Ecological Studies on Cotton Mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Sternorrhyncha: Coccoidea: Pseudococcidae) on Eggplant at Sharkia Governorate, Egypt

12 Arab Congress of Plant Protection ,ACPP ,4 -10 November, 2017 Hurghada Egypt 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
The solenopsis mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Sternorrhyncha: Coccoidea: Pseudococcidae) was described by Tinsley from weed roots in a nest of the ant Solenopsis geminata Fabricius in New Mexico, U.S.A in 1898.This highly polyphagous mealybug attacks major menace in many tropical and subtropical countries.It attacking 159 hosts plant species (agricultural and horticultural crops) belonging to 21 different families.It cause yield loss by direct and indirect infestation.In direct mode of infestation they feed on leaves, stems, fruits and roots of host plants causing general weakening, defoliation and death of susceptible plants.Whereas in indirect mode of infestation they secrete honey dew which causes development of sooty mould which inhibit photosynthesis which leads to host plant death.may also damage plants by serving as vector of plant diseases (Hodgson et al., 2008, Arif et al., 2009, Saini et al., 2009, Abbas et al., 2010, Wang et al., 2010and Vennila et al., 2011).
The first record of P. solenopsis damaging a crop was made by Fuchs et al. (1991) who recorded P. solenopsis on cotton cultivated in Texas, U.S.A.The P. solenopsis has been found on a relatively wide variety of host plants including species of economically important families such as Cucurbitaceae, Fabaceae, Solanaceae and Malvaceae (Culik and Gullan, 2005, Afzal et al., 2009, Wang et al., 2009& 2010and Zhu et al., 2011).Aheer et al. (2009) reported 22 host plants of P. solenopsis, besides cotton crop in Pakistan.Maximum prevalence was observed on China rose, Hibiscus chinensis followed by okra, Abelmoschus esculentus L. (Malvaceae) (Wang et al., 2010).
Therefore, the present investigation was planned with the aim of studying the population density and activity periods of different stages of P. solenopsis on eggplant.Evaluate the effects of some weather factors on the different stages of the pest.Calculate the number of generations and estimate the preferable leaf surface.Such study may help for designing a comprehensive pest management program and prediction models for the cotton mealybug.

MATERIALS AND METHODS
Filed experiments were carried out on eggplant field located at Hihhya district, Sharkia Governorate, Egypt.The study was continued from May to September for two successive seasons 2015-2016 to assess the population density of cotton mealybug, Phenacoccus solenopsis Tinsley by counting the number of nymphs and adult female.The study was conducted in an area of about one feddan for eggplant, Solanum melongena L. (Solanaceae).The field received normal agricultural practices and no chemical control was applied.

Population density and number of generations:
For sampling, forty leaves were picked up at random once a week, the samples were put in polyethylene bags and transferred into the laboratory for carefully inspection.These samples were examined in the same day using a stereomicroscope whereas the different stages of P. solenopsis were counted and recorded.The formula proposed by Audemard and Milaire (1975) and emended by Jacob (1977) was applied for estimating the number of P. solenopsis generations and their durations.Data of weekly counts of nymphal stage were indicated on millimeter papers to calculate the number of generations and their duration.

Effects of some weather factors on the insect populations:
The prevailing air temperature, maximum and minimum air temperature (˚C) and relative humidity percentage (RH %) in the experimental area during the periods of the present study were obtained from the Central Laboratory for Agricultural Ecological Studies on Cotton Mealybug, Phenacoccus solenopsis Tinsley 197 Meteorology, Agricultural Research Center, Ministry of Agriculture.The relationships between the tested weather factors and each insect population were studied.

Statistical analysis:
Simple correlation, partial regression values and coefficient of determination percentage (C.D. %) were calculated using COSTAT Computer Program (2005). .

RESULTS AND DISCUSSION
Population density of Phenacoccus solenopsis on eggplant: Females population density: Data given in Tables (1 & 2) and Figs.
(1 & 2) showed that in the first season (2015) the females had two peaks of activity in the last week of June (317 females / 40 leaves) and in the last week of August (726 females).
While, in the second year ( 2016) three peaks of females activity were noticed in first week of June, first week of July and first week of September with values of 100, 206 and 523 females, respectively.
In general, the total number of females was higher (5386 females) in the first season than the second one with total number of 3711 females.

