Factor effects on number of eggs laid of queen bee species Apis cerena at Northeastern region of Vietnam

Nguyen Duy Hoan and Phung Duc Hoan

Thai Nguyen University of Agriculture and Forestry,Tan Thinh Ward, Thai Nguyen City 50000, Viet Nam
ndhoan@tnu.edu.vn

Abstract

The most important mission of the queen bee is to lay eggs to maintain the number of workers bee in the hive, so the ability to lay eggs is not only an indicator of the quality of the queen but also an indicator reflecting the quality of the hive. To evaluate the effect of factors on the number of eggs laid by the queen Apis cerena, a total of 150 hives were selected from 458 hives in 3 provinces of Thai Nguyen, Bac Giang, and Bac Can, 50 hives per province. Research results show that the number of eggs laid by the queen bee Apis cerena in Northeast Vietnam is influenced by factors of laying month in the year, type, age, and body weight (BW) of the queen bee. The highest number of eggs laid corresponds to the following conditions: laying in July - August every year, type of queen is natural, queen's age is from 7 to 12 months old, and the queen has a BW greater than 190 mg.

Keywords: egg-laying, honey bee, queen bee, reproduction

Introduction

Vietnam is one of the countries with a developed beekeeping industry. According to the Ministry of Agriculture and Rural Development (MADR), by 2020, there are 1.28 million honey beehives in the whole country, producing more than 50,000 tons of honey, of which over 90% is for export, Vietnam became the 6th in the world and the 2nd country in Asia in terms of honey export. Honey beekeeping has become a profession to help farmers in rural and mountainous areas improve their family economy, increase their income and contribute to protecting the ecological environment. In Vietnam, two species of bees are commonly raised, namely, Apis meliffera imported from Italy and the domestic bee Apis cerena. Species Apis cerena, although has a lower honey production than Apis meliffera, is still raised because this species is easy to keep, does not require high technology, does not require a large area of honey plants. In addition, Apis cerena species is also favored by rural people because of low financial investment, farmers can take advantage of local materials to make bee hives, so Apis cerena honey bees are considered "bees of the poor farmer". This species has completely adapted to tropical climate conditions, with very good resistance to high temperatures, so it is suitable for tropical countries. Currently, Vietnam has more than 30,000 beekeeping farmers, beekeeping from small-scale, spontaneous farming has gradually shifted to form of beekeeping with investment in large numbers, on the other hand, has formed beekeeping clubs and cooperatives (Department of Livestock Production – MARD). The Northeastern region of Vietnam has a very large forest area, including many honey trees, so beekeeping here has been around for a long time and is now. very developed, the number of beehives accounts for over 30% of the total in the country Like other bee species, the Apis cerena queen bee plays the most important role in the colony, which is a determinant of honey and pollen production of the hive (Philip et al 2015). The most important mission of the queen is to lay eggs to maintain the number of workers bee in the hive, so the ability to lay eggs is not only an indicator of the quality of the queen but also an indicator reflecting the quality of the hive (Anna Koetz 2013; Esmaeil Amiri et al 2017. Previous studies have shown that there are many factors that affect the queen 's ability to lay eggs, such as breed, species, quantity, and quality of feed provided by worker bees, season, weather, age, and bodyweight of the queen (Koeninger et al 2011). The purpose of this study is to determine the influence of some internal and external factors on the ability to lay eggs of queen Apis cerena in the Northeastern region of Vietnam.

Materials and methods

Three provinces including Thai Nguyen, Bac Can, and Bac Giang were selected to conduct the study. These three provinces, on the one hand, represent the ecological characteristics of the northeastern region of Vietnam, on the other hand, have a large number of Apis cerena beehives, meeting the technical requirements for selecting samples for testing.

