Population dynamics of the purple scale , Lepidosaphes beckii ( Hemiptera : Diaspididae ) and its parasitoid Aphytis lepidosaphes ( Hymenoptera : Aphelinidae ) as a new threat pest on mango trees in Egypt

The purple scale, Lepidosaphes beckii (Newman) (Hemiptera: Diaspididae) is one of the most important pests attacking mango. The present paper includes population dynamics of the purple scale, L. beckii and its parasitoid. Dynamics of L. beckii and its parasitoid on mango trees was carried out in Giza, governorate, during 2009 and 2010. Only one parasitoid recorded in this work was Aphytis lepidosaphes Compere (Hymenoptera: Aphelinidae). Statistical analysis of the effect of weather factors on the population of L. beckii and its parasitoid during the two years under consideration was explained. The results indicated that maximum and minimum temperatures was significant on the population of L. beckii and its parasitoid, A. lepidosaphes while percent of relative humidity it is nonsignificant. As well as obtained results over both years indicated the occurrence of three generations per year for L. beckii on mango in Giza.


INTRODUCTION
The purple scale, Lepidosaphes beckii (Newman) ( Hemiptera : Diaspididae) is one of the most important pests of mango.L. beckii is regarded as a serious pest in different parts of the world (Hafez et al., 1987a and b, Danzig and Pellizzari, 1998, Claps et al., 2001and Foldi, 2001).
It is a polyphagous species that has been recorded from hosts belonging to 45 genera in 11 plant families including, mango, Mangifera indica.It attacks leaves, turnk and fruit (Davidson and Miller, 1990).Development time in females varies from 20 days at 27°C to 40 days at 20°C (Hafez and Salama, 1970).
Heavy infestation causes chlorosis of the leaves , defoliation, discolouration and poor maturation of the fruit and desiccation, weakening and dieback of the branches or even entire trees (Cohic, 1955 andGill, 1997).Damage to fruit occurs in heavy infestations, where spotting and often deformity of fruits affects market value.Areas surrounding scales on fruit remain green long after the rest of the fruit ripens.The areas surrounding the scale insects on leaves turn yellow and when severely infested the entire leaf may be discoloured prematurely and be shed.
Aphytis lepidosaphes Compere (Hymenoptera: Aphelinidae) one of the most important bioagent for controlling the purple scale in different parts of the world (Dean, 1961, Abdel-Fattah and El-Saadany,1978and Hafez et al., 1987 a and b).

Nadia Aly 2
The aim of the present work is to study population dynamics of the purple scale, L. beckii and its parasitoid, A. lepidosaphes on mango trees in Egypt.

MATERIALS AND METHODS
Dynamics of L. beckii on mango trees was carried out in Giza, governorate, during 2009 and 2010.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.Twenty trees were selected at each groves infested with this scale insects.Selected trees were similar in size, shape, height and vegetation.Samples were picked up at two-week intervals throughout the study.Samples random size was 60 leaves presenting from all directions.The samples were packed in polyethylene bags with minute holes and transferred to the laboratory for examination, using stereoscopic microscope binocular.All alive insects found on each leaf surface was assorted and recorded as: nymphs and adults.Obtained data was pooled for each inspection, direction and leaf surface.
The abundance of parasitoid of purple scale was carried out 2009 and 2010 on mango trees in Giza.The location was heavily infested by the purple scale, L. beckii was selected to achieve investigations and was sampled monthly.During the study, no chemical control for the pest was performed on these trees.In the location 20 trees were selected randomly for sampling.Units of sampling consisted of 60 leaves.These were detached off and brought to the laboratory for inspection.Each leave was stored in a well-ventilated emergence glass tube and monitored daily for parasitoid emergence.Rate of parasitism was determined by dividing the number of emerging parasitoid from each by the number of hosts scale existing.
Simple correlation and regression values were calculated to obtain information about the relationships between the three tested weather factors and the population of the purple scale and its parasitoid.
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 insects presents (i.e.population density).The number of generations was determined using the obtained data throughout the two successive years using the age-structure technique per sample over the year.Generation is defined, as the time required for an insect to complete its life cycle.In the case of diaspidids, eggs are oviposited under the female shield until they hatch and crawl out.The only way to detect ovipositon is by removal of the female shield.Gravid females are defined as females that have their eggs under their shields.The presence of gravid females is considered under 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.

