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Garden Insects

An Aid to Identification and Control

Harlequin Bug

The Harlequin Bug is a shield-shaped true bug. Both the adult and young are black with brilliant dorsal area colored red or yellow. These sucking bugs cause plants to wilt and leaves to turn brown as if scalded.

They pass the winter as adults with true hibernation doubtful. The three stages are egg, nymph, and adult. Egg masses are deposited in double rows and average 12 in number. Generations require 50 to 80 days.

Cultural control: Hand-picking and destruction of the insect pests and egg masses may deter damage where low numbers of insects are found. Hand destruction of the adults in the fall and spring as they emerge from "hibernation" before they lay eggs is an effective control. This may be aided by the use of trap crops of turnip, kale, or mustard in the very early spring or late in the fall after the main crop has been harvested. Once the pests have concentrated in these areas, they can be killed by applying insecticides or by covering the trap crop with straw and burning. Trap crops should never be used unless they can be given careful attention to destroy the bugs attracted to them.

Chemical control: The bugs may be controlled with insecticides.


Striped Cucumber Beetle

Adults are yellow to black, about 1/5 inches long, with three black stripes down their back.

The insect is a known carrier of mosaic and bacterial wilt. Adults feed on leaves, stems, and fruit. Larvae bore into roots below soil line.

Beetles emerge from hibernation about the time melons come up and begin flying when temperatures reach 60 degrees F. Eggs are laid about the base of plants, and larvae feed from 2 to 6 weeks on roots and stems below ground. Pupae stage- found in the ground- lasts about a week. Probably two generations occur.


Cultural, mechanical and biological controls. Crop rotation to a distant field (> ½ mile away) can help minimize the size of the beetle population. Simply rotating to new ground within a field, or to an adjacent field, is not effective due to the mobility of the beetle.

Delaying cucurbit plantings until the last week of June and using heavy seeding rates can help assure that plant stands survive. Floating row covers can also be used to exclude the beetles from the plants, but must be removed by bloom to allow bees to pollinate the crop. Planting on black plastic mulch reduces the survival of SCB larvae by up to 50%.

Perimeter trap cropping can be used to concentrate beetle populations in the border areas by completely encircling many types of cucurbits with a more attractive trap crop, like 'Blue Hubbard.' Do not use a trap crop that will act as a reservoir for the bacterial wilt pathogen (i.e. Turk's Turban) or disease incidence may increase and yields may decline. Even with light-moderate beetle populations, it may be necessary to spray the trap crop to control the beetles, to prevent the population from redistributing throughout the field over time. Perimeter trap cropping may not work in unrotated fields with extreme beetle populations or for the most preferred cucurbit crops. The tachinid fly, Celatoria diabrioticae, parasitizes both spotted and striped cucumber beetles in New England. Nematodes (Steinernema riobravis) can provide partial control of SCB larvae.


Chemical controls: The following materials are registered for cucumber beetle control on summer squash: esfenvalerate (Asana), carbaryl (Sevin), permethrin (i.e. Ambush), imidacloprid (Admire), kaolin clay (Surround). All of the above materials, except imidacloprid, should be applied to the foliage in a timely fashion (5-10 day schedule) to prevent excessive crop damage. Kaolin clay is an insect repellent that suppresses light populations of cucumber beetles. Imidacloprid is a systemic insecticide which is picked up by the roots of the plant and translocated to the foliage. Imidacloprid should be applied as an in-furrow or banded application, or through drip irrigation at the proper rate to avoid phytotoxicity problems. In areas with 2 beetle generations per season (i.e. Pennsylvania), additional foliar applications of a second (non-systemic) material may be necessary to control mid-summer adults. Imidacloprid can be used at reduced rates (0.67 fl. oz. /1000 plants) to treat transplants prior to field setting, but only provides effective control for 10 to 14 days. Higher rates will produce phytotoxicity and are not advised.



General color is green with white diagonal lines on its side. Prominent horn on rear gives name to the group. Larvae measures up to 4 inches long. Damage is done by larvae eating foliage and sometimes fruit on eggplant, pepper, and tomato. It passes the winter as a pupa, which gives rise to the hawk moth during late spring. Incubation period of eggs is about a week: larvae feed about 4 weeks. Pupae stage lasts about 3 week, except for the overwintering generation.


Control tactics: Hornworms are easily controlled by garden insecticides (e.g., carbaryl, permethrin, spinosad). A biological control organism that is also highly effective and sold commonly is Bacillus thuringiensis (e.g., Dipel, Thuricide). Hornworm larvae can also be hand-picked although they are surprisingly difficult to detect because of their cryptic coloration. Larvae tend to feed on the exterior parts of plants during shadier periods, near dusk and dawn, when they may also be more readily observed and destroyed.

