Vegetable Crops News

Wasp Attacks Asparagus Beetle

Asparagus is one of the most important vegetable crops in Michigan and a common backyard garden plant. The most important insect pest of asparagus is the common asparagus beetle (Crioceris asparagi). The adult is a slender, blue-black beetle with a red thorax. Its lemon-yellow and dark blue wings have a reddish border. Both adults and larvae feed on young asparagus shoots, reducing the quality of the shoots and rendering them unmarketable.

In the field, the eggs and larvae of asparagus beetle are attacked by the parasitic wasp Tetrastichus asparagi. The wasp lays its eggs in the asparagus beetle larvae. The wasp larvae eventually kill the beetle as they complete their development inside the beetle. The adult wasps also feed directly on asparagus beetle egg masses. A large percentage of the asparagus beetle eggs and larvae are destroyed in this way. In a Massachusetts study, almost half of the asparagus beetle eggs were eaten by T. asparagi, and about half of the remaining eggs were parasitized, so of all the asparagus beetle eggs laid, 75% never survived to become adults.

The abundance of T. asparagi is dependent on the availability of its host, so numbers will vary from location to location. There are two to three generations of the wasp each year to provide predation and parasitization through the season.

This natural enemy of asparagus beetle can be encouraged by reducing the use of insecticides in both commercial crops and home gardens. On small-scale plantings, the adult beetles can also be picked off the plants by hand to reduce the numbers of this pest.

- Palasuberniam Kaliannan, Michigan State University


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