Host preference of melon fruit fly Zeugodacus cucurbitae (Diptera: Tephritidae) on different cucurbitaceous crops

Introduction

Fruit flies (Diptera: Tephritidae) are among the most destructive insect pests of agricultural crops, causing considerable yield losses and economic damage worldwide (Shahzadi et al., 2019) [8] .The genus Bactrocera comprises several economically important species that pose serious threats to horticultural crops owing to their broad host ranges, high reproductive potential and in some species, considerable invasive capacity (Sarwar et al., 2013). [7] Among them, the melon fruit fly, Zeugodacus cucurbitae (Coquillett) (Diptera: Tephritidae) is an economically important and widely distributed pest of cucurbitaceous crops. The species was formerly referred to as Bactrocera cucurbitae (Coquillett), including in the original Ph.D. thesis from which the present study was derived. Following subsequent taxonomic revision, the species is currently recognized as Zeugodacus cucurbitae (Coquillett); therefore, the currently accepted name Z. cucurbitae is used throughout the present manuscript, except when referring to historical literature or the original thesis terminology. Zeugodacus cucurbitae infests a wide range of cucurbitaceous crops and causes substantial quantitative and qualitative losses. The larvae develop within fruits, resulting in tissue damage, premature fruit rotting, fruit deformation and reduced marketability. Under favourable environmental conditions and high pest pressure, yield losses may reach 90-100 percent (Sapkota, 2019) [7] . In addition to direct yield losses, fruit fly infestation can adversely affect the economic returns of vegetable growers through deterioration in fruit quality, rejection of infested produce and increased expenditure on pest management (Shahzadi et al., 2019) [8] . Host selection and preference play an important role in the population dynamics, infestation pattern and damage potential of fruit flies. Different cucurbitaceous crops and varieties may vary considerably in their attractiveness and suitability for oviposition and subsequent larval development. Understanding host preference under both field and laboratory conditions is therefore essential for identifying susceptible and relatively less-preferred hosts and for developing effective, targeted pest management strategies. Such information can also contribute to the optimization of monitoring programmes, improvement of biological control approaches and development of integrated and sustainable management practices.

In view of the economic importance of Z. cucurbitae and its association with a wide range of cucurbitaceous crops, the present study was undertaken to investigate the host preference of the melon fruit fly on different cucurbitaceous fruits under field and laboratory conditions and to study its life history and behavioural characteristics. The findings are expected to provide useful information for understanding host-pest interactions and for developing more effective and sustainable management strategies against Z. cucurbitae.

Materials and Methods

The present study was conducted at Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, (MS) India during Summer 2020-21 and 2021-22, to assess melon fruit fly host preferences on various cucurbitaceous hosts under field and laboratory conditions. The field experiments involved eight treatments with three replicates each, using a randomized block design (RBD) in plots measuring 3m x 2m. Observations on percentage of fruit damage were calculated by counting the total and infested fruits per plot. In laboratory conditions, the same eight cucurbitaceous hosts were tested using a completely randomized design (CRD). Mature, healthy vegetables were used with 100 g samples placed in plastic cages. For choice tests, 20 fruit fly adults were introduced to cages with 100 g samples of cucumber, bitter gourd, ridge gourd, pumpkin, watermelon, sponge gourd, muskmelon and bottle gourd. After 24 hours, the data on egg, larval, pupal and adult stages were recorded. In non-choice tests, 100 g samples of different vegetables were placed in separate cages with fruit fly adults for oviposition. Eggs were observed under a microscope to check hatch rates and development through egg, larval, pupal and adult stages was monitored.

Results and Discussion

Host preference of melon fruit fly on different hosts under field condition Summer 2021

The observations on mean percent fruit infestation are shown in Table 1. The mean infestation rates revealed significant differences among cucurbitaceous hosts. Sponge gourd was the least preferred host of melon fruit fly with lowest mean percent fruit infestation of 35.62 which was followed by ridge gourd, bottle gourd, muskmelon and cucumber (44.20%, 44.22%, 45.63% and 45.77%, respectively), which were statistically at par with each other. Watermelon (53.46%) and pumpkin (56.89%) had higher infestation rates, while bitter gourd was the most preferred host with the highest infestation of 62.12%.

Summer 2022

The mean percent fruit infestation data (Table 2) indicated that sponge gourd was the least preferred host of melon fruit fly (40.54%). It was statistically at par with bottle gourd (43.59%), ridge gourd (47.13%), muskmelon (49.00%), cucumber (50.91%) and watermelon (54.42%). However, pumpkin (56.89%) and bitter gourd were highly preferred host (62.12%).

