Exploring the potential of Amblyseius largoensis (Acari: Phytoseiidae) as a biological control agent against Aceria litchii (Acari: Eriophyidae) on lychee plants

Lychee (Litchi chinensis Sonn., Sapindaceae) is an important fruit crop native to Asia and is cultivated in Florida and across tropical and subtropical regions worldwide (Carrillo et al. 2020; Menzel 2002). In 2018, the invasive lychee erinose mite, Aceria litchii (Keifer) (Acari: Eriophyidae) was first detected in Florida, United States (Carrillo et al. 2020). Aceria litchii feeds exclusively on lychee (Nishida and Holdaway 1955; Papademetriou and Dent 2002), infesting newly formed tissue and significantly compromising crop yield (Prasad and Singh 1981; Waite and Hwang 2002). A key biological trait of Aceria litchii is its ability to induce the formation of open galls known as ‘erinea’, which are hairy structures formed on leaves, stems, inflorescences, and flowers.

The management of Aceria litchii has been challenging, with chemical and cultural practices being most commonly used worldwide (Castro et al. 2018; Menzel and Waite 2005; Revynthi et al. 2022). Biological control using predatory mites has long been thought of as a sustainable alternative for managing Aceria litchii (Azevedo et al. 2016; Ferreira Picoli et al. 2010; Ferraz et al. 2022; Navia et al. 2013). Predatory mites from the genus Amblyseius (Phytoseiidae Berlese) are considered generalists, known to prey on small insects, such as thrips and whiteflies, and on a wide variety of mites, including eriophyoids (Duso and Camporese 1991; McMurtry et al. 2013, 2015). Several phytoseiid mites have been found associated with Aceria litchii (Ferreira Picoli et al. 2010; Ferraz et al. 2022, 2024; Waite and Gerson 1994). Phytoseius intermedius Evans & MacFarlane was reported from Brazil, where its predation on Aceria litchii was tested under laboratory conditions, showing promising results (Azevedo et al. 2016). Recently, Ferraz et al. (2024) evaluated releases of Amblyseius herbicolus (Chant) and P. intermedius against Aceria litchii, also in Brazil. Both predators failed to establish populations on the lychee plants, resulting in ineffective control of Aceria litchii. This study aimed to: (i) identify phytoseiid mites associated with Aceria litchii in Florida, (ii) establish colonies of the identified mites, (iii) conduct predation bioassays under laboratory conditions, and (iv) evaluate the ability of these predators to control Aceria litchii under greenhouse conditions.

Surveys were conducted on Pine Island and in Homestead, Florida (25.7161111 °N, 80.3175000 °W). Leaves with amber color erinea, the stage when Aceria litchii is most abundant (Ataide et al. 2024), were collected and examined under stereomicroscope (Nikon SMZ-1270, New York, USA) for the presence of phytoseiid mites. The collected specimens were mounted on microscopy slides, using Hoyer’s medium (Walter and Krantz 2009), and clarified at 50 °C for approximately 2 days. The slides were examined under a phase contrast microscope (Zeiss, Germany). Two phytoseiid species, Amblyseius largoensis (Muma) and Phytoseius woodburyi De Leon were identified using the available morphological keys (Chant and McMurtry 2007) and the original descriptions (Muma 1955; De Leon 1965). Both species are considered generalist predators of phytophagous mites of different groups and of small soft-bodied insects (McMurtry et al. 2013). These two predators differ in the habitats they occupy. Amblyseius largoensis is classified as a generalist predator living on glabrous leaves (Type III-b, according to the classification by McMurtry et al. 2013), while P. woodburyi has morphological adaptations for living on pubescent leaves (Type III-a). Surveys conducted in lychee groves indicated that Amblyseius largoensis was consistently found associated with Aceria litchii on Pine Island and in Homestead, Florida. Amblyseius largoensis is a common species in Florida, from where it was originally described (Muma 1955). By contrast, P. woodburyi appears to have a more restricted distribution and has only been found in Homestead, Florida (De Giosa et al. 2025).

Both predators could be attacking Aceria litchi. To evaluate that possibility, attempts to establish colonies of those species were made by offering Carpoglyphus lactis (L.) (Acari: Astigmata), Brevipalpus yothersi Baker (Acari: Tenuipalpidae), Tetranychus urticae Koch (Acari: Tetranychidae) and Aceria litchi as prey, in an incubator at 27 °C, 80 % relative humidity (RH) and 12:12 h (light: dark). While the colonies of Amblyseius largoensis were successfully established on C. lactis, B. yothersi and Aceria litchii, the colonies of P. woodburyi declined progressively and eventually collapsed. Hence, only Amblyseius largoensis was used in our laboratory and greenhouse experiments.

