Effect of various depth on interspecific hybrid Bactrocera dorsalis ♀ and Bactrocera carambolae ♂ adult emergence
The depth of pupation significantly affected the adults of interspecific hybrid B. dorsalis and B. carambolae emergence (Fig. 1). The highest emergence of interspecific B. dorsalis and B. carambolae hybrids occurred in the control treatment (4 cm) and at depth of 10 cm where the percentages of occurrence were 91 ± 5.03% and 83 ± 3.83%, respectively (Fig. 1). This result indicates that the emergence rates of pupae from interspecific hybrids B. carambolae and B. dorsalis were higher than those of female parents. Amaral et al. (2021) found that the B. carambolae emergence rate was 89% at depths of around 0-4 cm. Most of the pupae from the B. dorsalis of male parents survived within the 4 cm depth.
Surprisingly, some interspecific hybrid pupae of B. dorsalis and B. carambolae were able to emerge at a depth of 60 cm and other pupae survived even though during the experiment they did not grow into imago or the imago became abnormal (Fig. 1, Table 1) and significantly difference with 4 cm and 10 cm depth (X2=26.47, df = 6, p= 0.0001). It was deeper compared with the appearance of peach fruit fly imago which was appear up to a depth of 40 cm (Darwish et al., 2014). The control treatment showed that not all the pupae appeared, because some died during the experiment.
Based on observation, some pupae were found dead in each treatment, but the percentages are low. Damaged or dead pupae showed several symptoms of a blackish brown color. Dead pupae in each treatment, in this case, did not show a significant difference. The pupae used in each treatment were uniform and in good condition. Unlike the case of dead pupae, there were variations in the number of imagoes that did not appear at every pupation depth. With every increase in pupation depth, the number of imagoes that did not appear also increased (Fig. 2).
The average rate of the emergence of hybrid imagoes began to decrease at a depth of 20 cm and continued to decrease until a depth of 60 cm. The decrease in the rate of imago appearance may be due to the imagoes’ difficulty to appear along with the increase in pupation depth. This relates to the energy required for the imagoes to reach the surface of the media. It can be seen in Table 1 that at a depth of 20 cm the rate of imago emergence can be reduced, as there is a significant difference when compared to the control group.
The appearance of imagoes at a depth of 20 cm, although different from the control group, still has a rate of appearance of over 50%, which is 59 ± 9.45%. Unlike the cases with depths of 30 and 40 cm, the average appearance of interspecific hybrid imagoes was only 30 ± 7.66 and 21 ± 7.57%, respectively. The rate of the emergence of hybrid imagoes at this depth was relatively low, as the rate of imagoes that were unable to surface and died was over 50%. This result is the same as that of B. cucurbitae that was unable to emerge at a depth of 46 cm. The imagoes’ difficulty to emerge to the surface of the media at depths of 50 and 60 cm was due to the insufficient energy possessed by the imagoes to reach the surface (Klungness, 2005).
Effect of pupation depth on imago of interspecific hybrid B. dorsalis and B. carambolae morphology
The morphology of a young imago that just emerged from the pupa is characterized as having a pale yellowish color, wings that are still wrinkled, an abdominal pattern that has not yet been formed, and a body that is longer, before it matures into a normal imago. The normal imago shows patterns on the wings and abdomen, which are distinguishing characteristics between fruit fly species (Fig. 3). Disruption of the pupa can cause some imagoes to be abnormal.
Interspecific hybrids of B. dorsalis and B. carambolae imagoes that were abnormal or defective were found at several pupation depths (Table 1). But abnormal imagoes were not significantly different among all treatment (X2=10.66, df = 6, p=0.09). Surface-appearing imagoes and defects were found many at depths of 30 cm to 60 cm. In general, pupa abnormality was found on the wings. The wings’ growth was imperfect, appearing to shrink or not develop. This is because, when the imagoes tried to reach the surface of the ground, it is suspected that the imagoes had developed before reaching the surface of the medium (Figure 4). Fruit flies take time to grow their wings to perfection. The time required for imagoes to become normal fruit fly imagoes is 25-35 minutes (Mir et al., 2014).
