Life cycle of a locust
Locusts and grasshoppers are insects in the order Orthoptera and the suborder Caelifera. Like many insects, locusts undergo metamorphosis as they develop into sexually mature adults. Unlike the type of development which butterflies and cicadas display, however, locusts exhibit incomplete or gradual metamorphosis, in which the juveniles resemble small adults and undergo gradual changes over a series of molts.[1] As such, locusts have three major life stages: egg, nymph, and adult.[2]
The life cycle of a desert locust spans approximately 2 to 6 months. Eggs typically hatch within 10 to 65 days, followed by the nymph stage, which lasts between 24 and 95 days, with an average of 36 days. After fledging, adults live for about 2.5 to 5 months. The period from egg laying to fledging takes 40 to 50 days, while adult sexual maturation occurs over 3 weeks to 9 months, typically averaging 2 to 4 months.[3]
The egg
Locusts lay many eggs together in a cluster, known as an egg pod. The eggs resemble grains of rice, and are cushioned and connected together by a foamy substance which the female excretes during laying.[3] Egg pods are buried in the soil, with laying females targeting fields with ideal conditions. Sometimes, many females gather together to lay in the same field.[4] Moisture and temperature of the soil are vital to the development and survival of the eggs. Outside of these two essential factors, exposure to wind, predation, parasites, inviability, and failure to hatch may impact survival.[3] Some species of locust or grasshopper will undergo diapause during embryo development, pausing the process indefinitely and resuming when ideal conditions are met to ensure best survival.[1] After egg incubation is completed, the brand new nymphs hatch and emerge from the soil, entering the next life stage.
The nymph
Locust nymphs are often called hoppers, as they do not have wings and cannot fly until adulthood. Depending on species, there are five or six nymphal instars, or life stages between successive molts.[5] Hoppers resemble tiny, wingless adults throughout their development. Some nymphs may develop short, useless wings in late instars as they approach adulthood.
The adult
Once the final molt is complete, the insect emerges as a winged adult. This process is referred to as fledging. The brand new adult locust must spend time, up to several hours, waiting for the exoskeleton to harden and for the wings to complete development. Locusts will reach sexual maturity over the next couple of days or weeks, and reproductive behavior (including migration, if applicable) will begin.[3] The majority of crop damage is done in summer by late stage hoppers, fledgling adults, and sexually mature, egg-producing adult females.[2] After a week or two of producing offspring the adults will begin to die off. Few individuals will survive past six or seven weeks.[5] On average, the locust population increases sevenfold with each generation.[2]
Locust or grasshopper?
Locusts and grasshoppers are closely related insects, and many of the same behaviors apply to both. The sole difference between the two is in phase change: grasshoppers only have a single, solitary life phase, while locusts have both a solitary phase and a social or gregarious phase. Gregarious behavior occurs in locusts as a reaction to high population density. This change often occurs in the hopper phase, with gregarious hoppers congregating to form migrating “bands.” These bands may become swarms when the individuals reach adulthood.[3] Phase change is both behavioral and physical, and gregarious locusts will typically take on different coloration than solitary locusts of the same species. As rainfall affects locust survival (and therefore population density), high rain is linked to an increase in gregarious marching or swarming behavior.[2]
References
- ↑ 1.0 1.1 Pfadt RE (2002) Field Guide to Common Western Grasshoppers. University of Wyoming 912. Available from: https://www.uwyo.edu/entomology/grasshoppers/field-guide/index.html.
- ↑ 2.0 2.1 2.2 2.3 Walton CS, Hardwick L, Hanson J (2003) Locusts in Queensland. Department of Natural Resources and Mines, Qld. Available from: https://www.publications.qld.gov.au/dataset/locust-invasive-animal-pest.
- ↑ 3.0 3.1 3.2 3.3 3.4 Symmons PM, Cressman K (2001) Desert Locust Guidelines 1. Biology and behaviour. Food and Agriculture Organization of the United Nations. Available from: https://www.fao.org/ag/locusts/en/publicat/gl/gl/index.html.
- ↑ Department of Jobs P and R (2024) Australian plague locust – identification, biology and behaviour - Agriculture. Agriculture Victoria. Available from: https://agriculture.vic.gov.au/biosecurity/pest-insects-and-mites/priority-pest-insects-and-mites/plague-locusts/australian-plague-locust-biology-and-behaviour (August 14, 2024).
- ↑ 5.0 5.1 Flint ML (1998) Pests of the Garden and Small Farm. 2nd ed. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 3332.