Species interdependence in nature confers many
benefits on the species involved, but it can also become a
point of weakness when one species involved in the relationship
is affected by a catastrophe. Thus, flowering
(5) plant species dependent on insect pollination, as opposed
to self-pollination or wind pollination, could be endan-
gered when the population of insect-pollinators is depleted
by the use of pesticides.
In the forests of New Brunswick, for example,
(10) various pesticides have been sprayed in the past 25 years
in efforts to control the spruce budworm, an economi-
cally significant pest. Scientists have now investigated
the effects of the spraying of Matacil, one of the antibudworm
agents that is least toxic to insect-pollinators.
(15) They studied Matacil’s effects on insect mortality in a
wide variety of wild insect species and on plant fecundity,
expressed as the percentage of the total flowers on
an individual plant that actually developed fruit and
bore seeds. They found that the most pronounced
(20) mortality after the spraying of Matacil occurred among
the smaller bees and one family of flies, insects that were
all important pollinators of numerous species of plants
growing beneath the tree canopy of forests. The fecundity
of plants in one common indigenous species, the
(25) red-osier dogwood, was significantly reduced in the
sprayed areas as compared to that of plants in control
plots where Matacil was not sprayed. This species is
highly dependent on the insect-pollinators most vulner-
able to Matacil. The creeping dogwood, a species similar
(30) to the red-osier dogwood, but which is pollinated by
large bees, such as bumblebees, showed no significant
decline in fecundity. Since large bees are not affected by
the spraying of Matacil. these results and weight to the
argument that spraying where the pollinators are sensi-
(35) tive to the pesticide used decreases plant fecundity.
The question of whether the decrease in plant fecun-
dity caused by the spraying of pesticides actually causes
a decline in the overall population of flowering plant
species still remains unanswered. Plant species dependent
(40) solely on seeds for survival or dispersal are obviously
more vulnerable to any decrease in plant fecundity that
occurs, whatever its cause. If, on the other hand, vegeta-
tive growth and dispersal (by means of shoots or runners)
are available as alternative reproductive strategies for a
(45) species, then decreases in plant fecundity may be of little
consequence. The fecundity effects described here are
likely to have the most profound impact on plant species
with all four of the following characteristics: a short life
span, a narrow geographic range, an incapacity for vege-
(50) tative propagation, and a dependence on a small number
of insect-pollinator species. Perhaps we should give special
attention to the conservation of such plant species since
they lack key factors in their defenses against the envi-
ronmental disruption caused by pesticide use.