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Purple Power

Pest: cabbage butterfly

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Pest: cabbage butterfly

(Pieris rapae)

 

 

 

 

220px-Pieris.rapae.caterpillar.jpg

 

 

 

 

Special Species Notes:

Cannabis is usually harvested before they finish their life cycle. 

 

Often referred to as the "imported cabbageworm" they are a serious pest to cabbage and other mustard family crops.  They are also called cabbage butterfly, small cabbage white, cabbage moth (erroneously), or budworms ( by cannabis growers).

 

It is a butterfly in the family Pieridae. It's a close relative of the large white, Pieris brassicae, that is called the same names (above). In appearance it looks like a smaller version of the Pieris brassicae.

 

The species has a natural range across Europe, Asia, and North Africa. It was accidentally introduced to Quebec, Canada around 1860 and spread rapidly throughout North America. The species has spread to all of North American life. By 1898, the small white had spread to Hawaii; by 1929, it had reached New Zealand and the area around Melbourne, Australia and found its way to Perth as early as 1943.

 

In Britain, it has two flight periods, April–May and July–August, but is continuously-brooded in North America, being one of the first butterflies to emerge from the chrysalis in the spring and flying until hard freeze in the fall. Cabbageworms over winter in the upper Midwest in green pupal cases. Adults start appearing in gardens in mid-May and are a problem through the remainder of the growing season. There are 3 to 5 overlapping generations a year.

 

Estimates show that a single female of this species might be the progenitor in a few generations of millions.

 

IDENTIFICATION

 

220px-Pieris_rapae_egg.JPG

 

 

 

Eggs yellowish and oblong, and are laid singly on both upper and lower sides of leaves. 12 longitudinal ridges. It is twice as high as it is wide, giving it a spindle shaped appearance.

 

 

pieris_rapae04.jpg

 

Damage to cabbage resulting from feeding by larvae

of the imported cabbageworm, Pieris rapae (Linnaeus).

Photograph by J. L. Castner, University of Florida.

 

The caterpillars when they first hatch, their head and body of the first-instar larva are pale yellow with fine transparent hairs arising from small white spots. Mature larva is about 3 cm long, its head and body are velvety green with short hairs. There is a faint yellow mid-dorsal line and numerous black, and occasional white, minute raised spots from which arise short translucent hairs. Segments have one or two yellow lateral spots. The larva has five pairs of prolegs.

 

 

 

220px-Pieris.rapae.mounted.jpg    220px-Pieris_rapae_male.jpg

 

Female                                                                Male     

 

The adults are white butterflies with black spots on the forewings that are commonly seen flying around plants during the day. Females also have two black spots in the center of the forewings. Its under wings are yellowish with black speckles. It is sometimes mistaken for a moth due to its plain appearance. The wingspan of adults is roughly 1.3–1.9 in. The small white is a strong flyer and fly throughout the day, except for early morning and evening. Although there is occasional activity during the later part of the night, it ceases as dawn breaks. Adult P. rapae can move many miles in individual flights. Adults have been observed to fly as much as 7 1/2 miles in one flight. On average, a female flies about 1/2 a mile per day and moves 1,056 feet from where she starts. Males patrol all day around host plants to mate with females.

 

In the northern hemisphere, adults appear as early as March and they continue to brood well into October. Spring adults have smaller black spots on its wings and are generally smaller than summer adults

 

 

Most Common Species:

 

Pieris rapae is easily confused with other common cabbage white butterflies: Pontia protodice, southern cabbageworm; Pieris napi, mustard white; and Ascia monuste (Linnaeus), the southern white. Prior to introduction of the imported cabbageworm, Pieris napi (Linnaeus) was the dominant cabbage butterfly in the north, and Pontia protodice (Boisduval & LeConte) was the principal cabbage-feeding butterfly in the south. Both have been largely replaced by P. rapae, although they sometimes co-occur on cultivated crucifers or on weeds.

 

The  subspecies P. r. rapae is found in Europe, while Asian populations are placed in the subspecies P. r. crucivora. Other subspecies include atomaria, eumorpha, leucosoma, mauretanicanovangliae, and orientalis.

 

 

Life Cycle

 

The complete life cycle of this insect requires three to six weeks, depending on weather and nitrogen levels on their host plants. The number of generations reported annually is two to three in Canada, three in the New England states, three to five in California, and six to eight in the south. Imported cabbageworm can be found throughout the year in Florida. The main issues with the weather are that strong winds can blow eggs from the leaves and strong rains can drown the caterpillars.

 

The male, when he spots a female, zigzags up, down, below, and in front of her, flying until she lands. The male flutters, catches her closed forewings with his legs, and spreads his wings. This causes her to lean over. He usually flies a short distance with her dangling beneath him. An unreceptive female may fly vertically or spread her wings and raise the abdomen to reject the male.

 

Once a female lands on a host plant, she will go through a “drumming reaction” or a rapid movement of the forelegs across the surface of a leaf. This behavior is believed to provide physical and chemical information about the suitability of a plant. She prefers smooth hard surfaces similar to a surface of an index card over rougher softer textures like blotting paper or felt.

