PPDL Picture of the Week
September 18, 2017
Flower with a view
Dan Egel, Clinical Engagement Associate Professor-SWPAC, Botany and Plant Pathology, Purdue University
The cucumber beetle in this photo has attitude. That attitude seems to be defiant of
everything it views from this watermelon flower, including the
photographer. Maybe this beetle is
defiant because it knows that, strictly speaking, the striped cucumber beetle, Acalymma vittatum, is a pest of watermelon plants. Early in the season, when
the watermelon plant is quite small, cucumber beetles can overwhelm a plant by
feeding. Later in the year, when fruit are present, cucumber beetles may feed
on the rind, reducing the marketable yield.
In mid-July, however, when this photo was taken, the danger to
watermelon plants from cucumber beetles is low. Cucumber beetles may spread bacterial wilt
in cucumbers and cantaloupe. However, watermelons are not a host for bacterial
Growers are advised to scout for cucumber beetles and only
apply pesticides when the numbers of beetles reach certain economic threshold
numbers. If insecticides are applied
regularly without regard to the numbers of cucumber beetles present, beneficial
insects may be killed in addition to cucumber beetles. The loss of beneficial insects such as lady
beetles, could mean that aphids will become a pest.
So, maybe this cucumber beetle’s assertive stance is because
it has nothing to fear. It is not
harming the watermelon plant and is not worth the cost of an insecticide
application. The beetle can continue to feed on the pollen from this male
watermelon flower. Note that there is a
bit of feeding on a flower petal just to the right of the beetle.
The attitude worked.
Shortly after taking this photo, I left without bothering the beetle or