Coconut sexava treehopper
Sexava treehoppers are a destructive pest insect of important crops in the Pacific. There is a high risk of population outbreaks where they are found.
Common nameCoconut sexava treehopper |
Scientific nameSexava nubila and other species |
on this page: Life-cycle and identification : Symptoms : Impacts : Distribution : Prevention : Controlling coconut sexava treehopper : Information sources and further reading
Life-cycle and identification
Coconut sexava treehopper species that have been found on coconuts in the Pacific are Segestes decoratus, Segestidia defoliara, Segestidia leefmansi, Segestidia novaeguineae, Segestidia rufipalpis, Segestidia uniformis, and Sexava nubila.
Sexava treehoppers belong to the Family Tettigoniidae of Orthoptera order of insects. Sexava treehoppers have long, slender antennae that are often longer than their body.
The sexava treehoppers jumping ability means they can spread easily among crops.
The insects are often hard to see as they are nocturnal and camouflaged by vegetation.
Sexava treehoppers have a relatively long development time for an insect. It takes between 30-40 weeks to develop from egg to nymph to adult.
Eggs
Sexava treehopper eggs are laid in soil (10–15 mm deep) or occasionally on other plants growing on palms or the base of fronds. The eggs are around 10 mm long, slightly curved and slim. The eggs hatch around 8 weeks after they have been laid.
NymphsNymphs look very much like the adults but have less defined wings. Nymphs have six growth stages (instars) within around 20 –26 weeks. At the first instar stage, nymphs will find a palm and crawl up to the crown. Here they will reach the adult length of 50-60 mm (not including the antennae). AdultsAdult sexava treehoppers can be seen resting on the base of fronds, the underside of fronds or on the ground during the day. At night they are actively feeding. In both the adult and nymph the antennae are longer than the body. Antennae have more than 30 segments and are very delicate. Depending on the species, nymphs and adults are green or brown. Nymphs and adults can run and jump. |
Adult male (top) and female (bottom) coconut sexava treehopper (© Ken Walker, PaDIL) |
Males may have short or long wings but these do not appear to be very functional.
Females can be identified by the curved ovipositor (egg laying organ) at the tip of the body.
Adult lifespans are around 110 days.
SymptomsCoconut sexava treehoppers have population outbreaks. These outbreaks can be:
A major symptom of sexava treehopper infestation is defoliation of the fronds. Coconuts can be severely defoliated and may show signs of damaged fruit and flowers. The treehoppers often attack the younger fronds first. Reduced fruit yields are apparent with only 40% defoliation. |
Coconut palms showing defoliated crowns (© Richard Markham, ACIAR) |
Impacts
Severe damage will likely occur during outbreaks when there are high numbers of treehoppers.
The defoliation of fronds reduces the ability of the palm to gain nutrients through photosynthesis (the process by which plants make sugars) causing the palm to produce less fruits.
The negative effects start to appear after around 40% of the fronds are defoliated. It can take coconut palms up to 2 years to recover from about 70% defoliation.
Distribution
Sexava treehoppers have a narrow distribution within Indonesia, Papua New Guinea and Solomon Islands.
Please check with your local biosecurity / quarantine or SPC for up-to-date distribution information.
Prevention
Most importantly, the International Guidelines for transfer of coconut germplasm should be strictly followed to prevent pests and diseases being moved to new locations.
For general information on preventing pests and diseases of coconut, see the Prevention section.
Controlling coconut sexava treehopper
We strongly recommend an integrated pest management (IPM) approach to the control of all insects, where possible. This is a combination of methods (pesticides, physical controls such as site hygiene, and biological controls) to minimise the use of pesticides and minimise the cost of control.
Integrated Pest Management (IPM)
The goal of IPM is to keep pest populations to a level below which they cause economic harm. IPM involves using multiple control options together for the economic control of pests (i.e. cultural, natural and chemical).
In an agricultural context the Food and Agriculture Organization defines IPM as "the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms".
Cultural
Most physical methods of removing sexava treehopper adults, nymphs and eggs are considered impractical and costly.
One method of removal involves using bands of gum resin around coconut trunks. Sexava treehoppers will stick to these bands when they move over them.
Eggs in the soil may also be uncovered by raking or hoeing.
To remove adults, look for sexava treehoppers blending in to the mid-vein of leaflets or resting at the frond base during the day. Care should be taken when removing them as they can give a nasty bite.
Natural
Biological control is the focus of sexava treehopper management in Papua New Guinea. Many parasitoids of eggs have been trialled. However, these have not been promising due to most eggs being buried deep within the soils or dense plants.
Stichotrema dallatorreanum (Strepsiptera insect order) is a parasite that is considered effective. This insect has been reported to parasitise Sefestes decoratus, Segestia novaeguineae and Sexava nubila in Papua New Guinea. Only female Stichotrema dallatorreanum parasitise sexava treehoppers. Parasitism reduces the lifespan of the females and consequently reduces the number of eggs laid.
Unfortunately, many potential biocontrol agents are not available for commercial use.
Chemical
Chemical control is not recommended. Pesticides are considered inefficient and costly, and are likely to negatively affect biological control agents/natural enemies. Many older insecticides (such as organophosphates) are now banned due to their toxic ffects on the environment.
Information sources and further reading
Howard et al. 2001. Insects on Palms. CABI Publishing, pp. 1-414.
PaDIL. 2012. Sexava Coconut treehopper. [ONLINE]
PestNet. 2017. Coconut sexava treehopper. [ONLINE]
content reviewed by Milen Marinov, Plant Health and Environment Laboratory, Ministry of Primary Industries, New Zealand, November 2018