Pooled

The pooled data from two seasons showed significant differences among treatments (Table 3 & Fig. 1). The overall results indicated that bitter gourd was the most preferred host, with the highest fruit infestation rate of 64.48%, followed by pumpkin (59.03%). Sponge gourd was the least preferred, with a minimal infestation rate of 38.08%. Other hosts like, bottle gourd, ridge gourd, muskmelon, cucumber and watermelon showed similar infestation rates ranging from 46.12% to 53.94% and all these treatments were statistically at par with each other. Earlier studies confirm similar findings on melon fruit fly host preferences. Singh et al., (2000) [9] , Mwatawala et al., (2010) [5] and Koswanudin et al., (2018) [1] identified bitter gourd as the most preferred and susceptible host. Kumar et al., (2006) reported bitter gourd with the highest infestation (77.03%) followed by ridge gourd (75.65%) and cucumber (73.83%). Gaine et al., (2013) found equal infestation levels in bitter gourd and ridge gourd.

Host preference of melon fruit fly on different hosts under laboratory condition Host preference of melon fruit fly on different cucurbitaceous hosts in choice test

Studies on laboratory choice tests with eight cucurbitaceous hosts (Table 4) revealed significant differences in melon fruit fly preferences. The data revealed that bitter gourd was the most preferred host with the highest averages for eggs (65 ± 1.14), larvae (58 ± 1.13), pupae (52 ± 0.92) and adults (52 ± 0.92). whereas, the lowest mean counts were observed in sponge gourd with 21 ± 0.79 larvae, 16 ± 0.65 pupae and 13 ± 0.58 adults. The cumulative results of choice test experiments clearly proved that bitter gourd was most preferred host of the melon fruit fly. The findings are in consistent with the results of Shahzadi et al., (2019) [8] who reported that in choice test, bitter gourd had greater fecundity, larval, pupal and adult rate as compared to other cucurbitaceous hosts i.e., 67. 59, 52 and 40, respectively. Manzar and Srivastava (2017) [3] and Sohrab and Hasan (2018) [10] were fairly close to this experiment.

Host preference of melon fruit fly on different cucurbitaceous hosts in non-choice test

Melon fruit flies reared on eight cucurbitaceous hosts revealed that bitter gourd was the most preferred host with the highest mean counts for eggs (58 ± 1.11), larvae (52 ± 1.24), pupae (46 ± 0.88) and adults (36 ± 0.92) (Table . 5). Other hosts showed lower counts: cucumber (52 ± 0.98 eggs, 48 ± 1.13 larvae, 44 ± 0.84 pupae, 36 ± 0.86 adults), pumpkin (44 ± 0.93 eggs, 41 ± 1.08 larvae, 38 ± 0.81 pupae, 36 ± 0.75 adults), watermelon (38 ± 0.88 eggs, 34 ± 0.98 larvae, 31 ± 0.78 pupae, 22 ± 0.83 adults), muskmelon (35 ± 0.85 eggs, 28 ± 0.95 larvae, 26 ± 0.75 pupae, 19 ± 0.75 adults), ridge gourd (29 ± 0.83 eggs, 25 ± 0.91 larvae, 22 ± 0.71 pupae, 15 ± 0.71 adults), bottle gourd (25 ± 0.81 eggs, 21 ± 0.90 larvae, 17 ± 0.68 pupae, 13 ± 0.67 adults), and sponge gourd was the least preferred and had the lowest counts (20 ± 0.79 eggs, 16 ± 0.88 larvae, 12 ± 0.61 pupae, 11 ± 0.65 adults). These host preference readings in nonchoice test are in conformity with the findings of Shahzadi et. al., (2019) [8] who recorded similar readings in various cucurbitaceous crops. More or less similar results were obtained by Mir et. al., (2014) [4] who revealed that in nonchoice experiment, bitter gourd was greater ranked as compared to cucumber, brinjal, pumpkin and muskmelon. The study confirms that bitter gourd is the most favored host for melon fruit fly (Zeugodacus cucurbitae), showing the highest infestation rates and developmental stages in both field and laboratory conditions.

Conclusion

The present study demonstrated a consistent pattern of host preference in Zeugodacus cucurbitae across field and laboratory conditions. Bitter gourd was the most preferred host, recording the highest fruit infestation and supporting greater development of eggs, larvae, pupae and adults, whereas sponge gourd was consistently the least preferred host. The agreement between field and laboratory observations strengthens the evidence for differential host suitability in Z. cucurbitae. These findings provide a useful basis for prioritizing highly susceptible cucurbit crops for monitoring and timely management, and may contribute to the development of more targeted and sustainable management strategies against this economically important pest.

data, Deshmukh K V and Ingale A S wrote the manuscript which was guided by Kadam D R.

Acknowledgement

AcknowledgementThe author thanks the Head, Department of Agricultural Entomology, VNMKV, Parbhani (MS) for providing research facilities throughout the experiment and their valuable guidance in research. The present study was a part of Ph.D. (Agri) dissertation submitted by Ingale A. S. to the Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani (MS) Financial Support No financial support was availed