IPBRG Investigators: Spence Behmer
First some history (updated January 2017). The post oak grasshopper, Dendrotettix quercus, is an oak defoliator first recorded from Texas (Bruner 1887) and Missouri (Riley 1888, 1893). It has been reported as occurring throughout much of the United States, most commonly in the eastern half. Since these first reports specimens have been collected in Oklahoma, Kansas, Arkansas, Tennessee, Illinois, Wisconsin, Michigan, New Jersey, New York, and as far west as the state of Washington. The ecology and natural history of post oak grasshoppers has been studied most thoroughly in New York (Davis 1912, 1915), New Jersey (Rehn 1946; Rehn and Rehn 1938) and Wisconsin (Valek and Coppel 1972). Recently Hilliard and Himes (2005) documented an infestation in east Texas. An adult (pictured to the left) is typically 3 cm in length (1 1/4").
Post oak grasshoppers became noticeable in Texas in 2003, and we first because acutely aware of them in the spring of 2006 (they occurred in large numbers in key areas around Bryan/College Station). Since 2007, their numbers around Bryan/College Station area have steadily declined, and in 2009 they were only found in small numbers in a few locations. We have not seen or heard of reports in the BCS area since. Nonetheless, they were still observed in large numbers in other parts of Texas, especially in the Dallas/Fort Worth Area (including Palestine, Argyle, Corsicana and Tyler). Starting in 2006 we began to track the occurance of post oak grasshopper populations across the state of Texas, and we continue to record their locations as we learn about them. Generally post oak grasshoppers hatch (from the ground) in late-March/early-April, and become very noticeable (due to their increasing body size) in late April. You can click on the picture to the right to see a larger view of immature post oak grasshoppers aggregating. Individual pictures of immature post oak grasshoppers can be seen below, in the biology section.
To learn more about the post oak grasshopper, continue reading. If you've seen any post oak grasshoppers, please email us and let us know (details below). We are building a database that documents their emergence time, developmental rates, and distribution. We need your help to do this, and would grately appreciate any information you could share!
As their name implies, post oak grasshoppers prefer post oak (Quercus stellata), but they can also be found on water oak (Q. nigra), blackjack oak (Q. marilandica) and bluejack oak (Q. incana). It is not uncommon to find them feeding on a range of other trees, including hickories (Carya spp.), white ash (Fraxinus americana), flowering dogwood (Cornus florida), red maple (Acer rubrum) and sweetgum (Liquidamber styraciflua) (Hilliard and Himes 2005). However, they tend to feed more on these non-oak trees following severe defoliation of their preferred oak trees. In general, tree feeding in grasshoppers is rare, and the large majority of the closest relatives to post oak grasshoppers tend to be generalist feeders that eat a mixture of grasses and broad leaf plants. Taxonomic information on the post oak grasshopper can be found at the Orthoptera Species File Online.
Adult females lay their eggs in the ground, and we have found that individuals typically produce 5-6 eggs at a time (although in Wisconsin single females have been reported producing as many as 12 eggs at a time). These eggs are contained within a pod, surrounded by a protective foam, and remain in the ground through the summer, fall and winter. In late March/early April, the eggs begin to hatch, shortly after the oak trees bud and produce new leaves. The hatchlings are great climbers, and seem to prefer to eat young, soft leaves. Immatures proceed through 5 developmental stages, called instars, before molting into adults. The first three instars are very cryptic on oak trees, and blend easily with the bark of the tree (the picture above is a 3rd instar, which on average is about 10-12 mm long). As they enter the 4th and 5th instars, they undergo a slight color change, becoming more yellow. The picture to the left is of a 4th instar, which grow to about 15-18 mm.
The adults (top picture) look rather different from the immatures, and the large majority (>95%) are characterized by having short wings and are flighless. The rest of the population has either long- or intermediate-length wings, although neither of these forms is capable of flight. The adults begin to appear in late April/early May, and remain alive until early/mid June. A significant proportion of the population can be infected with a pathogenic fungus, and this can be a major cause of mortality. Infected individuals that have died often burst when touched or disturbed and release fungal spores. In Wisconsin, vertebrate and invertebrate predators have been observed (Valek and Coppel 1972), and in Texas chickens are known to readily eat post oak grasshoppers (Terry Junek, personal observation).
As the grasshoppers get older, and weather gets warmer, it may become common to find post oak grasshoppers in large numbers on the sides of houses and buildings that are surrounded by oak trees. We do not completely understand this behavior - they either fall off the trees and climb any vertical object they encounter, or it may be an attempt to thermoregulate. Laboratory studies lead us to believe that post oak grasshoppers cannot tolerate high temperatures, and climbing onto east and south facing walls at the end of the day may be a way to escape high temperatures. For adults, this behavior may also be related to finding a mate. An unfortunate side effect of this behavior is that grasshoppers often defecate while they are hanging about, and this feces, once it dries, produces a stain that is difficult to remove. This is likely a side effect of tannins, a chemical found in oak leaves [used in tanning leather products]. The best advice we can give to avoid having these unwanted stains is to immediately spray affected areas with water, although there is no guarantee that this will be effective.
We do not recommend massive spraying with pesticides, because there is no effective way to treat an entire oak canopy, where most of the post oak grasshoppers reside. Additionally, there is no treatment that specifically targets grasshoppers, so any attempt to eliminate the post oak grasshoppers will also eliminate other arthropods, including beneficial ones. Post oak grasshoppers are unlikely to cause serious longterm damage to your oak trees, unless there are repeated outbreaks in the same location over a number of years.
Our lab is interested in studying the unique biology of these grasshoppers, and we'd like your help in mapping their distribution. If you think you have post oak grasshoppers on your property, please E-mail us the following information:
1) county and zip code (and state if you live outside of Texas)
And thanks again for your assistance!