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Parasitoids of Dipteran leafminers, Diglyphus spp. (Insecta: Hymenoptera: Eulophidae)

Jian Li and Dakshina R. Seal

Introduction

Diglyphus spp. wasps are promising biological control agents for agromyzid leafminers (Diptera: Agromyzidae). The species occurring in North America are Diglyphus isaea (Walker), D. begini (Ashmead), D. websteri (Crawford), D. intermedius (Girault), D. pulchripes (Crawford), and D. carlylei (Girault) (Lasalle and Parrela 1991; Stegmaier 1972).

Distribution

This genus of leafminer parasitoids occurs widely in Asia, Europe, North America, New Zealand, and Northern Africa (Minkenberg 1989).

Description

Adult

The adult parasitoid is a tiny wasp 1.5–2 mm long, depending on the species. The head, thorax and dorsal abdomen are generally metallic green in color, while the eyes are red. The scutellum has two pairs of setae, a submarginal vein with more than two dorsal setae, and the funicle is 2-segmented (Lasalle and Parrell 1991).

Figure 1. Adult Diglyphus sp. on a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 1.  Adult Diglyphus sp. on a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Figure 2. Adult Diglyphus sp. on a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 2.  Adult Diglyphus sp. on a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Egg

The adult female Diglyphus parasitoid stings the dipteran host larva to paralyze it. Then the female may lay one or more eggs on the late instar leafminer larva (Minkenberg 1986).

Larva

The parasitoid larva has three instar stages. The first instar larva is transparent, whereas second and third instars are yellowish. The parasitoid larva feeds externally on the leafminer larva, eventually killing the host. The parasitoid larva then pupates in the leaf mine before emerging as an adult. The development time is temperature dependent. Diglyphus isaea takes about 10 days at 25°C for complete development on both the American serpentine leafminer, Liriomyza trifolii; and the pea leafminer, L. huidobrensis (Bazzocchi et al. 2003).

Figure 3. Diglyphus sp. larvae, 1st, 2nd, and 3rd instar respectively left to right. The larvae were removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 3.  Diglyphus sp. larvae, 1st, 2nd, and 3rd instar respectively left to right. The larvae were removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Figure 4. Parasitoid Diglyphus sp. larva (top) feeding on a leafminer larva. The larva was removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 4.  Parasitoid Diglyphus sp. larva (top) feeding on a leafminer larva. The larva was removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Figure 5. Two parasitoid Diglyphus sp. larvae (one is feeding horizontally on top, the second is positioned vertically to the right side of the larger host larva) feeding on a leafminer larva. The larvae were removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 5.  Two parasitoid Diglyphus sp. larvae (one is feeding horizontally on top, the second is positioned vertically to the right side of the larger host larva) feeding on a leafminer larva. The larvae were removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Pupa

The third instar larva pupates in the leaf mine. The pupa is initially both transparent and light green, but eventually turns black.

Figure 6. Early stage of pupa of a Diglyphus sp. showing transparent and light green color, and red eyes (on right). The pupa was removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 6.  Early stage of pupa of a Diglyphus sp. showing transparent and light green color, and red eyes (on right). The pupa was removed from the mine of a bean leaf. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Figure 7. Late stage of pupae of Diglyphus spp. turn black in color. In this image the head is to the right. Larvae in this genus are external parasitoids of dipteran leafminers.
Figure 7.  Late stage of pupae of Diglyphus spp. turn black in color. In this image the head is to the right. Larvae in this genus are external parasitoids of dipteran leafminers.
Credit: Jian Li, UF/IFAS

Hosts

Diglyphus spp. are primary ectoparasitoids of dipteran leafminers in the family Agromyzidae. However, a Diglyphus sp. was also recorded parasitizing Lepidoptera (Lyonetiidae) larvae (Boucek and Askew 1968).

Economic Importance

Augmentative release of commercial Diglyphus spp. is used for controlling leafminers in greenhouses in North America and Europe. Bazzocchi et al. (2003) indicated that D. isaea parasitized at least 18 different agromyzid species. Diglyphis isaea is the most effective commercial biological control product for controlling the American serpentine leafminer, Liriomyza trifolii; the pea leafminer, L. huidobrensis; L. bryoniae; and the chrysanthemum leafminer, Phytomyza syngenesiae (Syngenta-bioline). Lasalle and Parrella (1991) indicated that D. begini also parasitizes L. trifolii, L. huidobrensis and L. bryoniae in North America. Kaspi and Parrella (2005) reported that the insecticide Abamectin has little impact on D. isaea adults or the larvae within the leaf mines of chrysanthemums.

Selected References

Boucek Z, Askew RR. 1968. Palearctic Eulophidae (excl. Tetrastichinac). (Hym. Chalcidoidea). Index of Entomophagous Insects. La François, Paris. 260 pp.

Bazzocchi GG, Lanzoni A, Burgio G, Fiacconi MR. 2003. "Effects of temperature and host on the pre-imaginal development of the parasitoid Diglyphus isaea (Hymenoptera: Eulophidae)." Biological Control 26: 74–82.

Kaspi R, Parrella MP. 2005. "Abamectin compatibility with the leafminer parasitoid Diglyphus isaea." Biological Control 35: 172–179.

Lasalle J, Parrella MP. 1991. "The chalcidoid parasites (Hymenoptera, Chalcidoidea) of economically important Liriomyza species (Diptera, Agromyzidae) in North America." Proceedings of the Entomological Society of Washington 93: 571–591.

Minkenberg OPJM. 1989. "Temperature effects on the life history of the Eulophid wasp Diglyphus isaea, an ectoparasitoid of leafminers (Liriomyza spp.), on tomatoes." Annals of Applied Biology 115: 381–397.

Minkenberg OPJM, Van Lenteren JC. 1986. "The leafminers Liriomyza bryoniae and L. trifolii (Diptera: Agromyzidae), their parasites and host plants: a review of Agriculture." University of Wageningen Papers 86: 1–50.

Stegmaier CE. 1972. "Parasitic Hymenoptera bred from the family Agromyzidae (Diptera) with special reference to south Florida." Florida Entomologist 55: 273–282.

Syngenta-bioline. Dig-line i: Leaf miner control. Syngenta Bioline Limited. http://www.syngenta-bioline.co.uk/controldocs/html/DiglyphusIsaea.htm (20 December 2010).

Footnotes

1. This document is EENY 484, one of a series of the Department of Entomology and Nematology, UF/IFAS Extension. Original publication date December 2010. Reviewed March 2020. Visit the EDIS website at https://edis.ifas.ufl.edu. This document is also available on the Featured Creatures website at http://entnemdept.ifas.ufl.edu/creatures/.
2. Jian Li; and Dakshina R. Seal, Department of Entomology and Nematology; UF/IFAS Tropical Research and Education Center, Homestead, FL 33031.