Coccus viridis (Green)

Bustillo, Alex, 2015, Part II. Pests, Compendium of Coffee Diseases and Pests, United States of America: The American Phytopathological Society, pp. 45-60 : 47

The coffee green scale, Coccus viridis (Green) ( Hemiptera : Coccidae ),

is the most important scale pest affecting coffee plants, causing serious losses in many coffee-growing regions around the world. The green scale develops a tough, scaly covering and does not move once it has established a feeding site. The adult green scale is oval (about 2 x 4 mm), fairly flat, bright pale green, and legless, with short, curved black markings on the back. They are found on coffee berries and stems but most commonly on the lower side of leaves, along the central vein ( Fig. 83 ). The green scale females reproduce without males. Each female may lay 100-500 eggs, which hatch within a few hours. There are three nymphal instars, each larger than the previous one. The first instar, called a crawler, has two long, taillike structures. It wanders over the plant before settling to feed. The lifespan from egg to adult is about 30-40 days. The adult lives for 2-5 months.

Damage

Green scales suck the tree sap and debilitate the plant, par ­ ticularly when the tree is young. The green scale excretes a sweet substance referred to as honeydew, which covers the leaves and supports the growth of a black sooty mold that reduces photosynthesis. Green scales require constant monitoring when the trees are young and growing rapidly, particularly in dry areas or during dry seasons. Unless green scale is controlled, coffee trees become stunted and sometimes die.

Population Management

Ants herd and protect green scales and, therefore, are chiefly to blame for the spread and increase of the green scale population. If ants are prevented from getting to a coffee tree, the green scale frequently disappears, controlled by its natural predators. Ants can be controlled by the use of natural baits (e.g., corn bran and sugar cane bagasse) amended with 1 % insecticides, such as carbaryl or diflubenzuron. The most suc ­ cessful biological control agent against the green scale is the fungus Lecanicillium lecanii (Zimmerman) Zare & W. Gams ( Verticillium lecanii (Zimmerman) Viégas ). L. lecanii invades and destroys green scales within 2 days. After 10 days, it grows out of the green scale to produce the characteristic white halo around the insect, which can be seen before it disappears ( Fig. 84 ). The white halo fungus requires high humidity to germinate and rain to spread its spores. Even at 96% relative humidity, germination falls by two-thirds, hence the lack of fungus activity during dry weather. Its action is favored by high humidity and lower temperatures. Many key natural enemies of green scales are parasitic wasps. Seven wasp species parasitize the green scale, but they are not effective in hot, dry, windy areas. Several predators feed on the green scale, such as Azya orbigera Mulsant and many members of the family Syrphidae ( Fig. 85 ).

Figures

Fig. 83. Coccus viridis on the lower side of a coffee leaf. (Courtesy A. Bustillo, Cenicafé)

Fig. 84. Coccus viridis infected by Lecanicillium lecanii on coffee berries. (Courtesy A. Bustillo, Cenicafe)

Fig. 85. A Syrphidae predator of coffee green scale. (Courtesy A. Bustillo, Cenicafé)