東亞飛蝗

簡述

東亞飛蝗在體型上較非州飛蝗為小。其存在可分為獨居階段及群居階段：獨居蝗蟲的顏色可以是綠色或褐色，但當蟲口數量增加，令生活空間下降，褐色的蝗蟲會變成佔多數。
蝗科的若蟲叫作「蝗蝻」（Nymph）或「跳蝻」（Hopper），因為牠們的翅螃還未成長，無法飛行。這些若蟲在初孵化時是灰棕色，但當成長後，牠們的顏色會變為綠色或棕色；而當環境變得乾燥時，棕色會變更常見。當牠們的密度增加，他們開始形成跳蝻帶，顏色變得更紅，呈橙楬色或紅褐色，有黑色斑紋。

分布

東亞飛蝗分布於東南亞。蝗災曾發生於馬來西亞西部、沙巴、華東及菲律賓。
Plagues of swarming locusts have occurred in these areas and as far away as Thailand, Malaysia, Java, Sulawesi and the southern tip of Japan.

Life cycle

The adult female Oriental migratory locust deposits a number of egg pods in the ground over the course of a few weeks. The sites selected include soft soils such as volcanic ash, alluvial soils and sand. Each pod contains between fifteen and a hundred eggs and most females lay from two to seven pods during the breeding season. The eggs hatch 10 to 24 days later and the nymphs develop through 5 or 6 instars, taking between 26 and 61 days to fully develop. Females do not lay eggs when the temperature is below 21 °C（70 °F）, and above this temperature, development times reduces as the temperature rises until 32 °C（90 °F） is reached, after which no further reduction takes place.
Locusts change their behaviour and are attracted to each other when there are large numbers in close proximity. This behaviour starts when the nymphs are quite small and form a band that move together as a cohesive unit. The band of hoppers can travel a distance of up to 4公里（2.5英里） per day, mostly moving downhill, stopping sporadically to feed and bask in the sun. When the insects are fully developed and have wings, they stay together as a swarm. Solitary adults usually fly by night but gregarious ones fly by day. The new adults mature and become sexually active in three or four weeks. There may be up to five generations per year in the Philippines, but in the cooler parts of China, there may be just one or two.

Outbreaks

Outbreaks tend to originate in two types of habitat; soft flood plains periodically inundated by floodwater and forest clearings. In the latter case, the land is cleared for growing crops but when the soil is exhausted it is abandoned and cultivation moves elsewhere. The grasses and weeds that grow in the clearing provide food for locust nymphs and cultivated areas nearby provide soft soil for mass egg deposition.
A serious outbreak of the Oriental migratory locust occurred in Indonesia in 1997-1998. It was first observed in the provinces of Lampung, South Sumatra and Bengkulu in 1997 and then seemed to disappear. It reappeared early in 1998 and intensified, with nearly 20,000 hectares of rice and 15,000 hectares of maize being affected. It may have been triggered by the drought conditions of 1997.
Outbreaks in China historically occurred about every ten years, usually after dry summers were succeeded by warm winters. The swarms were mostly restricted by the surrounding uplands to the river valleys. Low-lying land that floods intermittently in the delta areas of the Yellow River has been identified as outbreak centres. During the period 2002 to 2006, outbreaks of hopper bands in this locality were biologically controlled with the fungal pathogen Metarhizium acridum by ground and aerial applications, giving a kill rate greater than 90%.
In the Philippines, there were four major plagues in the first half of the twentieth century. They seem to have originated in southern Mindanao around Sarangani Bay. They tended to follow periods of below average rainfall. Since about 1960, the Oriental migratory locust has been less of a problem in the Philippines, probably because cultivation practices have changed and there is less untended grassland where populations can build up undetected.
An outbreak in southern Japan was discovered on an uninhabited island in 1986. A wildfire had restricted the area available to the locusts for feeding and later provided ideal conditions for egg deposition. Hopper bands with a density of 1000 insects per square metre roamed around and swarms of adults occurred over the whole island; the outbreak was brought under control later in the year by spraying.