Tomato Fruit worm

 Larva is variable-maybe green, brown, or pink with light stripes along sides and on back and may measure slightly less than 2 inches. It is one of the most important insects in the United States because it causes serious damage in a wide host range.

It passes the winter as a brown pupa about 2 to 6 inches below the surface of the soil. Moths emerge from these pupae during late April and May. The four stages are egg, larva, pupa, adult (or moth).

Moths fly and lay eggs at dusk on warm days. Eggs numbering from 500 to 3,000 are laid on hosts plants. Early generations feed on corn, tobacco, tomatoes, cotton, and legumes.


Biological Control: A tomato fruitworm egg parasite, Trichogramma pretiosum, the larval parasite Hyposoter exiguae, and predators such as bigeyed bug and minute pirate bug are available for biological control tactics. Conserve these parasites whenever possible and monitor their presence, as described in monitoring and treatment decisions.


Organically Acceptable Controls: Biological control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on organically certified produce and insecticide.


Colorado Potato Beetle

Adults are true leaf beetles, yellow with black stripes. Larvae are brick red, have a hump back, and are about 3/5 inch long.

Both larvae and adults devour foliage of eggplant, Irish potato, and tomato and may be very destructive. Adults hibernate and emerge during the early stages of shoot development.

Eggs are laid on the undersurface of leaves and hatch in about a week. Pupation occurs in an earthen cell in the soil, and adults burrow back to the surface. Then they mate, feed, and begin their life cycle anew.


Control Tactics: Bacillius thuringiensis var tenebrionis (Bt) is effective against small larvae (less than 1/4 inch) and should be applied at egg hatch or when larvae are first seen. A premature treatment may lose much of its effectiveness before the eggs hatch. Larger larvae are more difficult to control with Bt. Azatin, an extract of the neem seed, prevents the larvae from developing normally.

Frequently, control failures with Colorado potato beetle are due to other factors besides just insecticide resistance alone. Timing of sprays is critical for control. Overwintering beetles are attracted to fields over a period of several weeks; spraying an insecticide too early may only control a portion of those beetles. However, waiting until larvae are nearly full grown also increases the chances of control failure. Small larvae are much easier to control with an insecticide than large ones. Using the correct amount of insecticide as well as obtaining complete coverage of the plants is important.

Insecticides should only be used when needed. Potato plants can withstand considerable defoliation without yield loss. Plants can loss up to 30% of their foliage without yield loss. Generally, insecticides do not need to be applied unless there is more than an average of one beetle or larva per plant. Additionally, some beneficial insects such as birds, predatory stink bugs, and parasitic flies will help to reduce Colorado potato beetle numbers somewhat.


Other non-chemical control measures such as hand picking of adult beetles and immature stages is encouraged as this will aid to delay the development of resistance. Hand picking can be particularly effective in reducing the numbers of overwintering beetles coming to the young plants in the spring. Resistance by Colorado potato beetles should be managed on a field to field basis. While they may be resistant to one insecticide in a particular location, those in other areas within the same county may not have developed resistance to that insecticide.


Aphids or Plant Lice

Plant lice are small, soft bodied, sucking insects found on a large number of vegetable crops. The aphids, by sucking the sap, cause leaves and shoots to become distorted, curled, and weakened.

Generations are numerous, and the rate of increase is tremendous. Young are often born rather than hatched from eggs. Plant lice injure vegetables more during cooler periods in warm weather they are usually checked by natural enemies.


Organic Controls for Aphids: Sometimes, a strong blast of water from the hose will knock the aphids off of a plant and solve the problem. If you attract or purchase certain beneficial’s, such as lady bugs, lacewings, parasitic wasps, or damsel bugs, they will attack the aphids. Plants can also be sprayed with insecticidal soap, or a homemade tomato leaf or garlic spray to kill and repel aphids.

There are different chemical insecticides that can be used against aphids or plant lice.


Mexican Bean Beetle

Adults are lemon-to-copper-colored, oval in shape, and ¼ inch long with 16 black spots on back (wings). Larvae are orange to yellow with fuzz or spines and may be 1/3 inch long. Eggs are yellow and laid in masses. Pupae are attached to plant and are yellow to orange, depending on age.

Adults hibernate in protected places and first appear on bean plants during April and May. The yellowish eggs are laid in laid in large clusters on the leaves; larvae feed on undersurface of leaves and pupate on the plants. Young adults are light lemon-colored. Several generations occur each season.


Cultural Control: Clean up plant debris after harvest. Plant Beans as early as possible to so harvest is completed before the July peak of activity for this pest.


