Taxonomic identification and biological traits ofPlatystethynium triclavatum(Donev & Huber, 2002), comb. n. (Hymenoptera, Mymaridae), a newly recorded egg parasitoid of the Italian endemic pestBarbitistes vicetinus(Orthoptera, Tettigoniidae)

Abstract

The little known fairyfly (Hymenoptera, Mymaridae), Platystethynium (Platystethynium) triclavatum (Donev & Huber, 2002), comb. n. from Pseudocleruchus Donev & Huber, 2002, is newly recorded as an egg parasitoid of Barbitistes vicetinus Galvagni & Fontana, 1993 (Orthoptera, Tettigoniidae). This bush-cricket is endemic to northeastern Italy (mainly Euganean Hills of Veneto Region), where it has recently become an economically significant agricultural and forest pest. Data on discovery, distribution, and some remarkable biological traits of this gregarious egg parasitoid are presented. Its identification and availability of many well-preserved fresh specimens have made possible to re-define Pseudocleruchus Donev & Huber, 2002 syn. n., with type and the only described species Pseudocleruchus triclavatus Donev & Huber, 2002, as a synonym of Platystethynium Ogloblin, 1946 and its nominate subgenus, P. (Platystethynium), and also to describe the brachypterous male of P. (Platystethynium) triclavatum. It is the first known male for the entire genus. Enlarged mandibles of the megacephalous males are used to chew holes in the hard chorion of the host egg, allowing fully winged females, whose mandibles are strongly reduced and do not cross over, to emerge after mating with the males inside it. Up to 136 individual parasitoids (about 77 on average) can hatch from a single egg of B. vicetinus, with their sex ratio being strongly female biased (80–97% females per egg).

Illustrated key to the genera and catalogue of Mymaridae (Hymenoptera) in the Afrotropical region

“…The number of genera in the Afrotropical region is presently only two more than for the Nearctic region, which had 39 genera (Huber et al 2020), though Caraphractus Walker and Eofoersteria have since been lowered to subgenera. But it is far more than the 24 genera for Europe (Samková et al 2020), including Paracleruchus Donev & Huber, which has since been placed in synonymy under Platystethynium (Ortis et al 2020). Taking the above generic synonymies into account, only two genera in Europe, Cosmocomoidea Howard and Stethynium Enock,…”

Increasing temperatures affect multiyear life cycle of the outbreak bush‐cricket Barbitistes vicetinus (Orthoptera, Tettigoniidae)

“…1). Eggs in final diapause can be easily recognized with stereoscope by their turgescence sensu Warne (1972) and for the typical green coloration of the embryo visible by increasing the transparency of the chorion with water (Ortis et al ., 2020). All eggs with no evident embryonic development in progress were assumed to be in initial diapause.…”

“…Compared to other tettigoniids, oviposition occurs very early in June (Cavaletto et al, 2018). In spite of the presence of recent studies about population genetics, ecology and life history traits of B. vicetinus (Magello et al, 2003;Cavaletto et al, 2015Cavaletto et al, , 2018Cavaletto et al, , 2019Ortis et al, 2020;Martinez et al, 2021), there is a lack of data about the factors that influence egg development and survival, hampering the development of effective control strategies. In this study, we want to test if summer temperature affects embryonic diapause and how winter temperatures affect egg survival.…”

Studying genetic population structure to shed light on the demographic explosion of the rare species Barbitistes vicetinus (Orthoptera, Tettigoniidae)

“…Failure to identify the correct origin of a pest may lead to the use of unsuitable species as biocontrol agents with negative effects on control programmes [20,77]. Maximizing efforts to locate native natural enemies (native parasitoids), as the egg parasitoid reported in Ortis et al [13] will be useful for control programmes. Finally, although B. vicetinus is currently in outbreak status, control programme strategies should consider the intrinsic vulnerability of an endemic species.…”

“…The recent discovery of the species (Galvagni & Fontana, 1993) and increase in these northeastern areas affected by outbreaks during the past two decades has sparked a debate about the possible exotic origin of B. vicetinus. Recently, as a consequence of the outbreaks, some authors have thoroughly studied important aspects of the biology and ecology of B. vicetinus [7,9,12,13] but no data regarding population genetics is so far available. Genetic studies based on the use of high-resolution DNA markers allow to examine the structure of insect populations, identify haplotypes, reconstruct current or past patterns of gene flow and provide information on the origin and expansion routes of the insect [14].…”