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Volatiles from damaged cotton affect both male and female moth behaviours


Zakir Ali

The Egyptian cotton leafworm (Spodoptera littoralis) is a severe pest on cotton (Gossypium hirsutum) with great economic losses to farmers in Egypt. In addition, insecticides used to control the pest have negative effects on the environment. In order to control the moth in a sustainable way a deep knowledge is needed about the mechanisms of the insect’s reproductive behaviours, especially in relation to volatiles produced by a cotton plant under attack.

This research shows that cotton plants damaged by herbivores influence the reproductive behaviours of the Egyptian cotton leafworm in several ways. It affects not only oviposition but also the male attraction to females and thus their mating success. The damaged plant also defends itself and its neighbours. All these actions are affected by odours that are called herbivore-induced plant volatiles (HIPVs) which the plant under attack produces as a defence.

Attraction, calling, mating and oviposition

It is known from earlier research that when a plant is attacked by an insect it reacts by emitting chemicals, HIPVs. These volatiles from plants can affect the behavior of the insect directly or indirectly. The female moth avoids to lay eggs on a damaged plant (direct affect) and the volatiles attract natural enemies of the moth (indirect affect).

However, there are very few studies on the effects of HIPVs on the reproductive behaviors of herbivores. It is clear that they make choices when and where to call, mate and lay eggs, but what mechanisms control how they make their choices? This research gives some clues.

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Zakir Ali has been studying herbivore-plant interactions, where the Egyptian cotton leafworm and cotton were used as model organisms.

Behavioral experiments were carried out under both laboratory and field conditions. Special cages were used were the interaction between the insect and HIPVs from the plants was studied.

Damaged cotton plants or synthesized chemicals placed outside the cage were used to study the reactions
of the moths inside the cage. Click on the picture to enlarge it.

HIPVs affect male moths and calling females

Results from this research indicate that HIPVs affect both male and female moths.

Wind-tunnel experiments showed that male moths were less attracted towards female sex pheromone when odours from the damaged cotton plants were present in the background. Two possible mechanisms are proposed: 1) HIPVs  have a masking effect which makes the male moths unable to find a female. 2) HIPVs have an antagonistic effect on male attraction towards female sex pheromones. Furthermore, females kept individually with damaged cotton plants spent less time in calling. They are able to assess the quality of the plant and adjust their calling behaviour.

HIPV-blend affecting the oviposition identified

Specific chemicals from the cotton HIPV that affect the oviposition of the moth were identified in this research. In electrophysiological tests the female’s antenna reacted to 18 compounds of the collected plant volatile. From these a cocktail of 7 compounds specifically produced after herbivore damage was synthesized and tested on mated females in oviposition experiments. It showed that this blend of 7 compounds was sufficient to reduce oviposition and can provide a reliable signal of plant quality.

larv_mott_280.jpgThe cotton leafworm (Spodoptera littoralis) is a severe pest on many plants.

The cotton plant protects its neighbors

A cotton plant that is attacked by the insect and releases HIPVs can also protect its neighbors. This research shows that HIPVs emitted by the damaged plant has an active range of at least 60 cm and could therefore protect other plants from being attacked by the herbivore. The results indicate that HIPVs are repellant to the female and that the associated defense is directional. In this study, only cotton plants, gave increased resistance to neighboring plants, while the other plant species tested did not.

Important knowledge has been revealed within this research but further studies of HIPV interactions with insect herbivores are needed in order to develop sustainable and environmentally safe methods in monitoring and controlling insect pests.

Title of the thesis
Influence of herbivore-induced changes in host plants on reproductive behaviours in Spodoptera littoralis

Link to the thesis

Dissertation
2 November 2012

Funding
Linnaeus initiative IC-E3, The Swedish Research Council and Higher Education Commission (HEC) of Pakistan.

Pictures

To download a high resolution file click on the photo

 

 

 

 

  Zakir Ali with cotton plants.

  Zakir Ali with cotton plants.

  Zakir Ali with cotton plants.

 Cotton plant.

 

 

 Cotton leafworm, moth.

 Cotton leafworm, larvae.

Five questions to Zakir Ali

What is your driving force when it comes to research?

I get inspirations from ongoing research in the world and always try to do something new. I am interested in understanding the functions and mechanisms of ecological phenomenons. 

In your research: What has been the most difficult/most fun?
To find out the most appropriate assay for volatile compounds identified through GC-EAD and GC-MS. 

What expectations did you have before starting your work at SLU Alnarp?

I expected to work with a fantastic research group and got the same results. 

What do you do in five years?
I have been working with my full ambitions and dedications to the PhD work and tried my best to take maximum out of it. I hope that the time I spent in my research work will always motivate me in future as well. I have been busy with Sports as well as it was necessary to get energy for more work.  

Your favorite word/sentence in Swedish?

Tack så mycket!

Contact information

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Email ali.zakir@slu.se

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Email peter.anderson@slu.se

 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

© IC-E3, Updated 2014-08-01