Hi welcome to Taiga Bonzai, in this article we discuss poisonous lepidoptera with arguably the Monarch Butterfly Danaus plexippus and Pipevine Swallowtail Battus philenor being the most well known.

Introduction – although the Monarch and Pipevine butterflies and a large variety of moths are toxic. It is the larval stage (caterpillars) where they are most dangerous to humans, animals and a vast variety of trees, shrubs and horticulture in general, due to the huge devastation they cause.

Caterpillars of most species eat plant material (often leaves), but not all; some (about 1%) eat insects, and some are even cannibalistic. Others feed on animal products. For example, clothes moths feed on wool, and horn moths feed on the hooves and horns of dead ungulates.

Caterpillars are typically voracious feeders and many of them are among the most serious of agricultural pests. In fact, many moth species are best known in their caterpillar stages, because of the damage they cause to fruits and other agricultural produce. Whereas the moths are obscure and do no direct harm.

Etymology – caterpillars have soft bodies that can grow rapidly between moults. Their size varies between species and instars (moults) from as small as 1 millimetre (0.039 in) up to 14 centimetres (5.5 in). Some larvae of the order Hymenoptera (ants, bees, and wasps) can appear like the caterpillars of the Lepidoptera. Such larvae are mainly seen in the sawfly suborder.

However while these larvae superficially resemble caterpillars, they can be distinguished by the presence of prolegs on every abdominal segment. An absence of crochets or hooks on the prolegs. (these are present on lepidopteran caterpillars) One pair of prominent ocelli on the head capsule, and an absence of the upside-down Y-shaped suture on the front of the head.

Lepidopteran caterpillars can be differentiated from sawfly larvae by: the numbers of pairs of pro-legs; sawfly larvae have 6 or more pairs while caterpillars have a maximum of 5 pairs. The number of stemmata or simple eyes, sawfly larvae have only two, while caterpillars usually have twelve. (six each side of the head)

Defence – many animals feed on caterpillars as they are rich in protein. As a result, caterpillars have evolved various means of defence. These include defence against physical conditions such as cold, hot or dry environmental conditions. Some Arctic species like Gynaephora groenlandica have special basking and aggregation behaviours apart from physiological adaptations to remain in a dormant state.

Appearance – of a caterpillar can often repel a predator, its markings and certain body parts can make it seem poisonous, or bigger in size and thus threatening, or non-edible. Some types of caterpillars are indeed poisonous or distasteful and their bright colouring warns predators of this. Others may mimic dangerous caterpillars although they are not actually dangerous.

Many caterpillars are cryptically coloured and resemble the plants on which they feed. An example of caterpillars that use camouflage for defence is the species Nemoria arizonaria (shown below). If the caterpillars hatch in the spring and feed on oak catkins they appear green. If they hatch in the summer they appear dark coloured, like oak twigs.

Chemical defences – more aggressive self-defence measures have evolved in some caterpillars. These measures include having spiny bristles or long fine hair-like setae with detachable tips. These cause serious consequences as described in the previous article. (Unseen invasion 4 the ‘Pine knot-horn‘ or ‘Maritime pine borer‘ )  

Moreover, venom which is among the most potent defensive chemicals in any animal is produced by the South American silk moth genus Lonomia. Its venom is an anticoagulant powerful enough to cause a human to hemorrhage to death. In Brazil 354 cases were reported between 1989 and 2005 with lethality ranging up to 20% with death caused most often by intracranial hemorrhage. This chemical is being investigated for potential medical applications.

These toxic species including the Cinnabar moth Tyria jacobaeae and monarch Danaus plexippus caterpillars, usually advertise themselves with the danger colours of red, yellow and black. Any predator that attempts to eat a caterpillar with an aggressive defence mechanism will learn and avoid future attempts.

Caterpillars cause much damage, mainly by eating leaves. Such damage is enhanced by monocultural farming practices, especially where the caterpillar is specifically adapted to the host plant under cultivation. For example, the Cotton bollworm, Helicoverpa armigera is a major pest of cotton Gossypium spp. maize, Zea mays, pulses, Fabaceae tomatoes, Solanum lycopersicum and sorghum bicolour throughout most of the world.

This species of moth is a recent arrival in the Americas where it is rapidly spreading. It has documented resistance to 49 pesticides and is one of the most polyphagous and cosmopolitan pest species. Caterpillars have been the target of pest control through the use of pesticides, biological control and agronomic practices.

Such approaches are defeated over time via the evolution of resistance mechanisms in the insects, many species have become resistant to pesticides. Until next time, BW, Nik.

Hi, and welcome to Taiga Bonzai, in this post we continue our journey bringing to light the catastrophic failures of mankind’s idiosyncratic actions.

Introduction – according to the Botanical Gardens Conservation International (BGCI) and its network of 500 member organisations, there are 60,065 species of trees in the world; Many are rare and threatened with extinction.

If we multiply the number of tree species with the number of known pests and disease all with different triggers, the statistics would not only be bewildering but also incomprehensible. Here we highlight more increasing problems the world has to face beginning with a few examples of the many deadly diseases, for which at this juncture there is little or no control.

Disease – Armillaria Root, according to Guido Schnabel of the Clemson University School of Agricultural, Forest and Environmental Sciences. “Armillaria root rot caused by the fungus Armillaria tabescens wreaks havoc on rootstocks, killing young and old peach and cherry trees before spreading to neighbouring trees.” “Between 1987 and 1992 Armillaria root rot caused an estimated $3.86 million to the peach industry and between 2000 and 2002, more than $1.5 million in damage to the Georgia peach industry.”

The first symptoms of an Armillaria infection are chlorotic leaves, stunted growth and sudden collapse of shoots. An obvious sign that infection is there due to the presence of clusters of mushrooms around the base of an infected plant. Fungi sprouting from an A. mellea infection are honey-coloured to dark brown and have a domed cap. “Depending on species, the mushrooms may or may not have an annulus around the stalk or caps that are more disc-shaped.”

This devastating disease can be caused by other Armillaria species including, A. mellea a the primary pathogen in northern states causing premature peach tree decline. The potential for significant annual losses in Michigan, is due to the predominant fungus A. ostoyoe found in tart cherry orchards. There is no ‘silver bullet’ solution to protect trees and Armillaria infections have taken many prime orchard sites out of production causing a huge loss of revenue.

Anthracnose – high on the list of devastation is widespread and considered an important disease in most countries. It is caused by a group of fungi in the genus Colletotrichum, that attacks leaves, twigs, flowers and fruits of a great number of tree and shrubs.

Apple scab is a common disease of apple and crab apple tree varieties, as well as Mountain ash Sorbus and pear. It is caused by a fungus Venturia inaequalis that infects leaves and fruit, leaving the latter unsuitable for consumption. Leaf spots are olive green at first, later turning dark brown to black. Infected fruit turns colour in a similar fashion, ending up brown, corky and deformed.

Thousand canker disease – affects many plants including walnuts Juglans sp. It is mainly found in the Western United States however, black walnuts trees in Tennessee were found to be infected in the summer of 2020. It is vectored by walnut twig beetles Pityophthorus juglandis and forms small cankers around their galleries.

As time progresses these small cankers coalesce to girdle branches and stems, trees can be infected for years before symptoms become visible for example. Foliage in the upper branches of declining trees wilt and become yellow. Once a tree begins to decline it is often dead within a few years and at present there are no chemical management solutions to control the disease.

Thus far we have given examples (albeit in brief) of the devastation caused by some of the many thousands of insects and disease. Adding more examples would probably substantiate the argument further, but this task has already been accomplished. In the book ‘Taiga Bonzai – Simplifying The art’ (Revised Edition), where 2 chapters reveal extensive information on these subjects, c.13 concentrates on ‘Pest and Disease’ and c.14 discusses ‘Toxicity’.

We now turn our attention to plants required for our consumption namely fruit and vegetables starting with one of the world’s oldest fruits the humble apple. The bureaucracy over production and the controversy surrounding it including the diseases that attack various species of this particular fruit.

The apple – Malus domestica, its ancestor Malus sieversii originated in Central Asia 4 thousand years ago. Today there are 7,500 apple varieties throughout the world – 2,500 of which are grown in the United States. In the 2019/2020 crop year, China was the leading producer of apples, it’s production amounted to 41 million metric tons. The European Union came in second place with approximately 11.48 million metric tons.

The UK has been producing apples since the Roman occupation (AD 43 to AD 410) however, production is now in serious decline due to bureaucracy and trade problems with the EU. Hence growers are given payments to burn their orchards.

Natural England and the National Trust claimed 60% of England’s orchards had disappeared since the 1950s and have launched a £500,000 project aimed at halting the decline. The crisis has been even worse in some areas such as Devon, which has lost almost 90% of its orchards.

According to David Bullock, the head of nature conservation at the National Trust, “Traditional orchards have been disappearing at an alarming rate. We are in real danger of losing these unique habitats.” (https://www.theguardian.com April 2009)

The orchard – apple trees need space to grow, dwarf varieties require a minimum of 5m, standard trees need a distance of 9 to 11m. But this distance is inadequate because, as the trees mature they spread out, thus the risk of cross contamination from bacterium and fungal spores increases.

In 2017 the total area harvested in the world for apples was 4,933,841 hectares. But, apples are not the only fruit produced, other varieties include apricot, pear, peach, plum and damson. Hence the land mass required increases – these varieties predominantly cultivars are also susceptible to attack, thus the orchard becomes the playground for disease.

Such diseases include: Fire Blight a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to apple and pear producers and is believed to be indigenous to North America, from where it spread world-wide.

Powdery mildew Podosphaera leucotricha a fungus that forms a dense white fungal growth (mycelium) on the host tissue affecting leaves, buds and shoots. Black Rot and FrogEye Leaf Spot Botryosphaeria obtusa attack fruit, leaves and bark of apple trees. Phytophthora Rot a soil-borne fungal disease by the pathogen Phytophthora sojae causes seed rot and attacks roots and stems; trees infected by such pathogens are usually destroyed.

However, there are apple tree varieties that are said to be disease resistant for example, Liberty, Freedom, Dorsett Golden, Enterprise, Goldrush, Pristine, Arkansas Black and Williams Pride which are American cultivars. European apple trees include, Topaz, Herefordshire Russet and Otava, but can the claims of being disease resistant to all insects and pathogens be substantiated – in short the answer is probably not.

Arguably much depends on a particular climate zone; arid, humid, wet and cold. Moreover, these zones harbour other pests for example, the Round headed apple tree borer, European red mites, Red banded and oblique banded leaf rollers, Rosy aphids, Woolly aphids, Green fruit worms, Leafhoppers and Japanese beetles. Until next time, BW, Nik.