Abundance and generation determination of Lepidosaphes beckii ( Hemiptera : Diaspididae ) on sour orange at Qalubyia Governorate

Lepidosaphes beckii (Newman) (Hemiptera: Diaspididae) seasonal abundance on sour-orange, Citrus aurantium trees was carried out in Kafr El-Sohaby, at Qalubyia Governorate, Egypt, starting April, 2004 to March 2006. Population dynamics indicated mean population as 46.25, 49.20 individuals/leaf over 2004/2005 and 2005/2006 years, respectively. The mean number per leaf was 4.97, 18.96, 5.97, 8.06 and 8.30 individuals for crawlers, pre-adults, females, gravid females and male pupae, respectively over 2004/2005. The relative means were 7.51, 21.30, 5.56, 8.93 and 5.90 individuals/leaf, for 2005/2006, respectively. Both north and east directions harbored the heaviest infestation (i.e. 64.4 and 61.6 scales/leaf for north and 49.7 and 62.2 scales/leaf for east over the two years, respectively). The upper leaf surface harbored heavier infestation compared with the lower one in both years. Four generations per year for L. beckii were determined in this location using agestructure method (i.e. percent proportion of each stage population over the total).The first generation extended from Jun. 3, to Aug. 12, 2004. The second generation started there after and continued until Oct. 21, 2004. Third generation continued until Feb. 24, 2005. The last generation started Feb. 24, 2005 and continued to Jun. 10, 2005. This means that both first and second generations continued over 70 days each compared with the third generation which continued for 126 days. The fourth one continued over 106 days. Similar results were obtained for the second year (2005/2006). Three periods for chemical control of this pest on citrus at this location was recommended (where the relative abundance of immature stages was the most). The first period was during Apr. 15 to 30. The second was Jul. 15 to 30 and the third during Sept. 15 to 30. The parasitoids recorded from L. beckii on sour-orange were the primary parasitoid Aphytis diaspidis Howard (Hymenoptera: Aphelinidae) and the secondary one, Chartocerus niger (Ashmead) (Hymenoptera: Signiphoridae). Parasitism by A. diaspidis ranged between 0 to 24.6% with mean of 11.9% over the two years.


INTRODUCTION
Citrus orchards in Egypt are subject to infestation with serious different species of diaspidids.Lepidosaphes beckii (Newman) (Hemiptera: Diaspididae) is one of the most important ones.It infests leaves and fruits mainly.Understanding the relation between ecological factors and population dynamics of an insect and its

