Article 72 – ‘Small but deadly’

Hi, welcome to Taiga Bonzai we have written much on pests and disease which cause problems for agriculture and horticultural communities worldwide, in this article we discuss a candidate that not only kills trees, but is able to create serious problems to humans and domestic animals.

Introduction – the ‘Maritime pine‘ or ‘cluster pinePinus pinaster is native to the Mediterranean basin covering a large area that includes, Portugal, Northern Spain, Southern and Western France, Western Italy, Croatia, Tunisia, Algeria and Northern Morocco. It is a hard, fast growing pine containing small seeds with large wings and favours this region’s climate of cool rainy winters and hot dry summers. Pinus pinaster is closely related to Pinus halepensis commonly known as the ‘Aleppo pine’, because both species share many of the same characteristics and pests.

Pinus halepensis also grows in the Mediterranean region in Malta, Montenegro, Albania and east to Greece, Syria, Lebanon, Southern Turkey, Palestine, Jordan and Israel. Both these species are subject to attack from Dioryctria sylvestrella, commonly known as the new Pine knot-horn‘ or ‘maritime pine borer‘ a member of the Pyralidae family, which occurs naturally in Europe, much of Asia and North Africa. This pest has been discovered as far north as the Arctic Circle but is more common at lower latitudes, where it does most damage.

Dioryctria sylvestrella moth and caterpillar courtesy of Frank Hecker – wikipedia

Dioryctria sylvestrella – is a small mottled brown and white insect with a wingspan of 28 to 35 mm, which flies in a single generation from June to October. The female chooses fast-growing, vigorous host trees on which to lay its eggs. The larvae attack buds, shoots, cones and young stems. Damaged tissue attacked by the rust fungus Endocronartium allow the larvae to enter the tissues and tunnel under the bark into the phloem. The larvae usually remain close to where they were hatched, but occasionally migrate to other parts of the tree.

Larvae pupate inside a mass of resin mixed with frass (shown below) which they produce and continue to feed within. Their boring activity causes large quantities of resin to flow from the wounds weakening the tree allowing fungi and other pathogens to gain entry eventually threatening the trees health. D. sylvestrella was first detected in the UK in 2001 and is different from the three other species in the genus by the fact that the subterminal line is generally smooth with a single waved kink at its midpoint, in the other three species this line is dentate from the mid-point to the dorsum.

Resin and frass of D. sylvestrella images courtesy of ‘Project Portugal’

Efforts to control – these species of pine are under threat, young trees have no defence and eventually succumb, older more mature trees are able to withstand the onslaught but are severely weakened. In Italy the powers that be have thought of several methods to control D. sylvestrella for example chemical usage however, horticulturists are against such practice their arguments are that there is little or no control and many claim that an effective chemical solution has yet to be found.

In addition, it is argued that a chemical approach would have serious consequences to the horticultural industry. Because if used its properties become airborne resulting in contamination of other crops including, olive, fruits and vegetable production rendering such unmarketable, hence loss of income not only to the horticulture fraternity, but also to the state. Moreover, no one in their right mind would consume contaminated food produce, because of the possible side effects if they are unsure of its origin, which is a stringent mandate of the EU.

Finding a solution – the agricultural sector meaning the farmers and growers are of the consensus that it is virtually impossible to prevent the onslaught of D. sylvestrella due to its abundance in the Mediterranean region and its ability to invade. However, studies on D. sylvestrella behaviour indicate that larvae when ready to metamorphosize are compelled to descend the tree and conceal themselves in the litter at the tree’s base. Therefore, preventing the larvae from doing so seems a logical solution in stemming the birth of the next generation of moths.

Traps have been manufactured that can encircle the trunk capturing the larvae as they descend, which are then disposed of. Although these traps are efficient they cost approximately 30 to 50€ each depending on the region, to some this may appear inexpensive; but in reality it is the opposite because much depends on the amount of trees one has on the land. Hence farmers and growers are designing and constructing their own versions as shown below.

Homemade larvae trap image courtesy of ‘Project Portugal’
https://www.youtube.com/results?search_query=project+portugal+no+29

This homemade version consists of plastic base and wall with a layer of foam affixed to the inner diameter to fit snugly against the contours of the trunk. A hole is drilled into the base where a tube protrudes downward to which a plastic bag containing tree litter is tied on. The larvae walk around the trap eventually falling down the tube into the bag, when the bag is full the larvae are disposed of. This homemade trap costs approximately 3€ to construct. It can be argued that sometimes even the most simplest of inventions are more effective than expensive chemical alternatives.

D. sylvestrella – is harmful to humans and domestic animals due to its ability to shed toxic hairs (called setae or spines) from its body, which it is apt to do when disturbed. According to James H. Diaz of the National Center for Biotechnology Information (NCBI) “caterpillars bear highly specialized external nettling or urticating hairs and breakaway spines or setae to defend against attacks by predators and enemies“. These “can inflict serious human injuries ranging from urticarial dermatitis and atopic asthma to osteochondritis, consumption coagulopathy, renal failure and intracerebral hemorrhage.”

There are approximately 12 families of lepidoptera worldwide that are able to inflict serious injuries to humans and D. sylvestrella a member of the Pyralidae family is one of them. Andrea Seldeslachts, Steve Peigneur, and Jan Tytgat in their paper published online 2020 May 30. ‘Caterpillar Venom: A Health Hazard of the 21st Century’ states that “Depending on the family and species involved, some toxins provoke local urticating dermatitis, a burning sensation, allergic reactions, respiratory system problems and/or ophthalmia nodosa, whereas others cause systemic effects, including hemorrhagic syndrome, acute kidney injury and/oral phalangeal periarthritis.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7345192/

With domestic animals being inquisitive is their natural bent, prone to sniffing or licking, the effect of the toxic venom from the hairs (setae or spines) of D. sylvestrella has what only can be classed as a devastating tragic misfortune, in that there being no antibiotic treatment available at this juncture. These animals are at risk with the most vulnerable part being the snout a wet fur less surface around the nostrils of the nose called the rhinarium, if this is infected by venom the consequences are severe; hence contact with D. sylvestrella larvae should be avoided at all cost.

As we have stated pests and disease are a major problem in today’s world which have been highlighted through our recent articles ‘Bug apocalypse‘ and ‘Unseen enemies‘, not all can be attributed to mankind’s actions, but many can – we have a problem that needs our urgent attention; failure to address it will only lead to escalation. Until next time, BW, Nik.