Effect of temperature on the development and survival of immature stages of the peach fruit fly , Bactrocera zonata ( Saunders ) ( Diptera : Tephritidae )

The Peach fruit fly (PFF), Bactrocera zonata (Saunders) is known as a key pest of fruits in Egypt. The effect of temperature on the development and survival of the Peach fruit fly (PFF), Bactrocera zonata (Saunders) (Diptera: Tephritidae) from egg to adult was studied to understand the geographical pattern of occurrence of these fruit fly. Studding carried out in laboratory under four different constant temperatures: 15, 20, 25 and 30°C. Results showed that time required for development were decreased as the temperature increased from 15 to 30°C. Differences between the four tested temperatures in incubation periods were significant. Developmental time of the eggs significantly decreased over the range of 15 to 25°C but not between 25 and 30°C, Similarly, developmental time for the larva and pupa significantly decreased with increasing temperature from 15 to 30°C. The lower threshold of development (to) for the larval and pupae stages was 13 and 10.9°C respectively. The highest pupation rate of B. zonata was 87±.48 percentage at 25 ° C, which was considered the optimum and favorable temperature. The results will be good tool for predicting the fly’s population dynamics, which would help develop the fly management strategies.


INTRODUCTION
The Peach fruit fly (PFF), Bac tr oc er a zo n at a (Saunders) is known as a most serious pest of tropical and subtropical fruits, and considered as important fruit fly pest (Fletcher 1987).In 1924, B. zonata was first declared as present in Egypt based on detection in an imported consignment in Port Said, 1912 (Efflatoun, 1924).It originates in South and South-East Asia (Agarwal et a l ., 1999).
B. zonata is a highly polyphagous specie that attacks more than 50 host plants including guava, mango, peach, apricots, figs, date and citrus (White and Elson-Harris, 1992).Now, it is well established in most Egypt´s governorates even in the dry desert regions, Assiut (Darwish et al., 2012) and Sohag (Gaperallah et al., *E-mail: Mah.svu@gmail.com. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License 2013).Temperature is considering the main environmental factor that affect the survival and developmental rate through each immature stage of life history, also, hence the rate of survival from egg to adult emergence in other fruit flies such as Bactrocera tryoni (Meats 1984).Studying this parameter is particularly important for B. zo n a ta to obtain a useful forecasting and prediction of this insect population.Therefore, the aim of this study was focused on the following aspects: 1.
Studying some biological aspects of PFF different immature stages under constant temperatures (51, 20, 25 and 30 ± 1°C) as an aim to limit its required heat units to develop.

2.
Relationship between each constant temperature and rate of development, which give a quantitative expression for this relationship, using thermal accumulation.

MATERIALS AND METHODS
The experiments were conducted in incubators in the laboratory of zoology Department, Faculty of science, South Valley University, Egypt.Infested fallen fruits of guava used in this experiment were collected from the farm of the Faculty of Agriculture, South Valley University.These infested fruits where then transferred to laboratory and were kept under 25±1ºC.to get on a Full-grown larvae and pupae of B. zonata that needed in laboratory experiments.Pupae were collected daily from the sand and then transferred to Petri dishes until the emergence of adult flies.The Petri dishes were kept under average laboratory conditions 25±1º C, 50% RH.Adults of B. zonata were reared in a cage (60 x 40 x 40 cm) with wooden frames and covered from each side with metal screen (Figure 2).Flies in rearing cage fed on sugar and fortified protein hydrolysate at ratio of 3:1, respectively.In addition, water was supplied in a plastic bottle.A plastic ball that had many fine pores (as oviposition receptacles) (Figure 2) was placed inside the cage.These plastic balls filled with 3 cm of water to receive and prevent drying of the eggs.In addition, at the top of this plastic ball, small plastic vials containing cotton wicks saturated with guava juice was put to enhance egg laying within these false fruits.Larvae were reared on an artificial diet (Shehata et al., 2006) (Table 1).
These ingredients were carefully mixed in large plastic box.Then eggs were transferred and scattered on the surface of the diet, which placed in plastic trays of 25x15x10 cm that tightly covered with muslin clothes using rubber bands.After that, these trays placed in a cartoon cage with sand at the bottom to allow the jumping larvae to pupate (Figure 2).All pupae were separated by sieving from sand (Shehata et al., 2006).Mature larvae were removed from rearing cups and entered another plastic cups that contained a layer of 0.5 cm of sand on the bottom for pupation.B. zonata was reared for four successive generations before starting the experiments (Qureshi et al., 1974).

Effect of constant temperatures on the different stages of the Peach Fruit Fly
This study was carried out to evaluate the effect of different temperatures on the peach fruit fly development stages.The study was conducted with a laboratory culture reared on artificial diet.The time required for development for each stage was determined at the four following constant temperatures: 15, 20, 25, and 30°C (±1°C).The incubation experiments were conducted in the laboratory of Zoology Department, Faculty of Science-South Valley University.

