Co-infestation with Drosophila suzukii and Zaprionus indianus (Diptera: Drosophilidae): a threat for berry crops in Morelos, Mexico

Spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), that are native to Southeast Asia, have become an invasive pest in Europe and the USA since 2008, affecting various fruits such as cherries, blueberries, raspberries and blackberries (Stacconi 2022). D. suzukii can cause annual losses of up to US $511.3 million due to larval damage (De Ros et al. 2021). These species thrive in temperatures between 20 and 25 °C, with females capable of entering reproductive diapause for survival (Kirschbaum et al. 2020). Zaprionus indianus (Gupta) (Diptera: Drosophilidae) was originally from Africa but has been distributed widely in tropical countries around the world. Z. indianus was generally considered a secondary pest, as it typically did not attack unripe and undamaged fruits (van der Linde et al. 2006). However, Z. indianus is now known to cause direct damage to undamaged oranges, peaches, and figs while they are still on the tree (Tidon et al. 2003). The coexistence of D. suzukii and Z. indianus negatively affects fruits, as Z. indianus takes advantage of the damage caused by D. suzukii for oviposition and larval development (de Paiva Mendonça et al. 2023).

Weather plays a key role in insect dispersal (Bebber et al. 2013). Climate change influences habitat selection and range expansion by enabling species to exploit higher latitudes and warmer conditions (Eickermann et al. 2023). Insects adapted to colder environments may benefit from rising temperatures through extended foraging periods and shorter developmental times (Kovac et al. 2023). For instance, Z. indianus thrives at an optimal temperature of 28 °C, requiring at least 13 °C for ovarian maturation. Cold temperatures do not reduce its fitness; females enter an ovarian lapse without losing fertility (Lavagnino et al. 2020). Likewise, D. suzukii adapts to diverse environmental conditions, including altitude, wind speed, precipitation, temperature, and human land use, facilitating its global spread (Feng et al. 2024). It prefers temperate, humid climates, with optimal development between 20 and 25 °C. Mated females undergo reproductive diapause in response to low temperatures (Cini et al. 2012). Both species exhibit significant phenotypic flexibility and genetic diversity, enhancing their adaptability to varying climates and host plants (Gibert et al. 2019; Little et al. 2020; Olazcuaga et al. 2020). This adaptability has contributed to their success as invasive species. In Mexico, their activity is limited to morning and afternoon, likely as a strategy to avoid extreme midday heat (Cruz-Esteban, personal observation).

Mexico is leading in berry production and exports in Latin America, generating revenues of US $241 million and providing 350,000 jobs (Huerta 2019). The main producing states of these berries are Jalisco, Michoacán, Guanajuato, and Baja California, with a total cultivated area of 44,000 ha and an annual production of 800,000 tonnes/yr (Garcia et al. 2022). Morelos state is eighth in Mexico in terms of blackberry production (Garcia et al. 2022). The presence of D. suzukii and Z. indianus on berry crops has not been reported before in Morelos. Therefore, the objective of the current study was to survey raspberry and blackberry crops in Morelos for coinfestations of these drosophilid pests.

To detect the presence of drosophilids in Hueyapan, Morelos, Mexico on one farm that cultivates multiple berry crops, in a raspberry crop site (18.8658611 °N, 98.7006667 °W, 2,221 m. a.s.l.) and a blackberry crop site (18.8655000 °N, 98.7006667 °W, 2,221 m. a.s.l.), 12 multi-hole transparent traps were built (Cruz-Esteban 2021; Cruz-Esteban et al. 2021; Figure 1A). A cylindrical plastic container (14 cm in height × 10.5 cm in diameter) with a flat lid (Plásticos Adheribles del Bajío, León, Mexico) was used. Around the container, approximately 50 holes, each with a diameter of 2.5 mm, were evenly distributed 2 cm below the lid to allow the entry of insects. Inside, a piece of yellow cardboard was placed as a visual stimulus (5 × 5 cm, R = 245, G = 213, B = 39). The bait was a homemade fermented product, prepared as follows: 60 g of raspberries (harvested), 60 g of blueberries (Paradise S.A.P.I de C.V., Jalisco, Mexico), and 40 g of sugar (Zucarmex S. A. de C. V., Sinaloa, Mexico) were added to 1 L of water (Cruz-Esteban et al. 2024). The mixture was left to ferment for 7 days at 25 ± 2 °C before use, and 250 mL of the fermented juice was used as an attractant and drowning solution. On the farm, six traps were randomly distributed within and between each berry crop site, with a distance of 20 m between. The traps were placed 1 m above the ground. The traps were monitored weekly (every 7 days) for 5 weeks, from 6 May to 3 June 2024. In each monitoring session, the flies from each trap were collected, placed in containers with alcohol, and transported to the Insect Chemical Ecology Laboratory at Centro de Desarrollo de Productos Bióticos (CEPROBI), Instituto Politécnico Nacional, located in the state of Morelos, Mexico for the identification and counting of the captured drosophilid flies. Additionally, 32 ripe blackberry fruits and 32 ripe raspberry fruits were randomly collected, one from each plant, and transported to the laboratory in a cooler at 4 °C (Figure 1B and C). The fruits were placed in groups of five and one group of two in transparent 1 L plastic containers (14 cm high × 10.5 cm in diameter) with flat lids perforated with a needle to allow ventilation (Plásticos Adheribles del Bajío, León, Mexico). The fruits were kept in the laboratory at 25 ± 2 °C and 60–70 % relative humidity (RH) until the emergence of the offspring of the flies that may have oviposited in these fruits. The identification of the drosophilid flies captured by traps and those that emerged from the fruits was carried out based on the reports by Miller et al. (2017). Male D. suzukii have a black spot on the distal part of their forewings and 5–6 completely black tergites, while females have a large, dark, serrated ovipositor (Figure 1D). Z. indianus is characterized by two longitudinal white stripes bordered by black lines on the mesonotum (Figure 1E).

