This is a big subject, so I'll just give you a quick run down and some
links for further reading.
Here's a quote from "Introduction to Insect Ecology"
( http://www.humboldt.edu/~mac24/zoo580/lecture_notes1.html )
"By virtually any measure of "success", insects are among the most
ecologically successful terrestrial and freshwater organisms on Earth.
(Insects are....) taxonomically dominant, with estimates of the number
of insect species ranging from just over 1 M to greater than 30 M
species world-wide. The most most credible current estimates are
probably 3-8 M species, with greatest diversity in the tropical
forests...(and there is a )...general inverse relationship between
latitude and species richness."
Effectively, this means the further north (or south) you go, the less
species of insects there are.
The climate change due to latitude ( the macroclimate) is influenced
- the variation in intensity of heat from the sun over earth's surface
- Tilt of earth 23.5 degrees off the plane of orbit around sun imposes
annual variation in temperature i.e the seasons are more defined,
winters are colder and the breeding season for insects is shorter.
- Air circulation in earth's atmosphere i.e Seattle's temperature is
windier and generally more violent, so insect populations have less
chance to settle in large colonies.
There are several reasons why insects in general, and specific kinds
of insects in particular, do better in hotter climates.
First, insects are "cold blooded." Their metabolism, activity, and
physiology are directly influenced by the temperature. This means that
the hotter it is, the faster they grow, feed and reproduce. Insects,
such as aphids, that have an inherent ability to reproduce quickly can
especially become a problem.
Second, the lack of rain removes a major mortality source. Smaller
insects, including aphids, thrips, leafhoppers, and mites, are washed
off of plants and drown during heavy rain. Lack of rain means more
Some species are protected against predators, parasites, and
pesticides by dusty soil accumulating in their "nest areas". The drier
the soil, the more protection afforded to these pests.
So effectively, Seattle has less insects because it is further north,
has more severe swings in weather, and it gets too cold and wet for
the efficient breeding of many of the insect species you find in
warmer climes like New Orleans.
Insect sensitivity to the weather's influence has led to many cultures
noticing that they can "predict" weather depending on insect
behaviour, and scientists are beginning to catch on. The "Insect
Weather Folklore" page gives a good run down on one such study.
( http://www.pulseplanet.com/archive/Jun97/1413.html )
Hope that answered your question
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