| Summary: | Green lacewings (Neuroptera: Chrysopidae) are considered among the most effective generalist predators of aphids.
In the present experimentation, the use of 1st, 2nd and 3rd instars of the chrysopid Chrysoperla carnea (Stephens) larvae
against aphids pest was investigated under field conditions in Brassica napus L. Four releases of predator’s 1st, 2nd and 3rd
instar larvae were made from the time of aphid’s appearance on canola crop till its maturity at fortnightly intervals. The
influences on aphids due to the larvae of C. carnea predator were assessed by examining pest incidence and abundance of
the natural enemies at plant growth stage, and seed yield recorded at crop harvest in the test field. Results indicated that
predators, irrespective of their developmental stage, reacted very positively to their preys’ reduction except in untreated
control. Of the different larval stages tested, the applications of 1st instar followed by 2nd and 3rd instar larvae were most
effective in reducing aphids’ population compared with untreated control. In the similar fashion, the releases of 1st
and 2nd
instar larvae of C. carnea were more effective in increasing crop yields compared with check treatment. Obviously, the
applications of 1st and 2nd instar larvae of C. carnea involved efficiently in prey location and consumption, and performed
predation activity for longer period (2-3 weeks). On the other hand, the release of 3rd instar larvae was too late to play a direct
beneficial role in crop protection suggesting that they may have less time (1 week) to remain involved in efficient prey
consumption. Further, 1st or 2nd instar larvae may be much hungrier and eaten more pests in study areas without resting or
moving to new location and thus can potentially be used to enhance biological control of aphids.
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