Pest Control Newsletter Issue No.33 Jan 2014 Pest Control Newsletter Issue No.33 Jan 2014

Published by the Pest Control Advisory Section Common found in Hong Kong Mechanical carriers and Biological vectors: Issue No.33 Jan 2014 Two common roles of

INSIDE Mechanical carriers and Biological vectors: in diseases transmission THIS Common flies found in Hong Kong Two common roles of ISSUE arthropods in diseases transmission

The oriental latrine , megacephala, a blow fly commonly Common flies found in Hong Kong found in Hong Kong

Flies are that belong to the order Diptera. A House flies The sudden appearance pests are that are distinctive feature of Diptera is the presence of only one House flies belong to the family Muscidae. They are of a few blow flies and considered as harmful to humans. Some pair of flying wings on the thorax, whilst the hind wings generally medium-sized flies with a greyish brown flesh flies may sometimes indicate the presence of an of the pests not only cause a nuisance have evolved into the halteres. appearance, carrying four longitudinal black stripes on unattended dead body of an . or an injury through biting, but also Aedes albopictus (白紋伊蚊), one of the biological vectors of the thorax. These omnivorous flies usually breed in Old World Screwworm Fly, transmit diseases to humans and animals. Dengue Fever In general, flies usually refer to the urban dipteran general house refuse. They are particularly attracted to Prevention and Control Chrysomya bezziana Those arthropod pests are called “disease carriers”, which species covering the common filth flies in Hong Kong, sugary food, and could also feed on rotten organic matter According to the World Health Organization, transport pathogens to susceptible individuals, their food represented by the house flies, blow flies and flesh flies. or faeces. Their movement from faeces to our food, with environmental sanitation is the fundamental measure for be conducted to ensure that all food waste is promptly or surroundings. They can both affect the health of Apart from their apparent nuisance, they are also pests pathogens carried by their excrements, their mouth parts fly control. (Pesticides and Their Application, WHO 2006) detected and removed. If necessary, devices such as people and impose heavy economic burden on society, of significant public health importance, as they could and contaminated body surfaces, is a well-known cause window screens (10 mesh, i.e. 10 x 10 meshes per sq. especially in the developing countries. According to the mechanically transmit pathogens to our food. Some of food poisoning and other diseases. To prevent fly infestation, household refuse should always inch), electric fans or air curtains (preferably with air figures from the World Health Organization, a child dies Periplaneta americana (美洲蜚蠊), fly species may also attack animal and human tissues be properly bagged and disposed of in lidded refuse bins, velocity 8 m/s or higher), anti-fly curtains made of plastic every minute from Malaria in . Generally, there are a mechanical carrier of intentionally or accidentally, resulting in or wound The prevalent species of house flies in Hong Kong is the and the refuse bins should then be covered tightly with strips or strips with beads and self-closing doors could two ways in which arthropods transmit pathogens, either pathogens responsible for enteric infections of humans infections. Common House Fly (Musca domestica). the lid. Animal carcasses should be properly bagged to also help to reduce the entry of flies from the outside. mechanically or biologically. avoid exposure to the air, and should be transferred to cause Malaria) or developmental changes (e.g. nematodes In optimal conditions with ample breeding places, high Blow flies refuse collection points for disposal. Handling, storage For the control of existing fly infestations, special cleansing Mechanical carriers which cause Filariasis). Afterwards, the arthropod humidity and warm weather, the life cycle of the flies Blow flies belong to the family . They are and disposal of human and animal excrements should operations should be conducted with particular attention Mechanical transmission occurs when arthropod pests vectors are able to spread the pathogens to other hosts, could be completed in a few days; thereby swarms of flies medium- to large- sized flies that usually carry a metallic also be conducted properly. Frequent cleansing should to the breeding places of the fly species identified in the pick up pathogens on their feet, body hairs, body for example, through biting and hence they become could be produced within a short period of time resulting green or blue appearance. Most species breed in rotten vicinities of the area concerned. Properly installed glue surfaces or other body structures and finally transport infective. The relationship between the pathogens and in a relatively sudden nuisance. vegetables and fruits as well as animal faeces. They also boards, light traps or electrocution devices might the pathogens to susceptible hosts. After feeding on arthropod vectors are usually highly specific. For example, breed in meats and carcasses. also provide some relieve at and around premises. Under garbage or excrement, arthropods, especially flies and the viruses causing Dengue Fever are only transmitted by severe conditions or in case the removal of such breeding cockroaches, acquire pathogens onto their bodies. Those some mosquito species of the genus Aedes (e.g. Aedes Many species of blow flies are known for their facultative places would be impossible or impractical, application of arthropods may then deposit the disease-causing agents albopictus) while the protozoans causing Malaria are only or obligatory , capable of breeding in wounds appropriate pesticide by trained personnel could also be onto our food, cooking utensils, dining wares etc. Body transmitted by certain mosquito species of the genus or even natural body openings of human and farm considered as a supplementary measure for rapid control structures, like spines on cockroach’s legs, and certain Anopheles. animals. Most of the myiasis cases in Hong Kong are the in the short term. behaviours, like regurgitating digestive enzyme onto infestation results of the Chrysomya bezziana, also known food by flies, facilitate the pick-up and deposition of In both the mechanical and biological mechanisms of as Old World Screwworm Fly. Other flies found in Hong Kong pathogens. It has been reported that cockroaches are able disease transmission, the role of the arthropods is critical Apart from the flies discussed above, fruit flies or melon to carry bacteria including Escherichia coli, Salmonella in the propagation of infections. In order to control Flesh flies flies could often be found on rotten fruits. Flies such as species and Vibrio species that cause food poisoning in the vector-borne diseases, it is thus vital to suppress or Flesh flies belong to the family Sarcophagidae. They are phorid flies, hover flies and the blood-feeding stable flies humans. eliminate the arthropod vectors, if possible, which could relatively large flies with a greyish body, three longitudinal and horse flies also exist in rural areas in Hong Kong. be achieved by elimination of vectors’ breeding sites and black stripes on the thorax and usually the “checkerboard” Moth flies may sometimes be observed around drain Biological Vectors improvement on environmental hygiene. Avoiding bites Biological transmission involves a more complex pattern on the abdomen. They also have the holes (recently reviewed in Pest Control Newsletter Issue by the arthropod pests can also be an effective means of mechanism in which the arthropods also act as hosts in characteristic that they lay larvae instead of eggs. Urban No. 27). Last but not least, biting midges and the more prevention of vector-borne diseases. Personal protection the pathogens’ life cycles. The arthropods first acquire species mainly breed in decaying meat, but may also feed slender mosquitoes, crane flies and chironomids also measures, like applying insect repellents and wearing the pathogens from diseased hosts, for example, through on other decaying organic materials such as faeces and belong to the order Diptera and are therefore true flies in long-sleeve clothing at outdoor areas, can reduce the blood-sucking. Inside the arthropod bodies, the disease- rotten plants. Depending on the species, their larvae may a broader biological sense. chances of arthropod bites. also be cannibalistic or parasitic. A flesh fly Parasarcophaga albiceps causing agents may undergo multiplication (e.g. Dengue Common House Fly, Musca domestica C. K. YUEN, Assistant Pest Control Officer viruses which cause Dengue Fever and plasmodia which W. H. YAP, Assistant Pest Control Officer

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