Impact of Some Weather Factors on the Population Density of Phenacoccus solenopsis Tinsley and its Natural Enemies

Citation: Egypt. Acad. J. Biolog. Sci. (A. Entomology) Vol. 12(2) pp: 99108 (2019) 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
Okra plant, Ablmoschus esculentus L., is one of the most important Malvaceae crops which used as human food in Egypt, which infested by polyphagous mealybug throughout the growing season.The mealybug caused large damages of the quantity of yield either directly by sucking plant juice, weakening and death of some parts of plants or indirectly by excreted honeydew, which caused growth of sooty mould and inhibited photosynthesis process in plant.Also, it may transmit the pathogens to plants (Hodgson et al., 2008;Arif et al., 2009;Saini et al., 2009;Abbas et al., 2010 andVennila et al., 2011).The P. solenopsis had found on a wide range of vegetable crops including species of economically important families such as Malvaceae, Solanaceae and Cucurbitaceae which reported by many authors such as Abd-Rabou et al. (2010), Wang et al., (2010), Zhu et al., (2011), Ibrahim et al., (2015), Nabil et al., (2015) and Nabil (2017).The outbreaks often occur when mealybugs get introduced to new locations in the absence of their natural enemies.So, the biological agent should be considered an effective factor for decreasing the populations of the tested insect in different parts of the world (Sagarra et al., 2001;Bokonon-Ganta et al., 2002;Muniappan et al., 2006and Roltsch et al., 2006).Despite of the economic importance of cotton mealybug, which caused considerable economic damage to agriculture and vegetable plants, accordingly the researchers are interested in studying the ecology and activity periods of this insect to select the most suitable time to control.Therefore, the current study aimed to determine some ecological parameters of the different stages of this insect and its associated parasitoids on okra plants during 2017 and 2018 seasons.So, this study may help the researchers in the integrated pest management against the cotton mealybug and prediction models for this pest.

MATERIALS AND METHODS
The experiment was conducted in an area of about half feddan for okra plants, Abelmoschus esculentus L. which located at Hihhya district, Sharkia Governorate, Egypt.The study was continued from the third week of July to the second week of November for two successive seasons 2017 and 2018.The normal agricultural practices were applied in due time and all plots were kept without any insecticide treatments.Sampling started when the age of plants reached about one month after sowing dates and continued weekly intervals throughout the growing season.

Survey and Population Density of Cotton Mealybug:
Forty leaves were taken randomly from both diagonal directions of the experimental area.These samples were transferred to the laboratory and examined using a stereomicroscope in the same day.The different stages of P. solenopsis on both surfaces of the leaves were counted and recorded.According to the work of Audemard and Milaire(1975).The weekly data of the stages nymph were indicated on millimeter papers to calculate the number of generations and their durations.

Estimation the Percentage of Parasitism:
To study the percentage of parasitism of P. solenopsis, the insects on each sample were separated into healthy alive insects and Mummies of its insect which bearing emerging holes of parasitoid adults.Mummies of these insects were preserved in glass jars, covered with muslin cloth by the aid of rubber bands and kept under laboratory conditions until parasitoids emergence for each sample.The parasitoids emerged were identified with helping of Prof. Dr. A.R. Hamed, Chief Researcher emeritus, Biological Control Department, Plant Protection Research Institute, Agricultural Research Center, Giza, Egypt.The numbers of mummies, parasitoids and the percentages of parasitism were recorded.

Effect of Some Weather Factors on the Insect Populations:
The maximum of temperature, minimum of temperature, relative humidity and solar radiation were obtained from the Meteorological Central Laboratory, Agricultural Research Center, and Ministry of Agriculture.Light intensity (Lux) was measured at mid-day (12 a.m.)Using Luxmeter during the period of this studying.To indicate the effect of each factor of the tested climatic factors on the population of tested insect and its associated parasitoids.

Population Density of Phenacoccus solenopsis and Its Parasitoids On Okra Plant: 1. Females Population Density:
The infestation with Females of P. solenopsis started on the fourth week of July and the first week of August during 2017 and 2018 seasons, respectively.Data in Tables (1 and 2), illustrated the population of females had two peaks, the first one occurred on the third week of August with 199 females / 40 leaves and the second peak recorded on the fourth week of September with 552 females during 2017 season.While, in the second season 2018, three peaks of females activity were noticed on the fourth week of August, the first week of September and the first week of October with values of 64, 44 and 19 females, respectively.

Nymphs Population Density:
The population trend started to increase in July and was maximum during September and October, declined afterwards during the month of November at crop maturity.Results arranged in Tables (1 and 2), demonstrated that the population of nymphs had one peak of activity which recorded during the first season on the fourth week of September with a value of 31263 nymphs.While, in the second season the nymphs population showed four peaks of activity on the last week of July, the second week of August, the first week of September and the first week of October with values of 36, 39, 239 and 220 nymphs, consecutively.

Total Number of a Live Stage:
One peak of the total number of a live stage was observed on the 4 th week of September and represented by 31815 individuals during 2017 season.On the other hand, Three peaks of activity were noticed on the last week of July, the first week of September and the first week of October with values of 36, 283 and 239 individuals, respectively during 2018 season Tables (1and 2).Obtained results were in agreement with the finding of Jaydeep et al.,(2015) and Nabil(2017) studied that, the occurrence of P. solenopsis on some vegetable crops such as tomato, brinjal (eggplant) and okra observed that the mealybug infested eggplant from July to August.