Organic/Biological Control: Natural enemies include several species of assassin bugs and a tiny parasitic wasp, Pediobius foveolatus. Applications of a botanical insecticide may also help reduce Mexican bean beetle populations.


Chemical Control: Treat with a registered insecticide when damage first appears. For best control also direct sprays to undersides of leaves.


Black Cutworm

 Many species, cutworms may be dull grey, brown, black, striped, or spotted. These soft bodied, stout worms curl up tightly when disturbed.
They are most destructive to early season or cool season plantings of tomato, pepper, corn, and various vegetable crops. They may cut off plants at, above, or below soil surface. Some climbing cutworms may feed on buds, leaves, or even fruits.

Most pass the winter as partly grown to fully grown larvae. However, some hibernate as adults and some as pupae. The four stages are egg, larva, pupa, and adult. Usually there is only one generation per year, but some may have as many as four. Cutworms feed mainly at night. One must look under clods, rocks, and debris to find them during the daytime.


Cultural Control: Maintain healthy grass by fertilizing in the spring and fall and watering during periods of drought.


Chemical Control: Best efficiency is achieved when spraying the insecticide late in the day and not irrigating, but following the label directions for irrigation. Do not use broad spectrum insecticides routinely, as they will do more harm than good and will kill the beneficial insects that live in the turf, can cause the pest outbreaks.


Biological Control: Carabid ground beetles, staphylinid rove beetles, ants, and spiders.


Plant mortality risk: Medium


Biorational Pesticides: Azadirachtin, halofenozide, nematodes, spinodad


Conventional Pesticides: Acephate, beta-cyfluthrin, bifenthrin, carbaryl, chlorpyrifos, cyfluthrin, deltamethrin, imidacloprid, lambda-cyhalothrin and trichlorfon.


Spider Mites

Spider mites are not classified as insects but as close relatives. Several species, adults and young, are barely distinguishable to the naked eye but may be noticed at times when they move in the sunlight. Both adults and young may be red or greenish-red. They are usually found on the underside of leaves, but general infestations feed on all parts of the plant.

They may attack all vegetables grown in the garden, but especially beans, tomatoes, and melons. They cause yellow specks and webs on the leaves. Severe injury of foliage and fruits is frequent, and in many cases defoliation may occur.

Biological Controls: Various insects and predatory mites feed on spider mites and provide a high level of natural control. One group of small, dark-colored lady beetles known as the "spider mite destroyers" (Stethorus species) are specialized predators of spider mites. Minute pirate bugs, big-eyed bugs (Geocoris species) and predatory thrips can be important natural enemies.

A great many mites in the family Phytoseiidae are predators of spider mites. In addition to those that occur naturally, some of these are produced in commercial insectaries for release as biological controls. Among those most commonly sold via mail order are Galendromus occidentalis, Phytoseiulus persimilis, Mesoseiulus longipes and Neoseiulus californicus. Although these have been successful in control of spider mites on interior plants, effective use outdoors has not been demonstrated in Colorado. Predatory mites often have fairly high requirements for humidity, which can be limiting. Most suppliers provide information regarding use of the predator mites that they carry.

One reason that spider mites become problems in yards and gardens is the use of insecticides that destroy their natural enemies. For example, carbaryl (Sevin) devastates most spider mite natural enemies and can greatly contribute to spider mite outbreaks. Malathion can aggravate some spider mite problems, despite being advertised frequently as effective for mite control. Soil applications of the systemic insecticide imidacloprid (Merit, Marathon) have also contributed to some spider mite outbreaks.


Water Management: Adequate watering of plants during dry conditions can limit the importance of drought stress on spider mite outbreaks. Periodic hosing of plants with a forceful jet of water can physically remove and kill many mites, as well as remove the dust that collects on foliage and interferes with mite predators. Disruption of the webbing also may delay egg laying until new webbing is produced. Sometimes, small changes where mite-susceptible plants are located or how they are watered can greatly influence their susceptibility to spider mite damage.


Chemical Controls: Chemical control of spider mites generally involves pesticides that are specifically developed for spider mite control (miticides or acaricides). Few insecticides are effective for spider mites and many even aggravate problems. Furthermore, strains of spider mites resistant to pesticides frequently develop, making control difficult. Because most miticides do not affect eggs, a repeat application at an approximately 10- to 14-day interval is usually needed for control.


Control of Spider Mites on House Plants: Control on house plants can be particularly frustrating. There generally are no biological controls and few effective chemical controls (primarily soaps and horticultural oils). When attempting control, treat all susceptible house plants at the same time. Trim, bag and remove heavily infested leaves and discard severely infested plants. Periodically hose small plants in the sink or shower. Wipe leaves of larger plants with a soft, damp cloth. Reapply these treatments at one- to two-week intervals as long as populations persist.