Abundance, Generation Determination and Spatial Distribution Pattern of the Sunt Wax Scale Insect, Waxiella Mimosae (Signoret) (Hemiptera: Coccidae) Infesting Sunt Trees in Luxor Governorate, Egypt

The present work was carried out throughout two successive years (2016/2017 and 2017/2018) at Esna district, Luxor Governorate. As a basic study for developing future management of the sunt wax scale insect, Waxiella mimosae (Signoret), to determine the seasonal abundance of this pest and its spatial distribution pattern. The obtained results showed that insect population occurred on sunt trees all the year round and has two overlapping generations a year under field conditions. The first generation occurred in autumn season, started in September 10th and extended until March 10th in the two years and covered a period of 24 weeks per year and its peaked in November 10th and October 25th during the two years, respectively. Whereas, the second generation recorded in spring season, observed between the period in February 25th to August 25th, peaked in May 10th and its duration 24 weeks per year in the both years. In general, the population density was varied in the two generations; the spring generation of pest was the biggest one in size than the autumn generation during the two years. The obtained results showed that the favorable time for abundance and maximum values of total population density of W. mimosae, were recorded in autumn and spring months and were the optimal for the insect multiplication and build up, since the highest R.M.V.P values was achieved during the both two years. Lowest activity of population was recorded during winter months (this referred to the cold weather) during the two years. Also, the percentages of the age-structure population of W. mimosae species, during the both two years, were almost similar. However, the insect age-structured population was considerably differed among between months and between the two years. Data were analyzed using fourteen indices of dispersion to estimate the spatial distribution pattern of this pest. All models of dispersion indices exhibited an aggregated distribution and follows a negative binomial distribution pattern for all alive different stages and total population of W. mimosae in all seasons of the year and on the over year during the two years of study.


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we assume that this species reproduces parthenogenetically. In the case of wax scale insect, the gravid females are red and covered with bright white gummy wax. Eggs are brick red, and after laying them the female holds them in a cavity under her body until they hatch and crawl out. The only way to detect oviposition was by removal of the female cavity. Gravid females were defined as females that have their eggs under their cavities [8]. The wax scale insect was collected and Res. Center, Egypt.
Spatial distribution is one of the most characteristic properties of insect populations; in most cases it allows us to define them and is a typical trait in insect populations and is an important characteristic of ecological communities [12]. Knowledge of the spatial distribution provides useful information not only for theoretical population biology but for field monitoring programs [13]. Also, allows for the estimation of densities and in turn forms the basis for making decision in pest management programs [14]. Methods that are commonly used to describe the distribution of insect populations have been summarized by Southwood [15]. On the other hand, detailed knowledge of insect distributions and the primary factors affecting how insect populations utilize their available resources are critical to the development of accurate sampling plans in agro-ecosystems and integral to the study of population and community ecology of insects [16]. The behavioral patterns and environment could be determinant the spatial distribution of population individuals in an ecosystem [17]. The information of spatial distribution (i.e., regular, random or aggregated) can determine what sampling program must be carried out, especially sequential sampling [18]. The use of dispersion indices seems to be convenient decision-making methods for management programs because of their easy calculation procedure and simple results [19]. Having information about density and changes in population of W. mimosae during the year, identification of factors affecting population fluctuations and determination of their effects will help in management of this pest.
Rare informations in the literature concerning the seasonal abundance and spatial distribution pattern of this pest. So, it is necessary to do this study in Luxor region where there is no reported similar research. Therefore, the present work was carried out to study ecological aspects viz., the seasonal abundance of pest, the percentage out of year total population, the rate of monthly variation, the age structure of pest and its generations (duration, number and size) as well as, the estimation of its the spatial distribution under the field condition in Luxor Governorate.

Population studies
The population fluctuations of this scale found infesting sunt

Sampling
Four sunt trees were grown on the edges of water canals were heavily infested with the sunt wax scale insect, W. mimosae (Signoret) and were chosen for this study. The selected trees were almost similar and as uniform as possible in size, age, shape, height, vegetative growth and without application any chemical control measures before and during the period of study.

