Pediobius cajanus sp. n. (Hymenoptera, Eulophidae), an important natural enemy of the Asian fly (Melanagromyza obtusa (Malloch)) (Diptera, Agromyzidae) in the Dominican Republic

Pediobius cajanus sp. n. is described based on material from the Dominican Republic, where it is widespread, and it is anticipated to have a much larger distribution in tropical America. It is compared to other species of Pediobius from the New World, and is also compared to P. vignae (Risbec), a similar species from Africa with similar biology. The new species is a gregarious endoparasitoid of the pupae of the Asian fly, Melanagromyza obtusa (Malloch), an agromyzid that causes major damage to pigeon pea, Cajanus cajan (L). Millspauh. In the Dominican Republic P. cajanus sp. n. is the most important parasitoid of this pest. Details on its biology are provided.


Introduction
Pediobius is a cosmopolitan genus with 217 described species (Noyes 2015), 25 of which have been recorded from the Neotropical region (Hansson 2002).Species of Pediobius develop as primary or secondary endoparasitoids in eggs, larvae or pupae of other insects, and the host range is extensive (Bouček 1988).The host species belong mainly to Coleoptera, Diptera, Hymenoptera and Lepidoptera.Some species have been reared from egg sacks of spiders, but then act as secondary parasitoids of ichneumonid larvae (Hymenoptera) feeding on the spider eggs.In the Neotropical region Pediobius species have been recorded from Coleoptera, Hymenoptera, and Lepidoptera but not from Diptera (Hansson 2002).Some Pediobius species have been used in biological control, most notable is perhaps P. foveolatus (Crawford), which has been used successfully to control populations of the Mexican bean beetle, Epilachna varivestis Mulsant, 1850 (Coleoptera: Coccinellidae) in North America (Barrows and Hooker 1981).Here we describe a new species of Pediobius that is the main enemy and a potential biocontrol agent of the Asian fly, Melanagromyza obtusa (Malloch, 1914) (Diptera: Agromyzidae).The Asian fly is an invasive pest in tropical America that causes extensive damage to pigeon pea, Cajanus cajan (L) Millspauh.Pigeon pea is an important source of food in tropical America, and as processed food is an important source of income from export.
The components of the tritrophic system including Pediobius cajanus sp.n.
The pigeon pea, "guandúl" in Spanish (Fig. 1), is a legume native to tropical India, and it has been grown in the Dominican Republic and other countries in tropical America since the late 15 th century, when the Spanish came to the Americas.It is a very important source of nutrition: Miquilena and Higuera Moros (2012) gave a protein value of 17.52%, and compared it to lentil and soy, with 18 and 35% protein values respectively.The plant is very tolerant to heat and drought and in dry areas without access to irrigation, it is a valuable alternative to less tolerant crops.In addition to its usefulness as food for humans the plant fixates nitrogen and thus contributes to the fertilization of the soil; the empty seedpods are an important food source for livestock, the remaining plant parts can be used as firewood, and it also has some medicinal properties (Cedano 2006).
In the Dominican Republic, the study area for this paper, the pigeon pea is grown in approximately 25,000 hectares, by nearly 3,000 farmers (statistics from the Ministry of Agriculture 2013).However, this figure is underestimated because much of the production is in small lots, along paths and road edges, and it is used as property borders, and these areas are not included in the statistics.Thus, the total area of cultivation is unknown, but the unrecorded areas are significant and contribute to the diet of some of the country's population.In the Dominican Republic its cultivation has also been developed as a source of income for farmers who process the bean as canned or freshly frozen beans for export.The export of pigeon pea has diversified and today it is being exported to many countries, including countries in Europe, but the largest importers are in the arc of the Antilles.
The pigeon pea is attacked by a complex of insect pests, mainly from the orders Lepidoptera, Diptera, Hemiptera and Coleoptera (Schmutterer 1990).One of the major pests is the Asian fly (Fig. 4) which causes great damage to the crops of pigeon pea, considerably reducing the production and export volumes.
Studies in India have shown that the damage caused by the Asian fly affects 25.5 to 36% of the crop (Sharma et al. 2011).These data are in accordance with those found in the Dominican Republic, where the Asian fly was detected in 2000 (Phytosanitary Alert system 2004, andEtienne et al. 2004).An investigation in the Dominican Republic by Guzman et al. (2010) indicated that the percentage of damage, even though the crops were treated with insecticides every 21 days, reached a level of 27%.However, the amount of damage varies considerably between different localities and the state of crop development in the Dominican Republic.In 2012 the level of damage was evaluated in 122 localities and in the town of Rancho Los Vargas, Puerto Plata, it reached 76% (Taveras and Guzman 2013).Yadaf and Yadaf (2011) conducted a review of the parasitoids of the Asian fly in India and listed 21 Hymenoptera parasitoids in 10 genera.They found that Euderus lividus (Ashmead, 1886) (Eulophidae) and Ormyrus orientalis Walker, 1871 (Ormyridae) were the main parasitoids, and these two species were also the most studied parasitoids for control of the fly.Species of Pediobius have, prior to this paper, not been recorded from the Asian fly.
In the Dominican Republic Ormyrus orientalis and an unidentified species of Pediobius have been reared from the Asian fly on pigeon pea.In a paper by Taveras and Guzman (2013) the presence of these beneficial parasitoids was recorded from 103 sites that included 25 of the 31 provinces in the country.The level of parasitism was 27.8%, with the Pediobius species responsible for 25.8%, and Ormyrus orientalis for 2%.This information clearly indicates that these parasitoids are distributed throughout the country, which is also supported by this investigation, and very probably have a far larger distribution outside the Dominican Republic.It also indicates that the Pediobius species is an important natural enemy of the Asian fly, and as such might be considered as a biocontrol agent against this invasive pest.
Because of the economic importance of the pigeon pea, and because the unidentified Pediobius species obviously is an eminent natural enemy of its main pest, the Asian fly, in the Dominican Republic, it is important to identify this Pediobius species.After a close examination of several specimens of Pediobius we found that it belongs to an undescribed species.To facilitate the identification of this new species it is described and diagnosed here, and given a scientific name so that future information can be linked to it.

