Biology:Locusts can eat their own weight of green food each day.
Life Cycle:Eggs are laid in pods 10-80mm below the soil surface. Bare compacted soils are preferred for egg laying. Over-wintering eggs hatch in late August or September (in WA) as soil temperatures rise above 150C to become a nymph (or miniature adult) about the size of a house fly (3mm long). Initially they are white but darken within a few hours of hatching. They have 5 growth stages before reaching their final size in 4-8 weeks. If conditions are good and green food is available, they mate and lay eggs over the next three weeks. In dry conditions, egg laying may be delayed up to a month until rain falls. Three pods of 70 eggs may be laid by each female if green feed and rain is available during development. Under dry conditions there may be no egg laying. If the soil is dry eggs may not hatch until summer rain occurs. If conditions remain dry most of these eggs will die. If the soil is moist, the eggs will hatch in 2-3 weeks. Dry summers often kill most of this generation including eggs. The survivors mature and lay eggs which remain in the soil over winter to emerge in the following spring. There may be two or more generations per year which results in the quick production of plague numbers.
Habitats:The preferred food is green grass but any green material will be consumed including Pine tree seedlings.
Origin and History:Native to Australia.
Significance:Locusts may build up to large numbers after drought breaking rains in the semi arid grasslands. Plagues are more common in NSW, Victoria and SA than they are in WA. They usually build up when desert areas receive rain and then migrate to the coastal agricultural areas. If summer rain and green feed is available they survive and build up and may cause severe economic losses in the second and subsequent years. Individuals may migrate large distances (hundreds of kilometres) in dense swarms at night. During the day, swarms of flying adults or bands of hoppers move and devour crops and pastures in their path. The bands of hoppers develop from nymphs from dense egg beds. Swarms of Australian Plague Locusts occur more frequently than the Migratory Locust. They can cause severe economic losses and campaigns are often undertaken to reduce the effects. They will eat almost anything green and ripening cereals and perennial pastures may be devastated by swarms. In WA, cereals, broadacre crops and annual pastures are often dry by the time Locusts reach damaging sizes and densities so their impact is reduced. Perennial crops and pastures, trees, gardens and horticultural crops usually suffer the greatest damage. Green pastures, sparse, late maturing crops and the edges of crops near pasture are often damaged by young locusts. Older locusts may cause damage to partly green crops and may lop cereal heads. Mature tree plantations are not usually damaged by young locusts, but can be damaged by adults.
Management and Control:In most years control is not economical. When plagues occur concerted campaigns are mounted involving spraying of egg beds, hoppers, bands and swarms.
Thresholds:5 adults per square metre are usually worth spraying in pastures.
Related Species:Wingless Grasshoppers usually have a light coloured stripe down each side of the body. The wings are usually poorly developed and only occasional individuals can fly. The hind wings never have a black tip or blotch.
References:CSIRO. The Insects of Australia. Melbourne University Press. (1991) p70, 71(development diagram), 105, 107, 108, 371(diagram), 377, 391, 392(diagram).
Acknowledgments:Collated by HerbiGuide. Phone 08 98444064 for more information.