General sampling method:
We collected a total of 48 samples on 48 dates over a twoyears period. All sampling was conducted from 2880 branches i.e.
(15 branches x 4 trees x 48 dates). As before, we froze samples for later processing in the laboratory and recorded. To facilitate the comparisons within each studied year and among the two years, the bimonthly counts were accumulated monthly. These monthly counts were estimated in percentages out of the year total.
The percentage out of year total population by pest was This method was used by many investigators by Salah (2005) and Bakry [20,21]

Number of annual generations of W. mimosae in the field
Annual total population data were graphically plotted in figures.

Number and duration of annual generations under field conditions
were recorded on the basis (beginning of total population per leaf and its end) were determined by integration of the population curves in these figures. This method was used by many investigators by Elwan [23,24]

Analysis of spatial distribution
The spatial distribution among the sample units was determined by fourteen indices of distribution. Such indices were chosen in an attempt to get a consensus on dispersion because the use of a single index can lead to incorrect conclusions [25]. Soemargono [26] recommended that in evaluating distribution of an arthropod, one should use several different techniques before drawing conclusions about population distribution ( Figure 3).

Distribution indices
Several estimates are based on sample means and variances (such as index of dispersion, clumping, crowding and Green's).
Mean ( X ): X is the mean of population. . 100 S C V X = × Relative Variation: (R.V.) is employed to compare the efficiency of various sampling methods [27]. The relative variation for the sampling data was calculated as follows:

Range of means of population
.
Where, SE is the standard error of the mean and X is the mean of population.

Index of dispersion (I D ):
The index of dispersion is also known as the variance tomean ratio. Dispersion of a population can be classified through a calculation of the variance-to-mean ratio; namely: S 2 / X =1 random distribution, <1 regular distribution, and >1 aggregated distribution This index can be tested by Z value as follows: expressed as the ratio of mean crowding to the mean. As with the variance-to-mean ratio, the index of patchiness is dependent upon quadrate size [29].

Results and Discussion
Population studies    Females population (mature stages)

a) Adult females
The obtained results showed that the adult females gradually decreased in September and October until reach in November 25 th (less than one individual per branch) during the two years. Then, it started to increase in June 10 th and highly increased continuously  [8] in Israel, reported that the bionomics of W. mimosae they found that the first generation of adult females appear in March, and the second generation takes place in October.

b) Gravid females
The gravid female's population showed the first peak of activity

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These results were partial coincided with those obtained by Abd El Kareim [31] in Egypt, however with different insect species and different host, they reported that C. floridensis had three peaks of abundance in blood orange, Loquat and mango orchards.  These results were coincided with those obtained by Bakr et al.
[33] they found that the infestation with C. cirripediformis on guava trees a significant difference in the insect activity during autumn and winter.   As regarding in data represented in Table 4 Table 5. The rate of monthly variation in the population is considered an indicator to the favorable month for insect activity expressed as monthly the increase of this insect population through the year. When R.M.V.P. is > 1 it means more activity, < 1 means less activity and = 1 means no change in the population density during the two successive months [20]. It was shown as recorded in Table 5    April, when the rates of monthly variation were (6.33, 2.93 and 5.99), respectively in Table 5. Generally, it seems that autumn and spring months were the most favourable periods for activity of the first instar nymphs, the second instar nymphs, the third instar nymphs, the pre-adults total and total population of W. mimosae.

The monthly incidence, averages of W. mimosae stages and their percentages out of the year total
While, and adult females was more active during winter and summer months. But, the gravid females were maximum activity during February and March months during the two years under the climatic conditions at Esna district, Luxor Governorate. These results were in agreement with those obtained by Swailem et al. [34] and El-Emery et al. [23] who mentioned that C. floridensis had also the highest favorable period in September and October during the two studied years. and July months during the two years. Also, the percentages of the age-structure population of W. mimosae species, during the both two years, were almost similar. However, the insect age-structured population was considerably differed among between months and between the two years. These results may be attributed to the differences of environmental factors that prevailing during the two years. Metcalf and Luckmann [35] reported that certain environmental conditions may alter the physiology of the plant to the extent that it becomes suitable or unsuitable as a host for a certain pest. Dent [36] stated that the seasonal phenology of insect numbers, the number of generations and the level of insect abundance at any location are influenced by the environmental factors at that location.

