Aulacaspis yasumatsui
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Adults of Aulacaspis yasumatsui |
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| Aulacaspis yasumatsui | ||||||||||||
| Takagi , 1977 |
Aulacaspis yasumatsui is a scale insect from the family of cap scale insects (Diaspididae).
features
The shield of the female adults has a domed, broad shell-shaped to oval shape, which is very variable, as the shield often adapts to leaf veins, neighboring lice and other objects. It is 1.2 to 1.6 millimeters long, slightly transparent, white to pale yellow-brown in color. A yellow-brown exuvia is attached to the rear end . The male shield is much smaller, elongated, has parallel side edges and three grooves running from front to back. It is white in color, 0.5 to 0.6 millimeters long and also has a yellow-brown exuvia at the rear end.
The females have a broad and flattened, legless and wingless, orange-colored body. Your relatively large, more or less rounded cephalothorax has no openings for wax glands. These are found on the sixth abdominal segment, where there are one or two gland openings on each side. The species can be distinguished from the similar Aulacaspis machili by glandular openings on the back of the first and second abdominal segment. The animals are also similar to Pseudaulacaspis cockerelli , which however have a yellow body color and whose females have a slimmer body.
Occurrence
Aulacaspis yasumatsui is native to Southeast Asia , in the region around Thailand , where it was discovered by Takagi in 1972. In 1992 the species was first detected outside of Thailand in Hong Kong . However, due to the worldwide trade in the host plants of the animals, the species was quickly spread by humans. Occurrences from China , Singapore , Taiwan , Vietnam , Ivory Coast , Hawaii , Florida , California , Texas, the Bahamas , Cayman Islands , Guadeloupe , Guam , Martinique , Puerto Rico and the Virgin Islands are now known. In New Zealand , the species was successfully wiped out after it was introduced.
Way of life
The species develops only on the three families of the cycads : Cycas cycads (Cycadaceae), Zamiaceae and Stangeriaceae . They usually live on the underside of the pinnate leaves , only when the infestation is very severe are all areas of the plant above ground and occasionally even the roots, which is unusual for scale insects. They can then be found at a depth of up to 60 centimeters.
Reproduction and development
Reproduction is bisexual. In the tropics, at an average of 25 ° C, one generation continuously follows the other, with females being adult on average 28 days after hatching. The life span of the females is about 75 days, with three larval stages being lived through. They lay about 100 of their orange eggs below their shield, from which the next generation hatches after 8 to 12 days. The smaller males are usually clearly in the majority. The larvae represent the spreading stage of the species. They look for new, suitable places on the plants to suck up plant sap, but they can also be spread by wind and contact with animals. Their mortality rate is very high. Adult, immobile animals and eggs are only spread by humans.
Damage and economic impact
At first you can recognize the infestation by discolored spots on the leaves, but usually these die off relatively quickly and dry up. A plant can be killed within a few months. Heavily infested plants are almost completely covered with white wax deposits and dead, like living lice. The lice often sit in several layers on top of each other, so that up to 500 lice per square centimeter could be counted.
Since cycads are among the most expensive cultivated ornamental plants because of their slow growth, the damage caused by Aulacaspis yasumatsui to plant crops is particularly serious. The controlled, dead lice are also very difficult to remove, and practicable options have not yet been found. In Hong Kong, for example, 70 to 100% of the ornamental cycads cultivated there were destroyed by the infestation. The impact on botanical gardens, such as in Florida, is also considerable.
Natural enemies and combat
No natural enemies have been found outside of the natural range. Also ladybug which, although occasionally observed on the colonies, not eat the scale insects. Parasitoids can seriously decimate the populations of the cap scale louse, but little is known about them. From Thailand are Coccobius fulvus and species of the genus Encarsia parasitoids chalcids proven. The former were used together with the predator Cybocephalus binotatus from the family Cybocephalidae, also from Thailand, to control lice.
Attempts were made to combat the species chemically with insecticides based on dimethoate and imidacloprid , but this was only partially successful. The currently most effective method is spraying the plants with oil-water emulsions for several weeks . The oil primarily prevents the larvae from spreading, adult animals are only partially killed, but these gradually die naturally until the plant is finally free of pests.
swell
- Carlos E. Bográn, Boris A. Castro, Scott Ludwig: The Cycad Aulacaspis Scale, a Pest of Sago Palms in Texas , TAMU Entomology publication EEE-00038, September 20, 2006, online (English)
- GW Watson: Aulacaspis yasumatsui. In: Arthropods of economic importance. Retrieved February 24, 2013 .
- TJ Weissling, FW Howard, AB Hamon: Cycad Aulacaspis Scale, Aulacaspis yasumatsui Takagi (Insecta: Hemiptera: Sternorrhyncha: Diaspididae). University of Florida, Institute of food and Agricultural Science, accessed February 24, 2013 .
