Susceptibility of Certain Fruit Trees to Infestation With the White Peach scale, Pseudaulacaspis pentagona (Targioni -Tozzetti), With Some Ecological Aspects

Citation: Egypt. Acad. J. Biolog. Sci. (A. Entomology) Vol.8 (2)pp.49-58(2015) Egyptian Academic Journal of Biological Sciences is the official English language journal of the Egyptian Society for Biological Sciences, Department of Entomology, Faculty of Sciences Ain Shams University. Entomology Journal publishes original research papers and reviews from any entomological discipline or from directly allied fields in ecology, behavioral biology, physiology, biochemistry, development, genetics, systematics, morphology, evolution, control of insects, arachnids, and general entomology. www.eajbs.eg.net Provided for non-commercial research and education use. Not for reproduction, distribution or commercial use.


INTRODUCTION
White peach scale, Pseudoaulacaspis pentagona (Targioni-Tozzetti) (Hemiptera, Diaspididae) is the most serious pest of peach in the East Mediterranean region (Anonymous, 1993).This insect is a polyphagous pest with very wide host plant range, especially on fruit trees and ornamental plants including peach, apricot, plum and apple trees in many parts of the world (Kosztarab and Kozer, 1988).The infestation by this insect is mainly concentrated on the trunks, branches, twigs and may move to fruits.When occurs, injury is caused by different stages of the insect.They suck plant sap and cause wilting of twigs, death of branches, defoliation and considerable yield loss (Pan et al., 2003).Female white peach scales deposit all their eggs (≈100-150 total eggs/female) in about a week.Eggs hatch in 3-4 days and the young scales (crawlers) settle on the host plants within two days after hatching (Miller and Davidson, 2005).Crawlers are active up to 24 h and disperse primarily within plants (Hanks and Denno, 1993a), but aerial dispersal among plants does occur and is important in colonization of new hosts (Hanks and Denno, 1993b).P. pentagona has three annual generations, in Italy, the first was present approximately from April to July), the second from July to September and the third in September, overwintering as a gravid females (Kreiter et al., 1997).In Egypt Atteya (2004) recorded five generations in mid-March, early May, July, mid-August and in October, also Mousssa, et al. (2010) stated that white peach scales had five annual generations.
The objective of this study is to determine the susceptibility of peach, Prunus persica L., apricot, Prunus armeniaca L. and pear, Pyrus communis L. trees to infestation with the white peach scale, P. pentagona, to study its seasonal activity and distribution of this insect on tree cardinal directions over a two years of study from May 2013 to Abril 2015 at Nubaria district, El-Beheira Governorate.

MATERIALS AND METHODS
This experiment was carried out at Nubaria district, El-Beheira Governorate, Egypt from March, 2013 to April, 2015.Four trees of each of; peach (var.Florida Prince), apricot (var.Canino) and pear (var.Le-cont) were chosen and marked for this study.All of these trees were grown under the same ecological conditions and homogenous in size and age (ten years-old).There were no any chemical control applied during the period of investigation.

Artificial infestation
Heavily infested branches (20 cm) by nymphal stage of WPS were collected from infested mulberry tree from Nubaria on March 1, 2013.Every branch with approximately 300 nymphs was attached to the top of each fruit tree.Upon branch drying, nymphs moved to the branches of the fruit trees and then settled down.

Sampling
Sampling was taken once every fortnight within the studied two years from beginning May 2013 (two months after infestation) till mid April 2015.Sample of four branches (15 cm each) were selected from the four different directions of each tree i.e. east, west, south and north.The samples were transported to laboratory in polyethylene bags for examination.They were examined by counting P. pentagona different stages by means of a binocular microscope to study the susceptibility of peach, apricot and pear trees for this insect and seasonal abundance in the different fruit type.Analysis of variance and LSD value for comparing the mean of each fruit type was adopted by (Snedecor, 1970).

Calculating of monthly variation rate
The monthly variation rate (MVR) in population density was calculated according to the following formula (Abdel-Fattah et al, 1978):

Average count given at a month MVR = `
Average count given at a preceding month The number of generations of this scale was estimated from the changes in the halfmonthly nymphal stage percentages throughout the two successive years.

Distribution patterns of P. pentagona on the cardinal directions of fruit trees:
Directional preference was determine by applying the following formula (Mahmoud, 1981) Where: F1: Mean number of insects in the east direction minus insect numbers in west direction, if the former is higher, and the reverse if the latter is higher.F2: Mean number of insects in the north direction minus insect numbers in south direction, if the former is higher, and the reverse applies if the insect number in south direction is higher.The figure obtained represents the tangent: the corresponding values of which was obtained from the mathematical Table .tan.Q: Tan of the angle between the two forces.

