Development of Biological Control Tools against Bactrocera zonata (Saunders) (Diptera: Tephritidae) in Citrus Orchards in Egypt
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The peach fruit fly Bactrocera zonata, is a harmful insect that infests various fruit crops and vegetables worldwide, including Egypt. Its presence leads to significant damages and losses. To minimize the negative impact of pesticide residues on human health and the environment, a study was conducted to examine the seasonal behavior of Bactrocera zonata on navel orange trees. This investigation involved the utilization of sex attractants and the monitoring of fruit samples. The research was conducted over two consecutive seasons, namely 2020 and 2021. By utilizing sex attractants, pheromone (mass trapping) it was discovered that the number of male Bactrocera zonata captured and infested increased during the Autumn period, specifically in October, in both seasons. Additionally, it was observed that Bactrocera zonata males exhibited a single peak of activity each season. Fruit samples were monitored to assess fruit infestation, and it was found that infestation was positively correlated with the maturity of the fruits. The weekly count of males captured in the fly traps, along with the infestation rate of this pest, indicated that these traps could serve as a useful tool for predicting the infestation rates of Bactrocera zonata in their host fruits. The implementation of mass trapping techniques utilizing pheromone-based tools will result in a reduction of infestation by the end of the second season of 2021.
The Peach Fruit Fly, Bactrocera zonata “B. zonata” (Saunders), was initially recorded in Egypt in 1993 at Qalyubia Governorate on guava plants (El-Nagar et al., 2010). Over the past decade, B. zonata has become a significant pest due to the favorable climate and has started infesting various fruit hosts such as citrus, mango, peach, fig, guava, apricot, and apple. It also targets secondary hosts like tomatoes, peppers, and eggplant for food (Hashem et al., 2004; Ghanim, 2009). This species continues to pose a constant threat of invasion (Mohamed et al., 2012). Citrus fruit is one of the most important fruit crops in Egypt, occupying the largest area with an average of 488.003 feddans, accounting for 28.6% of the total fruit area from 2015 to 2019. The citrus varieties grown include grapefruit, tangerine, salty and sweet lemon, dahlia, orange, and eight orange types (Brisa, Al-Baladi, Al-Sukari, Al-Saifi, Al-Yafawi, Abu Damah, Al-Khalili, and Yusuf Suleiman). Oranges, with an average production of approximately 3118,115 tones, contribute to 71.04% of the overall fruit production in the country (Ekram et al., 2021). B. zonata primarily attacks ripe fruits, causing direct damage through ovipositional punctures and larval feeding on the pulp, resulting in soft and unsuitable fruit for human consumption. It also causes blotchy fruits, which hampers commercial opportunities, especially for fruit exports. As a quarantine pest, appropriate measures are taken to address this issue (Aluja et al., 1996; EPPO/ 2003; Shahen et al., 2019).
Control, as stated by Alzubaidy, (2000) is the act of maintaining the pest population below a predetermined threshold to minimize economic damage. The most effective approach for managing fruit flies is integrated pest management (IPM), which incorporates various techniques such as the Male Annihilation Technique (MAT), sanitation practices, protein-based baits, and the application of plant extracts regularly (Afzal and Javed, 2001). To reduce the risks associated with insecticide use, IPM strategies have been developed. These IPM approaches not only yield positive results but also have a minimal impact on the environment, thereby reducing infestations (Ketelaar and Kumar, 2002). Since fruit flies cannot be effectively controlled by a single strategy, multiple strategies are required. Each strategy has its advantages and disadvantages, and its implementation may or may not be feasible (Suckling et al., 2016). In North Africa, particularly in Tunisia, Morocco, and Egypt, several trapping technologies have proven effective in protecting citrus and summer fruits when integrated with IPM efforts. These methods can target either females or males depending on the species, to eliminate the maximum number of fruit flies possible. Due to their reduced reliance on insecticides and their environmental friendliness, these methods should be promoted (Trabelsi and Boulahia-Kheder, 2011; Boulahia-Kheder et al., 2015; Elaini and Mazih, 2018; Al-Eryan et al., 2018). According to Reddy et al., 2020) cultural control techniques often revolve around maintaining crop hygiene and orchard sanitation, which disrupt the typical life cycles of target pests. It is crucial to have a thorough understanding of fruit fly biology to achieve this goal. Preventing the larvae found in decaying fruit from developing into pupae in the soil is of utmost importance insect aggregation control measures involve collecting and disposing of every infected fruit, whether still on the tree or fallen to the ground. These fruits can be destroyed by grinding them and burying them at least 50 cm beneath the soils surface. Fruit fly populations can be significantly reduced through these mechanical control practices. This study aims to examine the effectiveness of pest control techniques, by evaluating the percentage of infestation of the peach fruit fly, B. zonata, on Navel orange. In addition, the study aims to evaluate the efficiency of sex-attracting pheromone traps for controlling and monitoring B. zonata in Qalyubia Governorate-Egypt, throughout the 2020 and 2021 seasons.
