Damage Characteristics and Control Techniques of Longhorn Beetles in Coffee Garden

Sitong LI, Qiongyin LIANG, Chengxiang XU

Life Sciences College of Zhaoqing University, Zhaoqing 526061, China

Abstract Coffee longhorn beetles are major trunk-boring pests of coffee trees, which are widely distributed in most areas of China. The biological characteristics, damage characteristics, life history and control techniques of two species of coffee longhorn beetles are reported in this paper.

Key words Coffee garden; Coffee longhorn beetles; Biological characteristics; Damage characteristics; Control technique

1 Introduction

Coffee (Coffeaspp.) is a major cash crop in tropical and subtropical regions. Yunnan, Sichuan and Hainan provinces are the main coffee producing areas in China, and Guangdong, Guangxi and Fujian provinces have a small amount of cultivation. Yunnan is the province with the largest area of small-grain coffee in China. In recent years, the planting area of coffee in China has been expanded, but the problems of diseases and pests have become increasingly prominent. Particularly, trunk-boring pests have a great impact on the yield and quality of coffee, which restricts the development of coffee industry to a certain extent. In Zhaoqing, Guangdong, longhorn beetles have been also found in coffee gardens, which should be concerned.

2 Morphological characteristics and species

Coffee longhorn beetles are insects belonging to Cerambycidae, Coleoptera. Adults long, slightly flat; antennae especially long, compound eyes reniform, surrounded at base of antennae; larvae body long, pronotum large and flat, other thoracic segments and abdominal segments with ossified areas or processes in dorsoventral surface, thoracopod degenerated, with remains. In China,XylotrechusquadripesChevrolat andAcaloleptacenaruinusHope cause great damage to coffee in China. The most prominent feature ofX.quadripesis the pattern in the shape of Chinese character "mie" on dorsal elytra. Adult 10-17 mm long, black, with densely yellow or grayish-green short hairs, notum with a black stripe in middle; yellow and green markings present on elytra, arranged in shape of Chinese character "mie".A.cenaruinusadult 15-27 mm long, without markings, pure dark chestnut or dark brown, antennae exceeding body length by 5-6 segments (Fig.1).

Fig.1 Adult morphology of Xylotrechus quadripes Chevrolat (left) and Acalolepta cenaruinus Hope (right)

3 Biological characteristics

3.1 Life historyThe occurrence regularity ofX.quadripesin different coffee planting areas varies with overwintering insect state and temperature.X.quadripesthat survives the winter as larvae in the stem will occur 2 generations in the following year, namely summer and autumn generation and overwintering generation. Some of them overwinter as adults, and the second generation of adults will appear early; in case of high temperatures and a long dry season, 3 generations can occur in a year, that is, the first generation occurs from March and April to June and July, the second generation occurs from June and July to August and September, and the third generation occurs from September and October to March and April of the following year. Due to the different overwintering insect states, the emergence period of adults in the next year is different. Therefore, adults appear throughout the year, but it can still be divided into the peak emergence period of overwintering generation and summer and autumn generation.

A.cenaruinusoccurs one generation a year in Yunnan, and survives the winter as larvae in the bark. The insect starts to pupate in late March of the next year, and reaches the peak pupation period from early April to middle May. Adults begin to emerge in early April, lay eggs in middle May, and reach their peak oviposition period in early and middle June. Larvae of the next generation hatch in middle and late June and bore into the tree trunk to cause harm. Throughout the life ofA.cenaruinus, the larval stage in the trunk lasts about 288 d, and the pupal stage, egg stage and adult stage last 10-15, 6-8 and 60 d, respectively.

3.2 Living habitA.cenaruinusoccurs one generation a year in Yunnan, which starts to pupate in late March, and enters the peak pupation period from early April to middle May. Afterward, it reaches the peak oviposition period in early June, and the larvae will bore into the tree trunk to cause harm in middle and late June.X.quadripesoccurs 2 generations a year in Guangxi, 3 generations in Xishuangbanna, Yunnan, and more than 3 generations in Hainan. Adults lurk in dark places during the daytime and are active at night. They are very active on sunny days and when the temperature is high at noon, and can fly over short distances. They usually stay still in the morning and evening or cloudy days. After mating, adults look for crevices in tree trunks to lay eggs. Adults usually roost in coffee trees before mating, and mate and lay eggs after 8-10 d. When laying eggs, the female first bites the bark into a 1-2 mm wide crack and lays eggs in the crack. They usually lay 1-2 eggs per 1-2-year old tree. Most eggs are laid 10-20 cm above the ground. Eggs are mostly produced in the sunny side, and shady coffee trees usually suffer light damage.

3.3 Damage characteristicsThe larvae ofX.quadripesandA.cenaruinusmainly cause damage from March to June and from August to September each year. The larvae ofA.cenaruinusare harmful to the stem cortex of coffee trees that are 2-3 years old. After hatching, the larvae drill cavities under the cortex of trunk. As the age increases, they gradually bore into the xylem, and the cavities are spirally shaped, irregular and continuous. The tunnel is usually 3-4 rounds in a row, and the phloem is completely cut off, leaving only the epidermis. Larvae will pupate from March to May, and adults begin to activate and lay eggs in May. Larvae cause the severest damage from August to September every year, and mainly damage the lower trunk of coffee trees (10-50 cm above the ground).

The larvae ofX.quadripesmainly harm the xylem of coffee trunk. They decay the xylem into a crisscross tunnel, and drill into the center of the stem to damage the medulla, then drill down to damage the root. In the late stage of infection, the damaged tissue forms a ring mass because of stimulation, and the water can not be transported upward as the epidermal cork layer is broken. The upper branches and leaves show yellow wilting, and the lower side buds are clustered. When the larvae bore into the roots, the plants will die, and the whole coffee garden will be destroyed in severe cases. The larvae ofX.quadripesmainly damage the middle trunk of coffee trees (40-100 cm above the ground).

