Material guide: pear ester — it makes a pear smell like a pear, and apple orchards use it to trap codling moths

About a 5 minute read.

The short version

• Name: ethyl (E,Z)-2,4-decadienoate, the pear ester, CAS 3025-30-7, FEMA 3148
• Odour type: green; odour: green, waxy, pear, apple, sweet, fruity, tropical, vegetable
• Strength: high (evaluate at 10% or less), rank 3; substantivity over 48 hours
• Suppliers: 46; oral LD50 > 5000 mg/kg
• It is also a plant-derived attractant (kairomone) for the codling moth
• Its refractive index field contains a typo

The evaluation field just says what it is

Most materials get a string of adjectives. This record gets an identity:

The characteristic odor of Bartlett Pear. Imparts a juicy, ripe Bartlett pear note of distinction to fruity florals.

Along with several others:

at 10.00% in dipropylene glycol. green waxy pear apple sweet fruity tropical (Luebke 1996) at 2.00%. Green, waxy, pear, vegetative, tropical and fruity (Mosciano, P&F 23(3):55, 1998) juicy, ripe pear, sweet, very fruity

This is one of those materials where one molecule equals one fruit. Most fruit aromas are the sum of dozens of compounds; the Bartlett pear (Williams pear in Europe) has one unusually dominant lead.

The notes field: "Constituent of the odoriferous principle of Bartlett pears. Also present in fresh apple, Vitis spp., quince and spineless monkey orange."

Its second identity

What Mitchell and colleagues did in Pest Management Science in 2008 has nothing to do with perfume, but it explains what this molecule means in nature.

The codling moth (Cydia pomonella) is the principal pest of apples and pears worldwide. Conventional monitoring uses the sex pheromone (codlemone), which has one fundamental limitation: it attracts only males.

They compared three lures in New Zealand apple orchards — pheromone, pear ester, and the two combined:

No dose response in trap catch of males was seen in traps baited with different amounts of pear-derived kairomone (0.01–10.0 mg). The number of females caught was significantly affected by the amount of pear derived kairomone used to bait traps, with the highest catch obtained at 10 mg loading.

Males ignore the dose; females do not.

And the combination result runs against intuition:

The mean number of males captured in traps was reduced by 44% when the pheromone and kairomone were combined at a ratio of 1:1 (0.1 mg pheromone : 0.1 mg kairomone) in separate sources.

Two lures that each work become worse together.

Why would a moth evolve sensitivity to the smell of a pear? Because it is the host plant saying there is ripe fruit here to lay eggs in. The molecule is "the taste of pear" to us and an address to the moth.

And that neural channel is shared

Gonzalez and colleagues, in Ecology and Evolution in 2020, worked on odorant receptor phylogeny, comparing the green budworm moth (Hedya nubiferana) with the codling moth:

The female sex pheromone of green budworm moth is a blend of two unsaturated acetates … Females produce in addition codlemone, which is the sex pheromone of another tortricid, codling moth. Codlemone also attracts green budworm moth males. Concomitantly, green budworm and codling moth males are attracted to the host plant volatile pear ester. A congruent behavioral response to the same pheromone and plant volatile in two tortricid species suggests co-occurrence of dedicated olfactory channels.

Two different species, one molecule, one channel.

The relevance to perfumery is indirect but worth holding onto: olfactory receptors are evolutionarily conserved, and the answer to "what does this smell mean" depends on who is smelling.

This record's refractive index is a typo

The refractive_index field:

1.48000 to 1.14860 @ 20.00 °C.

A liquid's refractive index does not fall below 1.2, and 1.14860 is far too low for an ester. The correct value is almost certainly 1.4860 — with one extra 1 in front.

In a separate article I swept five fields for ranges where A exceeds B and found 55, and this is among the best-supplied errors in that set (46 suppliers).

Catching it requires no chemistry: 1.48 is greater than 1.1486, and in "A to B" the A should not exceed the B.

How to use it

• Evaluate at 10% or less; strength rank 3. It is powerful, and its green and waxy sides overrun the pear at higher concentrations.
• It leads pear, but it also reinforces apple, mango and tropical fruits. taste_descriptions says "useful in pear, apple, mango, various fruits flavors."
• Substantivity over 48 hours, which holds up well for a fruity note.
• Oral LD50 > 5000 mg/kg (1988), and cosmetic_uses reads skin conditioning and skin protecting — it is still in use on the cosmetic side.
• Mind the isomer when you buy. The (E,Z) in the name is the point: (2E,4Z) is the pear one.

What this doesn't establish

• I have not smelled it. This is fields, whole-database statistics, and two papers.
• Both papers are entomology and pest management, not fragrance research. I cite their account of what this molecule does in nature and touch none of their control-strategy conclusions.
• Mitchell 2008 is a field trial in one New Zealand growing region; the absolute catch numbers do not extrapolate elsewhere.
• "1.14860 should be 1.4860" is inferred from the inverted range; I checked no supplier specification or handbook.
• "One molecule equals one fruit" is a simplification. A Bartlett pear's complete aroma is obviously more than this, and I have no GC-O data for this compound's share of it.
• I did not check the IFRA text.