MATERIALS AND METHODS
Abundance of L. beckii on sour orange, Citrus aurantium trees was carried out in Kafr EL-Sohaby, Qalubyia Governorate, starting April 8, 2004to March 23, 2006.The selected orchard did not receive any chemical control for two years before starting these studies and within studying period.All trees received the same horticultural practices.Ten trees were selected at the grove infested with this scale insect.Selected trees were similar in size, shape, height and vegetation.Samples were picked up at two-week intervals throughout the study.Samples size was 50 leaves presenting cardinal directions and tree core.The samples were packed in polyethylene bags with minute holes and transferred directly to the laboratory for examination, using stereoscopic microscope binocular.All alive insects found on each leaf surface were assorted and recorded as: crawlers, pre-adults, adult females, gravid females and male (pre-pupae and pupae).
Obtained data was pooled for each inspection, direction and leaf surface.Any parasitized individual observed was recorded and counted.Identification of scale and their parasitoids were carried out by taxonomy specialists at the Department of Scale Insects and Mealybugs, Plant Protection Research Institute, Giza, Egypt .To calculate the age-structure per sample, the mean number of each stage was divided by the total and multiplied by 100.This way gave each stage a percent proportion of the total per sample regardless the total number of presented insects (i.e.population density).The number of generations was determined using the obtained data throughout the two successive years.
Generation was defined, as the time required for an insect to complete its life cycle (i.e.egg to egg).In the case of diaspidids, eggs are oviposited under the female shield until they hatch and crawl out.The only way to detect ovipositon was by removal of the female shield.Gravid females were defined as females that have their eggs under their shields.The presence of gravid females (i.e. the transformation of adult females to gravid females) was considered in this study as presence of the egg stage.This phenomenon was used to determine the end of each generation and the beginning of the next one.97, 18.96, 5.97, 8.06 and 8.30 individuals for crawlers, pre-adults, females, gravid females and male pupae of L. beckii per sample/leaf, respectively.Crawlers' density per sample was the highest on Jun 17, 2004 showing 14.44 crawlers/leaf.Less abundance as 9. 24, 12.12, 9.88, 9.56 and10.58 crawlers/leaf occurred on Apr. 22, Jun. 3, Aug. 26, Nov.4, 2004 andMar. 24, 2005, respectively.However the lowest population was record on Jul. 15 to 29, Sept. 9, Dec. 2 to 30, 2004 andJan. 13 to Feb. 10, 2005.Pre-adult females reached its maximum on May 6, 2004, showing 50.46 preadults/leaf.Another period for pre-adults high density occurred on Apr 8 to 22, May 20, Dec. 16, 2004 andJan. 13, 2005 as 26.36, 37.82, 28.98, 24.35 and24.04pre-adults/leaf, respectively.However the lowest population was record on Jul. 29, Sept. 9 and Oct. 21, 2004.Females' density was the highest on May.6, 2004 as 18.60 females/leaf.Another period for females high density occurred on May 20, Jun. 3, 2004 andMar.10 to 24, 2005 showing 15.20, 13.52, 8.96 and8.50 females/leaf, respectively.The lowest females' density occurred on Jul. 29, Aug. 26, Sept. 9 to 23 and Oct. 21, to Dec. 2, 2004.Gravid females' density was the highest on Jun.17, 2004 as 22.32 females/leaf.Another period for gravid females high density occurred on Apr. 8, May 20, Jun. 3, 2004 andMar. 24, 2005 as 12.64, 14.24, 19.00 and 12.74 females/leaf respectively.Less abundance as 10.46, 9.12, and 9.28 occurred on May 6, Aug. 26, 2004 andMar. 10, 2005 respectively.The lowest population of gravid females was observed during Jul.15 to 29, Sept. 9, Dec. 2 to 30, 2004 andJan. 27, 2005.Male pupae density was the highest on May 6, 2004 reaching 20.44 male pupae/leaf.Less abundance as 15.22, 14.80, 14.38, and 12.48 male pupae/leaf occurred on Apr.22, May 20, 2004, Jan. 13 andFeb. 10, 2005 respectively.However the lowest population was observed on Jun 17, to Jul. 1, Jul. 29, to Aug. 12, and Sept. 9, 2004.The variance in different stages of abundance reflected on the total mixed population per leaf which had maximum values of 76.52, 103.04, 75.16, and Aug. 11, to 25, and Dec. 1, to 15, 2005.The results of applying the age-structure technique to the seasonal abundance data of L. beckii obtained from the Qalubyia location over the two years on sourorange are graphically illustrated in Figs.(3 and 4).Obtained trend over both years indicated the occurrence of four generations per year for L. beckii on sour-orange at Qalubyia location.Over the first year the over wintering generation continued (mainly as adult females) up to May 19, 2004 where part of them started to oviposit (i.e.transformation to gravid females).Therefore this generation was determined to end by May 30, 2004.The first generation started Jun. 3 until Aug.12, 2004 (marked by maximum population of adult females).The following count showed that most of these females were in ovipositing stage in a much synchronized fashion (which indicates the optimal conditions for the development of L. beckii).The date of Aug.12, 2004 was considered as the terminal for the first generation.The second generation started there after and continued until re-emergence of gravid females on Oct. 21, 2004.Therefore the date of Oct. 21, 2004 was considered as the end point of this generation and the start point for third generation which continued until Feb. 24, 2005.The last generation started Feb. 24, 2005 and continued to Jun. 10, 2005.This means that both first and second generations continued over 70 days each compared with the third generation which continued for 126 days, and the fourth one continued over 106 days.

Results
Over the second year of study similar results were obtained with little delay (Fig. 4).The relevant dates were Jun. 10, Aug. 16, and Oct. 18, 2005.These obtained results suggested 67, 63, 109, days for first, second and third generations, respectively.The fourth generation continued to the next year.The effect of cardinal directions on the population density of L. beckii on sour-orange during 2004/2006 revealed that both north and east directions harbored the heaviest infestation (i.e.64.4 and 61.6 scales/leaf for north direction and 49.7 and 62.2 scales/leaf for east  direction over the two years, respectively).The core came second (i.e.42.1 and 41.2 scales/leaf over the two years, respectively).Both south and west directions were the least (i.e.39.1 and 50.1 scales/leaf for south direction and 36.0 and 31.2 scales/leaf for west direction over the two years, respectively).