Methods
The color photos were made with a Nikon SMZ 1000 stereomicroscope and a Nikon DS-5M camera.To eliminate reflections from the metallic and shiny body, a dome light manufactured as described by Kerr et al. (2008), was used as the light source for photography.Photos were taken at different focus levels and Helicon Focus Pro version 4.75 was used to merge them into a single image.The SEM photos were made from uncoated specimens on their original cardboard mounts.These were taken in low vacuum mode on a JEOL® JSM 5600LV scanning electron microscope.
Pods of pigeon pea were collected in several different parts of the Dominican Republic and were placed in plastic bags with holes for ventilation and prevention of condensation inside the bags.The samples were brought to the laboratory where the pods were opened and fly larvae, pupae and adults were counted.The larvae and pupae were placed in plastic containers (9 × 9 cm) with a piece of cloth at the opening to facilitate aeration.The emerging parasitoids and imagines of the Asian fly were killed and stored in vials with ethanol.
Measurements were taken using the Nikon stereomicroscope mentioned above, using a eyepiece micrometer at 80 times magnification.The female holotype and ten paratypes of each sex were measured.

Pediobius cajanus
In the most recent keys to the Neotropical species of Pediobius (see Hansson 2002) and in the key to Nearctic species (Peck 1985), P. cajanus runs to P. pyrgo (Walker, 1839).It differs from P. pyrgo in having median third of scutellum smooth (Fig. 17) (completely reticulate in P. pyrgo), posterior margin of dorsellum tridentate (Fig. 18) (rounded in P. pyrgo), and petiole in female 0.7 times as long as wide (1.0 times as long as wide in P. pyrgo).
Pediobius cajanus sp.n. also appears to be morphologically similar to P. vignae (Risbec, 1951) from Nigeria, as described in Kerrich (1973).The host of P. vignae, Melanagromyza vignalis Spencer, 1959 in seeds of Vigna unguiculata (L.) Walp.(Fabaceae), is also similar to the host of P. cajanus.When Kerrich (1973) revised the tropical and subtropical species of Pediobius he was unable to find the type material of P. vignae and designated a neotype for the species, to be deposited in BMNH.However, this neotype, or the series it was pulled from, cannot be located in BMNH (Natalie Dale-Skey, pers.comm.).Thus we rely totally on the redescription of P. vignae in Kerrich (1973) for the interpretation of this species.Pediobius cajanus sp.n. differs from P. vignae in having eyes bare (Figs 15,16) (setose in P. vignae), scutellum smooth in median third (Fig. 17) (reticulate throughout in P. vignae), female first gastral tergite 0.5 times as long as length of gaster (Figs 13,19) (well over half the length of gaster in P. vignae), female with first gastral tergite with very weak and superficial reticulation posteromedially (Figs 13,19) (this part with strong and very distinct reticulation in P. vignae).
Petiole 0.7 times as long as wide, with strong irregular sculpture (Fig. 19).Gaster with first tergite smooth (Fig. 19), posteromedially with very weak and superficial reticulation, meshes incomplete; first tergite covers 0.5 times the length of gaster in both sexes (Figs 13,14,19).Ratio length of the mesosoma (measured along the median mesosoma from the pronotal collar carina to posterior margin of the propodeum)/ length of gaster: holotype 0.88, paratypes 0.81-0.93.