Table 1
Effect of pupation depth on imago of interspecific hybrid B. carambolae ♀ and B. dorsalis ♂ morphology.
| Depth (cm) |
4 | 10 | 20 | 30 | 40 | 50 | 60 |
Normal Imago (%) | 91.0±2.5a | 83.0±1.9a | 55.0±7.5ab | 24.0±2.8ab | 14.0±1.1ab | 5.0±1.0b | 0.0±0.0b |
Abnormal Imago (%) | 5.0±1.0 | 3.0±1.0 | 4.0±0.0 | 10.0±1.1 | 10.0±4.7 | 7.0±1.9 | 5.0±3.7 |
Note Values are shown as mean (standard error). Different letters on the right of the values indicate significant differences at the level of P<0.05 (Bonferroni) in Kruskal-Wallis analysis. |
It is difficult for the imagoes to come out perfectly, presumably because of the low pore space which limited the imagoes’ movement. The depth can also affect the development of the pupa into imago. The other factor is the weight of the soil that covers the pupae. The increases in the soil weight in each treatment cause the decreases in the rate of imago emergence. Soil weight can also be related to soil density, as soil with a finer size will settle to the bottom, which causes compaction. Finally, humidity can also be a factor in the disability of fruit fly imagoes that appear above the ground surface. Abnormal fruit flies are often found in wet soil conditions (Yee, 2013).
Emergence duration of the interspecific hybrid imago Bactrocera carambolae ♀ and Bactrocera dorsalis ♂
The interspecific mating hybrids of B. carambolae and B. dorsalis began to appear on the 10th day after formation, or the 8th day after treatment (Table 2). All treatment showed not significantly different (X2=10.66, df = 6, p=0.099).
Table 2
The number of interspecific hybrid imago B. carambolae ♀ and B. dorsalis ♂ appeared on different days.
Treatment (cm) | Development Time (Day) |
4 (Control) | 8.99 ± 0.10 |
10 | 8.90 ± 0.05 |
20 | 8.88 ± 0.14 |
30 | 9.13 ± 0.23 |
40 | 9.18 ± 0.33 |
50 | 10.17 ± 0.22 |
60 | 5.31 ± 3.07 |
Note Day after treatment |
The depth of pupation influences the duration of pupae development. The interspecific hybrid of B. carambolae and B. dorsalis took 10-12 days to develop and it was not different from other species that took 10-12 days to develop into imagoes, depending on the depth and other environmental factors (Naik et al., 2017). The highest average occurrence as shown in Figure 3 was on the 11th or 9th day after treatment, while the lowest occurrence was on the 12th or 10th day after treatment. Thus, the optimum time for pupa appearance in the experiment was on the 11th day after pupa formation. Fruit flies are diurnal or insects that are active during the day, and the imagoes generally appear most often in the morning between 06.00 and 12.00 (Shaheta et al., 2008).
Based on the results of the observations in accordance with the statement, the interspecific hybrid imagoes of B. carambolae and B. dorsalis were not found to emerge in the afternoon. Environmental conditions that are less than optimal can prolong the emergence of fruit fly imago. Larvae prefer to pupate on soil with larger soil particle sizes, making it easier for the new imagoes to emerge from the pupa (Alyokhin et al., 2001). Soil physical properties can affect the emergence of imagoes to the surface by increasing the porosity and decreasing the soil density so that imagoes emerge more easily. It can make it easier for newly emerging imagoes to reach the surface (Hou et al., 2006). In dense soil, it is difficult for imagoes to reach the surface due to the low total pore space of the soil. Therefore, the imagoes took longer to surface than the control.
This research indicate that it is suggested to bury rotten fruit in the soil at a depth of 50 cm as a preventive measure for the development of fruit flies. Besides, this finding may also be useful to develop the effectiveness of entomopathogenic fungi test related to the depth of the interspecific hybrid B. carambolae and B. dorsalis. Some soil entomopathogenic fungi such as Metharizium anisopliae isolate cause the high mortality of B. carambolae (Brito et al., 2019). Therefore, the results of this experiment indicates that the pupation depth on adult emergence can be developed so that pupation depth affects the performance of entomopathogenic fungi as the biological control of this fruit fly.