The Percentage of Parasitism:
During the course of this study, Aenasius arizonensis (Girault) was observed as associated parasitoid of P. solenopsis and Prochiloneurus aegyptiacus (Mercet) and Pachyneuron sp. were recorded as hyperparasitoids associated with the primary one.Data in Tables (1 and 2), revealed that the three and four peaks of parasitism percentages were recorded during the first and second seasons, respectively.These peaks were observed on the second week of September, fourth week of September and third week of October with 0.85, 0.54 and 6.86%, respectively for the first season.While, in the second one the parasitism percentage peaks occurred on the second week of August ,the fourth week of August , last week of September and the second week of October by 33.63, 23.59, 57.60 and34.48%,constructively.Attia and Awadallah(2016),recorded that, Prochiloneurus aegyptiacus (Encyrtidae) and Pachyneuron sp.(Pteromalidae) as hyperparasitoids associated with the primary parasitoids.Vinay et al.,(2016), found that, Aenasius sp. is the associated parasitoid of P. solenopsis .Finally, it was concluded that the total numbers of females, nymphs and a live stage were higher in the first season than in the second one because of the lack of natural enemies of its pest in the first season but after the increase of parasitoids associated with them in the second season, reduction the population of this pest was observed.The several control measures were applied to reduce the pest population in different areas but all went unsuccessful because of the loss of natural enemies on this invasive pest (Shylesha et al., 2010;Mahmood et al., 2011and Sahito et al., 2011).

Effects of Some Weather Factors on Different Stages of P. solenopsis :
Results presented in Table (3), illustrated that the correlation between the maximum of temperature and the population of females was positive and highly significant during the two seasons where r1=0.653** and 0.700**, consecutively.
While it was positively significant between the population of females and the minimum of temperature (r2=0.543*) in the first season .On the other hand, there was a negative and significant correlation between the percentage of parasitism and the minimum temperature in 2018 season (r2=-0.489*).
Relative humidity had a highly negative significant effect on the population density of females, nymphs and the total alive stages in the second season where r3= -0.816**, -0.749** and-0.831**,respectively.Meanwhile, in the first season relative humidity had negatively significant effect on females populations (r3 = -0.552*).
The correlation coefficient between the percentage of parasitism and solar radiation was negative and highly significant effects where r4 = -0.725** in the second season.The correlation coefficient for light intensity with the percentage of parasitism had negative highly significant (r5= -0.627**) in the first season .While it was positively significant with the number of females in the second season (r5 =0.550*).
The R 2 values and coefficient determination by the five aforementioned meteorological factors indicating that the considered factors had played a conspicuous role in detecting the activity of these insect pests during the investigated seasons Table (3).It is worth mention that the temperature and humidity had significant effects on the cotton mealybug population under study on some vegetable crops (Jeyakumar et al., 2009;Singh et al., 2012;Hameed et al., 2014 andTehniyat et al., 2015).

Number of Generations:
Data in Figures. 1 and 2 revealed that the P. solenopsis had two generations during the first season.The duration of the first generation was nine weeks, which occurred during the period from the fourth week of July to the third week of September.While the second one took eight weeks from the fourth week of September to the second week of November.On the other hand, the P. solenopsis had three generations in the second one.The first generation period was extended from the third week of July until the fourth week of August.While the second period occurred from the last week of August until the last week of September and the third generation period extended from the first week of October till the first week of November.

Preferable Leaf Surface:
Data in Table ( 4), illustrated the total number of alive stages of P. solenopsis was higher on the lower leaf surface (44757 and 1430 individuals) than those the upper leaf surface (21151 and 233 individuals) during the first and second seasons, respectively.Nabil (2017), who reported that the P. solenopsis had three generations during the first and second seasons and its population was higher on the lower leaf surface than those on the upper leaf one.

Conclusion
This study demonstrated that the population of cotton mealybug (CMB) was higher in the first season than in the second one.The population density of tested insect was indirectly correlated with the percentage of parasitism during the period of this investigation.The study highlighted the climatic changes which had a great impact on the population dynamics of cotton mealybug and its parasitoids .Therefore, the natural enemies of cotton mealybug should be introduced and utilized in the integrated pest management programs to control this pest.On the other hand, the continuous monitoring of the population dynamics of this pest is required to avoid crop losses.

Table 3 .
Statistical analysis based on correlation coefficient indicating the effects of climatic factors on different stages of Phenacoccus solenopsis Tinsley infesting okra plants at Hihhya distract, Sharkia Governorate during the first and second seasons 2017 and 2018 r1 =Simple correlation coefficients for maximum temperature, r2= for minimum temperature, r3= for mean relative humidity, r4= for solar radiation and r5= for light intensity.r* with 1 star indicates that the correlation coefficient is significant and with 2 stars (r ** ) indicates highly significant correlation at 0.01% level of probability

Table 1 .
Population density of Phenacoccus solenopsis Tinsley infesting okra plant at Hihhya distract, Sharkia Governorate during 2017 season  Each sample is forty leaves Table 2. Population density of Phenacoccus solenopsis Tinsley infesting okra plant at Hihhya distract, Sharkia Governorate during the 2018 season  Each sample is forty leaves

Table 4 .
Weekly numbers of Phenacoccus solenopsis Tinsley on upper and lower surface of okra plant leaves at Hihhya distract, Sharkia Governorate during 2017 and 2018 seasons Each sample is forty leaves