The management of B. zonata through pheromone-mass trapping was carried out in the field trials involving Navel orange trees, C. sinensis, at Al Shaeir Island, Al Qanater- Al Khayriyyah, Qalyubia Governorate, Egypt. The effectiveness evaluation was determined by monitoring the count of trapped flies per trap and the count of affected oranges on labeled citrus trees every week from September to December during the 2020 and 2021 seasons.
Monitoring and controlling the peach fruit fly, B. zonata on Navel orange, C. sinensis (L.) under field conditions
Implementation of Pheromone Traps
To effectively monitor and control the population of male adults of the PFF and B. zonata, a total of five traps/ feddan were utilized. These traps were equipped with liquid Methyl Eugenol (ME) sex-attracting pheromone, with a concentration of 98% L (Minstry of Agriculture-Egypt) as recommended by Ashfaq et al. (2020). The traps were strategically positioned within the citrus tree canopy, approximately 1.5 - 2m above the ground, and spaced at a distance of 50 - 65m from each other. This arrangement aimed to minimize any potential interference among the traps during the period from September to December in both 2020 and 2021, as suggested by El-Gendy, (2012) and El-Gendy & Nassar, (2014). Methyl Eugenol served a dual purpose in this study. Firstly, it attracted the male PFF, facilitating their identification and monitoring. Secondly, it aided in the control of B. zonata male adults by causing them to drown in water containing 1% Malathion insecticide. The attracted males were diligently counted and recorded every week, while the traps were replaced every week starting from September until December 1st. To ensure accurate data collection, climatic conditions were obtained from the weather underground site of Cairo International Airport Station (https://www.wunder ground.com). For this study, locally sourced plastic cylindrical bottles were utilized as the pheromone traps. These bottles were specifically designed with four holes on the top quarter body, evenly spaced in opposite directions. Cotton wicks were soaked in the lure solution and securely attached to the holes using wire. The bottles were then filled with 200-400 ml of water, depending on the bottles capacity (Fig. 1).
Mechanical Control
To manage fallen fruits, a systematic approach was adopted. Every 7 - 10 days, the fruits were carefully gathered and stored in plastic bags. These bags were then subjected to sunlight, eliminating any larvae inside the fruits. As an alternative, the fruits were buried at a depth of 50 cm in the soil, ensuring complete eradication of the pests (Fig. 2).
Cultural Management
Different methods like plowing, hoeing, and weeding can eliminate mature larvae and/or pupae of B. zonata (Fig. 3). Additionally, the pruning of tree branches in January is a crucial practice that promotes tree permeability and enhances the penetration of light.
Weed suppression
The citrus orchard was carefully cultivated with Trifolium alexandrinum, known as clover, to serve as an effective ground cover crop. This helped conserve natural enemies and played a crucial role in suppressing weeds and providing green fertilization. By incorporating these practices, the Integrated Pest Control process for managing the PFF (Pest and Fruit Fly) was significantly improved and enhanced.
