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Hungry Sticks Invade Landscapes

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Hungry Sticks Invade Landscapes

By Vincent Lazaneo

indian walking stickA strange looking insect from the other side of the world is damaging landscape plants in local neighborhoods. The exotic pest known as the Indian stick insect (Carausius morosus) is thin as a twig but has a big appetite. It hides during the day and emerges under the cover of darkness to feed on tender foliage. It likes a variety of landscape plants including azalea, blackberry, camellia, fuchsia, hawthorn, hibiscus, ivy, pittosporum, privet, pyracantha, raspberry and rose.

The first established population of Indian walking sticks in California was found during June 2001in a residential neighborhood in La Jolla. Additional infestations have since been found in other areas of the county, including Carlsbad, Encinitas, and the San Diego neighborhoods of Pt. Loma, Mission Hills and Balboa Park. Infestations have also been found in other coastal communities as far north as San Francisco.

Adult Indian stick insects are about three inches long, wingless and light green to dark brown in color with a characteristic red mark at the base of the first pair of legs. Its body and appendages are long and slender. When disturbed, the insect drops to the ground and plays dead, drawing its legs and antennae close to its body to resemble a stick, hence its common name.

Indian stick insects are female and parthenogenic which means they reproduce without mating. One female can lay several hundred eggs over a period of about four-six months. The small brown eggs are produced continually and fall to the ground beneath the host plant. They take about three months or more to hatch, depending on temperature and moisture. Upon hatching, the nymphs, which look like tiny versions of the adult, grow by shedding their exoskeleton or skin several times. 

 In California, stick insects have few natural enemies and can develop large populations. They are masters of camouflage and often cause extensive damage without being noticed. They hide inside host plants during the day and are difficult to see because of their cryptic shape, coloration and tendency to remain motionless. They are active at night and chew holes in tender foliage. The holes are similar to those made by snails, grasshoppers, and some other chewing pests.

Control and Protect

To find out if stick insects are damaging a plant, look for the pest at night when it is active. You can also check plants during the day when stick insects are hiding. First, place a light colored cloth on the ground under a host plant. Then shake the plant vigorously to dislodge any insects clinging to the branches and look for them on the cloth. You can also check plants by spraying them with water from a hose. This will disturb concealed stick insects and cause some to climb onto the outer foliage where they can be seen more easily.

The best non-chemical way to control stick insects is to hand pick them from infested plants. This can be done at night when the pest is feeding or during the day if plants are first sprayed with water to flush the sticks out of their hiding places. You can step on the insects to kill them or drop them into a bucket filled with a little soapy water. Hand picking works best if it is done often and only a few plants are infested. Chemical control may be needed when a large number of plants are infested.

To effectively protect plants from damage, stick insects must be killed before they begin laying eggs. This can be accomplished by treating plants with an insecticide that leaves a toxic residue on foliage. Lightly spray the outer surface of infested plants in the late afternoon before the insects emerge to feed. Re-treatment should not be necessary for at least two months and no more than three treatments should be required annually. All plants that harbor stick insects should be treated at the same time. Better control will be attained if adjacent neighbors also treat infested plants on their properties.

Before you buy an insecticide, read the label to find out if it is registered to use on the plants you want to treat, especially if they are edible crops. The insecticide Spinosad (Green Light Lawn and Garden Spray) is effective against walking sticks. It breaks down quicker and is less harmful to beneficial insects than more persistent chemicals like acephate (Orthene), Carbaryl (Sevin) and products containing pyrethroids like Cyfluthrin (Bayer Rose & Flower spray). 

Vincent Lazaneo is Urban Horticulture Advisor for UC Cooperative Extension.  He helped found the San Diego County Master Gardener Association more than two decades ago and serves as its advisor. He is the author of numerous articles on plants and pests that appeared in the San Diego Union-Tribune, California Garden and other publications.