Posts tagged larvae

Letting milkweed grow

A monarch caterpillar makes its way along a milkweed plant in late July in Cedar Rapids, Iowa.

A monarch caterpillar makes its way along a milkweed plant in late July in Cedar Rapids, Iowa.

  

 

This monarch caterpillar was munching on common milkweed at my garden this weekend. As noted below, habitat destruction has reduced the amount of milkweed growing in the Midwest, which is the only food source for the graceful Monarch butterfly. That’s one of the reasons I don’t kill off all the milkweed in my gardens. Another reason: the scent of milkweed flowers, as another gardener once described it to me, is intoxicating. Unfortunately, my nemesis, the Japanese beetle, has managed to suck all the milkweed flowers to brown this year. More plants are springing up, and hopefully will bloom after the destructive beetle has gone underground. Though the caterpillars look a bit ominous, they won’t bother your tomatoes or other plants, so don’t poison or otherwise kill them off, as Monarchs already face a number of obstacles to survival.

 

 

 

 

 

 

   For more information on milkweed, the following came from the Monarch Watch Web site at www.monarchwatch.org

    Monarch larvae appear to feed exclusively on milkweeds in the genus Asclepias and several other genera of viny milkweeds in North America. Milkweeds are perennial plants, which means an individual plant lives for more than one year, growing each spring from rootstock and seeds rather than seeds alone. In the Midwest, milkweeds were historically common and widespread on prairies, but habitat destruction has reduced their range and numbers.

    Milkweeds belong to the family Asclepiadaceae, derived from Asklepios, the Greek god of medicine and healing. Though most members of the genus Asclepias are tropical, there are approximately 110 species in North America known for their milky sap or latex contained in the leaves. Most species are toxic to vertebrate herbivores if ingested due to the cardenolide alkaloids contained in the leaves and stems.

    When Monarch larvae ingest milkweed, they also ingest the plants’ toxins, called cardiac glycosides. They sequester these compounds in their wings and exoskeletons, making the larvae and adults toxic to many potential predators. Vertebrate predators may avoid Monarchs because they learn that the larvae and adults taste bad and/or make them vomit. There is considerable variation in the amount of toxins in different species of plants. Some northern species of milkweed contain almost no toxins while others seem to contain so much of the toxins that they are lethal even to monarch caterpillars.

 

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Not so sweet pest

Entomologist Donald Lewis, of Iowa State University Extension, offers the following information about the bane of sweet corn:

One of the pure pleasures of summertime in Iowa is eating sweet corn fresh from the garden or farmers market. To the dismay of gardeners, growers and sweet corn aficionados, however, there is the matter of an occasional pest to consider. The most important and best known insect pest of sweet corn in Iowa is the pudgy, hairless “worm” found at the tip of an infested ear, the corn earworm.

Corn earworms come in a variety of colors, ranging from light green, to tan, brown, pink or nearly black. The caterpillar’s body is marked with light and dark stripes running lengthwise and the skin texture is coarse due to microscopic spines that cover the surface.  Earworms are only in the ear for three to four weeks but during that short time they grow to nearly 1 .5 inches in length.  Infestations may be present throughout the summer but are generally worse in late summer.

Unlike hardy residents of the state the corn earworm does not survive Iowa winters.  Instead moths that lived and grew in southern states on either corn or cotton last year are blown here during May and June each year to reinfest the state.

These recent-arrival-moths fly after sunset and reproduce by depositing their eggs on the fresh, green silks of the sweet corn ear. These eggs hatch in two to six days and within an hour the tiny, young larvae crawl into the silk channel and move to the tip of the developing ear. The larvae feed on the silk and developing kernels and foul the ear with excrement.  About three weeks after silking the sweet corn is ready to harvest and eat, and there, waiting for you at the end of the ear is the much-grown earworm caterpillar.

The amount of corn earworms in the sweet corn crop varies from place to place, from year to year and with the time of the year.  Mostly the damage is determined by the number of moths in the vicinity which depends on the weather and other factors. Some varieties of sweet corn are more or less susceptible to earworm attack, and genetically modified varieties are available that produce their own defense against caterpillar attack.

Growers and gardeners who want “clean” sweet corn must work to prevent the earworms from getting into the silks. If the caterpillars are already crawling toward the ear tip it is too late to stop them. A typical preventive management strategy is to spray insecticide on the corn ears throughout the entire period when green silks are present. 

Insecticides for the home gardener include azadirachtin (Neem), Bacillus thuringiensis, carbaryl (Sevin), or permethrin. Spray at the first sign of silk emergence (one or two days after tassels appear) and again two days later after silks have elongated. For complete protection, especially in later plantings, spray a third time three days after the second spray.  After the silks turn brown there is no benefit to spraying.  

Admittedly, this is an extensive amount of insecticide but it is currently the most practical method for assuring worm-free sweet corn.  The alternative is to not treat at all.  Instead, cut off the damaged tip of infested ears and enjoy the remainder of the ear.

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Bad “worms”

Iowa State University Extension gardening experts answer questions on damaging worms:

 

Worms are devouring the needles on my mugo pine.  What should I do?

 

The “worms” that are eating the needles on your mugo pine are the larvae of the European pine sawfly. European pine sawfly larvae are grayish green. Two light stripes and one dark stripe run down the sides of the body. The legs and head are shiny black. 

 

The larvae feed mainly on mugo, Scotch and Austrian pines, though other pine species are occasionally damaged. They do not feed on spruce or fir. Larvae typically appear in mid to late May in Iowa and are usually gone within a few weeks. 

 

European pine sawfly larvae feed on needles produced in previous years. (The needles on most  pines persist for two to five years.) They do not harm the new needles developing on the branches. As a result, the damage is mainly aesthetic. Larval feeding does not destroy the affected branches. The branches simply have fewer needles than normal. 

 

To keep damage to a minimum, the larvae of the European pine sawfly can be controlled by pruning off and discarding infested branches, knocking the larvae off affected branches into a bucket or other container and destroying them, or spraying them with an insecticide, such as Sevin. 

 

I occasionally find small, white worms in my cherries.  What is the best way to control them?

 

The small, white “worms” are probably the larvae of the cherry fruit fly (Rhagoletis spp.)  Cherry fruit flies lay eggs on developing cherry fruit in May. Damaged fruit appear shrunken and shriveled when ripe, and usually contain one off-white larva (maggot) that is slightly longer than one-quarter of an inch.

 

Cherry fruit fly damage varies greatly from year to year. It may be more practical to tolerate some damage and loss of usable fruit than to attempt effective preventive control.

 

To prevent maggots from appearing inside the fruit, the tree must be thoroughly sprayed with a labeled insecticide when the adults emerge and before the females lay their eggs inside the young fruit. Because the flies emerge over an extended period of time, several sprays will be needed. You can monitor fruit flies with yellow sticky traps hung in the tree in early May. Check traps daily after the first fruit fly is caught and repeat the spray application until flies no longer appear. 

 

Check for home orchard sprays and other insecticides at your local garden center. Carefully read and follow label directions.

 

 

 

 

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