Monday, June 23, 2014

Barcoding potential biocontrol agents

The soybean aphid (Aphis glycines) is an insect pest of soybean (Glycine max). The soybean aphid is native to Asia.but has been introduced to North America in 2000.  It has also been described as a common pest of soybeans in China and as an occasional pest of soybeans in South East Asia.

Soybean aphids suck fluids from soybean plants. The most important effect of aphid damage on yield is the reduction in the number of soybean pods. Thus, yield may be affected most when soybean aphids attack soybean plants that are flowering or setting pods. Sooty mold typically appears on heavily infested plants. The soybean aphid is also capable of transmitting several viruses that infect soybean, such as soybean dwarf virus and soybean mosaic virus.

Soybean aphid have a complex life cycle with as many as 18 generations annually. Two different host plants are required by the aphid. It spends the winter on buckthorn plants (Rhamnus) as eggs. Nymphs hatch in the spring, and after a few generations on buckthorn, winged females fly in search of soybean plants. The aphids pass through a series of wingless and winged generations on soybean during the summer. In September, winged aphids migrate to buckthorn plants to complete their annual life cycle.

In Asia, the soybean aphid experiences pressure from over 30 species of predators, 8 species of parasitoids, and some fungal pathogens. Field studies in showed that particularly some species of hymenopteran parasitoids contribute a lot to the drastic reduction of soybean aphid populations, e.g. Lysiphlebia japonica was determined as a keystone aphid parasitoid in the ecosystems and agro-ecosystems of Korea and China with parasitism rates of over 50%. This makes them ideal candidates for biocontrol agents that could be used to fight the aphids without extensive use of insecticides. 

However, the correct identification of these parasitoids is crucial for assessing their potential in biological control projects. Misidentification may result in serious economic losses. Due to their small body size (usually 0.5–2.0 mm), high-quality slide and card-mounted specimens are needed in traditional morphological identification. Even well-known species can be confused with closely related sister species.

That is the reason why a group of Chinese researchers tested the utility of DNA Barcoding to assist with parasitoid identification which to no surprise worked quite well:

The DNA barcoding approach greatly assisted the identification of the parasitoid complex of the soybean aphid in China. Our results revealed 15 species belonging to 10 genera of five Hymenoptera families. The DNA barcodes show high interspecific distance coupled with low intraspecific distance. 

It seems that DNA Barcoding not only allows us to identify pest species but also parasitoids we can use to fit them:

A reliable and comprehensive DNA database of insect pests and parasitoids is required for rapid species identification and understanding the parasitoid community. Accurate identification using DNA barcoding could be a pivotal step in the assessment of their performance and suitability as biocontrol agents in biological control programs

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