The brown planthopper is a tiny insect, about the size of a
sesame seed that threatens the rice crops of Asia each year. These insects hang
onto the stalks of the rice plants and siphon the sap from them with their
sucking mouthparts. This causes the plants to turn yellow and to dry up, known
as hopper burn. Large numbers of the brown planthopper can lead to the
destruction of thousands of acres of rice, which is the primary source of food
for approximately half of the world’s population. In order to do this these insects
have a developed a strategy, which involves the wing length of the brown
planthopper.
When the conditions in a rice field are stable the juvenile
planthoppers develop wings that are short. Short winged planthoppers cannot
fly, but produce offspring fairly quickly. A short winged female can lay more
than 700 eggs in her lifetime. However, as the fall approaches and the days
shorten and temperatures drop these insects start to develop longer wings. This
allows them to fly into new rice fields in search of food. Previously
scientists did not understand how the cooler temperatures and the shorter days
caused the insects to shift from short winged to long winged or which hormones
were involved, but a new study by Duke University reveals new information on
the topic.
The study involved using a technique called RNA interference
or RNAi. As a result of this technique genes for two different insulin
receptors were able to be silenced. The effects that doing this had on the
animals’ wings were then measured. In the past scientists had believed that all
insects have only one insulin receptor, but it was discovered that the brown
planthopper has two.
The researchers silenced the first insulin receptor and the
planthopper nymphs developed into adults with short wings. Silencing the second
insulin receptor caused the nymphs to develop into long winged adults. The scientists
pushed their research even farther and were able to determine that the long
winged form of the planthopper is the default form. However, the secretion of a
certain type of insulin due to changes in temperature and day length causes the
second insulin receptor to inactivate the first insulin receptor and short
winged planthoppers develop. Essentially, the second insulin receptor interferes with the
first and shuts down the signal.
The implications of the study could be numerous, but as of
yet it is too early to tell if these findings could lead to techniques for
controlling these insects. Scientists have discovered this mechanism in other
planthopper species and hope to determine if insulin plays a similar part in
other insects with flying and flightless forms.
To me this is astounding that these insects have evolved in
such a way. It is really interesting to think that these insects have evolved
such mechanisms to survive. It seems so complex and rather ingenious of these
organisms, but I also think it is excellent that scientists have discovered how
they are able to change from form to form. Hopefully, in the future researchers
will be able to find a way to stop these insects from invading the rice fields
and destroying the crops. It is exciting to think how far science has come and
what can happen with the new information these studies are providing.
