Abstract:
The number of species in many groups of parasitoid Hymenoptera
does not increase rapidly with decreasing latitude. Discussion
of the processes generating this pattern has focussed
upon changes in host demographic traits and upon the effect of
seasonality. Here we advance a further and compatible hypothesis,
that tropical parasitoid hosts are less available to parasitoids
than are extra-tropical hosts because their tissues are, on average,
more chemicidly toxic than are the tissues of extra-tropical
hosts. There is some evidence that suggests that tropical woody
plants are, in general, richer in toxic secondary compounds
than are extra-tropical species, and evidence exists to demonstrate
that these allelochemicals may have adverse effects on
parasitoids attacking phytophagous insects feeding on such
plants.