These provinces have similar ecological and geo-climatic conditions, belonging to a humid subtropical climate with cold winter, little rain, hot and humid summer with a lot of rain. According to the General Department of Climate and Hydrology, Vietnam (2021) the average altitude above the sea level of three provinces is from 200 to 300 m. The average annual temperature is 24 - 26 ⁰C, the highest in May - June (31 - 33 ⁰C), the lowest in December - January (16 – 17 ⁰C). The average annual humidity 81 - 83%, the highest in March - April (85 - 87%), the lowest in November - December (76 - 78%). The average sunshine hours is 132 -135 hours/ month, the highest in July - August (189 - 192 hours/month), the lowest in March - April (45 - 47 hours/month). The average rainfall is 168 -170 mm/month, the highest in June - July (380 - 400 mm/month), and the lowest in December - January (25 - 30 mm/month).

Figure 1. Research location

Table 1. Flowering calendar in the experimental area

Experiment design

A total of 150 hives of Apis cerena bee species were selected from 458 hives (50 hives/province -Photo 1, 1a and 1b.

The selected bee hives ensure the uniformity of factors such as the number of bee frames (4 - 6 frames), the number of worker bees (cover all frames), the rate of honey, pollen reserve at least 30%. After being selected, the hives were brought back to the study place 6 months before the experiment to familiarize themselves with the new place, classify and design experimental factors such as creating 3 types of queen, queen groups with differences in age and BW. Beehives were continue raised for 16 months to monitor indicators of the relationship between the number of eggs laid and related factors such as months of the year, the type of the queen, the queen's age, and queen weight.

Photo 1. Experimental field inThai Nguyen	Photo 1a. Experimental field in Bac Can
Photo 1b. Experimental field in Bac Giang

Design of research factors

Type of queen: Natural queen was selected from the available hives. Conduct production of artificial queen hats and put them into the beehives so that worker bees feed, take care become artificial queens. The unexpected queens are created by the method of suddenly separating the queen from the hives, worker bees will create a new queen from 3 - 4 days old worker bee larvae.

Queen age: Using artificial methods to create queens of 4 different ages: ≤ 6 months; 7 – 12; 13 – 18, and > 18 months of age.

Queen weight: Create artificial queen hats of different sizes, put in beehives to form 5 groups of queens of different weight, including ≤ 170 mg; 171 – 180; 181 – 190; 191 – 200, and > 200 mg/head

The method of Ruttner (1985) was applied to determine the number of eggs laid in 24 hours. This method is based on the principle that the life cycle of worker bees from laying eggs to sealed tightly with wax is 12 days (number of days pre-pupa and pupa), through which based on the number of worker cells is sealed tightly with wax, there it can calculate the number of eggs laid. Use steel wire tension bridge frame to form squares of 4.5 cm x 4.5 cm (each square corresponds to 100 worker cells). Measure both doubled-side of all frames in the hive. Estimate the number of worker cells is sealed tightly with wax in each frame to calculate the total of worker cells is sealed tightly with wax (Photo 3.). The number of an egg laid/24 hours = (N x 100)/12; N: Total of worker cell is sealed tightly with wax of hive; 100: Number of worker cell is sealed tightly with wax in the area measures 4.5 x 4.5cm; 12: Number of days pre-pupa and pupa.

Photo 2. Eggs laid by the queen bee	Photo 3. Determine the number of eggs laid

Data Analysis

The SAS 9.4 software and PROC MIXED of Statistical Analysis System (SAS Institute, Cary, NC, USA) were used to analyze the effect of factors on the number of eggs laid of queen bee per 24 hours. The Tukey test was used for determining the difference between the mean values between groups. The statistically significant difference was determined when P < 0.01.

Results and discussion

The effect of the laying months of the year on the number of queen's eggs laid

Honey beekeeping in general and the ability to lay eggs of queen bees, in particular, is highly dependent on external environmental conditions (Anna Koetz 2013). For successful beekeeping, depending on the external conditions, beekeepers design a bee calendar accordingly. The time and place are different, the bee calendar is also different. The bee calendar plays an important role for beekeepers because the weather, climate, type, area, and flowering time of honey plants will determine the effectiveness of honey beekeeping (Ruttner 1985). So the weather, climate, neighborhood, and even the type of bees will dictate what beekeepers should be doing (Crane 1995; Chinh 2012). This study is based on the bee calendar and the flowering schedule of honey plants in 3 provinces for 2 years (2019 - 2020) to monitor the evolution of the number of eggs laid in different months of the year (Figure 2.)

