INFLUENCE OF HOST PLANTS, TEMPERATURE AND RELATIVE HUMIDITY ON OCCURRENCE AND POPULATION DYNAMIC OF BLACK VINE THRIPS, RETITHRIPS SYRIACUS MAYET AT EL QASSASEEN DISTRICT, ISMAILIA GOVERNORATE

Abstract

this study was conducted at El Qassaseen district, Ismailia Governorate in the farm of El Qassaseen Horticulture Research Station and a surroundin area during the period from 8th Aug., 2013 till 11th Jan., 2016 to determine the specific host plants, occurrence ratios and periods on each host, annual population dynamic on the specific plant hosts; also to clear the effect of certain climatic factors (maximum, minimum temperature and mean of relative humidity (RH%)) on the population fluctuations of black vine thrips, Retithrips syriacus Mayet. The obtained results revealed that, this pest is found infesting two hosts: pear (Pyrus communis) family: Rosacea and persimmon (Diospyros kaki L.) family: Ebenaceae throughout the activity period extended from 8th Aug. 2013 till 9th Jan.2014; then migrate to infest the two permanent evergreen trees ( alternative hosts), Leucaena (Legume Forage Tree), (Leucaena leucocephala) family: Fabaceae and Brazilian pepper trees (Schinus terebinthifolius (Raddi)) family: Anacardiaceae throughout the 2nd period extended from 2nd Jan until 20th Aug. 2014. After that, the thrips return again to infest the main hosts of deciduous fruit trees which raised to four hosts, grapevine (Vitis vinifera) family: Vitaceae; jatropha, (Jatropha curcas) L. family: Euphorbiaceae, pear (P. communis); persimmon (D. kaki L.); throughout an activity period extended from 6th Aug. 2014 till 7th Jan. 2015. In the same trend, the thrips insects migrate again to infest the alternative hosts, Leucaena and Brazilian pepper trees throughout the period extended from 7th Jan. until 29th Aug. 2015. After that, it moved again to infest the main four fruit trees hosts throughout an activity period extended from 10th Aug. 2015 till 11th Jan. 2016. The thrips insects moved between main and alternative hosts throughout two overlapped periods observed through January and august months of the three study years. Also, highly significant differences appeared between averages of thrips numbers on different hosts (P˂ O.O1) with highest average numbers of 11.35, 12.83 and 13.06 individuals /leaf on main host, persimmon; 13.02 and 15.98 individuals /compound leaf of alternative host, Leucaena trees. In the same trend, the highly occurrence ratios of 67.33, 38.02 and 32.62 % were recorded on main host, persimmon; while, of 78.09 and 79.78 % (of the total numbers of thrips on the alternative hosts) wererecorded on leucaena trees. The highest population densities of R. syriacus were recorded throughout October on main hosts (where the weekly mean of maximum temperature during the two years of 2014 and 2015 ranged 26.44-35.08 C°, the weekly mean of minimum temp. ranged 17.4-22.59 C° and weekly mean RH% ranged 64.99 - 80.36) and throughout March on alternative hosts (where the max. temp. during the two years of 2014 and 2015 ranged, 22.03-34.25 C°, min. temp. ranged 10.68-21.95 C° and mean RH% ranged 62.62-67.59). In accordance to the correlation and regression analysis, the effects of tested climatic factors (Max., min. temp. and mean RH %) varied as activity period and host plant, where the highest combined effect was (EV %) = 83.15%, recorded on Leucaena trees during 2015, while the lowest, EV% =59.98% was recorded on pear trees during 2014.