Host Interaction and Population Dynamics of Ceratitis capitata in Agroecological Systems: Level Infestation in Key Hosts in Irrigation Oasis of San Juan, Argentina

Claudia C Rodriguez¹*, Flavia Jofré Barud2,3*, M Pía Gómez2,3 and M Liza López2,3

¹Departamento de Biología, Facultad de Ciencias Exactas Físicas y Naturales, Universidad Nacional de San Juan, Argentina ²Estación Experimental Agropecuaria INTA, San Juan, Argentina ³Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina Keywords: C. capitata; Fruit Fly Population; Pest-Host Interaction

Abbreviations

IPM: Integrated Pest Management; SIT: Sterile Insect Technique.

Introduction

Fruit flies are considered one of the most important invasive pests due to the significant losses they cause in fruit and vegetable production and the major impact it has on exports [1].

Ceratitis capitata, also known as the Mediterranean fruit fly, belongs to the order Diptera and the family Tephritidae. It is a species native to West Africa, which, due to a combination of factors such as various human activities, favorable climatic conditions, and the presence of host species, has spread across most countries in the Americas and worldwide [2].

San Juan, Argentina, is characterized by extensive agricultural valleys in irrigation oases, with a total cultivated area of 104,705 hectares. The local economy relies heavily on agro-exporting, with vineyards, olive groves, vegetable, and fruit crops standing out. Fruit production ranks fifth nationally in cultivated area, but it faces challenges due to the presence of the Mediterranean fruit fly, which causes significant yield losses and leads to quarantine restrictions for export markets. Since 2003, the Fruit Fly Control and Eradication Program (ProCEM) has implemented Integrated Pest Management (IPM), emphasizing the Sterile Insect Technique (SIT) as a primary tool, alongside chemical, mechanical-cultural control, and phytosanitary barriers. This strategy achieved a 79% reduction in the pest population by 2014. However, control remains insufficient in small family plantations, challenging the complete eradication of the pest in the province.

The Mediterranean fruit fly can infest a wide range of fruit hosts in an agroecological environment, categorized as “key” and “non-key” hosts based on their interaction with various fruit species and population fluctuations of the pest. Major key hosts include citrus fruits (excluding lemon and lime) and stone fruits, such as peach, apricot, and plum. The diversity of host species provides a sequential fruiting pattern throughout the year, allowing the fruit fly population to persist even under less favorable climatic conditions.

The host selection by C. capitata depends on factors such as the fruit’s ripeness during the oviposition period and the abundance of other available hosts. This behavior is complex, involving a dynamic hierarchy where certain fruits are prioritized based on their availability and the presence of more attractive host species. Additionally, the preference may vary according to the physiological state of the individual, such as its egg load, and previous experience with alternative hosts when preferred ones are unavailable [3].

Nutritional levels in the fruits play a significant role in the larval development of C. capitata, as fruits with higher protein content, like fig, peach, and orange, support faster larval development and produce larger individuals. In contrast, fruits like apple are less favorable, resulting in slower development and higher larval mortality [4].

The aim of this study was to determine the infestation percentage and pupal abundance of Ceratitis capitata in host species during the summer season in an orchard with different key and non key hosts available, evaluating their impact on pest population dynamics and contributing to the optimization of management strategies in agroecological systems in an irrigation oasis.

Results and Discussion

During the first sampling, a total of 160 fruits were harvested from the following hosts: common peach (CP) = 60; flat peach (FP) = 10; nectarine (N) = 30; apricot (A) = 10; plum (P) = 50; fig (F) = 0. Of these, 81 fruits were infested (CP = 44; FP = 9; N = 21; A = 4; P = 3; F = 0).

For the second sampling, 160 fruits were collected from the following hosts: CP = 60; FP = 40; N = 30; A = 20; F = 10. A total of 132 fruits were infested (CP = 48; FP = 39; N = 29; A = 16).

In the third sampling, 70 fruits were harvested from the following hosts: P = 40 and F = 30, with 50 fruits being infested (P = 29 and F = 21).

For the fourth and final sampling, 50 fruits were harvested, 30 of which were plums (P = 30) and 20 were figs (F = 20). The total number of infested fruits was 13, all belonging to the fig host (F = 13).

Table 2 shows the infestation percentages for each host in each sampling. The total infestation percentage was above 50% in all sampling, with at least two to three hosts contributing to the total infestation, while for the last sampling, only fig contributed to the infestation which was less than 30%. The plum presented available fruits, but no infestation was recorded.

Host showed that they significantly contribute to the infestation, with the greatest contribution coming from the different peach varieties and the least from the plum (Table 3).

Table 3: Generalized Linear Model of Binomial Response for the Effect of Host on Infestation. E (Estimator), SE (Standard Error), p (Significance Value) In the first two samplings, various peach varieties were available; they were preferred by C. capitata ovipositions since then contributed considerably to the infestation, while plum and fig (first and second samplings, respectively) contributed the least. Host availability explained 33% of the variation in infestation for the first sampling and 51% for the second one. On the other hand, in the third sampling, the plum and fig contributed similarly to the infestation, while in the final sampling, the variation in infestation was explained by 55%, with only the fig contributing to the infestation.

Figure 1 shows the pupal abundance per kilogram of fruit for each host during the different samplings. In each sampling, only those fruits that were mature were harvested. In the first sampling, flat peach showed the highest abundance, with 125 pupae/kg, while the lowest abundance was for plum, with 2 pupae/kg. During the second sampling, the number of pupae increased considerably for all hosts, with the highest number again recorded for flat peach at 558 pupae/kg, and the lowest number for apricot, with 211 pupae/kg. In the third sampling, only two hosts showed available fruit, fig and plum. In the final sampling, only the abundance of fig was recorded, with 336 pupae/kg. Although plum had fruit available, no pupae were found (0 pupae/ kg). As shown in Figure 1, the highest number of pupae was recorded in fig, while the lowest was recorded in plum.

Apricot Common P Fig

A

600 A

Abudance

400 A

A

200 A

A

A A

A A A A

0 Flat Pea Nectarin Plum

600 A

A

Abudance

1 2 3 4 Sampling Figure 1: Abundance (pupae/kg) during the four sampling dates (December-January).

The hosts that showed the highest percentage of infestation also showed the highest pupal abundance. In this way, all the peach varieties were the most selected by C. capitata, even when mature fruits from plum and fig were available.

On the other hand, as the availability of peach and nectarine disappeared, the percentage of infestation and pupal abundance increased in plum and fig.

These results align with the Segura, et al. [9], which identified peach and all its varieties as a key host, being the one that contributed the most to the pupae population. On the other hand, fig, also a key host, contributed fewer pupae during the sampling period, although was important at the third sampling.

This study, on a very small scale, supports the findings and analysis by Segura, et al. [9]. Their study mentions that peach exhibited key host behavior, as it was responsible for increasing the population of C. capitata. Although this study did not aim to measure wild populations of C. capitata, it can be inferred that peach exhibits the same key host behavior, as it recorded higher infestation and pupal abundance compared to other hosts. The fig also contributed, thus inferring that it would be the second host most responsible for maintaining the fly population in the orchard.

Concluding Remarks

On the infestation results, which provide an estimate of the preference of female fruit flies for certain hosts, along with the abundance results, suggest that the different varieties of peach, and fig, were the key hosts of C. capitata during the sampled period and in relation to the other fruit species present in the study area. However, some limitations of this study suggest that this kind of research could provide further insight into the population dynamics by monitoring the C. capitata populations over a longer period, simultaneously with the infestation of all hosts, as well as conducting chemical studies of each host.