Lemon tree borer facts for kids
Quick facts for kids Oemona hirta |
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| O. hirta by Des Helmore | |
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Chrysomeloidea
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Cerambycinae
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Oemona
Fabricius, 1775
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O. hirta
Fabricius, 1775
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The lemon tree borer (Oemona hirta) is a type of longhorn beetle. It is also known as the whistling beetle or singing beetle. This beetle is endemic to New Zealand, meaning it is found only there.
Its young, called larvae, eat the wood of many different trees. They bore into both native and introduced trees. When citrus farms first started in New Zealand, this beetle caused a lot of damage. That's how it got its name, "lemon tree borer."
Scientists have found four species in the Oemona group. This suggests there might be even more species to discover. When bothered by predators or humans, the adult beetle makes a "rasp" or "squeak" sound. It does this by rubbing its body parts together.
Long ago, Māori ate a liquid called "pia manuka." This liquid came from manuka trees when the larvae damaged their wood. When Captain Cook first came to New Zealand, his naturalists, Banks and Solander, collected a lemon tree borer. This was between 1769 and 1771. You can find this very old specimen in the British Museum. A few years later, in 1775, a Danish naturalist named Fabricius officially described the species.
Contents
What Does the Lemon Tree Borer Look Like?
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The lemon tree borer is a plain-looking beetle. It is medium to large in size, growing about 15 to 25 millimeters (0.6 to 1 inch) long. It has a thin body and long antennae. These antennae are usually as long as or longer than its body. They can rest in front or curve backward.
Adult beetles can be red-brown to almost black. They have light yellow hairs on their head and a small spot on their back. This spot is where the main body connects to their hard wing cases. Female beetles are bigger and heavier than males. However, their antennae are shorter in comparison. A special feature of O. hirta is the wavy pattern on the top of its main body section. This is very clear on males.
Eggs
The eggs are white and large, about 2.0-2.2 millimeters (0.08-0.09 inches). They have a fine, waxy pattern on their surface. Females lay them one by one in places like leaf or stem joints. They also lay them in pruning cuts, cicada scars, damaged bark, or dead twigs.
Larvae (Young Beetles)
The larvae have white to pale cream skin. You can see their orange to brown gut contents. They grow to be 25-40 millimeters (1-1.6 inches) long. Their bodies are round, and each body part has a swollen ridge. They have a large head with strong, short, dark brown to black biting jaws called mandibles. Many tiny, stiff brown hairs line their sides, especially near the head. When disturbed, larvae can move surprisingly fast. They use muscle ridges on their top and bottom to grip surfaces.
Pupae (Resting Stage)
Pupae are about 20-25 millimeters (0.8-1 inch) long. They are a pale reddish-clay color, with darker shades on their wing cases. The pupa rests in a short tunnel made by the larva. This tunnel is blocked at both ends with wood shavings. In this stage, the beetle's shape becomes clearer. You can see its long antennae folded next to its body and its bent legs. While pupating, the beetle can twist around its chamber. It uses small black spines on its belly to do this.
Lemon Tree Borer Life Cycle
Lemon tree borers have a long life cycle, usually about two years. Most of their life is spent as larvae.
Egg Stage
Eggs are laid one by one between September and January. They hatch quickly, from a few days to two weeks. Most eggs hatch in about 9 to 13 days.
Larval Stage
Once hatched, the larvae immediately start digging into the wood. They first go into the soft outer wood, then deeper into the hard inner wood. They dig about 10-20 millimeters (0.4-0.8 inches) deep. Usually, only one or two larvae are found in a single tree. They eat the wood, making long tunnels with side passages. They also make holes to push out their waste and to let air in. This helps stop fungus from growing.
Larvae dig lengthwise into stems, moving towards the main stem or branch. Sometimes, they dig all the way around a branch. This is called girdling and can kill the branch. Lemon tree borers can live in dead trees, but they prefer living ones. They need a certain amount of moisture and food to grow into adults.
