Influence of temperature, photoperiod, and food on the speed of development, longevity, fecundity, and other qualities of the Diamond-Back moth Plutella Maculipennis (Curtis) (Lepidoptera: Tineidae).
Authors: Atwal AS 
Published: June 2005

Larvae of Plutella maculipennis (Curtis) were reared on food of different
qualities at different temperatures and were exposed during their development
to different photoperiods. The plants on which the larvae were reared were also
exposed to different photoperiods during their development to see whether this
influenced the quality of food for the insect.
It was found that although caterpillars developed more quickly at 25�C
than at l8�C, they weighed less at pupation at 25�C than at l8�C, but the ratio
of dry matter to water was the same at both temperatures. Exposure of
caterpillars to different photoperiods influenced their speed of development.
There was an indication that the influence of light was different at different
temperatures. The influence of quality of food was more evident. Larvae
reared on white or young green leaves of cabbage developed more quickly than
those reared on green but mature or senescing leaves; the slower speed
of development was associated with a higher death-rate and a lower body
weight combined with a higher water content of the pupae. Irrespective of
temperature and the quality of the food, females developed more slowly than
males and also had more dry matter and a higher liveweight in the pupal
stage.
Insects bred at a lower temperature produced more eggs than those at a
higher temperature; the difference was thought to be due to a lower body
weight in the latter. Photoperiod also influenced fecundity but the effect was
not so clear. Caterpillars reared on plants grown in a long photoperiod were
more fecund in the adult stage than those reared on plants grown in a short
photoperiod, but the difference was not quite significant. Insects reared on
white or young green leaves of cabbage laid significantly more eggs than
those reared on green but mature leaves. Simarly when larvae were reared
on the better quality food they produced more silk, the resulting moths lived
longer, and a higher proportion of the males were fertile.
The general conclusion is drawn that for normal activities of Plutella a
balance of nutrients is required. For the normal activities of the insect body,
like healthy development and reproduction, nutrients may be required in
certain proportions. If owing to some cause (as probably, with change in
season) that proportion is upset, certain abnormalities may appear in the
metabolism or form of the insect, such as deformities in wings and shape of
body, slower development, reduction or impediment in egg-laying capacity or
diapause, etc. In the author's opinion this general conclusion may be a useful
hypothesis on which to base further work.
In the light of the above observations and observations on other insects,
the seasonal activity of Plutella is discussed. It is stated that although
apparently its behaviour and activity seem to be nicely adjusted to seasons,
showing a beautiful picture of adaptation, yet the recurrent heavy reductions
in numbers which this insect and many other species suffer in the field suggest
that the adaptations are not as efficient as may at first sight appear.