RESULTS
Susceptibility of peach, apricot and pear trees to white peach scale, Pseudaulacaspis pentagona (Targioni-Tozzetti): Results in Tables (1 & 2) showed that none of the tested fruit trees is immune to white peach scale, P. pentagona, but fruit trees varied widely in their susceptibility.The data showed that the populations of (WPS) were significantly different from a fruit species to other.The peach were significantly higher than apricot and pear through the two years of study.The general mean count per sample of the total population of WPS on peach, apricot and pear trees reached 136.96, 86.93 and 49.16 over the 1 st season.While in the 2 nd season these means reached to 170.5, 101.04 and 71.52.
Host plants often show varying degrees of susceptibility to a particular scale insect.Flanders (1970) suggested that some plants are genetically immune, some fluctuate from immune to susceptible and some are always susceptible.

Seasonal activity of P. pentagona:
In peach trees, during the 1 st season of study (2013/2014) as shown in Table (1), it was observed that, the total population of this insect started to increase gradually to reaching the 1 st peak of 211.9 individuals/branch in the mid of July.Then, the population decreased in beginning August and thereafter it increased continuously towards the 2 nd peak of 262.6 individuals that was recorded in the beginning of October.Another decrease in population took place in the next month and then it increased making the 3 rd peak in the beginning of January, when 112.5 individuals were recorded.The 4 th peak was recorded in the beginning of April, 2014 (160.6).Concerning the data during the 2 nd season of study (2014/2015) as shown in Table (2), it was clear that the total population was higher in comparison to the first season of investigation.The highest population was recorded in the beginning of June 2014, mid-August, mid-October, mid-January and beginning of April 2015, where population numbers being 202.3, 296.1, 320.6, 92.25 and 190.4

Number of annual generations of P. pentagona:
The previous data clearly showed that, P. pentagona had four annual overlapping generations in peach, apricot and pear trees.This results is in agreement with Ding (2003) who showed that the mulberry white scale, P. pentagona had four generations a year in Gutian area, China and Nalepa and Meyer (1990) who recorded, also four generations of this insect in North Carolina.These results are disagree with Habibian and Assadi (1989), Kreiter et al., (1997), andHalawa et al. (2015) who reported that P. pentagona has three annual generations and Atteya (2004) who recorded five generations.

Monthly variation of the insect population
The calculated monthly variations of P. pentagona population through the two successive years of investigation are tabulated in Tables (3 & 4).Data concerning the peach trees clearly show that the favorable periods for insect development and population increase were at July, September 2013 and March 2014 with MVR values of 2.211, 1.434 and 1.8, respectively (Table 3).In the 2 nd season the highest values of MVR were 2.164, 1.78 and 1.57 in June, August and March, respectively (Table 4).In apricot trees, these values were 1.527, 1.449 and 3.162 at July, October and March in the 1 st season, respectively.Months of August (1.612),October (1.58) and March (1.5) were the favorable periods for population increase in Apricot trees during the 2 nd season.Concerning pear trees, the favorable periods for insect development and population increase were at August, November and January with MVR values of 2.39, 1.28 and 1.44, respectively.In the 2 nd season, these values were 2.971, 1.99 and 1.36 at May, August and April, respectively.Mousssa et al. (2010) studied ecology of P. pentagona at Meet-Ghamer, Dakahliya Governorate throughout two successive seasons (1997)(1998)(1999), total population activity of P. pentagona occurred during the two years of investigation were recorded on mid-February, early of April, July, September 1997 early January 1998.The value of angular deflection from the east site which apparently tended the highest density of population was 18 °.74 ` and 25 °.71 ` towards the north in peach trees through the 1 st and 2 nd seasons, respectively (Fig. 1).These results showed that East direction followed by North direction were preferred by the various stages of P. pentagona as distribution direction.In case of apricot trees the value of angular deflection from the north site which apparently tended the highest density of population was 38 °.63 ` and 47 °.44 ` towards the east site through the 1 st and 2 nd seasons, respectively (Fig. 2).Concerning pear trees these values of angular deflection were 21 °.97 ` and 26 °.38 ` from the east site towards the north (Fig. 3).These differences in their distributions might be attributed to the effect of the wind direction or the duration of trees exposure to the sun rays.Such deduction seems to be logic in the light of the fact of the angle of the sun, the insects on east and north sides will get more degree day accumulation than insects on west cardinal directions.These results are important in the development of pest control programs.

Table 1 :
Fortnightly numbers of different developing stages of P. pentagona on peach, apricot and pear trees during the 1 st year (2013/2014) at Nubaria district, El-Beheira Governorate.

Table 2 :
Fortnightly numbers of different developing stages of P. pentagona on peach, apricot and pear trees during the 2 nd year (2014/2015) at Nubaria district, El-Beheira Governorate.

Table 3 :
Monthly variation rates of P. pentagona on Peach, Apricot and pear trees through the 1 st year (2013/2014).

Table 4 :
Monthly variation rates of P. pentagona on Peach, Apricot and pear trees through the 2 nd year (2014/2015).

Distribution patterns of P. pentagona on the cardinal directions of peach, apricot and pear trees:
The fortnightly mean cardinal distribution of P. pentagona (average no. of scales per 15 cm branch) at Nubaria district, El-Beheira Governorate, from May, 2013