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Ask the Expert, Questions & Answers Question - Can you explain why white flowers seem to attract more insects than red ones; in the present case, insects teem in the flowers of the white peony (Paeonia spp) while red peonies, only a few centimetres away, are not visited?
Question - This enquiry was sent to us by a member living in Cyprus. The plant in question is a 2-3m high shrub, growing on a track between Goudi and Polis, in western Cyprus, altitude <50m. As the photos show, it is well-clothed in mid-green entire leaves and red berries. The latter are sub-spherical, and with a distinctive sort of husk (green). The member adds: "I hope you can name this for me!"
Question - "This year we noticed a very beautiful moth in our garden in the Languedoc Roussillon part of France and took some pictures of it. I wonder if you know this moth? I understand that it comes originally from South America and that it is harmful to palm trees."
Question - "A few days ago we spotted the plant in the attached photograph flowering in the wild at Ostia Antica, near Rome. We have no idea what it is, can you help? Hmm, I would have said perhaps Trachymene caerulea except that I don't think the leaves look right. It was growing at sea level in the excavations: in ancient Roman times this was a sea port and is now about one kilometre inland because the Tiber estuary/delta has gradually silted up. I did not see any signs of underground water but perhaps was not observant enough. I found the plant growing in the ruins of a Roman building, as it were in a "room", of course open to the light. It was in a very sunny position, except that the shadow of the walls may fall upon it for a few hours; it was not close to the walls (but rooms in ancient Roman houses were not very large) and was growing in hard, dry, what seemed slightly sandy earth - probably calcareous since the water here is very hard indeed. I found it on 4 September, just before the first autumn rains. The plant was still making buds, and did not yet have any seed at all as it was just beginning to flower. Almost nothing else was growing there, it was so parched and sun-baked. So imagine the delight of suddenly coming upon sprays of blueish-purple!"
Question - "Can anyone identify the caterpillars that for the first time have been ravaging our santolinas this year? (Our garden is in a rather arid part of Provence.) There are small apparently black ones and larger slightly bristly ones of a dull brown with greenish-yellow markings on their backs and crescent shapes of the same colour outlined in black on their sides. I suspect that both are the same species, the ‘black’ ones being at an earlier stage of development, for although they appear uniformly dark to the naked eye, a magnified digital photograph reveals faint yellowish markings on their backs corresponding to the marks on the larger caterpillars. They appeared in late April and early May following heavier than usual winter and spring rains and they stripped 4-year-old santolinas of all their leaves (S. chamaecyparissus and S. neapolitana ‘Edward Bowles’). We have also found them on a neighbouring lavender plant and on wild rosemary plants. Clearly they have a taste for the aromatic. We have never seen caterpillars on any of these plants before. We’d love to know of what butterfly or moth they are the larvae."
Question - "It`s a cry for assistance! Our mulberries, which are very important in our garden have begun to die very quickly this week. There are yellow marks on the leaves on the branches and on the fallen leaves. No insects or caterpillars. Perhaps it`s a virus or the spring rains. What should I do? Please could you inform of any internet sites or experts which could help. I have looked at the internet but the information is a little confusing." Question - "Attached is a photo of flower taken in the Sibillini mountains yesterday, I have searched through my library of wild flowers and indeed the internet to no avail. Is there anyone among the experts who could please identify it for me? " Question - "I have long been contemplating some sort of water feature/watery element in my garden. I would like to attract wildlife, to enjoy the sight of an area of water and − why not? − when the weather permits, bathe in my "pool". I have read about "natural swimming pools" in a number of books and garden magazines but most seem to be in northern climes. One local garden designer and nurseryman told me categorically that the natural pool could not be achieved here because of our high summer temperatures. Could you advise, please?" Question - "I have recently seen articles which report that certain vermiculites could contain asbestos. Could you comment on the health and safety aspects of using vermiculite?" Question - "
Why do some plants like Hibiscus mutabilis or Rosa chinensis have flowers that turn a different colour as they open, mature and die?" Question -
"Can you identify this extraordinary plant (below) I found growing in gravel close to Anduze, in Languedoc, France? The gravel was brought in about 10 years ago and overlies an alluvial soil deposit." Question -
