Umbonia crassicornis, commonly known as the thorn bug, is a widespread member of the insect family Membracidae, and an occasional pest of ornamentals and fruit trees in southern Florida. The body length of the adult is approximately . This is a variable species as to size, color and structure, particularly the pronotal horn of males (which is more angled posteriorly than the females' and often somewhat expanded apically). This tall, essentially perpendicular thorn-like pronotum discourages birds and other predators from eating it, if only by mistakenly confusing it with a thorn. Typically, the adult is green or yellow with reddish lines and brownish markings.
Distribution
The species is restricted to warmer climates where temperatures stay, on average, above zero. This limits the species to the tropical regions of Northern South America to Mexico and Florida. Any range of temperature below 0 degrees is fatal resulting in a 10-90 percent decrease in the population as temperature decreases. Its preferred hosts are ornamental and fruit trees of subtropical regions feeding on sap inside the plants.
Reproduction
Female Umbonia crassicornis often deposit about 100 eggs at a time into a plant stem, under the bark. However, sometimes a female will lay her eggs in the leaf petiole even though they can be shed occasionally. The female will choose her brooding site based on if she can wrap her legs around the branch (diameter about 3.8mm) The mother will stay with the clutch (a group of young) until the nymphs are mature. Without an adult female present during the nymphs development, the survival rate of the clutch drops from 53% survival to 27%. If a clutch's defending female dies, the clutch can be adopted by a nearby female and the two clutches will combine into one, though the survival rate decreases significantly.
A clutch normally consists of all full siblings, since the female usually only mates once, and sibling are more likely to defend each other based on this close relatedness. A problem with a large group of closely related young growing up together is the possibility of Inbreeding once the individuals reach reproductive maturity. When this happens survival rate of the offspring drops significantly due to mutations cause my mating with a sibling.
Mate selection
Because a female U. crassicornis only mates once in her life (typically), males are forced to search and compete for a female. They do this using the 'fly-call-walk' strategy in which a male will fly from one plant to another, then will walk around and strut. Once he encounters a female, the male will present vibrational signals to the female and if there is no response he will fly to another tree. If the female responds to these vibrations the male will approach the female and climb onto her side to initiate mating.
Mechanical basis of the courtship call
When performing their courtship call, the thorn bugs use the muscles in their abdomen to generate a continuous call that decreases in frequency as the tone gets longer, and high frequency clicks at periodic times in the call caused by the muscles pulling on the horn of the insect resulting in the clicks.
Competition
Because of the method of active mate searching in males, there is a significant difference in the mating ability of older males (25–33 days old) and younger males (19–25 days old) due to a loss of the ability to sustain flight and compete physically against other males. Older males are found only walking to search for females and their encounter rate is much lower than males that can fly from tree to tree. Though if a female has the choice between a younger and older male she will almost always pick the older male, the theories predict that this is because of their increased sexual advertisement and that they perform more overall courtships.
Sex bias
When a female plants her eggs on a branch, her clutch uses up a lot of that site's resources. Due to this, some clutches use up more resources than the host plant can provide, this can result in adults being much smaller than preferred. A female having a smaller body size, though can lay fewer eggs than a larger female, will not impact her overall reproductive fitness and will still be able to produce viable offspring. Males, on the other hand, have to compete with other males to reproduce so being smaller than average will affect his ability to mate and find food. These factors contribute to the altered sex ratio we see in U. crassicornis being a larger number of females in populations than males.