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Evaluation of potential Pyrethrum Synergists on agriculturally significant insect species


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Joffe, T (2011) Evaluation of potential Pyrethrum Synergists on agriculturally significant insect species. PhD thesis, University of Tasmania.

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The indiscriminate use of pesticides in the control of agricultural and public health
pests has led to the development of insecticide resistance in many insect pest
species, posing a large threat to the continued success of chemical control
measures. Resistance towards pesticides can be due to a number of mechanisms,
but enhanced detoxification of the insecticide by metabolic enzymes, such as
esterases, glutathione-S-transferases (GSTs) or monooxygenases, plays a large role
in insecticide resistance. Synergists, such as piperonyl butoxide (PBO) can be used
to overcome metabolic insecticide resistance. Synergists are capable of inhibiting
enzymes involved in insecticide resistance, thus restoring a level of susceptibility. By
virtue of its enzyme inhibitory qualities, PBO is often used to enhance the efficacy of
pyrethrum (an organic insecticide). In some countries, however, PBO is no longer
certified for organic use and this study explored the use of natural plant oils or
extracts as potential organically-certifiable pyrethrum synergists. From a commercial
viewpoint, an effective natural synergist could potentially allow development of new
pyrethrum formulations into higher value niche markets, such as organic agriculture.
Synergised pyrethrum could also offer a new control option against insects resistant
to synthetic pesticides in mainstream agriculture.
The efficacy of various natural plant oils and extracts as pyrethrum synergists were
examined for synergistic potential towards pyrethrum with several agriculturally
significant insect pest species, Helicoverpa armigera, Frankliniella occidentalis,
Myzus persicae, Meligethes aeneus and Musca domestica, a serious public health
pest, using discriminating dose bioassays. PBO proved to be the most effective
pyrethrum synergist in all species tested, however, a number of natural plant oils also
showed efficacy. The most promising compounds were dill apiole oil and parsley
seed oil, synergising pyrethrum in all the species tested. Dill apiole oil and parsley
seed oil contain the methylenedioxyphenol ring structure that is characteristic of
Enzyme inhibition studies were used to examine the ability of the natural plant oils
and extracts to inhibit the enzymes involved in metabolic insecticide resistance
(esterases, GSTs and monooxygenases). In general, inhibition of esterases and
GSTs was not correlated to synergism of pyrethrum in vivo. However, in H. armigera
and M. persicae, with esterase mediated pyrethroid resistance, PBO, dill apiole oil
and parsley seed oil inhibited non-specific esterases. In M. aeneus and M. domestica, where resistance to pyrethroids has been linked to monooxygenases,
PBO, dill apiole oil and parsley seed oil showed significant inhibition of
monooxygenases. However, not all compounds that inhibited esterases or
monooxygenases synergised pyrethrum. The lack of correlation between enzyme
inhibition and synergism could be due to a number of factors, including the ability of
the synergist to penetrate the insect cuticle, speed of distribution of the synergist
through the insect, metabolism of the compounds in the insect and affinity for the
target site.

Item Type: Thesis (PhD)
Keywords: pyrethrum, synergism, insecticide resistance, esterases, glutathione-s-transferases, monoxygenases
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Date Deposited: 09 Dec 2011 05:21
Last Modified: 11 Mar 2016 05:53
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