Longhorn beetles, belonging to the family Cerambycidae, are a diverse group with over 20,000 species worldwide. These beetles are easily identified by their long antennae, which are often as long as or longer than their bodies. While some species are relatively benign, others can be serious pests, particularly to trees and lumber. This article delves into the dietary habits and nutritional needs of longhorn beetles, exploring what they eat, how they obtain their food, and the impact their feeding has on the environment.
Feeding Mechanisms and Dietary Diversity
Beetles, including longhorns, possess chewing mouthparts, characterized by two tough, approximately triangular jaws capable of exerting powerful biting or grinding pressure. This allows them to consume a wide variety of food sources. As scavengers, beetles contribute significantly to the ecosystem by feeding on leaf litter, mammal dung, carrion, and even other insects. They also graze on mold in compost bins, playing a crucial role as recyclers of dead wood and fungal decay. Some species have even adapted to stealing food from spiders' webs.
The diet of longhorn beetles varies significantly between the larval and adult stages. Larvae are primarily wood borers, while adults may feed on a variety of plant materials or not feed at all.
Larval Diet: Wood-Boring Specialists
Longhorn beetle larvae are wood borers, feeding on the stems, trunks, or roots of both herbaceous and woody plants. They often target injured or weakened trees, but some species can also attack healthy, living trees.
The Impact of Larval Feeding
The feeding activity of longhorn beetle larvae can have detrimental effects on trees. By burrowing into the wood, they disrupt the tree's ability to absorb and transfer nutrients. This can lead to leaf discoloration, limpness, and ultimately, the death of the tree. The presence of exit holes, typically over a centimeter in diameter, is a visible sign of larval activity.
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Specific Examples of Wood-Boring Behavior
- Asian Longhorned Beetle (Anoplophora glabripennis): This invasive species is known to attack hardwood trees, including maple, birch, horse chestnut, poplar, willow, elm, and ash. The larvae chew galleries into the inner parts of the tree, on which they feed during the overwinter process.
- General Wood-Boring: Longhorn beetle larva can live deep within the wood of trees that they feed on. They are often brought inside of people’s homes through firewood.
Adult Diet: Varied and Dependent on Species
The dietary habits of adult longhorn beetles vary depending on the species. Some adults do not feed at all, while others consume nectar, pollen, fruit, sap exudates, bark, plant stems, needles, or developing cones.
Pollen and Nectar Consumption
Some longhorn beetle species feed on pollen or nectar and act as pollinators. Flowers specializing in pollination by beetles typically display a particular set of traits, but pollination by longhorn beetles is not limited to these cantharophilous flowers. Some orchid species have been found to be largely reliant on longhorn beetles for pollination.
- Alosterna tabacicolor was found to be the main pollinator of a rare orchid species (Dactylorhiza fuchsii) in Poland.
- Another rare orchid Disa forficaria, found in the Cape Floristic Region in South Africa, relies on the species Chorothyse hessei for pollination. D. forficaria uses sexual deception targeting male C. hessei.
Consumption of Plant Tissue
Some adult longhorn beetles feed on bark, plant stems, needles, or developing cones. This can cause damage to the host plant, particularly in cases of heavy infestation.
Non-Feeding Adults
Adults of the subfamilies Parandrinae, Prioninae, and Spondylidinae do not feed. These beetles rely on the energy reserves accumulated during the larval stage for reproduction and dispersal.
Nutritional Strategies and Host Selection
Longhorn beetles locate and recognize potential hosts by detecting chemical attractants, including monoterpenes (compounds released en masse by woody plants when stressed), ethanol (another compound emitted by damaged plant material), and even bark beetle pheromones. Many scolytine weevils share the cerambycid's niche of weakened or recently deceased trees; thus, by locating scolytinids, a suitable host can likely be located as well.
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Specific Examples of Longhorn Beetle Diets
- Asian Longhorned Beetle: As larvae, they feed on the inner wood of hardwood trees, disrupting nutrient flow and eventually killing the tree.
- Evgenius plumatus: While specific dietary information is scarce, most adult longhorn beetles require some sort of food, such as bark, stems, twigs, buds, sap, or fruit.
New Zealand Spinach and Longhorn Beetles
A serendipitous observation revealed a longhorned beetle on a patch of New Zealand spinach. However, the beetle was not observed feeding on the plant, suggesting that New Zealand spinach is not a food source for this particular species.
Longhorn Beetles as Pests
Many of the over 135,000 specialist plant-feeders in the important beetle lineage Phytophaga are extremely host-specific. They will feed only on a single plant species - and often on just one part of that plant. This does mean that some beetles have become serious garden or crop pests.
Examples of Pest Species
- Lily beetle, Lilioceris lilii
- Colorado beetle, Leptinotarsa decemlineata, which devours potatoes.
- Western corn root-worm, Diabrotica virgifera, which attacks maize.
- Asian Longhorned Beetle: This invasive species is a significant threat to hardwood trees in North America and Europe.
Signs of Infestation
- Exit holes of over a centimeter in diameter in the wood.
- Leaf discoloration.
- Apparent limpness.
- Piles of sawdust left near the trunks of trees.
Control and Removal
The only known means of control is to burn, remove, chip or destroy the infested tree or trees. However, positive results have been seen through the use of the pesticide imidacloprid being used in conjunction with other control means such as traps and pheromone lures.
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