The larval stage can last one to two years. This depends on the environment. Larvae in warmer places with shorter winters grow faster. They grow slowly in their first summer, reaching about 15 millimeters (0.6 inches). They dig about 150 millimeters (6 inches) of tunnel. Larvae are less active in winter. But their activity greatly increases around October when it gets warmer. They produce more waste in their second summer as they reach full size.
Pupal Stage
The pupal stage lasts between 2 to 3 weeks, but can be longer. It starts from late May to early November. The larvae create a small chamber inside their tunnel for this stage.
Adult Stage
Adult beetles appear from early spring to late summer. Most come out between October and December. New adults stay in their pupal cells until their outer shell hardens. Once they come out, they become ready to mate about four days later. This can vary depending on the weather.
Adults eat pollen and nectar from plants. They are mostly active at night, looking for food and mates. During the day, they hide among plants. Adults may live for about 2 months, but often die after they reproduce.
Mating Behavior of Lemon Tree Borers
Adults are ready to mate about 3-4 days after they emerge. However, they usually wait about 10 days before they can actually reproduce. Mating usually happens at night. Males seem to wander around looking for a mate rather than actively finding one. They don't seem to have special courtship dances. Males quickly get on top of females after they meet.
Lemon tree borers have a long mating period. They can mate multiple times. The last mating session seems to be the longest, lasting about 50 minutes in total. Most males guard the female after mating for about 20 minutes. They stay on her back or close by. If the female tries to move away, the male might nip her antennae or lick her body. She then calms down and raises her abdomen for him to continue.
This behavior is somewhere in the middle compared to other longhorn beetles. Some males mate for hours without guarding. Others mate for a few minutes and then leave. After the male leaves, the female often stays still for a short time. Then she starts laying eggs by herself. Females lay eggs in cracks or wounds in bark or on branches. This includes fresh pruning cuts. A female can lay over 50 eggs in her lifetime, but she only lays about 66% of the eggs she produces.
Where Lemon Tree Borers Live
Longhorn Beetle Family Around the World
Oemona hirta belongs to a large family of longhorn beetles called Cerambycidae. There are over 33,000 species of longhorn beetles worldwide. In New Zealand, there might be around 200-300 species. This family of beetles can cause big problems for the economy. This is mainly because their larvae can damage hard wood with their special jaws. Because of this, they are on high alert lists for international security. If new species were accidentally brought in, they could cause huge losses to the timber and farming industries.
Where Oemona hirta is Found Globally
Oemona hirta is only found in New Zealand. It has not settled in other countries, but it has come close a few times. For example, some were found in the UK in 1983 and again in 2010. The latest beetle was found in a wisteria plant brought from New Zealand. It was seen as a very dangerous pest if it were to establish itself there.
Where Oemona hirta is Found in New Zealand
In New Zealand, lemon tree borers are native. They are the most common longhorn beetle found there. Until recently, people thought they were all over New Zealand. But they are mainly found in the North Island and the North-West Nelson region of the South Island. They have been found from sea level up to over 1200 meters (3,900 feet) high. They also live on several offshore islands like Kapiti Island and Mokopuna Island.
Like most other longhorn beetles, they are good at flying. This helps them spread far and wide to good habitats. The beetles mostly fly in the early morning and evening, which is when most mating happens.
What Lemon Tree Borers Eat
As their name suggests, the larvae of this beetle like to eat the living parts of citrus trees. However, they don't only eat citrus. Before European settlers brought new plants and farmed trees over 150 years ago, these beetles lived in native trees. Now, they are a highly adaptable species. They can eat over 200 different types of trees and vines, both native and introduced. This shows how well they can adapt. It means they will likely be in New Zealand for many years to come.
This causes problems for farms and tree nurseries in the North Island. They can often be invaded by these beetles. Adult beetles can also be found in orchards and gardens. They eat pollen and nectar from native and foreign flowers. But they cause much less damage than the larvae.