Figure 2. The number of eggs laid by the queen in months of the year in three places in Vietnam

In all 3 study places, the number of eggs laid tended to increase gradually over months and reached the highest in August (average 409.6 eggs/24 hours) and then gradually decreased until December (average 321.1 eggs/24 hours), thereby showing that months of the year have a significant effect on the egg-laying ability of the queen Apis cerena (P <0.01). This can be explained by 2 reasons, First: July and August is the autumn of the year, with favorable weather and climate suitable for the physiological characteristics of Apis cerena bees species, and The second: This is the flowering time of many crops with a large area in the study local (Table 1.), so it is the main time harvest of honey and pollen in the year (Table 2.). These external factors stimulated the queen bee to lay more eggs than at other times in the year.

Research results of Thai Pham Hong (2008) show that the Apis cerana cerena hive in Ha Giang province can reach 8 - 10 frames, when the tree area for honey is large, in warm weather, the queen can lay 1.032 eggs/24 hours, while the number of eggs laid by the queen Apis cerana indica in the North of Vietnam is 403.05 eggs/24 hours. The queen bee of Apis cerana strains in different geographical regions has different numbers of eggs laid. According to Chinh et al (2005), the queen bee of the Apis cerena cerana subspecies has the ability to lay 450 - 650 eggs /24 hours, higher than the Apis cerena indica subspecies 350 - 420 eggs/24 hours. According to Ruttner (1988) Apis cerana queen bee in Southern India has an average number of eggs laid from 300 - 500 eggs/24 hours, in Kashmir and North India 700 - 800 eggs/24 hours. Queen bee egg-laying ability usually changes according to the weather and climate in the months of the year. In the winter of temperate regions, the queen bee stops completely laying eggs. In the spring, when the weather warms up, they begin to lay eggs, and their ability to lay increases gradually and peaks in the summer (Koeninger et al 2011). The ability of the queen bee to lay eggs is also closely related to the area and bloom season of the plants that provide honey and pollen. When the food source is abundant, the queen bee's ability to lay eggs is higher than when it was scarce (Chinh, 2012). However, the fact that the queen bee's egg-laying ability often depends more on natural food sources than on the seasonal cycle (Crane 1995; Anna Koetz 2013).

The relation ship between the type of the queen and the number of eggs laid

Previous studies focused mainly on assessing the ability of artificial queens to lay eggs compared to natural queen bees and the harm of beehives when workers bee lay eggs, very few studies compare the number of eggs of the 3 queen types. To clarify that, this study has evaluated the comparative between the three types of queens with the number of eggs laid by them, results are shown in Figure 3.

Figure 3. Effect of queen type on number of eggs laid

A comparison of the three types of the queen shows that natural queen has the highest number of eggs laid from 378.6 to 382.3 eggs/24 hours, an average of 380.4 eggs/24 hours, followed by artificial queen from 357.2 to 365.7 eggs/24 hours, an average of 361.9 eggs/24 hours, and the lowest level is unexpected queen from 312.7 to 314.8 eggs /24 hours, an average of 313.6 eggs/24 hours. The difference between groups was statistically significant with P <0.01. The difference in the number of eggs laid between the natural queen and the artificial queen is not large (380.4 compared to 361.6 eggs/24 hours, but the number of eggs laid by the unexpected queen is significantly less than that of the natural and artificial queen. This is a very interesting result because if beekeepers do not change the new queen in time when the queen is lost or dies suddenly, worker bees will promote the formation of an unexpected queen created from worker bee larvae that are 3 days older. This will greatly affect the future of the beehive because worker bees are capable of laying an egg in an emergency, but they can only lay unfertilized eggs so as incapable to become a queen or worker (Nicholas et al 2013).