Antenna as in Figs 7, 12. Ratios: height of eye in frontal view/malar space: 1.75-1.94;height of eye in frontal view/width of mouth opening: 1.30-1.60.
Petiole 1.1 times as long as wide.Gaster with first tergite completely smooth.Ratio length of the mesosoma (measured along the median mesosoma from the pronotal collar carina to posterior margin of the propodeum)/length of gaster: 1.09-1.58.
Etymology.Named after the host plant.Distribution.The Dominican Republic.The first author of this paper has reared this new species from its host from 90 sites (Fig. 5, Table 1).
Biology.Pediobius cajanus sp.n. is a gregarious endoparasitoid in pupae of Melanagromyza obtusa.The female wasps lay 3-15 eggs per fly pupa (mean = 7.6, n = 50).In laboratory conditions, with 25 °C, the development time from egg to pupa of the parasitoid was 21 days.Without food the female wasps lived for four days and males for two days.The sex ratio female to male is 5:1 (n = 50).
Biology of the Asian fly.The female fly lays eggs on immature pods, and the emerging larvae feed in the developing seeds, initially feeding externally but after the first molt feed inside the seed, which they eventually destroy (Fig. 3).A single seed may be enough for a larva to complete its development, but usually more than one seed is devoured.The larva goes through three stages prior to pupation.Before pupating in the seed pod the larva emerges from the seed and opens a window in the wall of the pod (Fig. 2).
Conclusions.Pediobius cajanus sp.n. is so far known only from the Dominican Republic, but its distribution throughout this country suggests a larger distribution.It is certainly found over the entire island of Hispaniola, of which the Dominican Republic constitutes the larger part.It is possibly also found on neighboring islands in the Caribbean, e.g.Cuba, and perhaps also in tropical parts of the mainland in the Americas.Some Pediobius species have a very large distribution (Kerrich 1973, Hansson 2002), thus indicating a strong dispersal ability.If this ability is present also in P. cajanus sp.n. future investigations must establish.
In the Dominican Republic P. cajanus sp.n. is an important natural enemy of the Asian fly, killing on average 25% of the fly larvae in investigated areas.The fly is found in many tropical countries, in Asia, its native area, as well as in other tropical parts of the World, and is a serious pest on economically valuable crops in these areas.The record of parasitism of P. cajanus sp.n. in the Dominican Republic makes it worthwhile to investigate the potential of this parasitoid as a biocontrol agent of the Asian fly.

Figures
Figures 1-4. 1 pigeon pea, Cajanus cajan (L).Millspauh 2 seed pods of pigeon pea with marks indicating windows created by larvae of the Asian fly, Melanagromyza obtusa (Malloch), prior to pupation, a window that facilitates the emergence of the adult fly from the pod 3 opened seed pods of pigeon pea with pupae of the Asian fly 4 imago of the Asian fly with pupa.

Figure 5 .
Figure 5. Map of the island of Hispaniola showing localities in the Dominican Republic where Pediobius cajanus sp.n. has been reared from Melanagromyza obtusa during this investigation.Specific names of localities and coordinates are provided in Table1.