Influence of Various Ecological Factors on Population Fluctuations of Icerya Seychellarum (Westwood) Infesting Guava Orchard in El-Behara Governorate.

INTRODUCTION

There were various mealybugs species (Hemiptera: Margarodidae) were attacking the guava trees (Psidium gaujava L.) in Egypt, and the infestation by these species eventually causes losses in the crop's quantity and quality, (Sayed, 2008; Attia, 2010; Awadalla, 2013; El-Sherbenie 2004; Abdel-Mageed 2005; Bakry and Arbab, 2020). Because insect sap contains very little protein, the insect may have to suck a large amount of plant sap to get enough protein for growth and egg development. The insects  can attack  guava leaves, branches, and fruits as a result of a huge loss of plant sap, which in turn manifests as leaf loss, wilting of growing tips, early leaf drop, deformation of leaves and dwarfing (Mangoud, 2000; El-Said, 2006; Reda et al., 2010).

As well as, honey dew, direct damage, which is secreted by these insect pests, enhances saprophytic fungal damage and decreases Plant metabolism and photosynthesis (Mittler and Douglas, 2003; Zaki et al., 2013; El- Sayed, 2015 and Mohamed, 2015).  As well as, Mealybugs were difficult to kill because they live in protected areas, the mealybugs body walls on all developing stages are waxed, and most insecticides are ineffective.  The immobility  of Mealybugs, on the other hand, allows biocontrol chemicals to be successful. (Mani et al. 2011).

R.cardinalis (Coleoptera: Coccinellidae) is specialized on mealybugs. It had its important after its success in controlling Icerya purchasi Maskell in the citrus groves of California and many other countries (Bennett et al., 1985; Caltagirone and Doutt, 1989 and Mohamed et al., 2013). It became one of the most important predators that attack mealybug species in different areas in Egypt (Hamed and Saad, 1989; Ibrahim, 2005; Awadalla, 2013). The green lacewing, C.carnea (Neuroptera: Chrysopidae) is regarded as a common predator of I. seychellarum (Carrillo and Elanov, 2004; El-Serafi et al., 2004). It is regarded as one of the most significant predaceous species because, its extensive distribution, high relative frequency of occurrence, good hunting characteristics, and ease of rearing in the laboratory.

To achieve a good integrated pest management of any pest; ecological and biological aspects should be involved. As a result, the current work aimed to study the population fluctuations of I. seychellarum and its associated predaceous insects (R.cardinalis and C. carnea) and the synchronization between them as well as, the impact of  some climatic factors (temperature and relative humidity) on their populations.

MATERIALS AND METHODS

This study was performed for two following years in heavy infested guava orchards with I. seychellarum during (2020/2021) and (2021/2022) at ELbhera, Governorate. The chosen trees did not receive to any chemical treatments throughout the period of  this study. All trees received the same routine horticultural practices.

Sampling method and assessment

Five trees were similar in size, shape, height, vegetation and relatively homogenous in their infestation with I. seychellarumm were chosen to carry out this work. Samples of guava leaves were taken biweekly intervals throughout the investigation period from the four cardinal directions; East-West-North and South in addition to, the center of each selected tree. Sample size was 125 leaves represented 25 leaves for each direction. Samples were picked up randomly from each tree by using a garden scissors. The samples were packed instantly in polyethylene bags and transferred to the laboratory on the same day for assessment by using stereoscopic microscope (binocular) to record the number of I.seychellarum (as nymphs and adults). To investigate the population density of the two predators, the five trees were examined in the field and record the numbers of the observed predators which found.

Effect of ecological factors on population fluctuations of I.seychellarumand its associated predators:

 Meteorological Central Laboratory, Agricultural Research Center, and Ministry of Agriculture provided us with the data of temperatures, as well as average daily relative humidity, for the seasons 2020/2021 and 2021/2022.We investigated the simple correlation and regression values to study the relationships between the tested weather factors and the population density of the I.seychellarum and its associated predators. Also, multi regression analysis was done to estimate the combined effects of the abiotic factors of  I.seychellarum and its associated predators as well as, estimated the combined effects of abiotic and biotic factors on  population of  seychellarum scale. Correlation also, the regression analyses were done by using SAS program (SAS Instue, 1998).

