Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
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General Introduction 25<br />
leaves and webb<strong>in</strong>g <strong>of</strong> leaves to fruits to make protective shelters causes calluses on<br />
the fruits and leaves (Lo et al., 2000). The export market requires nil tolerance <strong>of</strong> both<br />
<strong>in</strong>sect and <strong>in</strong>sect damage on fruits. These str<strong>in</strong>gent measures put <strong>in</strong> place calls for the<br />
development <strong>of</strong> better and susta<strong>in</strong>able control measures for this pest. From the 1960s,<br />
chemical control was used <strong>in</strong> the form <strong>of</strong> pesticide sprays. The major chemicals used<br />
were az<strong>in</strong>phos-methyl and chloropyrifos sprayed on fruits. However, these chemicals<br />
are toxic to some natural enemies <strong>of</strong> the moth and <strong>in</strong> 1980s, populations resistant to<br />
the chemicals were reported. This called for alternative control measures. Bacillus<br />
thur<strong>in</strong>giensis (B.t) was looked <strong>in</strong>to but due to high UV radiation <strong>in</strong> New Zealand, this<br />
microbial <strong>in</strong>secticide is easily deactivated (Suckl<strong>in</strong>g et al., 1994; Suckl<strong>in</strong>g et al.,<br />
1999; Markwick et al., 2002). The naturally occurr<strong>in</strong>g baculovirus enemy <strong>of</strong> the moth<br />
that kills the larvae, nucleopolyhedrovirus was used as sprays to some success.<br />
However, the most susta<strong>in</strong>able control came from the use <strong>of</strong> mat<strong>in</strong>g disruption and<br />
pheromone trapp<strong>in</strong>g <strong>of</strong> the adult moths. Small scale mat<strong>in</strong>g disruption showed that the<br />
best results were achieved through <strong>in</strong>tegrated pest management (IPM), by us<strong>in</strong>g the<br />
20:1 ratio <strong>of</strong> the sex pheromone components together with a few applications <strong>of</strong><br />
<strong>in</strong>secticide (Suckl<strong>in</strong>g and Shaw, 1990). Scale up <strong>of</strong> this mat<strong>in</strong>g disruption showed<br />
similar results <strong>in</strong> larger fields (Suckl<strong>in</strong>g and Shaw, 1995). The efficiency <strong>of</strong> this<br />
system is however h<strong>in</strong>dered by factors such as migration <strong>of</strong> mated females from<br />
nearby untreated sources, or a high population density requir<strong>in</strong>g a second application<br />
(McLaren et al., 1998). The biggest issue fac<strong>in</strong>g mat<strong>in</strong>g disruption is the high<br />
concentration <strong>of</strong> pheromone required hence the high cost <strong>of</strong> this pest control method.<br />
The limited knowledge <strong>of</strong> actual pheromone mechanism h<strong>in</strong>ders the success <strong>of</strong> this<br />
system. Understand<strong>in</strong>g the underly<strong>in</strong>g mechanisms <strong>of</strong> receptor adaptation to different<br />
compounds, the actual behaviour that mat<strong>in</strong>g disruption targets and whether males<br />
respond to any rema<strong>in</strong><strong>in</strong>g pheromone plumes will enhance its success. Reviewed <strong>in</strong><br />
Suckl<strong>in</strong>g and Brockerh<strong>of</strong>f (2010).<br />
The sex pheromone <strong>of</strong> E. postvittana is released at night or dur<strong>in</strong>g the dark period,<br />
and has been identified to be a 20:1 ratio <strong>of</strong> (E)-11-tetradecenyl acetate (E11-14:OAc)<br />
and (E,E)-9,11-tetradecadienyl acetate (E9,E11-14:OAc), respectively (Bellas et al.,<br />
1983) shown <strong>in</strong> Figure 1.6. The components on their own do not produce any<br />
response <strong>in</strong> male moths but when present <strong>in</strong> the specific ratio, the blend produced<br />
response <strong>in</strong> both field trials and laboratory bioassay. The biosynthetic pathways