Estimating the percentages of Navel orange infestation
Samples of mature and overripe Navel oranges, whether found on the trees or accidentally on the ground beneath them, were gathered and transported to the Biological Control Department (BCD) laboratory at the ARC for examination. To determine the extent of infestation, a random selection of 25 fruits was collected from nine different trees. These collected fruits were placed in plastic containers, each containing a 3cm layer of soft sand. The purpose of the sand was twofold: to absorb any secretions from decaying fruits and to serve as a suitable pupation site for third-instar larvae as they emerge from the fruits. The plastic containers were covered with a muslin cloth, and secured in place by rubber bands (Fig. 4). The total number of fruits and the number of infested fruits were recorded. Subsequently, the percentage of infestation was calculated using the following formula: Percentage of infested fruits = (Number of infested fruits) / (Total number of collected fruits) X 100
Statistical analysis
The data obtained from the study were subjected to statistical analysis using various methods. A one-way ANOVA was performed to analyze factors affecting plant quality, and the means were compared using the LSD and Tukeys HSD tests at (P= 0.05 level). The analysis of the population of the PFF (Plant Fruit Fly) was conducted about weather factors such as maximum (Max) and minimum (Min) temperatures (T.), as well as relative humidity (RH%). These weather factors were considered linear variables. Additionally, the age of the plants, measured in weeks, was presented as a third-degree polynomial to represent the ripening stage of the fruits. The multiple polynomial regression equation used in the analysis included variables such as max. and min. temperatures, RH%, plant age, and their respective higher-order terms. To analysis the insect count data, running means were calculated before conducting the analysis. The obtained results were analyzed using the Process Correlation and Regression functions in SAS software (Anonymous, 2003; Uddin et al., 2023).
The initial season of 2020 Witnessed the utilization of Pheromone traps containing Methyl Eugenol 98% on Navel orange, C. sinensis trees. This practice commenced on September 2nd, 2020, and continued until the second week of November in the same year. The outcomes of the number of captured male insects are presented in Table 1 and Fig. 5. The data reveals that the peak population of trapped adults, amounting to 10,510 individuals per five traps, was observed on October 26th, 2020. This occurrence coincided with a mean (Max. T.) of 27.57 °C, a mean of (Min. T.) of 20.71 °C, and a mean of (R.H.) of 81.00%. Conversely, the lowest number of trapped adults, totaling 3,550 individuals per five traps, was recorded on November 9th, 2020. On this day, the mean of Max. T. was 28.57 °C, the mean of Min. T. was 20.00 °C, and the R.H. was 92.57%. The data presented in the table and figure indicate that the abundance of the B. zonata population was higher in October compared to September and November.
The statistical analysis in Table 2, revealed that there was no observed correlation (r = -0.2577, -0.28480, and -0.30832) between the number of males captured by traps and the average Max. T., average Min. T., and average R. H. Conversely, the impact of weather factors (expressed as E.V.%) either individually or in combination was found to be insignificant, accounting for only 23.03% of the variation in male numbers. However, the age of the fruits and their physiological state, represented by Age-Age3, exhibited a significant relationship with the male numbers. E.V.% explained a substantial 93.64% of the variation in male numbers, with a P-value of 0.8260 and 0.0267 for the respective factors (Table 2). There is a pressing need to minimize the utilization of chemical insecticides in the management of pest control. Therefore, the current study focused on employing eco-friendly methods in Integrated Pest Control of the peach fruit fly, B. zonata. These methods included the use of Methyl Eugenol traps, mechanical control, cultural practices, and evaluating their effectiveness. The data revealed that all of these methods contributed in some way to reducing injury in Navel orange trees, particularly in the second season. Thus, cultural practices such as plowing, hoeing, weeding, and pruning may play a crucial role in reducing infestation and flies. These findings align with Vijaysegarans research