RESULTS AND DISCUSSION
The results of L. beckii population dynamics on mango trees in Giza over 2009 and 2010 years are presented in Tables (1 and 2  During the first year (2009) no occurrence of parasitism was noticed during January and February Presence of parasitism continued low numbers until late Summer and increase gradually till early of Autumn reaching to maximum numbers of individuals 25 individuals per 60 leaves (Table 3).During the second year (2010) no occurrence of parasitism was noticed during January, February and March.Presence of parasitism continued low numbers till late Summer and increase gradually till early of Autumn reaching to maximum numbers of individuals 31 individuals per 60 leaves (Table 4).Calculated means for obtained weather factors data over the fourteen days previous to each sampling date for the study period are presented in Tables (1 and 2).Temperature reaches its minimum around the year about Mid-Feb.(i.e.daily max.as 22.1C and min.as 13.7ºC).It reaches its maximal around Mid-June (i.e.daily max.as 38.5C and min.as 26.1C).The general temperature pattern over the year for Giza can be characterized by mild Winter and hot Summer.Temperature reaches its minimum around the second year about Mid-Feb.(i.e.daily max.as 22.1C and min.as 16.2ºC).It reaches its maximal around First-Oct.(i.e.daily max.as 38.3C and min.as 28.0C).
Statistical analysis of the effect of weather factors on the population of L. beckii and its parasitoid during the two years under consideration was explained in Tables (5&6).It is concluded that maximum and minimum temperatures was significant on the population of L. beckii and its parasitoid, A. lepidosaphes while percent of relative humidity was nonsignificant.The results of applying the age-structure technique to the seasonal abundance data of L. beckii_obtained from the Giza location over the two years are tabulated in tables (7& 8) and figs (1&2).Obtained trend over both years indicated the occurrence of three generations per year for L. beckii on mango in this location.These three generations can be nominated as Autumn-Winter, Spring and Summer generations.
Over the first year the Autumn Winter generation continued up to March with percentages of occurrence 1.420 where part of them started to oviposit by March, 1.696.Therefore this generation was determined to end by March, 1.580.The Spring generation started from this point up till May 2.776.The date of June 3.534 was considered as the terminal time for the Spring generation.The Summer generation started there after and continued up till on September 9.866.Therefore the date of September was considered as the start point for the next Autumn Winter generation (Table7).Over the second year of study similar results were obtained.The Autumn Winter generation continued up to March with percentages of occurrence 0.915 where part of them started to oviposit by March,1.196.The generation was determined to end by March, 1.550.The Spring generation started from this point up till May 2.064.The date of June 2.540 was considered as the terminal time for the Spring generation.The Summer generation started there after and continued up till on October 13.600 Therefore the date of October was considered as the start point for the next Autumn Winter generation (Table 8).In the present work the results indicated that the occurrence of three generations per year for L. beckii on mango in Giza.There are one to four generations depending on climatic conditions.In USA, California, there are 3-4 overlapping generations per year, (Gill, 1997), in Chile there is one generation annually (Zuniga,1971), and two in France (Bénassy et al.,1975).Later In Alabama Satsuma (USA), Fadamiro et al. (2008) stated that all stages of the purple scale were present in the orchards yearround, indicative of overlapping generations; however, the highest densities were recorded during the early season.
A. lepidosaphes was the most common parasitoid on L. beckii (Abdel-Fattah andEl-Saadany, 1978 andHafez et al., 1987a).During the present work no occurrence of parasitism was noticed during January, February and March.Presence of parasitism continued low numbers until late Summer and increase gradually till early of Autumn.These results was contradicting with the data observed by Hafez et al., (1987b).They stated that the large number of L. beckii parasitized by the immature stages of Aphytis spp.were associated with the increase of living scales during January and February.The highest percentage of parasitism with the immature stages of Aphytis spp. was observed during the Winter season, and the lowest percentage occurred during Spring, Summer and Autumn.Emerging of adults of Aphytis spp. was high from March to August and dropped during the period from September to February (Hafez et al., 1987b).On the other hand the results of the present work agree with the results of Abdel-Fattah and El-Saadany (1978).They stated that the two periods of high activity of this parasitoid were found to occur throughout the year of study, the first from middle of August until the middle of December, whereas the second period lasted between the middle of March until the middle of June.The rate of parasitism reaches 58.5% in April, 66.5% in June and a peak of 84% in October.

Fig. 1 :
Fig. 1: Occurrence percent of the different stages of the purple scale, Lepidosaphes beckii on mango trees during 2009 season, at Giza Governorate.
).The mean number of individuals were 588.2 and 330.2 individuals for nymphs and adults of L. beckii, respectively.Nymphs density reached its maximum on September 15 th , 2009, showing 1385 Nymphs/sample.Lowest Nymphs density occurred during the period of January 1st showing 103 Nymphs/sample.Adults density was highest on September 15 th , 2009 as 790 Adults/sample.Lowest population of adult was observed during Jan. 1 st , 2009 with 68 Adults/sample (Table 1).The mean number of individuals were 1107.5 and 495.1 individuals for nymphs and adults of L. beckii, respectively.Nymphs density reached its maximum on October 15 th , 2010, showing 3610 Nymphs/sample.Lowest Nymphs density occurred during the period of January 15 th showing 137 Nymphs/sample.Adults density was highest on October 15 th , 1621 Adults/sample.Lowest population of adult was observed during January. 1 st , 2010 with 81 Adults/sample (Table 2).The parasitoid recorded in this work was A. lepidosaphes.

Table ( 1
): Population dynamics of the purple scale, Lepidosaphes beckii on mango trees in Giza Governorate) during 2009 season.

Table 2 :
Population dynamics of the purple scale, Lepidosaphes beckii on mango trees in Giza Governorate) during 2010 season.

Table 3 :
Population dynamics of parasitoid, Aphytis lepidosaphes associated with the purple scale, Lepidosaphes beckii on mango trees in Giza Governorate during 2009 season.

Table 4 :
Population dynamics of the parasitoid, Aphytis lepidosaphes associated with the purple scale, Lepidosaphes beckii , on mango trees in Giza Governorate) during 2010 season.

Table 5 :
Simple correlation and regression values of the population dynamics of the purple scale, Lepidosaphes beckii and its parasitoid Aphytis lepidosaphes on mango trees in Giza Governorate during 2009 season.

Table 6 :
Simple correlation and regression values of the population dynamics of the purple scale, Lepidosaphes beckii and its parasitoid Aphytis lepidosaphes on mango trees in Giza Governorate during 2010 season.