Common Host Plants
Exotic (Introduced) Plants: Citrus, lemon, orange, tangelos, grape, apple, gooseberry, tamarillo, cherry, fig, peach, pomegranate, plum, blueberry, persimmon, camellia, elm, wisteria, willow, hakea, poplar, tree lucerne, almond, walnut, chestnut, and macadamia. Gorse is also a host plant, which is one of the few benefits of the beetle, as gorse is a weed in New Zealand.
Native Plants: Kowhai, rangiora, mahoe, tauhinu, tarata, Coprosma rotundifolia, and manuka.
Lemon Tree Borer as a Pest
This beetle is very important to the economy. It has become an agricultural pest. This is because its larvae eat many different types of trees, both native and foreign. Some important farm crops it damages include lemon (Citrus species), apple (Malus species), almond (Amygdalus species), chestnut (Castanea sativa and C. crenata), persimmon (Diospyros kaki), cherry (Prunus species), walnut (Juglans regia), and grape (Vitis vinifera).
This makes them a big problem for businesses and border security. They could cause widespread crop damage in New Zealand and other countries. So, strict rules are followed when exporting these crops. This helps stop O. hirta from being accidentally introduced, as they could quickly settle in new places. O. hirta is a threat to the timber industry, commercial fruit crops, and garden shrubs.
These beetles can be accidentally moved when plants are shipped. They were first found in the United Kingdom in 1983 and again in 2010. Both times, they were on Wisteria plants at plant nurseries.
Signs of Plant Damage
The first sign of a borer problem is when leaves wilt and branches start to die. But this might not be obvious right away. Trees will have small holes, about 1-3 millimeters (0.04-0.12 inches) wide. You can see the beetle's waste (frass) outside these holes.
As the larva digs through the living branches of young trees and vines, the stems get weak, dry out, and break. This quickly harms the plant's health. If many beetles are present, they can even kill the tree over time. Digging through the stem stops the sap flow. This causes branches to die back in late summer. It can also make the plant more likely to get fungal infections. This happens because the stems are weakened and have holes from the larvae.
How to Control Lemon Tree Borers
Lemon tree borers are very hard to control. The larvae live deep inside the wood, so they are not easy to see. This makes it hard to study their natural behavior and difficult for people to control them as pests.
You can physically remove infested wood, but this takes a lot of effort. Usually, people spray chemicals to deal with insect pests. This might work for adult beetles, but it takes time and doesn't work well for larvae. This is because the larvae are hidden inside the wood.
In New Zealand, the best way to control the lemon tree borer is by preventing them and treating problems early. To reduce infestations, affected plants need to be pruned regularly. The cut branches should be removed and burned. However, this should not be done when female beetles are laying eggs. Cutting branches then would create more places for larvae to infect. So, painting the ends of trimmed branches can help stop new infections.
Another thing that makes Oemona hirta hard to remove is that larvae can keep growing into adults in pruned twigs or branches on the ground. But for them to survive, they need to be old enough to keep eating before the wood dries out and decays.
Scientists are looking into ways to improve natural control methods. This is hard because the stems they live in protect them from most predators. However, their natural predators, native parasitic wasps, are being studied.
Predators and Diseases
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The main natural enemies of lemon tree borers are solitary parasitic wasps. These include two types of ichneumonid wasps (Xanthocryptus novozealandicus and Campoplex sp.) and one braconid wasp (Apsicolpus hudsoni).
The parasitic ichneumonid wasp Xanthocryptus novozealandicus is native to New Zealand. Scientists are researching it as a possible way to control the beetle naturally. Female wasps lay an egg inside wood-boring beetle larvae, including the lemon tree borer. The wasp egg then grows and slowly eats the grub, which eventually dies. Female wasps do this by piercing through the wood with a special egg-laying tool called an ovipositor.
X. novozealandicus prefers to attack larvae that are in their second year of growth. Female wasps seem to decide the sex of their offspring based on the size of the larvae. Larger larvae usually get female offspring, and smaller larvae get male offspring. This is probably because adult female wasps are larger than males. When scientists looked at the tunnels left by the larvae, they saw that the larvae stopped growing once they were parasitized. Also, a parasitic fungus called Cordyceps aemonae has been found to affect larvae.