 

The small white female will readily lay eggs on both cultivated and wild members of the cabbage family, P. rapae is known to lay eggs singularly on the host plant. Females tend to lay disproportionate number of eggs on peripheral or isolated plants. A single larva is less likely to exhaust the whole plant, therefore laying eggs singly prevents the likelihood of larval starvation from resource exhaustion.

 

The eggs hatch into caterpillars, which is the stage that damages plants. P. rapae larva are  voracious. Once it hatches from the egg, it eats its own eggshell and then moves to eat the leaves of the host plant. It bores into the interior of the cabbage, in buds, or feeds on the new sprouts, or leaves.

 

The larvae adjust their feeding rate to maintain a constant rate of nitrogen uptake. Survival rates do not differ depending on nutrition availability of host plant.  They will feed faster in low nitrogen environment and utilize the nitrogen more efficiently. They move around the plant mostly spending their time feeding. A feeding bout is immediately followed by a change in position, either to a new leaf or to another part of the same leaf. This dispersal of damage is seen as an adaptive behavior to hide the visual cues from predators that rely on vision. The mustard oil from the host plant makes the larva distasteful to birds.

 

Larvae feeding and growth is highly dependent on their body temperature. While the larvae survives from as low as 50F, the growth of larvae changes with changing temperature. From 50F to 95F, growth increases, but declines rapidly at temperatures higher than 95F. Past 104F, larvae start showing substantial mortality. The diurnal variation of temperature can be extensive with daily range of more than 68 degrees on some sunny days and clear nights. Larvae are able to respond well to a wide range of temperature condition, which allows them to inhabit various locations in the world.

 

The elevated nutrition level also decreased the fourth instar’s consumption rate and increased its food utilization efficiencies. Larvae on cultivated host plant was observed to have higher growth efficiency than those fed in foliage of wild species. In short, larvae fed on high nutrition foliage show shorter duration of development, less consumption rate, higher growth rate and food processing efficiency plant nutrient levels decrease larval duration and increase larval growth rate.

 

 

pieris_rapae01.jpg

 

Larva of imported cabbageworm, Pieris rapae (Linnaeus). Photograph by John L. Capinera, University of Florida

 

Mature larva are about 3 cm long. After feeding for a period of weeks on cole crops, the larvae pupate in protected areas on the plants, pupa is attached with a cremaster and girdle to some part of the host plant, or sometimes to a rock, fence or wall some distance away from the host plant. The pupa is 18-20 mm long and has a pointed anterior spine. The thorax and abdomen have a dorsal ridge with paired pointed dorsolateral ridges.

 

 

220px-Pieris_rapae_pupa.jpg

 

Pupa

 

When attached to the food plant the color of the pupa is usually green, but pupae attached to other objects tend to assume the color of the background and they are often gray or pink.

 

Host plants

 

There is a three phase to host selection by the P. rapae adult female butterfly: Searching, landing, and contact evaluation .

 

They seem to limit their search to open areas and avoid cool, shaded woodlands even when host plants are available in these areas.  They use both vision and olfactory cues to identify flowers in their foraging flight. No significant preference for the shape or size of the oviposition substrate. females responded most positively to green and blue/green colors for oviposition.   

 

The adult flies around feeding from nectars at a number of plants. The cabbage butterfly prefers certain colors among green vegetation (purple, blue, and yellow)  over other floral colors (like white, red and green) and extend the proboscis before landing. they visit these flowers multiply during its life. Younger plants often had yellow/green color while older plants display a darker and stronger green. Female butterflies preferred the older plants due to the attraction to the darker green color. However, larvae perform better on younger plants.

 

They probe for nectar after landing. The butterfly identifies the flower through vision and odor. The search for nectar is also limited by the memory constraint. An adult butterfly shows a flower constancy in foraging, visiting flower species that it has already experienced. The ability find nectar from the flower increased over time, showing a certain learning curve. Furthermore, the ability to find nectar from the first flower species decreased if the adult butterfly started to feed nectar from other plant species.

 

cultivated and wild members of the cabbage family cabbage, kale, radish, broccoli, horseradish, Brussels sprouts, cauliflower, collard, kohlrabi. Also sometimes attacked are flowers such as nasturtium and sweet alyssum, and weeds in the family Cruciferae.

 

First Sign:

 

Chewed leaves, hearts, buds, and curds. Young larvae hatch on the outer leaves and feed on them superficially leaving the upper leaf surface intact.

 

Older larvae make holes in the leaves and are more likely to eat through small veins, they also damage the outer leaves of the hearts of cabbages or the curd of broccoli or cauliflowers. They often bore into the center of the head damaging the edible portion of the plant.

 

Heavily infested plants become ragged and stunted but no webbing occurs. The presence of masses of wet greenish-brown excrement deep among leaves is indicative of this pest. In large infestations of P. rapae the plant may be reduced to a partial or complete skeleton, in which all the leaf tissue except the veins has been eaten.

 

What to do:

 

Checking for caterpillars on cole crops soon after planting. Many transplants purchased at garden centers may be infested with moth eggs or newly hatched larvae. Inspect your plants at least once a week, and more often as the season progresses. Check both sides of leaves for caterpillars and their feeding damage. The older, larger caterpillars cause the most feeding damage.