Figure 1:

(A) Trap used in the monitoring of Drosophila in raspberry and blackberry in Morelos, Mexico in 2024. (B) Infested blackberry. (C) Infested raspberry. (D) Drosophila suzukii and (E) Zaprionus indianus.

Trapping data were analyzed using R software version 4.4.2 (R Core Team 2022). The number of Drosophila captured (captures/trap/week) was analyzed using a generalized linear mixed model with a negative binomial distribution, with crop and monitoring date as fixed variables, and replicate (trap) as a random effect (α = 0.05). Captures by sex were compared using the Chi-square test with Yates correction with the package DescTools (Signorell et al. 2016).

Most of the specimens captured were D. suzukii (62.4 %, 755 individuals), Z. indianus (2.4 %, 29 individuals), and Drosophila melanogaster (Meigen) (Diptera: Drosophilidae) (20.8 %, 252 individuals). The remaining specimens were: other Diptera (12.3 %), Coleoptera (1 %), Hymenoptera (0.6 %), arachnids (0.3 %), Thysanoptera (0.1 %), and Hemiptera (0.1 %). Statistical analyses showed a non-significant effect on D. suzukii captures between crops (F = 2.2, df = 1; P = 0.1420), monitoring dates (F = 0.98, df = 4; P = 0.919), or their interaction (F = 5.6, df = 4; P = 0.2308) (Table 1). Numerically, more D. suzukii were captured in raspberries (15.2 ± 1.7) than in blackberries (10.0 ± 1.6), with similar values across all monitoring dates. Both males and females were captured in similar proportions (G = 1.2, df = 1, P = 0.2752) (Table 1).

Similarly, Z. indianus captures showed no significant effect between crops (F = 0.28, df = 1; P = 0.5961), monitoring dates (F = 1.1, df = 4; P = 0.8939), or their interaction (F = 0.3124, df = 4; P = 0.9890), with similar captures across all crops and monitoring dates. Both males and females were captured in similar proportions (G = 1.0, df = 1, P = 0.3167) (Table 1).

Notably, 23 male and 25 female D. suzukii, along with three Z. indianus and 27 other drosophilids, emerged from the collected blackberries (32 fruits), while 19 male and 21 female D. suzukii, along with two Z. indianus and 13 other drosophilids, emerged from the raspberries (32 fruits).

The presence of D. suzukii and Z. indianus attacking various hosts has been reported in different regions or states of Mexico (SENASICA 2019; Supplementary 1). There are records of both species in guava crops in Veracruz (Lasa and Tadeo 2015), and in blueberries, blackberries, and raspberries in Michoacan (Cruz-Esteban 2021). The first report of Z. indianus in Mexico was in 2002 in Chiapas state (Castrezana 2007), and was confirmed by Cruz-Esteban et al. (2022). Both species also were captured in the mountains of Tehuacan, Puebla (Cruz-Esteban et al. 2022), in Argentina (Escobar et al. 2018), and Z. indianus has reported on the Island of Maui, Hawaii, USA (Willbrand et al. 2018), and North-East Algeria (Khaldi et al. 2021). There is a previous report of D. suzukii and Z. indianus on fig fruits in Morelos, Mexico (Bautista et al. 2017), which is somewhat unusual, as it is not known that D. suzukii has a strong preference for this fruit. In our study, adults of D. suzukii and Z. indianus were captured in fermented juice traps and emerged from blackberry and raspberry ripe fruits (Supplementary 1). The fact that both species were captured by the same trap is due to the fact that both are attracted to chemical volatiles produced by fermentation (Cruz-Esteban 2021; Cruz-Esteban et al. 2021; Cruz-Esteban et al. 2022). This is the first time that D. suzukii and Z. indianus have been captured using traps baited with home-made fermented products in commercial berry crops in the state of Morelos, México.

Castro-Sosa et al. (2017) identified Morelos as a suitable habitat for D. suzukii, noting that environmental conditions were favorable for its establishment and reproduction, based on modeling of environmental variables and non-cultivated host fruits. At that time, only guava, a non-cultivated host, was available in Morelos. However, the situation has changed with the introduction of cultivated fig, blackberry, and raspberry crops. In addition, environmental changes in various regions of this state in recent years have been marked by temperature fluctuations, including lower temperatures that have persisted for longer periods. Calabria et al. (2012) observed that D. suzukii prefers higher altitudes with cooler summers and high humidity, unlike the warmer climates in the U.S. and Europe. Feng et al. (2024) found that the species has adapted to various environmental conditions, which may contribute to its spread in Morelos, aided by the presence of host crops. In contrast, Z. indianus typically thrives in warm climates but has shown adaptability to colder conditions (da Mata et al. 2010), demonstrating environmental plasticity and the ability to persist in temperate regions. This suggests that the potential distribution of both species may be influenced by climate change. The presence of these invasive species in Hueyapan, Morelos, underscores the need to define their ecological niche and assess their interactions with other pests and natural enemies in berry crops. It is essential to prioritize research on their impact, distribution, and infestation of commercial and wild fruits in the region, as well as emphasize the need for monitoring and management strategies for both populations.