Estimate the Annual Field Generations of Lepidosaphes tapleyi (Williams) Infesting Guava Trees and Predicting its Expected Peaks Using Thermal Units Accumulation under Luxor Governorate Condition, Egypt.

Abstract

The aim of this study was to determine the approximated numbers, occurrence date, size of the generations and their peaks of Lepidosaphes tapleyi were determined on guava trees at Esna district, Luxor Governorate during two successive years of (2017/2018 and 2018/2019) in order to predict the degree day's units and annual generation peaks by studying the relationship between the accumulated thermal heat units expressed as degree-days (DD's) and the population fluctuations of insect that help to find out a proper controlling time. The obtained results revealed that L. tapleyi has four to five overlapping generations per year under the field conditions in Luxor Governorate.During the first year of (2017/2018), five generations were from early March to mid-May, mid-April to early July, beginning of June to early September, mid-July to mid of November and early October to early January for the 1st, 2nd, 3rd, 4th and 5th generations, respectively. These generations lasted 10, 11, 12, 16, and 13 weeks, respectively. These generations size was 81.42, 99.44, 159.54, 306.07 and 236.24 individuals/ leaf, respectively. While, the second year of (2018/2019), four generations were from early March to mid-July, early June to mid-September, mid of July to mid-November,andmid of September to early January for the 1st, 2nd, 3rd and 4th generations, respectively. These generations lasted 13, 18, 14, 16, and 14 weeks, respectively. These generations' size was 188.73, 222.50, 347.92, and 282.34 individuals/ leaf, respectively. In general, the fourth generation in the first year and the third generation in the second year, which started in both of them from mid-July and continued until mid of November was the longest one and biggest in size than the other generations during the two years. Using available meteorological data provided for Luxor area, the mean ± STD daily heat units per generation for L. tapleyi over the two years were estimated to be 18.01 ± 2.63DD's. The simple regression analysis indicated that the numbers of cumulative individuals of L. tapleyi per leaf were relatively more correlated with the accumulated heat units for two years. The obtained results indicated the occurrence of five actual observed peaks that took place in (early April, mid-May, mid-July, early-October and mid-November) and has five expected peaks that occurred in May, 5th; June, 30th; August, 21st; October, 15th and January, 4th, respectively during the first year (2017/2018). However, through the second year (2018/2019), has four actual observed peaks that recorded in (mid-April, mid-July, mid-September, and early-November) and has five prospective peaks that occurred in April, 9th; June, 7th; July, 31st; September, 23rd and December, 3rd, respectively. Also, the predicted peaks ofgenerations could be detected when the accumulated thermal units reached 1112.35 ± 6.00-degree days under the climatic conditions in Luxor Governorate.