"I want to ask someone about green manures that might help in citrus cultivation. I live in drought-devastated Cyprus and cannot give the many trees I have as much water as they need. (I know they are not good plants for dry gardening, but my house came with lots of them). So I thought I might at least help them with some organic companion plants. I have constraints of what is appropriate and what is available." Question -
"Cestrum nocturnum gives off its scent at night in pronounced waves or pulses. How does the plant do this physiologically? And what are the advantages of a pulsed scent rather than a steady scent?" Answer (November 2008) - " All flowers have evolved mechanisms to achieve successful pollination. C. nocturnum produces an intensively fragrant "volatile" scent during the night to attract its pollinator, a moth of the noctuid family (Agrotis spp), see page 40 of TMG number 35. The moth relies on the fragrance to guide it to the flower: it has its own GPS system. Moths may be attracted from a distance of over six metres. The first interesting point is that the scent release is an endogenously (internally) controlled circadian rhythm, i.e. it is found in a cyclic (24h circadian) manner, both in constant darkness and constant light at constant temperature. As scent is usually released in the evening, but the corolla behaves endogenously, there must be an additional ' zeitgeber' (from the German for time-giver, synchronizer) which synchronizes the flower's endogenous (internal) time-keeping system (clock) to the earth's 24-hour light/dark cycle. This might be in another part of the plant, for example the leaves, as the strongest 'zeitgeber' in plants is light although it can also be temperature. Although in nature in constant conditions this rhythm is a period of roughly 24 hours, it is affected by temperature, with the cycle lengthened in colder temperatures and reduced at higher temperatures (Overland, 1960). As mentioned in the previous answer, there may be a number of reactions which would lead to the release of scent, therefore if one or more of these reactions were temperature-dependent the cycle would be extended. Research has also been carried out to examine the constituent components of the scent (Al-Reza et al., 2009). The extract was found to contain alkaloids, flavonol glycosides, steroidal saponins, fatty acids, essential oils phenols, and others (Bouchbaver et al., 1995). The chemical components of the scent are volatile compounds which facilitate their release into the atmosphere. As mentioned in the previous answer, scents are usually produced by metabolism of compounds within the cells and the corolla is often involved. The corolla was shown to control this mechanism as the cycle exists independently in excised corolla tips (Overland, 1960). In snapdragon flowers, the same endogenous activity was shown by examining the release of methyl benzoate, one of the most abundant scent compounds of bee-pollinated snapdragon flowers (Kolosova et al., 2001). This research showed that the total amount of benzoic acid available in the cells was a determining factor in the regulation of the rhythmic emission of scent. This could be evidence that scent is only released once a sufficient supply of precursor chemicals is built up, leading to a pulsed scent. A simpler explanation for the observed release of scent could be atmospheric conditions, i.e. temperature fluctuation, humidity or simply very gentle breezes that give the impression of a pulsed release of scent, or additional release of the volatile compounds from the cell surfaces. I have discussed this with an evolutionary biologist, Dr Elisabet Sahtouris, and she offered an additional theory that it could also be an economic use of the volatile compounds over a longer period." Answer (November 2008) - "The best chemicals to use are the synthetic pyrethroids − not pyrethrum. They are extremely active at very low dosages and very effective on most insects but they are broad-spectrum, killing both the good and the bad. There are several products to choose from. The common names of some of the active ingredients are: permethrin, deltamethrin and cypermethrin. Answer (December 2008) - "Our first expert was dubious of the value of cover crops, saying that citrus trees are natives of South East Asia where rain is usually plentiful and that irrigation is indispensable. Any benefits accruing from companion plants may be outweighed by the competition for water with the citrus trees. Answer (December 2008) - "It is impossible to identify accurately plants a) from a photograph and b) without floral parts. Identification from vegetation is at best, a best guess. Answer (January 2009) - "Flower colour depends on the presence of pigments in the flower (or leaves, stems and fruit), upon the pH (the acidity or alkalinity), the genetic make-up and other conditions of the sap in the plant cell. Several pigments are concerned. The most common are the yellow and orange colours contained within the cell plastid (a cellule containing the chloroplasts), the