An Asian wasp discovered early in the 20th century is being used today to control the spread of citrus greening disease. Is this an effective method of control? Read below to learn more and decide for yourself.
Highly Efficient Parasitoid
During the 1920s, Scottish entomologist James Waterston first discovered Tamarixia radiata in an area of northern India that is now known as Pakistan. As adults, these insects have light-colored legs, wings, and antennae. While the abdomen can be slightly darker in males than females, both sexes have blackheads and thoraxes.
This Asian wasp is a parasitoid. The difference between a parasitoid and a parasite is that the parasitoid will eventually kill its host. The female adult wasp lays her eggs under Asian citrus psyllid nymphs, generally in a one-to-one ratio. The nymph’s wings have not fully developed, therefore leaving them flightless and unable to escape. Once the wasp’s egg has hatched, the larvae attach themselves to the nymph and begin feeding on their hemolymph (bodily fluids).
Once the new wasp has fully excavated the body of its host, it will excrete silk to attach the nymph husk to the leaf or twig it is on and then continue to grow inside its new shell. The wasp emerges as a fully grown adult and continues the cycle.
Officials in California, Florida and Texas are hoping releasing Tamarixia radiata in infected citrus groves will help control the spread of citrus greening disease by killing its vector, the Asian citrus psyllid.
This globally devastating citrus disease, also known as HLB, causes citrus to be green, bitter and deformed. Citrus greening disease leads to premature fruit drop and eventually kills the tree. The effects on the taste and look of the fruit makes it undesirable to consumers and worthless to the grower.
]Increased use of insecticides and predation of the wasps have limited their success in the States. If insecticide use can be limited, Tamarixia radiata may be able to help decrease the Asian citrus psyllid population. Decreasing the numbers of the psyllid may help decrease the spread of citrus greening, and when coupled with a formidable treatment for HLB, may help stop the disease all together.
Figure 1. Tamarixia radiata has been released widely in southern California for biocontrol of Asian citrus psyllid. Survey data reported here suggest that this ACP natural enemy may have been established in about 91 of 100 (i.e., 91 percent of study sites) surveyed release and non-release sites in urban areas. (Photo courtesy of Mike Lewis, Center for Invasive Species Research, UCR)