Chapter 38: Smallest Adult
Jerry E. Gahlhoff, Jr.
Department of Entomology & Nematology
University of Florida, Gainesville, FL 32611-0620
April 17, 1998
Based on overall length, the smallest adult insect is a parasitic wasp, Dicopomorpha echmepterygis (Hymenoptera: Mymaridae). Males of this species are blind and wingless and measure only 139 µm in length. This newly described species recently replaced Megaphragma caribea (Hymenoptera: Trichogrammatidae), which measures 170 µm, as the smallest adult insect.
The intent of this paper is to identify the smallest adult insect. For holometabolous insects, an adult insect is defined as an individual that has emerged from the pupa and/or is capable of reproduction. Insects which undergo hemimetabolous or ametabolous development are considered adults when growth and/or molting ceases or when the insect becomes sexually mature.
Methods
A preliminary review of the secondary literature and advice from entomologists who are experts in Coleoptera and parasitic Hymenoptera yielded several candidates. In particular, the Entomo-L Listserv and the Internet proved to be very useful. AGRICOLA was used to investigate the primary literature of the candidates.
Results
Obviously, wasps that parasitize the eggs of other insects are quite small. Wasps of the egg-parasitic family Mymaridae not only represent some of the smallest known Hymenoptera, but are also among the smallest of all insects. A mymarid, Dicopomorpha echmepterygis, holds the record as smallest adult insect. The males of this minute wasp are wingless and measure as little as 139 µm in length. Females of this species are approximately 40% larger than the males.
Discussion
Mockford (1997) described Dicopomorpha echmepterygis, and its discovery displaced a trichogrammattid species, Megaphragma caribea, as smallest adult insect (Delvare 1993). At 170 µm in length, M. caribea is only about 20% longer than D. echmepterygis. Adult feather-winged beetles in the family Ptiliidae also rival the small size of both species of parasitic wasps described above. Some feather-winged beetles measure as small as 250 µm in length (Borror & White 1970).
Mockford (1997) provided a complete physical description as well as a brief biological observation of D. echmepterygis. When parasitized by D. echmepterygis, an egg of its psocid host, Echmepteryx hageni (Psocoptera: Lepidopsocidae), typically yields 1 to 3 males and a female of the parasite. The male of D. echmepterygis is blind and wingless but possesses long legs that it uses to attach itself to a female wasp that is emerging from the egg of its host. The diminutive males of D. echmepterygis require less nourishment to develop and are relegated to perform their primary responsibility, mating. On the other hand, vigorous females of this species are winged and possess compound eyes suited to aid in dispersal (Mockford 1997). Mockford (1997) also suggests that the great degree of sexual dimorphism in this species may be attributed to the limited nutritional value provided by the egg of the psocid host.
Diminutive males such as those of D. echmepterygis may often be overlooked by researchers (Mockford 1997). Tiny male wasps that parasitize eggs in families such as Mymaridae and Trichogrammatidae may be present in species with females that are thought to reproduce parthenogenetically. Therefore, males smaller than those of D. echmepterygis may exist among parasitic wasps, especially those that parasitize eggs of other insects.
Acknowledgements
I thank John S. Noyes (Entomology Department, The Natural History Museum, London) and Greg Evans (Department of Entomology and Nematology, University of Florida) for helping to identify pertinent literature.
References Cited
- Borror, D.J. & R.E. White. 1970. Peterson field guides: Insects. Houghton Mifflin, New York.
- Delvare, G. 1993. Sur Les Megaphragma de Guadeloupe avec la description d'une espèce nouvelle (Hymenoptera, Trichogrammatidae). Rev. Fr. Entomol. 15:149-152.
- Mockford, E.L. 1997. A new species of Dicomorpha (Hymenoptera: Mymaridae) with diminutive, apterous males. Ann. Entomol. Soc. Am. 90:115-120.
© Copyright 1998 Jerry E. Gahlhoff, Jr. This chapter may be freely reproduced and distributed for noncommercial purposes. For more information on copyright, see Copyright & Permitted Uses.