Abstract |
The economy of many countries and specifically countries of Mediterranean is based in
agricultural production. Insect pests are a big hazard, since they are responsible for the damage
of many crops. Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a relatively new pest
for Europe, affecting a wide variety of small and stone fruits. Infection by D. suzukii causes fruit
to be unsuitable for distribution and consumption resulting in significant economic damage. In
order to control this pest and limit the economic damage on fruit crops, farmers usually resort to
the use of organophosphate, spinosyn and/or pyrethroid insecticides. Unfortunately, the
insecticide efficacy on D. suzukii is limited and the impact on biodiversity, ecosystem, food and
water ecosystems is devastating. Nowadays, biological control methods play a crucial role for
the Integrated Pest Management (IPM) with the ability to suppress pest population below
economic thresholds rather than only providing a temporary control based on broad range
agrochemicals. For this reason, the search for alternative insect management strategies of D.
suzukii in food crops is of vital importance.
The cuticle of insects is covered with a layer of wax that consists of lipids, a class of compounds
that includes alcohols, fatty acids, acylglycerols and hydrocarbons. Cuticular hydrocarbons
(CHCs) are found at all life stages of insects and their production can be affected by several
factors such as reproductive status, sex, age, maturation, food, temperature, social experience and
photoperiod. One of the main roles of these compounds is to serve as means of communication
and signaling, providing both inter-and intraspecific information including aggregation, mating,
alarm, aggression and recognition.
In this thesis a method coupling gas chromatography with electron ionization mass spectrometry
was developed for a better structural identification of CHCs of D. suzukii. In addition to the
known CHCs reported in previous studies, three new compounds, nonadecane, 2-methyleicosane
and 2-methylheneicosane, was observed.
We evaluate the effect of solvent extraction time on the amount of D. suzukii CHCs. Extraction
time can affect the detection as well as the relative amount of substances in both male and female
flies. Specifically, it was shown that the increase of the extraction time had a profound effect on
the amount and type of CHCs determined in both sexes of D. suzukii. Increasing the extraction
time, we were also able to detect new compounds in the fly, which subsequently were used to
evaluate their role on insect’s behavior. Based on the quantitative results obtained, we further
evaluated the biological role of two compounds, dodecane and 9-pentacosene. It was found that
the D. suzukii adults are repulsed when exposed to dodecane (C12) acting as alarm pheromone.
On the other hand, 9-pentacosene (9-C25) seems to enhance mating behavior of D. suzukii males
acting as sex pheromone
Furthermore, the study of the effect of age and sex in CHCs production showed that there are
prominent changes in CHC profiles in function of age-related maturation and less prominent
changes in function of sex. Specifically, we concluded that D. suzukii has a sexually
monomorphic CHC. Both sexes at age of 1 day produced compounds in high abundance which
they have long carbon chains (C25-C33), while at the age of 2 and 25 days insects produced
CHCs with short carbon chains (C19-C25). The results of bioassays demonstrate that 9-
heneicosene (9-C21) positively regulated the aggregation.
We investigate the aggressive behaviour of D. suzukii. Inter-male and inter-female aggression
was determined ethologically consisting of several behaviour patterns. Two hours starvation
period increase locomotor activity of flies, promoting increased aggressive behaviour. Number
of male encounters was higher in flies held in isolation than in those that had been reared with
siblings whereas in case of females, only those that were isolated exhibited increased aggression.
Females and males D. suzukii that were 4-day-old were more aggressive. In addition it is found
that on the 3rd hour after the beginning of photoperiod, regardless of age, both genders rise to
high intensity aggression patterns. Also the effect of socialization in CHC profile of insect was
study. It is observed that non-socialization resulted increased amounts of 7-tricosene (7-C23).
Evaluation of biological role of 7-C23 showed that it is a compound that increases the aggressive
behaviour of male D. suzukii.
Our findings offer potential new routes for IPM strategies. Many potential IPM strategies such as
attract-and-kill, mass trapping and mating disruption rely on chemical communication used by
insects. We propose that 9-C21, C12, 9-C25 and 7-C23 CHCs could be part of an IPM for D.
suzukii
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