SIMULTANEOUS EFFECT OF CERTAIN ENVIRONMENTAL FACTORSON D,ENSITY OF SOME COTTON P

Abstract

The present field and laboratol)' studies were conducted at Shalakan, Qalyubyia governorate to achieve certain biological and ecological aspects for the cotton leafworm, pink and spiny bollworms as principal and prior steps based on heat units (DO") for each stage of the target insect-pests when forecasting programs are considered. The obtained results revealed that the time needed for completion of embryogenesis decreased as the temperature increased for the three tested insect pests. The estimated threshold of development values for the egg stage were 11.85"C for cottonleafworm, 12.2"C for the pink bollworm and 114"C for the spiny bollworm. The thermal units required for egg development were 61.48 day-degrees for the cotton leafworm, 82.17 dd 's for the pink bollworm and 106.1 dd's for the spiny bollworm. The same trend was achieved for the larval duration. The lower threshold of development for this stage was 7.77"C, 12.6"C and 9.7"C tor CLW, PBW and SBW, respectively. The calculated thermal units (dd's) required for completing the larval stage of each of the three tested insect pests were 360.38, 171.37 and 143.76 for CLW, PBW and SBW, respectively. The duration of pupal stage was 17.66, 194 and 26.5 days at 20"C These averages were 13.2 and 8.4 days at 35"C for cotton leafworm and pink bollworm It was 11.3 days at 30"C for the spiny bollworm. The developmental threshold values for the pupal stage were 11.92"C, 9.03"C and I 2. 5"C for the considered three cotton pests, respectively. The total thermal units needed for the pupal development were I 79.94 dd's for CLW, while lor the PBW it was 213.2 dd's and 199.0 dd's for the SBW The longest life span of male moths was estimated 20"C while the shortest was estimated at both 30, 35"C. Accumulated thermal units were 129.85, I 02.2 and 256. I dd's for S. littora/is, P. go. sypiel/a and£. in.m/ana. respectively.