Ants, nectar and a myster

The pttrpose of ectaries itt flowers is well known; they nourish insects which. in feeding, may effect pollination. Nec-

tarics also occttr on non-ﬂower parts of sotne plant species bttt tlte function of

these extraﬂoral ttectaries (or E.F.N.’s for short) is not understood. One leading botanist has called tlteir fttnction "mysterious".

I knew of the occurrance of I5.I-‘.N.‘s on sonte cultivated plants bttt it was not until local naturalist Al (‘rrass asked tne what I kttew about tltent that I became interested in their occurrance in our native plants. I scanned the literature. fottnd that they occur rather erratically, —— in ferns. itt relatives of the confers and in the higher ﬂowering plants. Studi'es were only beginning to define their fttnetion and field observations from field naturalists were deetned to be needed.

My own interest in E.F.N.'s in our native plants is not far advanced; such as it is my interest may stimulate other the observe.

In our native and domesticated cher- ries E.F.N.’s occur on tlte lowest part of a leaf stem (petiole); commonly there are two, one on each side of the petiole. just below the leaf blade; however their number. shape and size varies frotn loca- tion to location itt our Province. It may well be that the amount and nature of the nectar they produce varies also. It is now documented that sugars are only one class of many compounds found in nectar.

Chokecherry (Prmms demissu), corn- tnon itt the drier parts of B.C., has well developed E.F.N.’s; the E.F.N.‘s of bit- ter cherry (P. entergima), which is found more widely in somewhat more humid environtnents, are small and are often reduced to mere pits. Barbara Bentley, who has studied E.F.N.'s of many species in several parts of the world, finds that ants make use of the E.F.N.‘s nectar and that itt doing so repel other insects which might devour the all im- portant green leaf; plants and ants have developed a relationship of benefit to both. Ther‘ are now some experiment with cultivated plants e.g. cotton where if E.F.N.’s and/or ants are removed substantially reduced harvests result. I common observe ants feeding from chokechcrry L’.I~'.N.‘s but not very often from those of bitter cherry.

ls plant-ant tnutualism the only system in which E.F.N.‘s: to name but a

' 4‘" Extra ehokeeherry (I’runus demissa)

few-bracken fern, willow, poplar, smart- wecd, lousewort. Ants on many of these do not scent to be very common or are absent. ()ne group of plants with E.I7.N.'s in which I have been interested are the jewclwecds (also known as touch-me-not, or policetnan's helmets) (IIIUHII/UIM‘Ali/1.). ’l ltey normally grow itt damp shady habitats where ants are few or absent; their [3.I".N.‘s are prominent and usually clustered below the flowers and developing fruits. l have observed most closely I. g/undu/t'fera (presumed to be an introduction front Asia) and I. ec‘ulearala. I cannot state that I ltave never seen ants in their vicinity but they are rare; on the other hand I have seen aphids and a few other insects using the nectar. Could it be that the E.F.N.‘s are a lure to keep predators front the reproductive structures? Many nectars contain constituents which may be nar— cotic or toxic. Perhaps these are present

:, V“. . .,

* @gﬁﬁxa i“ "’"’_‘ n .ﬁﬁ3gggﬁ.

l neetaries can be seen as small structures on the petiole of the leaf of

in the Impatiens net'tar? There are lots of examples of nectats which are nar- cotic. Maybe in some species such as a bitter cherry, where Ii.I-‘.N.'s are very small, they are in the process of becom- ing, useless or vestigcal because they are few ptcynaciotts ants iii the habitats to which the bitter cherry has become adapted? Questions then remain about E.F.N. function which, maybe field observations by B.C. naturalists could help to answer?

1. THE BIOLOGY OF NEC- TARINES. B. Bentley, and T. Elias,

editors. Columbia University Press (I983).

2. EXTRAFLORAL NECTARIES AND PROTECTION BY

PUGNACEOUS BODYGUARDS. I3. Bentley. Ann. Rev. Ecolo. and Systems 8:427 (I977).

V. C. Brink

(reprinted from the December I986 issue of the

B.C Naturalist)

AND JUST A FEW BIRD SIGHTINGS FOR THIS ISSUE!!

Geoff Hogan saw a cuckoo Sp.

on Oct. 6. On Oct.

in Dunstaffnage

10, Dan McAskill saw two mature and one immature red—tailed hawk,

and

one rough-legged hawk (dark phase) in Irish-

town .

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