Eggs treatment
100 eggs for each temperature dirge were divided to 4 replicates (4treatment ×4 replicats×25units) every 25 eggs were placed in clean Petri dishes.Diet guava slides was used for natural conditions and put in Petri dishes .The surface of the diet guava slides was covered with a layer of toilet tissue paper.25 eggs were counted under a binocular microscope.These were carefully transferred on the tissue paper.The Petri dishes were covered and placed in incubator) set to four constant temperatures (15, 20, 25, and 30°C [± 1°C])).After 24 h, each Petri dish examined for egg hatching by observing the eggs intervals under a stereo microscope.Incubation period, number of hatching eggs, unhatching eggs and developmental rate were recorded.

Larvae treatment
For each treatment 100 larvae were used, each treatment repeated four times every replicate content 25 larvae(4×4×25).Each 25 larvae were put in Petri dish, Petri dishes maintained at the different experimental temperatures (15 °C, 20 °C, 25 °C and 30 °C).When the larvae reached third instar, the Petri dishes were put inside a larger plastic container bottomed with a layer of sand for pupation, where larvae jumped (by curling into a 'U'-shape and then rapidly straightening) out of the diet from the Petri dishes onto sand for pupation.The plastic containers were checked daily from the fifth day for pupae; pupae were separated from the sawdust by sifting.The mortality, duration, and developmental rate were recorded.

Pupae treatment
100 pupae/temperature degree (4 T×4 R×25 Pupa), pupae kept in four cups provided with sand.25 pupae /cup and cover with plastic net and maintained the same four constant temperatures until emergence.All developmental tests were replicated five times for each constant temperature.The mortality, emergency flies, duration, and developmental rate were recorded.

Data analysis
Data were analyzed by the analysis of variance (ANOVA) and Duncan's multiple range.Day-degrees "DD's" were calculated using linear regression method.Development rate (100/developmental time) was plotted against temperature.The lower development threshold to (the temperature at which the development rate is

Hatchability and incubation period
As shown in Table 2, there are reverse relationship between the effect of temperature and incubation period, the embryonic development (incubation period) of B.zonata eggs significantly decreased over the range of 15 to 25°C but not between 25 and 30°C (F = 55.462,df = 3, 12, P < 0.05).However, the developmental times for egg stage varied from 1 to 11 days.Differences between the incubation periods at the three constant temperatures were highly significant.The shortest mean incubation period (2.00±.408Days) was recorded at 30°C whereas the longest one (9.50±.645days)took place at 15°C.
The mean hatching percentage of eggs varied from a minimum of 20.25±0.85 % (at 15°C) to a maximum of 83.00±2.20%(at 25°C).It is worth noticing that the percentages of hatching increased with the increase in the number of deposited eggs (Table 2).On the other hand, the lower threshold of egg development was 12°C as shown in Table 2, the thermal units required for the development of this stage were 28.5, 46, 39 and 36 day-degrees at 15, 20, 25 and 30 °C respectively.The fourth observed values of egg's rate of development at the constant temperature range (15-30 °C), gave a remarkable good fit to the calculated temperature-velocity line having the formula Y = 2.69x -32.65 (Figure 1).A linear regression model established for Egg stage, a strong and positive relationship observed between temperature and development rate (R 2 ) = 0.9704.A lower developmental threshold for the egg was 12°C . For the hatchability, results showed that the highest percentage of hatchability (83.00±2.20%)was recorded at 25 °C.Statistically, significant differences-( R² = 0.9704)were recorded at 15 °C and values of 20, 25and 30 °C, whereas there are no significant differences between the values at 25 and 30 °C.

Larval stages
The average larval durations of B. zonata varied from 27.25±.629days at 15 °C to 4.50±.289days at 30 °C (Table 3).Significant differences (F = 492, df = 3, 51, P < 0.05) were observed between the mean larval durations at the different constant Temperatures, it gradually decreased with the increase in the tested temperatures.
The developmental rates of B. zonata larvae gradually increased with the increase in the tested temperatures, they were 3.67, 7.69, 12.50 and 22.22 at 15, 20, 25 and 30 °C, respectively, and it increased with the increase in the tested temperatures.from The four observed values of larval developmental rate at the constant temperature range (15 to 30°C), gave a remarkable good fit to the calculated temperature-velocity line having the formula Y= 1.2093x -15.688 (Figure 2).The calculated lower threshold of development (t o ) for the larval stage was 13°C as indicated in previous figure and the average of the thermal units required for the development of this stage was 79.5 DD's as determined by the thermal summation equation K= y (x-13).The highest pupation rate of B. zonata larvae was 87±.48percentage at 25 ° C, which was considered the optimum and favorable temperature.Although, mortalities of larvae decreased with the increase of temperature till 25 °C then its increase followed  Thermal units (DD) for larval stage based on a developmental threshold (to) 13 °C.Means within a column followed by the same letter are not significantly different at 5% probability.