DISCUSSION
Egyptian wide it has been reported that L. beckii had three to four generations depending on the host plant and the location.Obtained results in this study indicated four generations for L. beckii on C. aurantium using the age-structure method.These results are in agreement with Salama (1962); Hafez and Salama (1969); Amin (1970) and Habib et al. (1971), they mentioned three to four generations for this scale.
Horizontal distribution of L. beckii on C. aurantium trees indicated that the north and east harbored the heaviest infestation compared with other direction in both years with preference to the upper leaf surface.The result is in agreement with Rodrigo and Garcia-Mari (1994), they reported that populations were at their lowest level in summer and preferred the upper side of the leaves where 60-70% of individuals were found.Hemiberlesia latania (Signort) (Homoptera: Diaspididae) at Ismailia on olive trees preferred north and west directions over east or south ones of the trees (Mohamed, 1999).Parlatoria oleae (Colvee), (Homoptera: Diaspididae) on olive was found to be heaviest infestation at the east direction of the tree compared with other directions (El-Amir 2002).Pseudaulacaspis pentagona (Targioni-Tozzeti) (Hemiptera: Diaspididae) on peach at Qalubyia preferred the north direction followed by west (Moharum 2006).Abdel-Ghaffar et al. (2008) reported that east direction was preferred by Chrysomphalus aonidum at the same location and host.
Using age structure method for determining the generations for scale insects has been reported.This method is proper in case of existing all developmental stages at the stages at the same niche.The advantage of this method over using the absolute population counts, that it overcomes sampling errors.This method also is useful in determining the proper time for introducing control measurements being biological or chemical.This fact is based on introducing these measurements when the most susceptible stage is the most relative abundance.Using age structure method for determining the generations El-Amir (2002) reported three generations for P. oleae on olive at Ismailia (regardless of olive variety).Serag (2005) used the same technique on fig at northern cost of Egypt and reported three generations for both Lepidosaphes ficus (Signort) and H. lataniae while reported two generations only for Russellaspis pustulans (Cockerell) (Hemiptera: Diaspididae) on the same host.Moharum (2006) using age structure of P.pentagona on peach at Qalubyia, plum at Giza and apple at El-Behara to determine its generations.She reported three generations on peach and plum while two generations only on apple.Four generations were reported for Chrysomphalus aonidum (Linnaeus) (Hemiptera: Diaspididae) using age structure method on sour orange (Abd El-Ghaffar et al., 2008).
Using our findings three periods is recommended for control of this insect population (depending on scouting and population determination).The first period is during Apr.15 to 30 to compact the first generation coming out of over wintering one.The second is during Jul.15 to 30 to protect the new formed fruits.The third is during Sept. 15 to 30 to reduce the over wintering ones.In this respect Helmy (1975) reported that Jul. was the proper time for chemical control of L. beckii.Rawhy, et al. (1976) indicated that Jul. or Oct. was the best time for controlling L. beckii on orange grove at Qalyubia Governorate, Egypt.El-Amir (2002) recommended three periods for control of P. oleae on olive.The first was during Apr.The second is from 15 to 30, Jun and the third during Oct. Abdel-Ghaffar et al. (2008) recommended similar dates for controlling C. aonidum.The main primary parasitoid recorded from L. beckii on sour-orange was A. diaspidis.Percent parasitism was 11.91% and 9.81% over the two years, respectively.Hafez et al. (1987) stated that, the main parasitoid of L. beckii was A. lepidosaphes.Total parasitism of the diaspidid was recorded at the main peak in Oct.-Dec.(29.7-40.2%),with additional moderate peaks in Jan. as21.6%,May as 16.1% and Jul. as 15.4%.Moraes and Silva (1987) mentioned that parasitism of L. beckii was found to be highest from Aug. to Nov. and the rate was not affected by climatic factors.The dominant parasitoid was A. lepidosaphes.Abbas (1992) reported that L. beckii was attacked by the parasitoid A. lepidosaphes which may play a considerable role in regulating its population.Soares, et al. (1997) revealed that Encarsia citrina (Crawford) (Hymenoptera, Aphelinidae) contributed considerably to the biological control of L. beckii, in summer and spring, these seasons of high parasitic activity on citrus orchard.
of L. beckii population dynamics on sour-orange over 2004/2006 years are illustrated in Figs.(1and2).Results showed that the mean population per sample was 46.25, 49.20 individuals over 2004/2005 and 2005/2006 years, respectively.Over 2004/2005 year, the mean number was 4.