in 1985, which demonstrated that maintaining sanitation in orchards significantly reduces the number of fruit flies. Similarly, Yangs study in 1991 successfully managed B. minax, a highly destructive citrus pest, through the widespread destruction of fallen fruits in orchards and villages. Makhmoor and Singhs research in 1997 reported that hoeing attributed to 43-80% of pupal mortality in B. dorsalis. In Egypt, the use of killing bags (bags for collecting fallen fruits) has effectively controlled B. zonata (Mohamed and El-Wakkad, 2003). Additionally, according to (Rethwish et al., 2002, Andy, 2007; Wagan et al., 2015), Berseem clover is known as a trap crop for natural enemies, encouraging the presence of predator insects and non-insect species in the Berseem agro ecosystem more than other crop plants. Previous studies have also shown that good sanitation techniques can significantly reduce B. minax infestation (Wang & Zhang, 2009). Furthermore, fruit fly pupae in the soil can be exposed to environmental conditions that promote mortality through ground flooding and ploughing (soil disturbance) (Vargas et al., 2015). Furthermore, the findings revealed that the Navel orange orchard experienced its population peaks during the Autumn season in October. The high number of male individuals captured coincided with the ripening of the fruits, with temperatures ranging from 22.57 to 35.42 °C (Max. T.) and 11.85 to 24.28 °C (Min. T.). The mean relative humidity ranged between 60.28 to 100.57%. These results are consistent with the study conducted by Deepa et al. (2009), which reported that the highest catches of B. zonata occurred in the second week of October. Similarly, Draz et al. (2011) discovered that the peak population of both fruit flies, C. capitata and B. zonata, in Navel orange coincided with the fruit ripening in October. El-Gendy and Nassar, (2014) also found that B. zonata males were abundant in Autumn months in citrus and other fruit orchards. Draz et al. (2016) investigated that B. zonata males were most abundant and active during the Autumn season, specifically on October 11th, November 8th, and December 13th. Additionally, Al-Jassany and Abu-Raghef, (2018) found that the highest population of B. zonata occurred in the Autumn months of October and November. However, these results contradict the findings of Mahmood and Mishkatullah, (2007) who observed a decline in the population peak of the Bactrocera genus during October. Noaman et al. (2022) observed that the captured fruit flies of Bactrocera spp in mango and citrus had high numbers in September but declined from October 3rd to December 25th as the mean temperature decreased.
Regarding abiotic factors, Agarwal et al. (1999a) demonstrated a positive correlation between B. zonata population and maximum and minimum temperatures, rainfall, and relative humidity. Ali Matching et al. (2011) also found a significant positive correlation between B. zonata incidence and maximum and minimum temperatures. On the other hand, Kausar et al. (2022) recorded a negative correlation between relative humidity and population abundance of Bactrocera species, with the lowest numbers observed in November and December.
Table 3 data indicated that the infestation of fruits commenced on September 21st, 2020, with one infested fruit out of 25 randomly collected Navel orange, C. sinensis fruits, accounting for 4%. The number of infested fruits progressively rose, leading to the first peak of 8 infested fruits, representing 32%, on October 14th, 2020. Subsequently, the infestation percentage briefly declined, reaching 20% on October 26th, 2020, with five infested fruits, before escalating to its second peak on November 9th, 2020, at 48% with 12 infested fruits. Consequently, the infestation percentages surged toward the end of the season as the fruits attained maturity.
The second season 2021. Pheromone traps were installed on Navel orange, C. sinensis trees on September 3rd, 2021, for this season. The highest count of adult male insects (7240 adults/5 traps) was observed on October 12th, 2021, with a Max. T. of 33.00 °C, a Min. T. of 21.85 °C, and a R. H. of 87.28%. Subsequently, the number of males decreased, reaching 356.7 males on November 22nd, 2021, with a Max. T. of 22.57 °C, a Min. T. of 15.28 °C, and R. H. of 81.00% (Table 4 & Fig. 6). The results indicate that similar to the previous season, the highest population of B. zonata adult males occurred in the autumn month of October, rather than in September and/or November.