Nymphs population density
Results arranged in Tables (1 & 2) and Figs.
(1 & 2) demonstrated that nymphs had four peaks of activity were recorded during the first and second seasons.There were in the third week of June, third week of July, fourth week of August and second week of September with values of 1820, 2969, 11636 and 14458 nymphs, consecutively.Also, in the second season four peaks of activity were recorded during last week of May & June and during first week of August & September with 505&2205 and 2561 & 12796 nymphs, successively.
Generally, the highest total number of nymphs population 81463 nymphs was obtained during the first season compared with 58157 nymphs during the second one.

Total number of alive stages:
As shown in Tables (1 & 2) and Figs.
(1 & 2) the total number of alive stages showed four peaks of activity during the first season.They were in third week of June, third week of July, fourth week of August and second week of September with values of 1912, 3219, 12315 and 14795 individuals, consecutively.While, during the second season, three peaks of activity were noticed in the last week of June, first week of August and second week of September with 2409, 2758 and 13150 individuals, respectively.
In general, the highest total number of alive stages was 86849 individuals obtained in the first season compared with 61868 individuals in the second season.

Effects of some weather factors on different stages of P. solenopsis : Females population density:
Results presented in Table (3) indicated that in the first season each of maximum temperature, minimum temperature and relative humidity had positive significant, positive highly significant and positive significant effects on females population where r =0.508*, 0.579** and 0.517*, respectively.
While, in the second season minimum temperature and relative humidity had a positive significant and positive highly significant effects on females population where r = 0.471* and 0.725**, consecutively.Coefficient of determination (C.D. %) obviously cleared that the three considered weather factors affected females population by 62.42 and 52.72%, in the first and second seasons, successively.

Nymphs population density:
As shown in Table (3) in the first season each of maximum temperature, minimum temperature and relative humidity had positive significant, positive significant and positive highly significant effects on nymphs population where r = 0.473*, 0.485* and 0.638**, consecutively.While, in the second season only relative humidity had a positive significant effect on nymphs population where r = 0.546*.According to C.D.% nymphs population were affected by 61.32 and 30.89 % during the first and second seasons, respectively.

Total number of alive stages density:
Data given in Table (3) revealed that in the first season each of maximum temperature, minimum temperature and relative humidity had positive significant, positive significant and positive highly significant effects on total number of alive stages where r = 0.479*, 0.494* and 0.638**, consecutively.While, in the second season relative humidity only had a positive highly significant effect (r = 0.613**).Coefficient of determination percentage demonstrated that the total number of alive stages was influenced by 62.28 and 37.90% during the first and second seasons, respectively.
These results are in agreement with those obtained by Suresh and Kavitha, 2008b, Dhawan et al., 2009, Jeyakumar et al., 2009, Hanchinal et al.,2010, Patil et al., 2011, Singh and Kumar, 2012and Hameed et al., 2014 who mentioned that cotton mealybug population showed positive significant relationship with maximum temperature, minimum temperature and R.H.%.(3 & 4) revealed that P. solenopsis had three generations during the first and second seasons.The first generation was taken seven weeks.While, the second and third generations took sex weeks.The first generation was during the period extended from the third week of May till the end of June.While, the second one took place from the first week of July till the second week of August and the third generation was during the period extended from the third week of August till the third week of September.
Our findings are in agreement with the results of Fand and Suroshe, 2015 who reported that P. solenopsis can complete about 8 -12 generations in a year on cotton plants, Gossypium hirsutum L.  Preferable leaf surface: Data given in Table (5) showed that the total number of alive stages of P. solenopsis was higher on the lower leaf surface (69646 and 44602 individuals) than those the upper leaf surface (17203 and 17266 individuals) during the first and second seasons, respectively.

Table ( 3
): Statistical analysis based on correlation coefficient and multiple regression indicating the effects of climatic factors on different stages of Phenacoccus solenopsis Tinsley on eggplant at Hihhya distract, Sharkia Governorate during the first (2015) and second (2016) seasons.Data given in Table (4) and Figs.

Table ( 5
): Weekly numbers of Phenacoccus solenopsis Tinsley on upper and lower surface of eggplant leaves at Hihhya distract, Sharkia Governorate during the first (2015) and second (2016) seasons.
* Numbers per 40 leaves