Biocontrol of Comstock mealybug

The polyphagus Comstock mealybug (Pseudococcus comstocki), native to Eastern Asia, is an invasive pest in other regions of the world. It is a serious pest in apple, pear and citrus orchards. It is also damaging to several ornamental and shade trees. The bug injures the plant by extracting large quantities of sap and producing honeydew that serves as a substrate for the development of sooty mould, which prevents photosynthesis. Fruit can be damaged by spotting and producing a change in the skin texture. Feeding activity can also stimulate the growth of gall-like formations on the bark and near the leaf veins.

In Asia and North America successful biocontrol programs using e.g. the beetle Cryptolaemus montrouzieri, also known “Crypt” or “Mealybug Destroyer” or some hymenopteran parasitoids were established in the 1960s and 1970s. The species arrived in Europe in the early 2000s and e.g. France initiated biocontrol investigations in 2008. Researchers of the French National Institute of Agronomy (INRA) began with a study of the French populations of Pseudococcus comstocki and surveyed their the natural enemies in France. Subsequently, they investigated populations and their natural enemies elsewhere (Italy, Syria, China, Japan, Turkey). For each step molecular methods were used and 28S, ITS2 and the barcode region were studied.

Three mealybug species (P. comstocki, P. viburni and P. cryptus) were identified during the survey, together with at least 16 different parasitoid taxa. We selected candidate biological control agent populations for use against P. comstocki in France, from the species Allotropa burrelli (Hymenoptera: Platygastridae) and Acerophagus malinus (Hymenoptera: Encyrtidae).

The authors list several advantages of the use of molecular data:

• Facilitation of the choice of relevant material for examination and the sharing of complementary information (sequence haplotypes versus morphological characters), leading to particularly fruitful collaborations.
• Identifications were consistent despite the heterogeneity of the material to be identified, in terms of both sample conservation state and development stage.
• Identification was repeatable throughout the program, providing reliable and consistent identifications on which the team could base decisions.
• The availability of DNA barcodes made it possible to comply with the requirements of the French government regarding import and use of exotic biological material. In particular, the existence of multilocus DNA data for Allotropa burrelli facilitated the authorization for import by French government services.