red, purple, blue and orange anthocyanins and the yellow to ivory anthoxanthins. Flowers contain some pigments but not others. Answer (March 2009) - "Vermiculite is a naturally occurring mineral generally derived from mica. On heating, mica granules expand greatly to give a lightweight highly water-absorbent material that is used in horticulture and in numerous industrial applications including in plaster, mortar, in concrete and as insulation in walls, floors and ceilings. It has been demonstrated to be safe to use, and no serious health risks have been found to result from exposure to vermiculite. Answer (March 2009) - "Our experience is that it is perfectly possible to have a swimming pond in quite an extreme climate: we are zone 10 in gardening terms, which means that we rarely get frost and have highs of 40°C occasionally in the summer months but more regularly up to 30°C air temperature. The aim of the pool constructors is to match the plant community used to clean the pond water to the make-up of the water itself, thus copying nature and providing an experience similar to that of bathing in a river or lake. Size and shape is not important and you can have a dizzying variety of shapes, with large rocks, cascades, bridges etc. Have a look at the gallery section on the web site below for some ideas. Answer (June 2009) - "The plant has been identified as Cynoglossum magellense, a Boraginaceae and an Italian endemic. Answer (July 2009) - "It is very difficult to give a precise answer from a written description however there are two diseases recorded on “mulberry”. Gibberella moricola or canker and die-back of mulberry has been recorded in France and Italy. The most conspicuous features are large cankers on the stems beyond which the foliage turns yellow and wilts leading to die back. This genus has been reported to cause rapid wilting of the leaves followed by chlorosis and necrosis. A cross-section of the infected leaf/branch should show vascular discoloration. Answer (August 2009) - "The plants on which caterpillars feed are very indicative of their species. A search for santolina indicates (as far as I can discover – but my information could be very far from complete) two species of moth whose larvae feed on this plant: Eupithecia santolinata, a rare species found in Provence, and Cucullia santolinae, which seems to be more common around the Mediterranean. I tend to plump for this species. The members raising the question also agree that their caterpillar resembles the latter species." Answer (September 2009) - "This is Trachelium caeruleum, a not uncommon plant in the Mediterranean. It often likes damp walls in shade, though." Answer (December 2009) - "This is a photograph of Paysandisia archon, a moth belonging to the Castniidae family with a palm-boring caterpillar. It is a native pest of Argentina and Uruguay and was first recorded in France in 1999, in Spain in 2001 and in Mallorca in 2003. It is now recorded throughout the Mediterranean Basin including in France, Italy, Spain and the Balearic islands. Its larvae attack many palms, but prefer - in order - Chamaerops humilis, Phoenix canariensis, Trachycarpus fortunei and Washingtonia spp. At home the Paysandisia archon larva infests palm trees but it is kept in check by natural predators and parasites. It appears to have been brought to Europe accidentally on imported palms which are now being planted by many municipalities throughout the Mediterranean Basin to replace the existing plane trees, many of which are old and diseased. The beautiful moth is large, some 90-110mm across, with dark green front wings with brown streaking, and bright red back wings with bold black and white markings. The adults fly during the day from May to September. Eggs are laid in the palm crowns where the grubs hatch. The caterpillar first eats tender leaves at the heart and then bores into the trunk during a period of one to two years.The first sign of attack is a very regular series of holes in the emerging fronds. Later, there will be piles of sawdust mixed with excrement at the base of the fronds and finally, after pruning, holes and even cocoons will be seen in the base. The grub will over-winter and will stay in the larval stage for up to 18 months. Without control the plant will eventually wilt and die. Detection and control are difficult as larvae cannot be seen or reached easily within the crown. Periodic inspections will reveal any damage in the emerging young fronds. Chamaerops humilis is especially vulnerable as its heart is so small. Since this moth is not a pest in its native country no control method has yet been developed. It is believed that the moth could spread to a much larger region in the future if measures are not taken; however, natural predators may also be introduced with the imported palms. A good soaking of the heart with an insecticide containing chlorpyriphos and dimethoate should be effective; this is not a general recommendation, however, and appropriate authorities should be contacted before any attempt is made to spray these pests. In Nîmes, specimen palms are covered with large plastic netting