 

Destroy crop residue immediately after harvest to eliminate potential over wintering sites for imported cabbageworms. Eliminate weeds from the Brassicaceae family such as wild mustard, peppergrass, and shepherd's purse, as they are alternate hosts for these pests.

 

Handpicking the caterpillars, especially in smaller gardens, can be an effective means of control. Drop the caterpillars into a pail of soapy water, or give to your chickens (make sure you have enough for all, or they'll fight each other) to kill them.

 

Floating row covers will help to prevent adult moths from laying eggs on plants. A floating row cover consists of lightweight all-purpose garden fabric draped either directly over garden plants or over metal hoops or a wooden frame for support. Fit the row covers over the cole crops at seeding or transplanting. The row covers may be removed upon harvesting the cole crop.

 

Natural control

 

Birds are a major predators. only in late-instar larvae or on overwintering pupae House sparrow, goldfinch, skylarks, chickens.

 

Beneficial insects

 

Shield bugs (Hemiptera: Pentatomidae), ambush bugs (Hemiptera: Phymatidae), predators, such as, paper wasps, and parasitic flies and wasps, e.g., the parasitic wasp, Cotesia glomerata.

 

 

pieris_rapae06.jpg

 

Vespid wasp preying on a larvae of the imported cabbageworm, Pieris rapae (Linnaeus). Photograph by Andrei Sourakov, Florida Museum of Natural History.

 

 

Some wasps and flies parasitize the caterpillars while others attack the pupae. As the wasps or flies develop within the caterpillar or pupae, they eventually kill their hosts. Some wasps also parasitize the eggs of these caterpillar pests. These wasp and fly parasites are small and do not sting or bite people.

 

P. rapae caterpillars are commonly parasitized by a variety of insects. The four main parasitoids are Cotesia rubecula, Cotesia glomerata, Phryxe vulgaris, and Epicampocera succinata. Cotesia rubecula and Cotesia glomerata, previously in the genus Apanteles, were introduced in North America from Asia as biocontrols. C. rubecula lays its eggs in the 1st and 2nd instar caterpillars.

 

The larvae then grow within the caterpillar and continue to feed on the caterpillar until they are almost fully grown, and at that point the caterpillar is killed. C. glomerata is similar to C. rubecula in that both parasitize the host in either the 1st or 2nd instar. The main difference is that C. glomerata always kill the host in the 5th instar and multiple larvae can be raised within one host.

 

Ladybugs

 

http://freemygreenpdx.com/topic/14338-beneficial-bug-ladybugs/

 

Lacewings

 

http://freemygreenpdx.com/topic/14337-beneficial-bug-green-lacewing-larvaeeggs/

 

Insecticides

 

The best time to treat caterpillars is while they are still small and before they cause too much feeding damage. Insecticides are not as effective in killing older caterpillars. When possible choose a low impact insecticide that is less toxic, and "easy" on natural enemies (i.e., paper wasps, parasitic flies and wasps) and pollinators such as bees and flies.

 

There are several options when considering a low impact insecticide. Neem is a plant based insecticide and acts primarily as an anti-feedant. Although insects are not killed quickly, it causes them to stop feeding and they eventually die.

 

Spinosad is derived from a naturally occurring soil-dwelling microorganism, provides excellent control, and does not harm natural enemies.

 

Bacillius thuringiensis (Bt) is a bacterium that occurs naturally in the soil. Bt is specific to caterpillars and must be ingested in order to kill the insect which is different compared to residual products. Because of this, good spray coverage is essential. I spray BT in this range mid-July to early August.

 

Conventional, or broad-spectrum insecticides, are generally longer lasting but kills a variety of insects, including natural enemies. Common examples of broad spectrum insecticides include permethrin, carbaryl, bifenthrin, and lambda-cyhalothrin.

 

 

The link below will take you to "An Intro to beneficial bugs and beneficial insect food" it has a list (been worked on) to pests and beneficial insects

 

http://freemygreenpdx.com/topic/14334-an-intro-to-benefical-bugs-and-beneficial-insect-food/?p=124257


gallery_2188_61_23224.png  

Classy, sassy, and a bit of a smart assy

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 I seen 2 of these today fling around the plants in the back yard. I had them last year as well and they did cause damage. What should I do this year to stop the fliers before they  lay  eggs?

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I have some lightweight all-purpose garden fabric,  I'll try that tomorrow. Seems simple enough. Where would I buy Bacillius thuringiensis (Bt)?

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So I got my BT in the mail and read the instructions. It says to apply after they hatch but before they start pulling leaves together, (Gluing themselves in a top set of leaves)

 

Question is: How do I know when i should apply this?  

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This is the time of year I spray my plants, so on their first bite they are being poisoned. If I were you I'd spray tonight once your plants are out of direct sunlight. 


gallery_2188_61_23224.png  

Classy, sassy, and a bit of a smart assy

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This is the time of year I spray my plants, so on their first bite they are being poisoned. If I were you I'd spray tonight once your plants are out of direct sunlight. 

Will do, Thanks Purple Power.

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