damage crops by direct feeding on foliage and flowers, and also by
transmitting bacterial wilt. This bacterial disease kills the vines; there is no control
beyond controlling the beetles. Lest you think all cucurbitacins are
bad, know they are also responsible for the smell and taste of a
Cucumber fruits can produce high levels of cucurbitacins in
response to environmental stress such as high temperatures and
drought. Low soil fertility and low soil pH can also contribute to
high cucurbitacin levels in cucumber crops. However, high
cucurbitacin levels in zucchini and other summer squash varieties do
not appear to be a result of environmental stress, but rather the
influence of a single gene. Assuming you grew and cared for all four
plants the same way, your experience would seem to bear this out.
Zucchinis are members of the Cucurbitacea family along
with pumpkins, cucumbers, squash, melons and gourds.
Plants that produce extremely bitter zucchinis are rare, but
it does happen. If you are unlucky enough to have such a plant in
your garden, tear it out and do not eat any of the fruit or give it
away. Do not save any seed from this plant since it is very likely
that the resulting plants would also produce bitter zucchini. A
small number of cases of human poisoning from eating minute amounts
of bitter zucchini have been reported in the United States and
There are wild members of the Cucurbitacea family that occur
as weeds; they tend to contain very high cucurbitacin levels that
render their fruit inedible. All members of this family depend on
bees for pollination of the female flowers. If seed production
fields are in proximity to wild populations of cucurbits, it is
possible that bees could transfer pollen from the cucurbitacin-rich
weeds to the seed fields. The resulting seeds would produce bitter
fruit because the bitterness gene is dominant.
How can you
There is no way to tell by looking if a zucchini plant will produce
these bitter fruits, and no sure way to avoid the problem.
Fortunately, it is not very common. If you save your own seed, make
sure none of the wild cucurbits are growing near your garden.
Prickly cucumber (Echinocystis lobata) and bur cucumber (Sicyos
angulatus) are the wild cucurbits commonly found in
Bees in your vegetable garden
Eggplant flea beetles