Megastigmidae can be found all around the world, but most genera can be found in Australia. Until recently, Megastigmidae was considered as a subfamily of Torymidae. However, Megastigmidae are now considered to be their own family because researchers have found that both Torymidae and Megastigmidae are not as closely related as formerly believed (Janšta et al., 2018).
There are 12 genera in total in the Megastigmidae. There is biology known for 10 of the 12 genera. Most species are phytophagous in seeds all around the world, including Rhus (Anacardiaceae), Schinus (Anacardiaceae), Pandanus (Pandanaceae), and also conifers. While, some phytophagous species are thought to be severe pests and/or parasitoids (Jansta et al., 2018). 2 genera are thought to be parasitoids; Megastigmus and Mangostigmus are attacking Eupelmus pistaciae and Cecidomyiidae respectively.
Megastigmidae can be most easily recognized by the enlarged stigma in their fore wing. Many of the species can be recognized by their orange-yellow body color. Although they may be patterned black, entirely black, or in metallic coloration. Their ovipositors are long and usually curving upwards and their hind coxae are relatively small. Their setae can be seen to be distributed symmetrically throughout the thorax.
Megastigmidae include 12 genera and there are a total of 228 species. The 12 genera include: Bootanelleus (13 species; worldwide), Bootania (12 species; worldwide), Bootanomyia (25 species; Australia and Palaearctic region), Bortesia (3 species; Australia), Ianistigmus (1 species; Australia), Macrodasyceras (2 species; worldwide), Malostigmus (1 species; worldwide), Mangostigmus (3 species; Australia and Asia), Megastigmus (156 species; worldwide), Neomegastigmus (9 species; worldwide), Paramegastigmus (1 species; Australia), Westralianus (2 species; Australia).
There are two genera of Schinus introduced in California, which are Schinus molle and Schinus terebinthifolius. Both trees produce clusters of red berries that when dried are what is considered as Rainbow Pepper seed. Their seeds are attacked by Megastigmus transvaalensis. The wasp is found worldwide wherever the Schinus is present. Researchers were able to sample these wasps genetically through the use of molecular markers by sequencing mitochondrial cytochrome oxidase I (COI). They were able to conclude that the species in the New World all had the same haplotype, whereas there was significant variation in Africa. The variation was vast enough to be able to define the country of origin of each wasp. The North American haplotype was identical to that of those from the Island of Réunion. A major export crop of Réunion was Rainbow Pepper seed. It turned out that they had mistakenly transported the wasp along with the Rainbow Pepper seed all over the world. Try it and go rear some berries in a ventilated jar and watch the wasps emerge. Females are mostly yellow and black with long ovipositors, whereas males are almost always black.
Pistachio is a common crop in California. In 1967, Megastigmus pistachiae (pistachio seed chalcid) was introduced from Iran into the city of Chico and as a result, up to 37% of the pistachio nuts were infested in California. It’s considered to have originated in Northern Africa and Mediterranean and Middle East countries (i.e., Morocco, Italy, Greece, Syria, Iran, etc.). In these countries around 50 to 80% of the seeds can be infested by Megastigmus pistachiae, thus turning the edible pistachios into commercial losses. It wasn’t discovered until 1985, through the use of x-rays and different examination methods, that the infestation of pistachio seeds had spread throughout Sacramento, San Joaquin Valley, and different areas within Northern California. Megastigmus pistachiae could be considered a threat; however, the damage can be controlled with winter sanitation by removing overwintering pistachio seed chalcid larvae on the trees or the ground.
Card image, Megastigmus transvaalensis by Gio Jansen