Gynaikothrips (Thysanoptera: Phlaeothripidae) comprises approximately 40 species of dark brown to black thrips that originate in Southeast Asia and that induce galls on developing leaf tissues of Ficus species (Rosales: Moraceae) (Dang et al. 2014). These galls cause aesthetic impacts to ornamental Ficus, although they are otherwise not harmful, and provide habitat for other arthropods (inquilines), including natural enemies of Gynaikothrips (Mound & Morris 2005; Tree & Walter 2009). In recent years, Gynaikothrips species have colonized Asia, Africa, and Central America, probably through international trade in Ficus plants. For example, the weeping fig thrips G. uzeli Zimmerman was discovered in the United States in Florida in 2003 and spread rapidly throughout the southeastern states via shipments of ornamental weeping fig (F. benjamina L.) originating from nurseries in southern Florida (Held et al. 2005). This pest has since been reported from at least 10 states in the contiguous United States, as well as Hawaii and Puerto Rico (Cabrera-Asencio et al. 2008; Held & Boyd 2008a; Dara & Hodel 2015), and from Brazil (Cavalleri et al. 2011), Australia (Tree 2012), India (Tyagi 2012), Panama (Goldarazena et al. 2012), and Syria (Ali 2014).

Weeping fig thrips is very similar to the earlier-described Cuban laurel thrips, G. ficorum Marchal, which has been known from the continental United States since at least 1887 (Denmark 1967). The only known difference between G. uzeli and G. ficorum is the length of the pronotal setae (Mound et al. 1995). However, these species are associated with different hosts. Whereas G. uzeli is known to infest F. benjamina, G. ficorum is primarily associated with Chinese Banyan, F. microcarpa L.f., and has established a pantropical distribution wherever this plant occurs (Mound et al. 1995; ThripsWiki 2015).

Although host plant is thought to be a good indicator to differentiate G. uzeli and G. ficorum, identification of Ficus species by entomologists may not be entirely reliable. A recent study reported that G. ficorum was able to produce leaf galls on both F. benjamina and F. microcarpa under greenhouse conditions, whereas G. uzeli was able to induce galls only on F. benjamina (Tree et al. 2015). However, the ability of G. uzeli to feed upon or reproduce on other Ficus species is unclear. Furthermore, preferences of G. uzeli among cultivars of F. benjamina have not been reported. We therefore conducted host specificity tests of G. uzeli among various Ficus species and on various cultivars of F. benjamina.

Materials and Methods

Results

Discussion

There is little information concerning host preference of G. uzeli on Ficus species. Our studies documented the apparent host specificity of G. uzeli for F. benjamina when exposed to young plants under greenhouse conditions in central Florida. As reported earlier (Tree et al. 2015), we found that G. uzeli was unable to reproduce on F. microcarpa; however, we extended this observation to several other Ficus species. Although it appeared that adult thrips can feed sporadically on other Ficus species, they did not induce galling or lay eggs. There is a report of G. uzeli infesting tomato in India, although no reproduction was observed (Chavan et al. 2014).

Fig 1.

Cage setup for Ficus benjamina variety choice test with Gynaikothrips uzeli in the greenhouse (year 2).

We also documented some differences among cultivars of F. benjamina. In general, all cultivars appeared to be susceptible; however, we noted differences in the 2nd study, with some varieties such as ‘Profit Compacta' and ‘Dwarf Nina' having fewer thrips than others. A possible explanation is that genetic variation in resistance to G. uzeli infestation exists among cultivated F. benjamina (Fang et al. 2007), particularly for those adapted to Florida environmental conditions, such as ‘Dwarf Nina', ‘Pandora', ‘Profit Compacta', and ‘Silver Cloud'. The use of more pest resistant cultivars in production may reduce economic loss in Ficus production. Differences also may have reflected host plant growth, because the generation of new leaves available for galling was not always consistent among species or cultivars. We noted lower overall density of thrips in the final study, which may have affected their dispersal and host selection behavior.

Our studies confirmed the inability of G. uzeli to initiate galls in fully expanded leaves; only leaves under differentiation could be induced to gall. We noted that adult thrips selected young expanding leaves, apparently causing rapid cell differentiation on the upper surface, and causing the leaf to fold along the mid-vein and purplish spots to develop inside the gall within 2 to 3 d. Females deposited white cylindrical eggs in batches of 100 or more, and a generation of thrips developed inside each gall over approximately 4 wk. We observed that the galls were relatively persistent and did not immediately fall off plants once the new generation of thrips had departed. Galls made by G. uzeli can be inhabited by inquilines, including other members of the Phlaeothripidae, as well as mealybugs, scales, whiteflies, and various natural enemies (Mound et al. 1995; Held et al. 2005).

Ficus benjamina and F. microcarpa are among the most widely cultivated ornamental figs (Fang et al. 2007). The ‘leaf-fold' galls made by G. uzeli in F. benjamina contrast the ‘leaf-roll' galls made by G. ficorum in F. microcarpa (Mound et al. 1995). However, the ability of G. ficorum to induce leaf galls on F. benjamina (Tree et al. 2015) suggests the possibility for inter-specific competition in areas where both thrips species are sympatric. The fact that G. ficorum is rarely reported from F. benjamina in the field suggests that G. uzeli might be a superior competitor on this host, although this remains to be confirmed experimentally.

Due to its cryptic habitat, control of G. uzeli with contact insecticides is not effective (Held & Boyd 2008b). In established landscapes, natural enemies can prevent large outbreaks of this pest. In southern Florida, the predatory pirate bug Montandoniola confusa Streito and Matocq (Hemiptera: Anthocoridae) is an effective predator (Arthurs et al. 2011). Desiccated (fed upon) eggs inside old leaf galls are the most common sign of M. confusa activity in the landscape (authors' personal observations). Other natural enemies of G. uzeli include the predatory thrips Liothrips takahashii Moulton (Tree et al. 2015) and Androthrips ramachandrai Karny (de Melo et al. 2013) (Thysanoptera: Phlaeo thripidae), as well as generalist predators including green lacewings and spiders, and at least 2 eulophid parasitoid species that specialize on phlaeothripine thrips (LaSalle 1994; Held et al. 2005). Preserving the activity of these natural enemies will help reduce the need for insecticides.

Table 1.

Species and cultivars of Ficus in which leaf galls initiated by Gynaikothrips uzeli were recovered (+) at 3 and 60 d post infestation under greenhouse conditions.

In conclusion, this study provides new information on the host selection of G. uzeli. It appears that this species can complete its life cycle only on F. benjamina, not on other Ficus species. Among the 27 F. benjamina cultivars tested, variation existed in response to G. uzeli infestation. The recent (2014) detection of this pest in Los Angeles County, California (Dara & Hodell 2015) confirms that this invasive species is still spreading and that further efforts to improve its detection and management are warranted.

Table 2.

Mean numbers of curled leaves observed at 3 points in time and numbers of adult and larval Gynaikothrips uzeli thrips at the end of the study for 23 Ficus benjamina cultivars (year 1).

Table 3.

Mean numbers of curled leaves observed at 3 points in time and numbers of Gynaikothrips uzeli life stages at the end of the study for 27 Ficus benjamina cultivars in greenhouse cages (year 2).