|MadSci Network: General Biology|
Hi Jethra! How long does it take for a gall to form on the stem of a plant? Thatís a very good question! The short answer: different types of galls induced by different insect species on different plants will develop at different times. There are an estimated 1500 species of insects that cause galls in plants within the U.S. alone (800 of which are associated with the oak trees of North America!). Typically, however, the galls induced by diapausing insects will become apparent within 2-3 weeks of egg laying by the female insect in the Spring (mid-May to late June) and continue to develop and enlarge for several weeks into the early Summer. The goldenrod gall fly (Eurosta solidaginis), for example, will lay an egg in the terminal bud of a goldenrod plant in mid-May and the egg will hatch into a hungry larva 10-12 days later. This larva burrows into the apical meristem (i.e., the terminal growing tip region of the plant), which will initiate gall formation. These stem galls will be visible within 3 weeks, but they will continue to grow through the summer as the larva itself grows, feeding on the plant tissue growing inside of the gall. The mature gall will measure 10-30 millimeters in diameter at the end of the growing season (i.e., end of Summer-early fall). Remember, these gall-forming insects secrete substances that act as potent stimulants of plant growth, typically by locally stimulating the production of auxins (plant growth hormones); therefore, the capacity of an insect to stimulate plant growth (tumor-like cell proliferation) will influence the rate at which the gall develops. Hereís the web address to a great website detailing the ecology of the goldenrods and stem galls: http://www.oswego.edu/wscp/GOLDGALL.htm A good website outlining the history, importance, and classification of gall-making insects can be found here: http://www.wcrl.ars.usda.gov/cec/insects/gallmake.htm I hope this response helps! My sincere apologies for its delay. Regards, Shireef
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