ortatlies anonga t larvae and subsequent pupae and the percentages of adul ts eLlergence were recorded. Dead larvae were thoroughly ins)ecteci to detenJine the cause of death. The highest percentages of total mortality was recorded at Sharkyia governorate (30.62 %. average of two seasons) and that was correlated with the lowest larval population that was co~~ted at the same governorate (68 larvae/IOO cotton bolls; average of two seasons). The lowest total mortality percentage (27.14%) was oD,the other hand, recorded at Fayoum governorate, and that was correlated with the highest rate of infestation that was recorded at this governorate (100.2 larvae/IOO bolls). That gave an indication that the natural mortality factors may playa role in suppressing the rate of infestation with ~. sossypiella in cotton fields. Studies on the percentages kill by different causes, amongst dead larvae, indicated that the majority of dead larvae were killed by bacteria (53.57 - 80.28 % of dead larvae). Virus ranked the second after bacteria at Fayoum governorate (19.41 % of dead larvae). -- --- - 122 - Estimation of the rate of natural infection of P. gossypiella larvae, in the field, with diseases and other mortality factors before planning for any program of the pest management is recommended. B. Laboratory infectivity tests with B. thuringiensis : 8.. On the first instar larvae of E. insulans. and --------------------------------------------- ~. gossypiella : Pour concentrations in water of each of the two commercial preparations (Dipe1 and Bactospeine) were used in this experiment; 0.05 % (8 x 103 l.U./ml. suspension), 0.1 % (16 x 103 r.U./m1.), 0.2 % (32 x 103 r.U./ml.) and 0.4 % (64 x 103 I.U./ml.), using the dipping technique of okra disks or green cotton bolls. The obtained data indicated that Dipel w8S,generally,more efficient on !. insulana 1st instar larvae than. Bactospeine, where the averages of values in percentage mortality after 7 days of treatment, % of malfor.med pupae, LeSO end ~50 were 55.4 %, 12.2 %, 0.0675 % (lO.B x 10 3 I.u.I mI.) and 5.9 days in case of Dipel treatment and S3.6 %, 9.03 %, 0.1 % (16.5 x 103 l.U./m!.) and 7.0) days in case of Bactospeine treatment, respectively. On~. gossypiel1a l~ instar larvae, Bactospeine treat~ent showed that -E. insulana 1-st instar larvae were more auaceptib2e, where ~he L050 in case of the former insect was 0.15 % (24 x 103 r.U./ml. suspension). - 123 - b. On the 2~ and 4t&-instar larvae of P.gossypie11a: -------~----------------------------------------- Five concentrations of Bactospeine were 1ncorporated with the larval artificial medium (80, 160, 240, 320 and 400 I.U./7 gm. diet) and tested against 2ll£ and 4th instar larvae of ~. gossypiella. The illustrated concentration-mortality lines indicated that the effect increased with the increase in the bioinsecticide concentration and the decrease in larval age. The LeSO values were 154.7 and 429.8 I.U./7 gm. diet for treatment of the 2~ and 4!a insters, respectively. The LTSO values averaged 3.15 and 11.15 days, respectively, indicating higher susceptibility of the former instar. A latent effect could be, also, detected amongst the resulting pupae and adults emergence, but the effect was generally low. c. On resting larvae of l.. gOBsypiella. : ----------------------------------- Intrahemocoele injection of five doses of Bactospeine (8, 16, 24, 32,and 40 I.U./larva)was carried out in healthy diapaused larvae of l.. gossypiella. Yortalities amongst treated larvae increased, successively during the first 3 days after treatment, though the highest mortality rates occurred after 24 - 48 hours - 124 - of’ treatment. kiter the Jrd day of treatment; mortalities amongst treated larvae were very low. As the applied dose increased; the effect on larval mortality increased, however the LTSO value decreased. The ~50 after 72 hours of treatment was 11.29 r.u./ larva. c. Effect of field application of Bactospeine on !. gossypiella : Bactospeine suspensions were applied on cotton plants (sown at two 28th) at two rates; of water/fedden and planting dates; Karch, 7i!! and 2.5 Kg. (40 x 109 1.U.)/200 litres 9 . 4 Kg. (64 x 10 I.U.)/feddan. Bioinsecticidal application took place on August, lOth on the two plantations. Data indicated that treatments caused a significant reduction in larval population of P. gossypiella than control. The percentages of reduction in larval population averaged 47.11 and 35.16 %, respectively for the first plantation and 31.15 and 33.84 %, respectively for the second plantation. Thus the low rate of Bactospeine (40 x 109 I.U./feddan) was recommended. The oviposition rates amongst adults that developed from larvae of treated and untreated areas were, also, estimated. Data indicated that treatments, markedly, reduced the females oviposition rate. However, a slight effect on the percentages of eggs hatching was detected. |