Lepidoptera Pheromones (unfinished) Flashcards
First known pheromone
Bombykol, from the silk worm.
Male moths - uses, dimorphism
Males have huge antenna with lots of hairs and millions of receptors which are very finely tuned. Female antenna not as feathery.
Good for studying pheromones as they have a macroglomerular complex (MGC) - clearly defined brain region devoted to processing female pheromones (less clear/non existent in other insects).
Moths have over 1600 sex pheromones
Pheromone detection (2 studies)
Released in pulses - filamentous signal.
Vickers et al. 2001 showed tracking of this signal by recording from an electrode acting as artificial antenna stuck onto the moth. EAG (electroantennagram) showed peaks in response corresponded to lumps of pheromone found at the centre of plumes.
Another study looked at pulses of pheromones. Potato tuberworm moths display anemotaxis towards source of sex pheromone (mixture of brief flying and walking). Showed they can discriminate between pulse frequency 0.1 - 2 Hz. 1 per second easiest for them to discriminate. Applications for pheromone traps in pest control.
Blends
Most moth pheromones are blends with precise ratios.
Components differ in length, functional groups, saturation, configuration etc.
Often 10-18C acetates, aldehydes or alcohols with 1-3 double bonds.
Fatty acid synthesis key to insect pheromone biosynthesis.
Pheromones across species?
For response in moth, must have.. (4)
Moth and elephant use same pheromone. But no response from elephant due to minute quantities. No response from moth due to it being used in a blend/bouquet.
1) Right components
2) Right ratios
3) Right concentrations
4) appropriate temporal structure
Male moth antenna receptors
Antenna covered in trichoid sensilla. One contains BmOR1 (responds to bombykol), other BmOR3 (responds to bombykal), both contain BmOR2 (Orco)
Effects of background signal
Need to be able to pick out signal from background signals. Pheromone OSNs in Spodoptera littoralis have been shown to NOT respond to plant linalool, however linalool does reduce the response to pheromone. Increases heterogeneity of response.
MGC
Pheromone-detecting cells project to MGC, composed of two structures; toroid and cumulus. Projection neurons responding to bombykol –> cumulus, bombykal –> toroid.
Then go to higher brain areas. Toroid –> inferior lateral protocerebrum. Cumulus –> lateral horn,
Pheromones and food
Codling moths are always more attracted to blend of pheromone plus food.
Macroglomerulus and OSNs –> more excited
Different projection neurons are sensitive to different blends of fruits and pheromones.
Some odours are repressive too.
Vampire moths
Feed on fruit but subset (20%) of males feed on blood, perhaps to pass salts to female.
Non-biters have fewer coeloconic sensilla on antennae.
These are sensitive to vertebrate-related odours such as ammonia - would expect more of them?
CHCs
Cuticular hydrocarbons, first discovered in Drosophila. Act as pheromones. Also found in moths.
B. anynana
1) B. anynana covered with CHCs, different structures (legs, wings etc) show sex and age differences.
2) Courtship involves physical contact - may involve CHCs as pheromones.
3) Ratios of male pheromones changes with age, females prefer to mate with older males.
Chemical defence
Plants have compounds to stop being eaten by herbivores eg. pyrrolozidine alkaloids (PA). Moths can eat it without being harmed (as caterpillar). Sequester it. Secreted as a foam if adult is attacked.
If raised on a PA diet, spiders won’t eat them (but they will if raised on a PA-free diet).
PA can also be transferred to the female via sperm (5 minutes after mating, they are rejected by spiders)
Males can announce to females the level of PA in sperm via hydroxydanaidal in the coremata (removing coremata and females wont mate with them)