The predation rate and oviposition rate of Amblyseius largoensis females were determined through no-choice bioassays. We adapted the methodology described by Azevedo et al. (2016) by placing one lychee leaf disc with erinea (d = 0.5 cm) on a mixture made of 1 % agar (Fisher Scientific, Maryland, USA) and activated carbon powder (Belle Chemical, Montana, USA) in a Petri dish (d = 0.5 cm). We offered Amblyseius largoensis females three distinct prey (treatments): 40 adult Aceria litchii (N = 21), 60 eggs of T. urticae (N = 18) or 100 eggs of B. yothersi (N = 21) on small leaf discs. For each treatment, we recorded prey consumption at 24 and 48 h. We replenished the initial number of prey after 24 h to ensure an adequate food supply. Statistical analyses were performed using R program version 4.2.2 (R Core Team 2022). The variation in predation and oviposition among different prey types was assessed using generalized linear mixed-effects models (GLMMs) and the lme4 package (v1.1-29) under normal (predation) and negative binomial (oviposition) error distribution (Bates et al. 2015). Post-hoc tests were performed using estimated marginal means (EMMs) (v1.7.3) (Lenth 2022). The average predation rate of Amblyseius largoensis on Aceria litchii (26.1 ± 1.9 adults/day) was significantly higher than on T. urticae (17.9 ± 2.0 eggs/day, LMM: χ ² = 22.3; P = 0.013) and B. yothersi (11.6 ± 1.9 eggs/day, χ ² = 22.3; P < 0.001). Oviposition rate of Amblyseius largoensis was low and similar across the treatments (χ ² = 0; P = 1).

Finally, we evaluated the ability of Amblyseius largoensis to control Aceria litchii under greenhouse conditions. Twenty-four lychee seedlings, approximately 60 cm tall, were infested following the method described in Ataide et al. (2023). After 2 months, plants were placed in individual cages inside a greenhouse (20–28 °C, 50–70 % RH and 12:12 h) and split into two groups. Half of the plants (N = 12) each received 30 Amblyseius largoensis adult females, and the rest were left without predators serving as the control group (N = 12). The colony of Amblyseius largoensis was offered Aceria litchii for a minimum of three generations prior to testing. Predators were placed directly onto infested leaves early in the morning. The total number of leaflets with and without erinea on each plant was assessed weekly to evaluate whether the presence of Amblyseius largoensis would affect erinea formation. The variation in number of leaflets with and without erinea per plant was assessed using GLMMs with negative binomial error distribution and assuming compound symmetry (‘split-plot-in-time’) in repeated measures, including plant and day of evaluation as nested random effects (Crawley 2012).

Twenty-one days after the predator release, a few plants from each treatment were inspected for the presence of Aceria litchii and predators; while Aceria litchii was present, predators were not found. Thus, an additional release of 30 predatory mites per plant was made. After 2 weeks the procedure was repeated, and again, no predators were recovered from the plants. Although Amblyseius largoensis did not significantly prevent the formation of new erinea on the plants (GLMM: χ ² = 0.9; P = 0.34; Figure 1a), there was a slight increase in the total number of erinea over time in the control plants (GLMM: χ ² = 2.4; P = 0.12; Figure 1b), but the underlying cause remains unclear. Additionally, the low reproductive performance on Aceria litchii might have contributed to the predators failure to establish on the plants and long-term control of the pest.

Figure 1:

Formation of new erinea (a) and total number of erinea (b) on lychee plants infested with Aceria litchii with (blue) and without (orange) the presence of Amblyseius largoensis over time (days). Shaded areas represent the variability with the ± SE range (GLMM: P < 0.05).

In summary, although P. woodburyi was found associated with Aceria litchii in the field, attempts to establish a colony under laboratory conditions were unsuccessful. Our field sampling and predation assays demonstrated the reduced potential of Amblyseius largoensis to feed and reproduce on Ac eria litchi, which could have led to the inability of the predator to establish on the released plants and to control the pest. The environmental conditions within the greenhouse could have affected the survival and reproduction of Amblyseius largoensis, which requires high levels of relative humidity (>72 %) to complete development (Gómez-Moya et al. 2018). This factor is particularly important considering the prevailing conditions in areas where lychee is cultivated in Florida, under high humidity levels. In addition, the erinea may constitute a physical barrier for the predators, hindering their movement and limiting their ability to prey upon Aceria litchii. This latter aspect deserves further investigation to understand the interplay between erinea formation, predatory mite behavior, and their ability to prey on Aceria litchii inside the erinea. Future studies evaluating the timing and number of predators released may help to improve their establishment on the plants. The results, however, may also suggest that the presence of Amblyseius largoensis in association with Aceria litchi in Florida may just be casual, given the presence of food items preferred by the predator in the same habitat. Investigating these factors could provide insights into improving the use of predatory mites as a biological control agent against Aceria litchii.