Pupal stages
As shown in Table 4, the developmental trend for pupa was similar to that which was observed in the egg and larvae stages.The developmental time for B. zonata pupa decreased from 36± 1.08d at 15°C to 8± .408dat 30°C.The developmental time decreased with increase in temperature.
Developmental times measured at all other temperature tested were significant (Table 4).The developmental rates of B. zonata pupa gradually increased with an increase in the temperatures, it was 2.78, 6.25, 9.30 and 12.50 at 15, 20, 25 and 30°C, respectively.The lower threshold of development (t o ) for the pupal stage was 10, 9°C as shown in Figure 3, and the thermal units required for the development of pupa stage was 147.6, 145.6, 151.575 and 152.8 DD's at 15, 0, 25 and 30°C respectively, with an average of 149, 3938 DD's as estimated by the thermal summation equation K= y (x-10.9).From the previous, the results showed that the time required for development was decreased as the temperature increased from 15 to 30°C.Differences between the four tested temperatures in incubation periods were significant.Individuals reared at 30°C completed their life cycles in significantly shorter period; 25°C was the most preferable temperature for the pest development.The threshold temperatures were 12°C for egg, 13°C for larvae, 10.9°C for pupae.The average thermal requirements needed for completing the development were 37.38, 79.5, 37.38, day-  Thermal units (DD) for pupal stage based on a developmental threshold (to) 10.9 °C.Means within a column followed by the same letter are not significantly different at 5% probability.

DISCUSSION
Temperature is one of the most important factors affecting the developmental rate through the various life stages of fruit fly (Fletcher, 1987).Linear approximation is one of the commonly used models for describing the relationship between temperature and developmental rate of insects (Wagner et al., 1984).Data obtained indicated that the immature stages of B. zonata developed successfully within a temperature range between 15 and 30°C.Where, temperature thresholds of eggs, larvae and pupae were 12, 13 and 10.9°C, respectively.Meanwhile, the thermal units for eggs, larvae and pupae ranged between 36 and 48.5, 54.5 and 76.5, and 147.6 and 152.8 degree days, respectively.These findings are in general agreement with those obtained by many authors such as Duyck et al (2004) and Afia (2007) who had reported nearly similar results for incubation period.On the other hand, Mohamed (2000) who recorded 3.0 to 4.66 days obtained different results, and Younes and Akel ( 2010) who recorded 2 to 4.5 days also agree with many authors, who showed that the hatching period decreased with increase in temperature from (15°C to 30°C) (Vargas et al., 1997;Brévault and Quilici 2000;Duyck and Quilici 2002;Rwomushana et al., 2008, Vayssières et al., 2008;Younes et al., 2010;Hosni et al., 2011;Danjuma et al., 2014;Gomina, 2014).These results are similar to the findings of Qureshi et al. (1993), Mohamed (2000) and Afia (2007) who reported that the larval stage lasted 5.8 to 12.2, 6.13 to 13.06 and 5.35 to 14.8 days, respectively but these result different with Vargas et al. (1996) found a lower temperature threshold of 5.2°C and a thermal constant of 139 DD for the larval stages of C. capitata, whereas the pupal stage elapsed 7. 9-18, 7.44-16.1 and 7.47-18.68days, respectively.Also similar with Younes (2010), Solomon Danjuma (2014) they found similar result.

Conclusion
The Peach Fruit Fly (PDF) B. zo n a ta (Saunders) (Diptera: Tephritidae) was reared on artificial diet to study the effect of three constant temperatures (20, 25, and 30°C) on certain biological aspects.The incubation period, larval duration and pupal duration were estimated.The time required for development was decreased as the temperature increased from 15 to 30°C.Differences between the 4 tested temperatures in incubation periods and adult longevity were significant.Low mortality of larvae and pupae occurred at 30°C.Larvae reared at 30°C pupated in significantly shorter time than those developed under other temperatures.Pupation periods differed significantly at all temperatures.
Individuals reared at 30°C completed their life cycles in significantly shorter period.25°C was the most preferable temperature for the pest.The threshold temperatures were 12°C for egg, 13°C for larvae, 10.9°C for pupae.The average thermal requirements needed for completing the development were 37.38, 79.5, 149.39 and 232.37, 487.92 day-degrees for egg, larvae and pupae, respectively.

Figure 1 .
Figure 1.Linear regression of the relationship between the developmental rate of B. zonata eggs and different constant temperatures.

Figure 2 .Figure 3 .
Figure 2. Linear regression of the relationship between the developmental rate of B. zonata larvae and different constant temperatures , larvae, and pupae respectively.

Table 2 .
Incubation periods, hatching percentages, developmental rate and thermal units for B.zonata at different constant temperatures.
zero) was then determined by the regression line back to the x-axis.The day-degrees required for development of each stage were calculated byFletcher (1989)equation:K = y(x-t)Whereas: 1.K represents day-degrees 2. y represents stage duration (in days) 3. x represents temperature (°Q during development) 4. t represents the lower development threshold (°C).

Table 3 .
Developmental time, survival percentages, developmental rate and thermal units for B. zonata larval stage at different constant temperatures.

Table 4 .
Developmental time, survival percentages, developmental rate and thermal units for B. zonata pupal stage at different constant temperatures.