Biology and population dynamics of Jasmine whitefly Aleuroclava jasmini Takahashi (Hemi:Aleyrodidae) and the efficacy of its predator Clitostethus arcuatus Rossi on citrus in north of Khuzestan

Nowadays, Jasmine whitefly Aleuroclava jasmini (Takahashi) (Hem.: Aleyrodidae) is the most important pest of citrus groves in Khuzestan province, Iran. From May 2010 to Oct. 2013 explored data sets were collected from 78 citrus groves all over Khuzestan, and two special citrus groves (a Sweet lime Citrus limonium Tan. and a grapefruit C. paradisi Macfad. Grove) in Safi Abad of Dezful, Iran. In this research some trails and experiments were carried out to determine the field population biology, the distribution patterns of Jasmine whiteflies developmental stages on leaves, and to develop reliable standardized and two stages sampling plans for estimating its densities, and to study its seasonal fluctuation of developmental stages, and investigation of efficiency of its predator Clitostethus arcuatus Rossi. Using RV and RNP indices and regression relationships, it was revealed that one cm2 quadrates are suitable for assessment of population. The height of 1.5m was determined the most suitable for sampling in all of times. There wasn't significant difference among geographical directions for RV values. The best leaves for sampling from branches were changed by passing of times. Hence, from the end of branches, 10th to 14th leaves on March, first to 5th leaves on April, 6th to 7th on July and 9th to 12th on January had the least values of RV. On the average the maximum of mean population for eggs and pupae in each citrus grove was 34.9/cm2 and 49.13/cm2 of leaf, respectively. There is no significant differences between the relative variation each developmental stages at two spring and autumn generations, geographic directions of trees in citrus groves, different geographical sides of each tree. The data of spatial distribution for the pest population among all of citrus groves with both Iowa's Patchiness regression method and Taylor's Power Law indicated that Taylor's Power Law showed a better fit than Iwao's model (R2 between 0.94-0.96). The regression coefficient (b) for eggs, pupae and exuviae were 1.82, 1.67 and 1.79, respectively, which showed negative binomial distribution among populations. The common K for egg, pupae and exuviae, sum of alive stages and total population were determined 0.29, 0.57, 0.36, 0.7 and 0.79, respectively. Number of fixed samples for developmental stages were calculated in the determined permissible precision levels of 12.5, 15, 20 and 25%. Results of seasonal fluctuation in sweet lime grove indicated that adult population had two big peaks, the spring peaks occurred in late April 2011 with the average of 29.9/cm2 and late May 2012 with the average of 39.08/cm2 yellow card, respectively, and the autumn peaks appeared on mid October 2011 with the average of 8.28/cm2 and late September 2012 with the average of 12.14/cm2 yellow cards, respectively. All developmental stages were found active throughout the year. The peaks of egg, 1 to 4 instars, and pharate pupa population were recorded late April 2011 with the average of 24.29, 39.09 and 3 per cm2 leaves and early May 2012 with the average of 19.29, 15.15 and 0.27 per cm2 leaves, respectively. The highest winter mortality of nymphal stages were observed early Jan. 2011, late Dec. 2012 and mid Jan. 2013 with 38.6%, 89.4% and 48.37%, respectively. The most significant of effective weather elements on the different developmental stages ranked as the temperature and precipitation. There was a positive and significant relationship between egg and also pupal exuviae undersurface of leaves with sooty mould on them. In Khuzestan province, 29 host plant species belong to 17 family as main and secondary host for the pest were collected and identified, which there weren't in any its original countries. Its sex ratio was 1:9 (male: female) in Spring and 3:7 in Autumn. The stage specific survival rate varied from stage to stage, But overall survival rate of the pest was 0.16- 0.21. There were variations in developmental durations among different stages. During period of study a significant fraction of the population did not emerge as adults in the same season, but remained in the fourth nymphal stage until the Autumn. Hence , percentages of fourth instar nymphs that hibernated from these populations were 12.7 and 17.4 % in North and South sides of trees, respectively. Developmental times for normal individuals and these longer-developing nymphes in south side of tree was averaged 86 and 187 day, respectively, and was provided a emergence of adults in Autumn. No evidence of parasitism was present in the populations during this study. The peak of appearance adults of C. arcuatus has been on May in Khuzestan and depending on weather conditions will be continue until late of October. The population of this coccinelid was affected by the blow of wind and precipitation. In natural conditions, active adults of C. arcuatus was showed highest correlation with the eggs and adults of Jasmine whiteflies. The overall average of coccinelid sex ratio was 1.38:1 (male: female) in period of adult appearance on citrus. The different developmental stages of coccinellid which feed on eggs were higher than nymphal stages. On the contrary to anticipation, the highest eggs and nymphs Jasmine whiteflies which have been eaten by the male and the fourth instar larvae of predator, respectively. Feeding rate of female predator from the eggs of pest was 59.3% of male. Disproportion between whitefly and predator populations, lack the attractiveness of jasmine whitefly for the colonization and reproduction of predator in citrus groves, unsuitable sex ratio, and severe effect of wind on coccinellid population, are some reasons of failure this predator for jasmine whitefly control. However, the greatest impact of this predator is in the early colonization of the pest that is egg stage. So, support operations for predator and avoidance any chemical control measure is necessary at this time.