ICHNEUMONIDAE: : Diplazon Nees 1819
Diagnosis:Recognisable from the colouration of the hind tibia = bands of black-white-black-orange.
Characteristics of Diplazon include: 1. Body size <10mm; 2. Position of spiracle on T1 at, close to, or before centre; 3. Shape of aerolet in forewing pentagonal (but open); 4. Colour of face not all black; 5. Metasoma compressed dorsal-ventrally; 6. Size of ocelli small; 7. Length of antennae shorter than body; 8. Length of ovipositor barely visible; 9. Wings present; 10. Colour of wings hyaline (clear); 11. Sternaulus absent; 12. Shape of face in lateral view flat or only weakly bulging; 13. Sternite on T1 (viewed laterally) not extending past spiracle; 14. Shape of T1 (viewed laterally) evenly curved, slightly humped; 15. Number of teeth in mandibles 3; 16. Metasoma black but with the middle section orange; 17. Length of T1 vs T2 subequal in length; 18. Sculpture on mesoscutum finely pitted, many hairs; 19. Width of T1 (viewed dorsally) uniform width (slightly widening posteriorly); 20. Glymma on T1 present (groove or deep pit); 21. Sculpture on metasoma punctured (sometimes less densly or densly punctured); 22. Propodeum very short (not reaching beyond coxal insertion).
Similarity to Other TaxaRecognisable from the colouration of the hind tibia = bands of black-white-black-orange. Some other species may have >1 colours on the legs (e.g. Glabridorsum , some Diadegma ), but the pattern is different.
Although this can be hard to see, Diplazon has 3 teeth in the mandibles. The only other genus to have this in New Zealand is Woldstedtius . However, Diplazon has a distinct colouration on the hind tibia, whereas Woldstedtius have the same colour throughout.
Distribution in NZ
North Island: ND, AK, BP, GB, HB, RI, TK, TO, WI, WN. South Island: BR, NN, MB, NC, MC, SC, DN, MK, CO, OL, SI, SL. Offshore Islands: CH, KE.
Species in NZOne species: Diplazon laetatorius (Fabricius 1781).
Biology & hostsAlthough the majority of species in this genus occur in the Holarctic region, one species, Diplazon laetatorius is common throughout the world (Gauld 1984). Its global distribution is probably the result of human dispersal of agricultural products. This species can reproduce by thelytokous parthenogenesis, where females are produced from unfertilized eggs. This means it can rapidly establish populations. Males are vey rare.
Diplazon laetatorius is very common in agricultural areas. It is often regarded as a pest species because it attacks hoverflys (syrphids) who are preying on aphid pests of crops.
This is a very widespread and quite common species in New Zealand. Its host records in New Zealand include: Melangyna novaezelandiae , M. ortas , M. viridiceps , and Melanostoma fasciatum (all Diptera: Syrphidae) (Valentine & Walker 1991). However, it is recorded as a host of over fifty different species of Syrphidae (Diptera) worldwide (Yu et al. 2005).
Sources of informationGauld ID 1984. An Introduction to the Ichneumonidae of Australia. London, British Museum (Natural History). 413 p.
Valentine EW & Walker AK. 1991. Annotated Catalogue of New Zealand Hymenoptera. DSIR Plant Protection Report 4. General Printing Services, 84 pp.
Ward DF. 2013. Diplazontinae (Hymenoptera: Ichneumonidae) from New Zealand. New Zealand Entomologist 36 (1): In Press.
Yu DS, van Achterburg K, Horstmann K. 2005. World Ichneumonoidea 2004. Taxonomy, Biology, Morphology and Distribution. CD/DVD. Taxapad. Vancouver, Canada.
CitationWard DF & Schnitzler FR. 2013. Ichneumonidae of New Zealand. Genus Diplazon http://ichneumonidae.landcareresearch.co.nz
Accessed: 13 July 2020