Parasitism rate
The parasitism rate of D. giffardii after exposure to Z. cucurbitae pupae was determined. The results showed that the highest parasitism rate (52.60 ± 2.84%) by D. giffardii was observed after 48 h exposure to Z. cucurbitae pupae, followed by 72 h exposure (37.73 ± 4.80%) (F = 8.67; df = 2, 8; P = 0.017) (Fig. 1). For B. dorsalis, the highest parasitism rate (42.73 ± 2.74%) by D. giffardii was observed after 48 h exposure to B. dorsalis pupae, followed by 72 h exposure (39.47 ± 1.39%) (F = 20.1; df = 2, 8; P = 0.002) (Fig. 1). In addition, the comparison between parasitism rate for different pupae groups and different exposure durations showed significant difference at 24 and 48 h (F = 4.75; df = 2, 8; P = 0.03) (Fig. 1). In the context of correlation, the results showed a positive correlation for parasitism rate of D. giffardii vs. exposure duration for Z. cucurbitae pupae (R2 = 0.7172) (Fig. 2a) and B. dorsalis pupae (R2 = 0.9181) (Fig. 2b).
Parasitoids can discriminate between host pupae. They provide a survival advantage to parasitoids population and the preference of D. giffardii that may be influenced by different hosts as they possess different nutritional qualities (Harvey 2000). The present study highlighted on the parasitism activity of D. giffardii on B. dorsalis and Z. cucurbitae. The parasitism potential of D. giffardii against B. dorsalis and Z. cucurbitae might be a virtuous source for controlling fruit flies (Van Lenteren et al. 2006). The results of the present study showed significant differences in parasitism rates at different exposure durations for both species of fruit flies. The maximum emergence rate of D. giffardii was observed on Z. cucurbitae than that on B. dorsalis pupae. Similar results were observed by Rasool et al. (2017), where Z. cucurbitae pupae showed a maximum parasitism rate of D. giffardii. The present study focused mainly on exposure duration and its effect on the parasitism activity of D. giffardii. The parasitoid showed the maximum parasitism rate of Z. cucurbitae and B. dorsalis pupae after 48 h of exposure. Kacar et al. (2017) described the parasitoids functional response in which the maximum number of parasitoids was observed after the hosts pupae were exposed for 48 h to parasitoids which support findings of the current study.
Adult emergence
Adult emergence data of D. giffardii from Z. cucurbitae pupae was determined at 5-, 10-, and 15-day intervals. The maximum adult emergence of D. giffardii (63.55 ± 4.02) was observed on 10-day intervals after exposure of 24 h. The minimum adult emergence (13.85 ± 4.20) was observed at 5-day intervals after exposure of 72 h (F = 2.78; df = 4, 26; P = 0.0473) (Fig. 3).
Additionally, adult emergence data of D. giffardii for B. dorsalis pupae was also determined at 5-, 10-, and 15-day intervals. The maximum emergence rate of D. giffardii (51.67 ± 2.33%) was recorded at the 10-day intervals after exposure of 24 h. Minimum emergence (11.66 ± 0.50%) was observed at 15-day intervals after exposure of 72 h (F = 4.61; df = 4, 26; P = 0.006) (Fig. 3).
In the context of correlation, the results showed no correlation for the daily emergence of D. giffardii vs. exposure duration for Z. cucurbitae pupae (R2 = 0.0085) (Fig. 4a) and B. dorsalis pupae (R2 = 0.004) (Fig. 4b).
The present study demonstrated the adult emergence of the parasitoids from infested hosts in relation to days. Interestingly, in the case of D. giffardii and B. dorsalis, a significant difference was observed for different exposure times; however, maximum emergence occurred at 10-day intervals for all exposure durations. Similarly, the results were observed for the D. giffardii and Z. cucurbitae, where a maximum emergence of flies and parasitoids occurred at 10-day intervals, although the present study showed that exposure duration had a significant effect on the adult emergence of parasitoids. However, Guillen et al. (2002) reported non-significant differences in parasitism rates of Coptera haywardi (Hymenoptera: Diapriidae) and Pachycrepoideus vindemiae Rondani (Hymenoptera: Pteromalidae) after exposure periods of 24, 36, 48, and 72 h.
Besides, the age of host, food source, and age of parasitoids are important factors that play a vital role in the development of parasitoids (Sitthichaiyakul and Amornsak 2017; Naveed et al. 2014). Keeping in view the importance of biological control and potential of D. giffardii, future studies will be conducted aiming on the assessment of parasitism and host preference of D. giffardii under choice and non-choice scenarios. Also, the present studies were conducted in the laboratory conditions and small arenas, which may not reflect field conditions. However, choose the scenario that could help us to identify some key factors, i.e., host selection and exposure time may aid in improving mass rearing protocols and comply with demands for rearing and maintenance within the context of research or commercialization.