Relationship between the age of the queen bee and the number of eggs laid

The longevity of the queen bee depends on many factors, including breed and species. Queen Apis cerena has average longevity from 16 to 20 months (Crane, 1995), the longevity of queen Apis meliffera from 12 to 24 months (Remolina et al 2008). The mean longevity of the queen bees of Apis meliffera in the Northeast region of Brazil was 6.4 ± 2.9 months (Renata Valéria Regis de Sousa Gomes et al 2019). Previous studies have reported that the age of queen bees is closely related to their fertility, the older the queen bee, the less likely it is to lay eggs, so the fewer worker bees are produced. The queen bee has the best ability to lay eggs in the period of 6 - 9 months of age (Chinh 2012). The results of the study on the relationship between the age of the queen bee and the number of eggs laid are presented in Table 3.

The results of the study on the influence of the age of queen on the number of eggs laid at all 3 places follow the same rule that the number of eggs laid increases gradually from the young queen period to ≤ 6 months of age, peaks at 7 - 12 months of age and then gradually decreases. The average data of 3 study places shows that the number of eggs laid by the queen group ≤ 6 months of age is 329.4 eggs/24 hours increasing to 348.1 eggs/24 hours in the period of 7 - 12 months of age and the lowest 180.8 eggs/24 hours for the period greater than 18 months of age. The statistical difference between the age groups with P <0.01. The results of this study are consistent with that of previous studies. Repasky and Stephen (2016), Wei Hao et al (2019) demonstrated that the younger the queen bee, the higher the egg-laying ability and vice versa, the older the queen bee, the lower the ability to lay eggs.

The relationship between the bodyweight of the queen bee and the number of eggs laid

The BW of the queen bee depends on many factors such as breed, species, age of the eggs, quality of royal milk supplied by the worker bee, the size of the queen cell's hat (Crane, 1995; Chinh 2005). Research by Masry et al (2015) on 243 queen bees from three genotypes ofApis mellifera lamarckii, Apis mellifera carnica, and Apis mellifera ligustica (81 queens of each genotype) reported a queen bee's BW of 110 - 200 mg, of which the queen bee had BW greater than 170 mg, accounting for 79.23%. According to Abd Al-Fattah et al (2016) the queen bee's BW of species Apis cerena depends on the location of the queen cage, the queen in the cage placed above and on the edge of the hive has a weight from 172.5 to 174.9 mg higher than the queen placed below and inside bees 167.4 to 169.8 mg. Md. Abul Hasnat (2018) reported that due to inbreeding, queen bee Apis meliffera in Bangladesh had low BW (average 160.75 ± 3.65 mg) was found much lower than the earlier studies in different countries. Normally the greater the BW of a queen bee, the more oviduct number and the higher the ability to lay eggs, thereby showing that the number of eggs produced has a positive correlation with the queen bee's BW (Esmaeil Amiri et al 2017; Chinh 2012).

Results of monitoring 150 queen bees with weight from 160 to 210 mg divided into 5 groups (Table 4.) showed that the queen bee's BW correlated positively with the number of eggs laid, the number of eggs laid gradually increased from the group with the weight of ≤ 170 mg (288.2 eggs/24h) to a group with a weight of 181 to 190 mg (325.4 eggs/24 hours) and was highest in the group with a weight greater than 200 mg (354.3 eggs/24 hours). The difference between the groups is reliable with P <0.01. This rule is true in all 3 research locations (Figure 4).

Figure 4. Effect of bodyweight of the queen on number of eggs laid

Conclusion

• The number of eggs laid by the queen bee Apis cerena in Northeast Vietnam is influenced by factors of weather, climate, and flower calendar in months of the year, type, age, and bodyweight of the queen bee. The highest number of eggs laid corresponds to the following conditions: laying in July - August every year, type of queen is natural, the queen 7-12 months old, and the queen has a body weight greater than 190 mg.
  
  
• In order to raise honey bees with high efficiency, depending on the specific conditions of each locality, beekeepers need to refer to these conclusions to build a bee calendar and use good quality queens.

Conflict of interest

We acknowledge that there is no conflict of interest with any person or entity associated with the manuscript of this article.

Acknowledgment

The authors gratefully acknowledge funding of the National Agriculture Extention Center, Vietnam. We also would like to thanks to Agriculture Extention Center of Thai Nguyen, Bac Giang and Bac Can provinces to facilitate the experiment.

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