Diglyphus isaea
Diglyphus spp. wasps are promising agents of biological control of leafminers (Diptera: Agromyzidae). The most common species are Diglyphus isaea (Walker), Diglyphus begini (Ashmead), Diglyphus websteri (Crawford), Diglyphus intermediateus (Girault), Diglyphus pulchripes (Crawford) and Diglyphus carlylei (Girault).
Distribution
This genus of leafminer parasitoids is widespread in Asia, Europe, North America, New Zealand and North Africa and is cosmopolitan.
Lifestyle
Diglyphus isaea stings miner larvae with its ovipositor while they are in the mesophyll of the leaf, making their tunnels (mines). The injection transfers the paralysing toxin to pests. The toxin acts immediately, and the larvae stop feeding. But Diglyphus doesn’t stop there. Then they lay 1-5 eggs next to the paralysed larvae — up to 50 eggs during their lifetime. Wasp larvae, emerging from eggs, eat miner larvae from outside to inside (ectoparasitism). After that, the larvae of the parasitoid wasp create columns of faeces around the remains of the pest. It is believed that in this way they protect the larvae they need from drying out the leaves during pupation.
The lifespan of these wasps is approximately 2 weeks in the immature stage, and then 3 weeks in the adult state. Conditions for optimal operation: 24-32 °C at a relative humidity of about 80%. But these are optimal conditions, and not at all a prerequisite for successful implementation. It should be noted that lower or higher temperatures and humidity fluctuations can affect the formation of the population and search activity.
Description
Imago: The adult is a tiny wasp with a length of 1.5 to 2 mm. The head, thorax and abdominal part of the dorsal shield are usually metallic green, and the eyes are red or brown. The shield has two pairs of bristles, a submarginal vein with more than two dorsal bristles and a two-membered flagellum.
Egg: An adult female of the parasitoid Diglyphus stings a miner larva to paralyse it. After that, it lays from 1 to 5 eggs next to the victim.
Larva: the larva of the parasitoid goes through 3 age stages. The larva of the first instar is transparent, the larva of the second and third instars acquires a yellowish tint. The larvae of the parasitoid feed on the larvae of miners from the outside, eventually killing the host. The parasitoid larva then pupates in a leaf mine before becoming an adult. The time of appearance depends on the temperature. The life cycle of Diglyphus isaea is about 10 days at 25 °C.
Pupa: The third instar larva pupates in a leaf mine. The pupa is initially transparent and light green, but eventually turns black.
The hosts are victims
Diglyphus isaea are primary ectoparasitoids of leafminers of the family Agromyzidae. However, they have also been recorded parasitizing the larvae of other Lepidoptera, such as Lyonetiidae.
Economic significance
The release of Diglyphus isaea is used to fight miners in greenhouses in Europe and North America. Diglyphus isaea parasitizes at least 18 different species of leafminers. Entomophage is the most effective commercial biological control product for the management of such types of miners as — Liriomyza trifolii, Liriomyza huidobrensis, Liriomyza bryoniae, Phytomyza syngenesiae.
Compatibility with insecticides
Kaspi and Parrella (2005) reported that the insecticide abamectin has little effect on adult Diglyphus isaea and their larvae in chrysanthemum leaf mines.
Advice
Yellow sticky traps can become a problem for the entomophage. When using them, more careful control is needed. If the number of parasitoids on the traps becomes too large, you should remove the traps or use them no more than 2-3 days a week.
Application environment
Greenhouses, fields, conservatories, and gardens. This type of parasitoid wasp successfully works on almost any site.
Release rate
Diglyphus isaea is introduced from 0.25 to 0.5 individuals per 1 square meter. It is recommended to carry out 2 injections with an interval of one week. These recommendations for use are approximate and vary depending on many factors. For proper use, it is necessary to consult a specialist for advice.