Estimation of insect age-structured population for W. mimosae inhabiting branches of the sunt tree
These data reflect the changing frequencies in the population.

Number of annual generations' determination of W. mimosae
Obtained trend over both years indicated the occurrence of two overlapping generations per year for W. mimosae on sunt trees at Esna district, Luxor Governorate are represented in Table 6.

a) First generation (autumn)
The first generation started in September 10 th and extended individuals per branch) were recorded on the first instar nymphs, the second instar nymphs, the third instar nymphs, the pre-adults total, the adult females, the gravid females and the total population of pest for the first and second year, respectively.

b) Second generation (spring)
The second generation occurred between the period from This evidence may be due to the different fluctuations of climatic factors. In both years, the two overlapping generations could be arranged according to their size in the following order as follows: First > second generation for the two years of study.

Sampling program
The obtained values in Table 7  [39] however with different insect species and different host, also stated that the relative variation for the primary sampling data of different stages of Pulvinaria floccifera (Hemiptera: Coccidae) were less than 25% and were acceptable.

Distribution indices
The obtained results in Tables 7 & 8 showed that the spatial distribution among the sample units was determined by fourteen indices of distribution. The results of distribution with using the variance to-mean (S 2 / X ) was >1, by using Index of mean clumping (I DM ) was positive value for negative binomial, using Z test > 1.96, by using index of patchiness ( * X / X ) was >1 and with using green's index (GI) was > 0 and positive values. All these indices of dispersion indicated were aggregated distribution for all different stages and total population of W. mimosae in all seasons of the year and on the over year during the two years of study. Nestel et al. [40] however with the same genus of insect and different host, they suggested that the spatial distribution of P. oleae was discerned aggregate. Moradi-Vajargah et al. [17] reported that the aggregated distribution suggests that the presence of an individual at one point leads to an increased probability of another individual being close.  Table 7: Estimated parameters for spatial distribution of different stages of W. mimosae infesting sunt trees during the first year of (2016/2017).

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The lowest values for the variance to-mean (S 2 / X ), the index of dispersion (I D ), the index of mean clumping (I DM ), the Z value, and the green's index (GI) were recorded on adult females of W. mimosae as compared with the other different stages of W. mimosae when the comparison was directed for each season separately, during the two years of study. On the contrary, the pre-adults of W. mimosae were exhibiting the highest one in these measured parameters of distribution in all seasons of the year and on the over year during the two years of study (Tables 7 & 8). Similarly, however with different values that the adult females of W. mimosae were exposed the lowest values in all indices of dispersion (14 models) when the comparison was directed for the combined effect on the whole year, during the two years of study (Tables 7 & 8). In contrary, the pre-adults of W. mimosae were exhibiting the highest one in most measured parameters of distribution during the two years of study (Tables 7 & 8). These results agree with that obtained by Southwood [41] stated that the higher the variance to mean ratio, the greater the extent of aggregation. Siswanto et al. [42] however with different insect species and different host, also suggested that when the population of Helopeltis antonii (Signoret.) (Hemiptera: Miridae) was high, the insects tend to aggregation. Chellappan et al. [43] stated that the value of mean crowding increased with the increase in mean population density of Paracoccus marginatus (Hemiptera: Pseudococcidae).
In general, the differences in our values may be due to the differences are at least partly caused by the population density of pest and environmental conditions such as weather and ventilation. Other studies have used these indexes to determine the distribution pattern of insect pest population in different crops [44][45][46][47][48]. Generally, the all models of dispersion indices to estimate the spatial distribution of pest, exhibited an aggregative distribution and follows a negative binomial distribution pattern for all alive different stages and total population of W. mimosa.