RESULTS AND DISCUSSION

This study was performed for two following years in heavy infested guava orchards with I. seychellarum during (2020/2021) and (2021/2022) at ELbhera, Governorate. The chosen trees did not receive to any chemical treatments throughout the period of  this study. All trees received the same routine horticultural practices.

Sampling method and assessment

Five trees were similar in size, shape, height, vegetation and relatively homogenous in their infestation with I. seychellarumm were chosen to carry out this work. Samples of guava leaves were taken biweekly intervals throughout the investigation period from the four cardinal directions; East-West-North and South in addition to, the center of each selected tree. Sample size was 125 leaves represented 25 leaves for each direction. Samples were picked up randomly from each tree by using a garden scissors. The samples were packed instantly in polyethylene bags and transferred to the laboratory on the same day for assessment by using stereoscopic microscope (binocular) to record the number of I.seychellarum (as nymphs and adults). To investigate the population density of the two predators, the five trees were examined in the field and record the numbers of the observed predators which found.

Effect of ecological factors on population fluctuations ofI.seychellarumand its associated predators:

 Meteorological Central Laboratory, Agricultural Research Center, and Ministry of Agriculture provided us with the data of temperatures, as well as average daily relative humidity, for the seasons 2020/2021 and 2021/2022.   We investigated the simple correlation and regression values to study the relationships between the tested weather factors and the population density of the I.seychellarum and its associated predators. Also, multi regression analysis was done to estimate the combined effects of the abiotic factors of  I.seychellarum and its associated predators as well as, estimated the combined effects of abiotic and biotic factors on  population of  seychellarum scale. Correlation also, the regression analyses were done by using SAS program (SAS Instue, 1998).

(Fig.1) Population fluctuations of I.seychellaruminfesting guava trees during 2020/2021 (A) and 2021/2022 (B) in El-Behara governorate.

Effect of some weather factors on the seasonal activity of I. seychellarum on guava trees.

Table 1: Simple correlation and regression coefficients between the tested weather factors and each of nymphs, adult females and total populations of I. seychellarum on guava during 2020/2021.

Impact of temperatures (maximum, minimum) and relative humidity on the totality of population of  I. seychellarum during the two studied years were illustrated in Tables (1 & 2). During the first year (Table, 1), there were slow positive relationship between the nymph density of the  I. seychellarum (r =0.58) with maximum and minimum temperatures; while, with relative humidity it was negative (r =- 0.45). Multi regression show that the combined effect of weather factors  had low effect (E.V. = 37.34 %).

There were slow positive relationship between the adult female population of the  I. seychellarum (r = 0.55 & 0.59) with maximum and minimum temperatures; while, with relative humidity it was negative (r = - 0.38). Multi regression show that the combined effect of weather factors had 50.19 % of the total factors affecting  adult female population (Table, 1).

There were significant effects of maximum and minimum temperatures on  I. Seychellarum total population during the first year (r =0.62 & 0.63) and there were insignificant effects  of relative humidity during (r =- 0.46). Multi regression show that the effect combined of weather factors exhibited 43.45% of the total factors affecting total population (Table,1).

In the second year (Table, 2), there were positive relationship between the nymph population of the  I. seychellarum (r =0.70 & 0.63) with maximum and minimum temperatures; while, with relative humidity it was negative (r =- 0.68). Multi regression show that the effect combined of weather factors reached 56.32%.

There were positive relationship between the adult female population of the  I. seychellarum with maximum and minimum temperatures (r = 0.69 & 0.63); while, with relative humidity there was a negative coloration (r = - 0.68). Multi regression show that the combined effect of weather factors had 56.37 % of the total factors affecting  adult female  population (Table,2). There were significant positive effects of maximum and minimum temperatures on  I. seychellarum  total population during the second year (r =0.70 & 0.63). Significant negative effects of relative humidity (r =- 0.68). Multiregression showed  that, the influence of weather factors reached 56.37 % (Table, 2).