The statistical analysis in Table 5 demonstrates the impact of abiotic factors on the population of male B. zonata in the Navel orange, C. sinensis crop during the 2021 season. Two different methods were employed: simple correlation and multiple regression. For the simple correlation analysis, the variables Max. T. and Min. T. showed a positive correlation with the population of male B. zonata, with correlation coefficients of 0.82503 and 0.8953, respectively. Both correlations were statistically significant, with p-values of 0.0005 and 0.0003, respectively. In the case of multiple regression analysis, the variable Max. T. had a slope of 235.23, but it was not statistically significant (p-value = 0.2347). The variable Min. T. had a slope of 377.23, but it was also not statistically significant (p-value = 0.1289). The variable R.H. showed a weaker correlation with the population of male B. zonata, with a correlation coefficient of 0.65188 and a p-value of 0.0158. The slope for R.H. was -5.29, but it was not statistically significant (p-value = 0.9363). The variable Age - Age3 did not have any correlation or regression coefficients reported. However, it had a significant effect on the population of male B. zonata, as indicated by the F-value of 23.9 and a p-value of 0.0001. The explained variance (E.V.%) for Age - Age3 was 88.50. When all the variables were combined in the analysis, the F-value was 9.04, with a p-value of 0.0085. The explained variance (E.V.%) for the combined variables was 90.04. Overall, the statistical analysis provides insights into the relationship between abiotic factors and the population of male B. zonata in the Navel orange, C. sinensis crop during the 2021 season.
Table 6 B. zonata infestation experienced its initial peak on September 18th, 2021, with 8 infested fruits accounting for 32% of the total. Subsequently, the infestation percentage declined, reaching its lowest point on October 3rd, 2021, with only one infested fruit representing 4%. The infestation percentages then began to rise again, culminating in a second peak on November 15th, 2021, where 32% of the fruits were infested, totaling eight. On November 22nd, the percentage decreased once more to 16%, with four infested fruits, and eventually reached zero percent on December 1st, marking the end of the season. The findings revealed that the infestation percentages in the second season exhibited two peaks, the first in September and the second in November, which differed from the previous seasons peaks in October and November. Moreover, the infestation rate decreased towards the end of the season, possibly attributed to the implementation of Integrated Pest Control (IPC) practices. Results from the first season of infestation in Navel oranges showed that the percentage of infestation occurred during the Autumn period of October 14th and November 9th, 2020, with infestation rates of 32% and 48% respectively, when the fruits were ripe. However, these percentages changed in the second season, with infestation rates reaching 32% on September 18th and November 15th, 2021. There was a decrease in infestation towards the end of the season, indicating the effectiveness of the Integrated Pest Control (IPC) strategy. These findings align with a study conducted by Ashfaq et al. (2020), which demonstrated that the Male Annihilation Technique (MAT) as part of Integrated Pest Management (IPM) effectively controlled infestation of the fruit fly B. zonata in citrus orchards.
This study aimed to investigate the effectiveness of various integrated pest control (IPC) practices in controlling and monitoring the B. zonata population on Navel orange trees, C. sinensis. The IPC practices included mechanical and cultural methods, as well as the use of Methyl Eugenol trps. Notably, no chemical insecticides were used throughout the study. The results revealed that the highest population of B. zonata was observed during the Autumn period, particularly in October. This could be attributed to certain abiotic factors and the condition of the fruit, which may have provided favorable conditions for the pest. Additionally, the infestation percentages decreased in the second season in the Navel orange orchard. Based on these findings, it is recommended to implement a combination of methods to effectively control the PFF, B. zonata, and minimize the damage it causes.
I am grateful to Prof. Mohamed Abou-Setta, PPRI-ARC., for his assistance in conducting the statistical analysis. Funding: This manuscript was by the project, PLANT-B, through the EU/PRIMA Foundation under grant number 1812.
The authors declare no potential conflict of interest.
Academic Editor
Md. Ekhlas Uddin Dipu, Managing Editor, Universe Publishing Group (UniversePG), Dhaka-1344, Bangladesh.
Biological Control Department, Plant Protection Research Institute, Agricultural Research Center, Giza, Egypt.
Shairra SA., and Sallam RF. (2024). Development of biological control tools against Bactrocera zonata (Saunders) (Diptera: Tephritidae) in citrus orchards in Egypt. Int. J. Agric. Vet. Sci., 6(4), 75-85. https://doi.org/10.34104/ijavs.024.075085
