Description of a new species of cecidomyiid (Diptera: Cecidomyiidae) predator of mealybugs (Hemiptera: Pseudococcidae) on sugarcane

Diadiplosis saccharum sp. nov. (Diptera: Cecidomyiidae) is described based on male and female prey on nymphs of mealybug Saccharicoccus sacchari (Cockerell) (Hemiptera: Pseudococcidae) on Saccharum  spp. (Poaceae) in São Paulo State, Brazil. Herein, the genus is composed by 33 species. The key of the eight species of the Diadiplosis distributed in Brazil is updated. Key-Words. Biodiversity; Ecological association; Neotropical region; Predaceous insect; Taxonomy.


INTRODUCTION
Diadiplosis Felt (Diptera: Cecidomyiidae) is a cosmopolitan genus, better distributed in the tropical regions of the world, once thirteen of the 32 described species are distributed in Neotropical region (Gagné & Jaschhof, 2017). Larvae of these cecidomyiids are predators of several species of scale insects, especially mealybugs (Hemiptera: Pseudococcidae), and whiteflies (Hemiptera: Aleyrodidae) of which many are pests of crops of agricultural importance.
The genus Diadiplosis belongs to the supertribe Cecidomyiidi by possess 12 antennal flagellomeres, but this genus is unplaced to tribe. Other systematic studies need to be carried out to clarify the relationship among the genus of this supertribe. Diadiplosis is characterized by the eyes separated laterally or facets very sparse there; facets usually hexagonal above and below, circular and farther apart laterally; tarsal claws curved at the basal third; tarsal claws toothed or simple; presence of strap like adult abdominal sclerites; female tergite 10 with a pair of strong setae, with or without lesser ones; female cerci ovoid and without differentiated apical sensorial setae; gonocoxites may have ventro-apical lobes; gonostylus variously shaped, completely setulose, tooth pectinate; hypoproct entire to deeply bilobed (Gagné, 1994(Gagné, , 2010. The systematic and biology of the cecidomyiid predators on the World Coccomorpha was made by Harris (1968Harris ( , 1997, followed by taxonomic changes to Nearctic (Gagné, 1973) and Neotropical fauna (Gagné, 1994). Since then, little new information has become available, and four species have been described for the genus in the Neotropical region (Culik & Ventura, 2012, 2013a, 2013b. In this paper, a new species named Diadiplosis saccharum sp. nov. is described based on male and female specimens reared from nymphs of Saccharicoccus sacchari Cockerell) (Hemiptera: Pseudococcidae) in São Paulo State sampled on Saccharum spp. (Poales: Poaceae). An identification key to males of Diadiplosis distributed in Brazil is updated.

MATERIAL AND METHODS
Sampling of the natural enemies, among them the new species of Diadiplosis, collected from sugarcane stem (Saccharum spp.) prey on mealybugs (Saccharicoccus sacchari) between August 2016 and August 2017. Infested nodes were inspected visually mainly in looking for immature predators in Jaboticabal (21°18.00′34.70″S, 48°19.39′25.92″W, 605 m a.s.l.) and São Carlos (22°04′33.87″S, 47°48′37.59″W, 11.v.2017, 856 m a.s.l.), both in State of São Paulo, Brazil. From 10 to 20 individuals of S. sacchari per sample were transferred to plastic tubes for rearing its natural enemies in BOD for 28 days. The adults of cecidomyiids were obtained in this process. They were preserved in 80% ethanol and later were mounted on permanent slides using the methodology outlined by Gagné (1994) and deposited in Museu de ZoologIa da Universidade de São Paulo. Topotypes of cf., Diadiplosis abacaxii (2 ♂ and 6 ♀), cf., D. bellingeri (1 ♂ and 1 ♀) and cf., D. jamboi (3 ♀) from Instituto Capixaba de Pesquisa, Assistência Técnica e Extensão Rural (INCAPER) were examined. The specimens of D. martinsensis and the male of D. jamboi were not available for examination, and in this way, their characteristics were compared with original description from literature. The larvae of cecidomyiids obtained among the sorted biological material was totally directed to obtain adults, by the small number of specimens. The areas where the larvae were found are more shaded and moist fields, which could be limiting for insects as small and with fragile bodies as the dipter in question. Furthermore, in sugarcane fields, even though scale insects are frequent, there is a constant application of insecticides to control various pest insects, which negatively end up interfering in beneficial insects as natural enemies.

Etymology:
The name saccharum is based on the name of the sugarcane genus (Saccharum), cultivar in which the specimens of the new species was found prey on nymphs of Saccharicoccus sacchari.
Biology: Adults of Diadiplosis saccharum sp. nov. were reared from leaf sheaths on stem nodes of sugarcane (Saccharum spp.) with larvae of cecidomyiids preying on nymphs of of Saccharicoccus sacchari (Fig. 3), which is a potential pest for Poaceae plant species, since sugarcane producers have reported frequent infestations in Brazil (Cruz et al., 2019).
Remarks: Despite the new species resemble the Neotropical Diadiplosis, D. bellingeri, D. martinsensis and D. aleyrodici (Felt, 1922), with the eyes undivided, palp 4-segmented, tarsal claws toothed at base or not (except in D. martinsensis), cercus and hypoproct bilobed, Diadiplosis saccharum sp. nov. differ from all known species based mainly on the combination of the characters of male terminalia (Fig. 2B): gonocoxite oblong with the dorso-lateral distal margin surpassing the insertion of gonostyli, gonostylus rectangular and stout. The new species and D. pseudococci have prolongation of the dorso-lateral distal margin of gonocoxite after the insertion of gonostyle, but in this species, the prolongation is larger and shorter than in D. pseudococci (Fig. 4E). A long and triangular aedeagus is shared with D. bellingeri and D. martinsensis, but in the first, the hypoproct is deeper bilobed (Fig. 4G) than in the new species, and in the latter the aedeagus is smaller than hypoproct and cercus (Fig. 4F). The male terminalia of D. saccharum resembles the general shape of the D. abacaxii terminalia by the sclerotization, but they differ greatly in aedeagus, bulbous in D. abacaxii and regular in D. saccharum. In addition, they also differ in the number of segments of palpi, three in D. abacaxii and four in D. saccharum. This is the first register of a cecidomyiid larvae preying on an insect pest on Saccharum spp. (Poaceae) -a major agricultural commodity in the tropics and used mainly for making sugar and ethanol for fuel. Saccharicoccus sacchari can be classified as an emergent pest in Brazil, since sugarcane producers have reported infestations frequently (Cruz et al., 2019). Further studies can indicate if the cecidomyiid can be used in biological control of S. sacchari in sugarcane plantation.