Table 2:  The simple correlation and regression coefficients between the tested weather factors and each of nymph, females and total population of I. seychellarum on guava trees during 2021/2022.

3- Seasonal activity of R. cardinalis and C.carnea on guava trees:

Data presented in Fig. (2 A&B) illustrated that seasonal activity of R. cardinalis  and  C.carnea  had two peaks on guava trees during first  and second years.

Population  of  R. Cardinalis  recorded  its first peak on the 24^th  of  October and 20^th  of November (with 31 and 26 individuals /sample), throughout the first and second year, respectively. The second peak was recorded on the 22^th  of May and 4^th of  June with 23 and 34 individuals / sample, respectively (Fig., 2).

With respect to C. carnea population (Fig., 2), it recorded its first peak on the 7^th  and 20^th of November  of first  and second year  (14.1 and 8 individuals /sample, respectively). The second peak was recorded on the 22^th  and 7^th  of May of first and second year  (19 and 23.1 individuals/ sample, respectively).

(Fig.2) Seasonal activity of R.cardinalisand C.carnea on guava trees infested with I. seychellarum during 2020/2021 (A) and 2021/2022 (B) in El-Behara governorate.

Impact of some climatic factors on the seasonal activities of R. cardinalis and C.carnea on guava trees.

Impact of temperatures (maximum & minimum) and (R.H %) on the populations of R. cardinalis and C. carnea throughout the two years  of study were illustrated in Tables (3 and 4).

There were positive relationship between the R. cardinalis  and both of maximum & minimum temperatures (r =0.68 and 0.66) during the first year; while, with relative humidity it was negative (r =- 0.56). Multi regression show that the combined effect of weather factors 51.81% of total factors affecting R. cardinalis  (Table, 3).

There were no relationship between the C. carnea  population and both of maximum & minimum temperatures (r =  0.19 and 0.01) during the first year;  while, with relative humidity it was significantly negative (r =  - 0.49). Multi regression show that the combined effect of weather factors had a moderate effect (E. V = 35.51%) (Table,3).

Table 3:  The simple correlation and regression coefficients between the tested weather factors and populations of R. carinalis and C. carneaduring 2020/2021.

There were positive relationship between the  R. cardinals  and  temperatures (maximum and minimum where r-values were 0.66 and 0.63) during the second year; while, with relative humidity it was negative (r =-0.49). Multi regression show that the combined effect of weather factors contributed 44.25% of the total factors affecting  R. cardinalis  (Table, 4).

There were relatively low effect of  maximum and minimum temperatures  on  C. Carnea  population during the second year  (r = 0.42 and 0.27); while, with relative humidity it was significant (r = - 0.57). Multi regression show that the combined effect of weather factors had moderate effect (E.V. = 44.12%) (Table, 4).

Table 4: Simple correlation and regression coefficients between the tested weather factors and populations of R. cardinalis and C. carnea during 2021/2022.

Synchronization between I.seychellarum and its predators.

Correlation coefficient values between predators (R. cardinalis and C. carnea) populations and each of the nymphs, females and totality of population of I. Seychellarum during the two studied years are represented in Table (5). There were positive relationship between the R. cardinalis  and each of nymphs  (r =0.69 and 0.78), adult females  (r =0.62 and 0.76) and total population (r =0.72 and 0.77) during the first and second year, respectively.

As it was noticed with R. cardinalis, the was a good synchronization between  C. Carnea  population and each of nymphs  (r =0.63 and 0.61), adult females  (r =0.29 and 0.56) and total population of  I. seychellarum   (r =0.54 and 0.57) throughout 1^st  and 2^nd seasons, respectively (Table, 5).

Table 5: The correlation coefficient values between denisities of predators(R. cardinalis and C. carnea) and each of nymphs, adult females and total populations of I. seychellarumin guava orchard during 2020/2021 & 2021/2022.

Combined effect of ecological factors on I.seychellarum population: