Guest blog: St Helena

St Helena, a tropical island on the mid-Atlantic ridge in the South Atlantic Ocean, is part of the UK’s Overseas (OTs) Territories. The island is home to a wide variety of wildlife, some of which is not found anywhere else in the world, and along with the other OTs makes a significant contribution to global biodiversity.

Invasive non-native species are one of the biggest threats to the wildlife on islands. Native wildlife has evolved away from other predators, diseases and competitors making it particularly vulnerable to new threats. Below we hear how invasive non-native species affect the wildlife and people on St Helena and how residents and government staff are working to protect the island.

Image: St Helena National Trust

Biodiversity threats

Almost 800 non-native species have been recorded on St Helena. Most of these are plants and invertebrates but there are a small number of introduced vertebrates. These species have a significant impact on the native wildlife of St Helena, including the St Helena Plover (Charadrius sanctaehelenae), a bird which is found nowhere else in the world.

Since the 1970s the St Helena Plover, locally known as the Wirebird due to its thin legs, has been decreasing in numbers on the island. In 2007 the species was listed as Critically Endangered in the IUCN redlist.

Non-native cats, rats (mostly Rattus noregicus) and to a lesser extent, the Common Myna Acridotheres tristis are known predators of wirebird chicks and nests and have played a significant role in its decline. Invasive plants have had an impact too.

Some of the wirebird’s population is found in pastureland in dry, flat short-sward pastures. Livestock grazing has become unprofitable and less common, leading to the decline of arable land and invasive plants such as bullgrass (Juncus cappillaceus & Juncus tenuis) becoming established. Extensive vegetation growth of this species can delay or prevent wirebird breeding.

Thanks to successful management, there are now more than 500 St Helena Plover adults found on the island and this species has been downlisted from Critically Endangered to Vulnerable. However, their population is still extremely small and declining due to land-use change and continued predation by invasive predators.

Impacts on food production

There is a large range of introduced plant pests on St Helena, some of which cause significant damage to agricultural and horticultural crops. Anthony, a part time farmer selling vegetables to the public, and Nicholas Stevens, a commercial farmer using hydrophonics, explain how invasive whitefly impact on their businesses.

“Very limited crops can be grown, [we] can’t grow squash, cucumber, pumpkin and tomatoes as the whitefly destroy these crops. Biggest pest [is] Greenhouse whitefly (Trialeurodes vaporariorum) they feed on plants sucking all the nutrients. The white fly has built up a resistance to most sprays, so most chemicals don’t work. The biocontrol (Encarsia formosa) are on the plants, but very slow working. Other natural methods like washing-up liquid may work in a polytunnel but not in an open field.”

Whitefly was first recorded in St Helena in 1995. They are resistant to most chemical pesticides, which means farmers need to work hard lowering their numbers and prevent them from climbing high enough to damage the plant. Sometimes assistance is needed from local pest controllers, such as Pest Control, SHG.

“We assist the farmers and the public by helping to control agriculture pest/weeds on request. There are many calls for pests from Greenhouse whitefly (Trialeurodes vaporarioru), Rust Mite (Tetranychus evansi) and aphids.

As always in warmer months, at the moment the Mediterranean fruit fly (Ceratitis capitata) is very destructive; it mines the soft stone fruit (especially peaches, plum, nectarines, mango and apricot) laying their eggs in the fruit and the larvae feed on the fruit, making it really difficult to grow fruit locally. Pruning and removal of fallen rotten fruit from under the tree that might contain the fruit fly larvae is encouraged as a healthy tree is actually quite good at keeping the fruit flies away.

Since arriving in the 1980’s, despite efforts to control, is difficult with high numbers and inaccessible locations.”

Invasive pests don’t just affect plants. Melvin, a retired beekeeper battles with an invasive moth which lays eggs in his hives.

“[I am the] owner of small holding known as Hermitage Enterprises, comprising egg production, beekeeping and vegetable garden. I have been keeping bees for about 14 years and currently have two hives.

The biggest insect pest to me as a beekeeper is the Wax Moth (Galleria mellonella), and I have lost several swarms through wax moth infestation.

Images: St Helena National Trust

It takes one moth to enter a hive, lay eggs and hatch larvae to infiltrate a colony. Once the larvae hatch they immediately start burrowing through the comb of the hive and line the resulting tunnels with a silken web. The burrowing process causes damage to the cells of brood comb and honey comb. In brood comb, damage to cells can sometimes result in deformed brood. Once the larvae have grown they will find a place to pupate, which usually takes place on the wooden frames of the hive. The larvae will chew a cavity into the frame, causing permanent damage to equipment, before forming a cocoon from silk thread. In large numbers, the hardening of the wax moth cocoons between stored combs can cause a box of combs to become fused.

Melvin has found a treatment for wax moth, but this impacts on honey production.

“[I use a] chemical called “Certan” which is a safe and environmentally friendly product based on a concentrated solution of Bacillus thuringiensis, a micro-organism can be used in the control/eradication. It cannot be used on honey or combs meant for human consumption. I have used this before and it has worked. In most cases I have had to burn the whole hive to fully eliminate the infestation.”

Some invasive non-native species are a pest in residents’ homes and gardens. Mavis explains how they affect her:

Ants are a nuisance in the house , every summer their activity increases – even eating the plastic door liners and cat food and getting into my fridge, I have tried removing the ants by using ant powder, but it still find its way back. At the moment I’m trying flea powder which is keeping them at bay.”

Rosalie Peters protects her small kitchen garden from invasive pests:

“My biggest garden pest is the cutworm (Agrotis ipsilon and Agrotis segetum). It lives in the soil and eats the plant from the bottom to the top by cutting the plant from the soil surface. I don’t like using chemicals, but I control them by using a soil drench systematically spraying the soil first and then putting seedlings out after.”

Pine pests

Pine is an important resource on St Helena, and makes up approximately 37% of the National Forest Estate. A new woodwasp could be a serious threat to pine populations. Forestry staff are working hard to find a solution. Myra, Forestry Officer for Agriculture and Natural Resources Department, St. Helena Government explains:

“Our role in the Forestry Section is to ensure sustainable management of both the National and Dedicated Forest Estates across the Island; the sections remit is quite extensive and covers forest management, husbandry and production activities for both commercial and amenity end uses, as well as forest protection, recreation and amenity values and tree nursery management.

Although there are other pests such a termites that can affect forest plantations and actively growing trees, at this time the biggest pest is Sirex noctilio (Woodwasp). This pest is quite new to the Island there are lot of unknowns in relation to its behaviour; primarily a pest in the Northern hemisphere, it apparently thrives here in the South. Initial sightings were seen in 2016 with one specimen found and it has thrived undetected over the years to a population that now appears to be Island wide.

It has potentially devastating consequence for the Islands pine populations, which accounts for approximately 37% of the National Forest Estate. A loss of the volume of wood (although currently at all different stages of development) is quite significant, should we not address the pest we can expect losses in firewood material, timber and forest products such as posts, rails, Christmas trees etc. which would have an impact upon the Island as a community, and of course our natural environment. A lot of information has been done to assist in the control of this pest, until this is addressed it is not practical to plant any further pine plantations, so essentially we could be an Island without pine.

From our observations and monitoring the pest has already spread across the island and have affected the pine plantations; how we address these infected plantations is an area which we are currently looking into. In February of this year local trials were set up across the National Forest Estate to determine how the pest behaves in local conditions. We are currently in the trial phase where the data collected. Trial areas have been established to determine the time within a year of early and peak emergence for the wasp as well as the temperatures at which this emergence occurs. There are many micro-climates across the Island therefore it is a possibility that there is not once period of emergence per year, but several depending on temperature across the microclimates. This information will help us determine our approach to dealing with this pest.

It is known from our research that the wasp attacks trees that are stressed and often in plantations that are un-thinned; we’re now working to ensure that our young pine plantations are thinned to promote more vigorous tree growth and overall health of trees to limit the pest attack, we’re also looking at the best method if utilising potentially infected material, possibly through our normal firewood route, however this has not been agreed as yet. Discussions are being held around this as a possible control options, however again, this has not been sanctioned.

Our message to the public, be aware when processing pine firewood as to the presence of possible wood wasp larvae, and to destroy it where possible.

Image: St Helena National Trust

Protecting the island from future threats

With increased travel and trade, there are many species which could become a problem on St Helena in future. That’s why biosecurity, measures to prevent new species from being introduced to the island, is so important. Julie Balchin and Nicholas Stevens work on biosecurity on St Helena:

“St Helena is very vulnerable to the introduction of new pests, weeds and diseases which can adversely affect agricultural production, the natural environment, and also human and animal health. We work across the biosecurity continuum focussing our efforts on pre-border, border and post-border operations. This includes carrying out monthly monitoring at the airport, inspection of fruit and veg along with containers that are imported.”

Visitors to St Helena can help by reading the following guidance.

Find out more about St Helena.

Thin strip of image show tree trunk and bark