Lecture notes Biodiversity: Exploiters and Exploited Locusts (BI2EEE4)

15.10.19


L3 – Locusts
Keywords:
Gregarious, fledgling (newly malted adult locust), oviduct, ovipost, spermatospore (male sperm sac
transmitted into female internally), recessions (periods w/o widespread/heavy swarm infestations),
outbreak (concs and multiplications cause increase in locus #/density to gregarize), upsurges (↑
conc lead to outbreak), plaque (widespread outbreaks affect extensive land in successive years)

Lecture:
 O = Orthoptera, SO = Caelifera, F = Acrididae (short-horned grasshoppers) – arose 320
million years ago
o Order characteristics:
 Pronotum extends over thorax
and sides
 Thick jumping hind legs
 Wings over abdomen at rest
o Caelifera = Grasshopper (235 million years
ago)
 Shorter antenna
 Diurnal
 No pupal stage and 4 molts
 3 segmented tarsi (outermost limb)
o Locusts = grasshoppers that are gregarious (behavioral grasshoppers – cause issues)
 12 species
o Ensifera = crickets (250 mya)
 Larger antenna
 Large ears on their tibia
 Nocturnal
 Main locusts
o Desert locusts – Schistocerca gregaria
o Migratory locust - Loucsta migratoria (sub species – change morphs)
o Australian plague locust – Chortoicetes terminifera (smaller locusts purely in Austral-
Asia)
 Lifecycle
o Lay up to 10 batches of eggs in life
o Required to be large bc needs to feed self
o Eggs laid underground (female expands abdomen 3x into soil to dig hole) via
ovipositor (hole to release eggs)
 Froth substance around eggs = keeps moist
 Wet & warm = hatch in 10 days
 Cold & dry = 70 days
o Mature in 10 days to 6 months
o 1st instar stage = smaller than adults w/large heads, no wings or sexual organs
o 3rd instar stage = wing buds shown
o 6th instar stage = last stage w/ wings
o Life phases
 Solitary

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 No aggression (like grasshopper)
 Solitary
 Adults move alone @ night
 Gregarious (↑ chance w/ ↑#)
 ∆ within gens
 Adults and nymphs congregate
 Swarm in day in bands
o 1958 = 1000km2 area (10k mil)
o Crop destroyed
o 12h flight (if correct temp)
o Rolling swarm (rolling deflated ball)
 1km in air flying (30 min) and then land and rest
 Swarm passes over and then fly again
 Hoppers move on ground together
 ∆ colour and shape compared to solitary
 ↑ disease resistance
 ↓ # of eggs laid
o
 Species types
o Swarming species – eg desert locust (does not have settled home)
 Breeds in different areas depending upon season
o Migratory locusts
 Breed in local area
 If weather = perfect then become gregarious = ↑ land covered
 Can stop swarm if initial breeding area controlled
 Hopper bands
o Harder to study
o 50-20,000m2 bands
o Rest in trees and roost in mornings and eat in evenings
 What induced grasshoppers → locusts?
o Crowding (4h required)
 Under 2-4m apart
 500 adults/ha (desert locust), 2000 adults/ha (migratory) and 5000 (red)
 Caused by wind, sparce veg/weather
o Mech contact (jostling) – touching hind femur (receptors = hormonal change)
o Sight/sound of other grasshoppers
o 500+ genes involved (↑ serotonin in thoracic ganglia → ∆ in state)
o Aggression caused by pheromones
o Reversable w/dispersal
o Foam secreted ∆ when gregarious vs solitary (reversable)
 Locust environment (how it affects outbreak chances)
o Requires patchy food source (leads to congregation)
o Good weather = multiplication (↑ swarms) and fly in day (body temp between 30֯C
40֯C)
o Swarms = ↓∆ of being picked off by predator
o ↓ plant defense
o Swarm in wind patterns into inter-tropical