4 Control technique

4.1 Surveillance and quarantineQuarantine of coffee seedlings in the infected area of longhorn beetles is the most effective control measure to prevent its introduction into the non-infected area. In coffee cultivation and management, insects in coffee garden should be monitored, so as to achieve the purpose of early detection and early prevention.

4.2 Agricultural control

4.2.1Selection of planting plot. The longer the sunshine hours of the plot, the severer the damage of longhorn beetles. The plots with west slope should not be selected, while those with east and north slopes have relatively short sunshine hours and will suffer relatively damage from longhorn beetles.

4.2.2Interplant of shade trees. Coffee trees can be interplanted with rubber, mango and macadamia nuts to increase the canopy density to 50%-60%, which can effectively inhibit the oviposition of coffee longhorn beetles and has the best prevention effect against longhorn beetles.

4.2.3Strengthening cultivation management. Coffee trees should be reasonably pruned, and variety configuration should be concerned to create the planting environment with biodiversity. Dead branches and dead plants should be cleaned up timely and burned, to reduce the number of overwintering insects.

4.2.4Formula fertilization. Timely remove of grass, heavy application of farm manure and rational formula of fertilization should be carried out to strengthen the cultivation management of coffee garden and to ensure robust growth of coffee plants, which is also an effective method to control the breeding of coffee longhorn beetles.

4.2.5Renewal and rejuvenation. The coffee trees seriously harmed by longhorn beetles should be cut at 30 cm above the ground, taken away from the coffee garden, and burned intensively. After cutting off, the trunk is smeared and sealed with paraffin or vaseline. The trees that have been smeared or cut should be better managed, and weeds in the garden must be removed in time. The sprouting trees should be repaired, and 1-2 healthy straight branches are retained and cultivated into trunk.

4.3 Physical controlPhysical control refers to the use of sound, light, heat and other physical factors or mechanical action and tools to control pests. Artificial capture has the advantages of strong pertinence, simple operation, no pollution, low cost and remarkable control effect.

4.3.1Artificial capture and smearing trunk. The adults ofX.quadripesappear from February to late November, and those ofA.cenaruinusappear from middle May to late June. White armyworm board can be used for trapping at 2:00-5:00 pm on sunny days from April to May and from August to September. Or the trunk can be artificially smeared with lime paste in the above two periods.

4.3.2Removing dead branches. When parasitized branches of longhorn beetles are found, about 20 cm of damaged young stems should be cut off, and dead plants are removed and burned intensively. When the stems and leaves suddenly wither from July to August, dead branches must be removed.

4.3.3Scarping egg scar. The damaged bark should be scarped to longitudinal furrows 0.5 mm deep.X.quadripesusually spawns in 1-2 mm wide cracks of coffee trunk 30 cm above the ground. The scraped wood residue should be destroyed in time.

4.3.4Cutting trunk for rejuvenation. Coffee trees more than 10 years old are cut at base. After budding and branching out, 2-3 robust new branches are retained and cultivated into new main branches, and the remaining straight branches are removed.

4.4 Biological controlWoodpeckers, magpies and other birds prey on the larvae of coffee longhorn beetles.Crematogasterrogenhoferi,DastarcushelophoroidesandSclerodermaguaniprey on the larvae of coffee longhorn beetles.BeauveriabassianaandAspergillusaspergillusare parasitic fungi of the larvae of coffee longhorn beetles. Protecting natural enemies is an important way to prevent and control the harm of coffee longhorn beetles. Therefore, chemical agents should not be sprayed during the peak parasitic period of natural enemies to facilitate the proliferation of natural enemy population.

High sporopollen ofB.bassianais poisonless, tasteless, pollution-free, and has sustained effect on coffee longhorn beetles, and can continuously invade and spread once infected. It kills the larvae and pupae of longhorn beetles mainly through parasitized breeding. In the forest,B.bassianapowder (20 billion spore/g) can be sprayed by a duster (B.bassianaspore powder releaser), and cotton ball dipped with bacteria suspension can be used to plug the boring hole or bacteria suspension can be directly injected with a syringe.

4.5 Chemical controlChemical control mainly targets eggs and newly hatched larvae in bark crevices, but is basically ineffective or less effective to spawning female adults and harmful larvae and pupae in tree trunks. According to the emergence time of adults, spraying chemicals during adult emergence period will receive better control effect. During the peak occurrence period of adults from April to June and from August to September, 16% Chongxianqing EC 200-300 times dilution (or other biological drugs with high efficiency and low toxicity) can be used to spray the trunk 2-3 times per month.

Before the middle of April, water, clay, lime powder, parathion methyl-trichlorphon powder, salt and sulfur powder can be mixed evenly at the ratio of 2∶1∶5∶1.2∶0.005∶0.005, stirred into paste that can stick on the trunk steadily, and evenly brushed the coffee trunk 50-80 cm above the ground. The epidermis of coffee tree can be wiped off with gloves or dried with lime paste, which can effectively remove and kill eggs on the epidermis of tree trunks.

Before the peak emergence period of adults, 8% cypermethrin microcapsule is usually used for control. The capsule should be shaken well before use, and 200-300 times dilution is prepared to spray on the trunk and big branches. During the peak incubation period of eggs, 2.5% deltamethrin EC 500 times dilution or 20% fenvalerate EC 1 000 times dilution can be used to spray the trunk. The boring hole, stoma and excretion hole of longhorn beetles must be found, and blocked with cotton ball dipped in 80% dichlorvos EC or 50% methamidophos EC, then sealed with soil to fumigate and kill larvae.