Historically in agriculture, most insects have been considered as pests causing damages to agricultural economy, but that point of view is being changed. Nowadays, insects are considered as valuable resources in many aspects including viable human diet and animal feed resources, pharmaceutical and medicinal product, pollinator insect, natural enemy of insect pest, and environmental cleanup. Especially, many insects belong to
The common diseases occurring in Korean horn beetle are white muscardine and green muscardine disease when infected by fungi
The diseased larvae were collected from several local farms rearing larvae throughout Korea from Apr. 2014 to Sep. 2015. Collection sites include Anseong-si, Buyeo-gun, Cheongwon-gun, Daejeonsi, Geoje-si, Geumsan-gun, Gyeongsan-si, Hoengseong-gun, Mujugun, Naju-si, Namyangju-si, Pocheon-si, Siheung-si, Uiseong-gun, Wanju-gun, Yeongam-gun, Yongin-si, and Youngdong-gun.
To diagnose the diseased larvae, DNA was isolated from diseased larvae and viral DNA was amplified by PCR with three pairs of primers (primer AdV-F1 and -R1, primer AdV-F2 and-R2, and primer AdV-F3 and –R3) which were previously designed in our lab (Lee
Peroral virus infection of third instar larva was accomplished by dropping 30 μL of hemolymph extracted from diseased larvae on the mouthparts of thirty healthy larvae, respectively. The infected larva was independently reared in plastic container filled with moist fermented oak sawdust. To avoid other infection, the sawdust was sterilized before use. The infection experiment was repeated for three times.
The diseased larvae of Korean horn beetle were collected from local farms rearing larvae throughout Korea. Table 1 describes the collection date, location, and sample numbers, and the location map is shown in Fig. 1. In several locations, samples were collected couple of times in the space of several months to a year. It was because in some locations, the viral disease was not found or not severe, and in a few farms, the disease was examined again after the farmer tried to improve the rearing conditions. Result is, the severity of disease did not ease but even became worse. Currently, the only clean area is Gangwon-do, as shown in Fig. 1. However, it could be simply because there are not many larvae-rearing farms in Gangwon-do, and they are relatively small scaled. Thus, they hardly needed to trade their larvae for crossbreeding with the farmers from other province, and kept their beetle clean from the viral disease. However, this luck did not visit other farms. Many farmers trade their larvae with others for many reasons and this accelerates the fast and wide spread of the disease all over the country. Moreover, many local farms are located near mountains or oak forest filled with wild beetles. The crossbreeding between wild and reared beetles is happening already in several farms, and this increases the possibility of virus transmission to the wild
Current state of OrNV disease spread to A. dichotoma larvae rearing farms throughout Korea.
[Fig. 1.] Location map of OrNV disease-diagnosed farms. Red circle is where collected larvae were diagnosed as OrNV positive, and larvae from blue circle,OrNV was not detected. Each number refers to following province: 1: Pocheon-si, 2: Siheung-si, 3: Namyangju-si, 4: Anseong-si, 5: Yongin-si, 6: Hoengseong-gun, 7: Youngdong-gun, 8: Cheongwon-gun, 9: Daejeon-si, 10: Geumsangun, 11: Buyeo-gun, 12: Uiseong-gun, 13: Gyeongsan-si, 14: Geojesi, 15: Muju-gun, 16: Wanju-gun, 17: Naju-si, 18: Yeongam-gun.
The visible symptom development of the viral disease was appeared after one week post infection, and the diseased larvae began to be killed after two to three weeks. Hemolymph was taken from every dead larva, and it was examined by PCR for viral DNA amplification with primers AdV-F1/R1, -F2/R2, -F3/R3. It was confirmed that all the perished larvae were infected by
[Fig. 2.] Mortality and metamorphosis ratio after peroral infection. Thirty healthy larvae were infected with 30 μL of hemolymph from diseased larvae, orally, and only 21.1% of larvae went through metamorphosis and became adult beetle. Among the survived adult beetle, 95% of them were diagnosed as OrNV positive. Peroral infection experiment was repeated for three times.
Among the survived adult beetles, nine of them were successfully mated with healthy beetles and laid eggs. Six of them were female and three were male. When these adults died after they laid eggs, they were also examined for
Also, peroral infection of
Sometimes the farmers may not realize exactly that they have disease issue in their farms. Because most local farms are growing the larvae in the open field, covered with plastic greenhouse and stuffed with oak sawdust in the ground, it is not easy to find the disease spreads in the sawdust pile. The diseased larvae will be rotted away and only the larvae near the dead larva will be infected. Unless the disease is extremely severe in the farm, the disease will not affect the whole bunch of larvae during the spring and early summer. However, the viral disease cause devastating loss especially when the larvae are harvested and stored for overwintering or waiting to be sold to a merchandiser. During the storage period, one or two hundreds of larvae are stored together in a big plastic container filled with moist sawdust for couple of months at low temperature. Thus, a few virus infected larvae can easily transmit the virus and kill the whole box of larvae. The transmission of virus is mostly made by having the feeding and excretory activity in the same fodder, and also by the cannibal behavior of larvae. The motion activity of a diseased larva is greatly reduced and these “weak” larvae or diseased cadaver get easily eaten by other larvae. In a severely diseased farm, more than 70% of container filled with larvae can be annihilated. Therefore, early detection and removal of the diseased larvae from the container box are extremely important. To analyze the virus, full genome sequencing is under way and it will be compared with