to prevent egg-laying but this does take away some of the beauty of the palm tree. Rhynchophorus ferrugineus is another pest of imported palm trees. This is a member of the coleoptera originating in Asia and Malaysia which arrived in Spain in 1995 and was first detected in Mallorca in 2006. It attacks a great variety of palms, with a preference for Phoenix canariensis, Phoenix dactylifera, and Washingtonia spp. The adult is 2-5cm long and 1 cm wide, coloured red, with black spots on the body, corrugated wing sheaths, and a long beak. The first parts of the palm to be attacked are the most tender leaves at the heart and then the trunk. Usually the first sign of damage is the collapse of the central fronds, by which time the palm is moribund. In view of the dangers posed by this pest and the absence to date of effective treatments, experiments are being carried out in many different areas of the Mediterranean, ranging from spraying regularly through the summer, through avoiding pruning except in the winter, to zapping the crown of an infected palm with a batch of microwave "ovens" mounted on extended forklifts. Please see page 15 of TMG 56 for additional information" Answer (January 2010) - "I think the plant is a species of Lycium and some of our specimens, L. barbarum (Duke of Argyll's tea-tree), match the photos. L. barbarum is not recorded for Greece in the Flora Europaea, but it does say that this Chinese plant has been widely planted as hedging in the Mediterranean. It has bright red fruits that look like little tomatoes, though with this family they could be poisonous! Answer (June 2010) - "Over the years, research has been carried out investigating flower colour and attractiveness to insect pollinators. Within a single plant species where flower colour differences exist research has been concentrated on the flowers on a plant that change colour with age. Investigations have shown that the effect of floral colour change has a direct effect on attractiveness to insects. Research carried out by Oberrath studied the effect of floral colour change on the attraction of insect pollinators to the herb lungwort, Pulmonaria collina. Lungwort flowers change colour with age from red to blue. Young red flowers had a significantly greater pollen and nectar reward and were significantly more often unpollinated than old blue ones. Red and blue flowers both influenced the long-distance attractiveness of plants but short-distance attractiveness, defined as the number of flowers visited successively on an individual plant, was influenced mainly by the number of young red flowers. The co-occurrence of the change in reproductive ability, in amount of reward, and in flower colour enabled lungwort plants to direct pollinators to reproductive, highly rewarding red flowers. The data suggest that by maintaining changed flowers lungwort plants can increase their long-distance attraction and simultaneously enhance the probability of visits to pre-changed flowers. Oberrath proposed floral colour change as a mechanism that can increase the efficiency of pollen transfer to enhance plant fitness. Research was also carried out by Ida and Kudo (2008) on bees visiting Weigela middendorffiana whose flowers change colour from yellow to red. Red-phase flowers no longer have a sexual function and nectar, and bumblebees selectively visit yellow-phase flowers. These authors found that retaining red-phase flowers (unlike in the lungwort research above) had no effect on attractiveness to bee visitors. Specific research carried out on the peony in 2006 (MacKenzie et al.) concentrated on scent rather than colour. This research centred on the wasp Polistes dominulus and its attraction to budding peonies. It concluded that the wasps showed significant orientation response to peony bud odour, but no response to peony foliage odour when compared to the control. Pheromone traps of various colours were investigated by Clare et al. (2000) to investigate capture of non target bee species. It found that honey bees were most attracted to white traps followed by blue, while bumble bees were most attracted to blue traps. Native bees (New Zealand) were seen most often in white traps followed by in yellow and green ones. The study found that the target pest insects were not influenced by colour and thus recommended use of green or red traps to avoid capture of bee species. Other potential reasons for colour preference could involve colour contrasts and the time of day when insects visit. White gives a much stronger contrast to the green foliage of peony than would exist in the red variety. Blue colours appear stronger later in the afternoon and may appeal to certain insect species. Some insects may also have a stronger attraction to UV radiation or a combination of colour and, over larger distances, odour. It would seem reasonable to conclude that each insect species has different colour and odour preferences. Perhaps while the white peony was visited most by certain insects, the red peony may be visited by another species at a different time of day." |
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