Anderson,
The leaves are dark and leathery, the undersides covered with aphids. Will the caterpiller be able to develop---it is now over an inch long and seems to searching for something. Is there any reason for leaving or destroying this plant?
2 Answers
country bumpkin
Monarch butterflies depend on the milkweed to survive, but other insects also call it home
Gardeners are scrambling to help the threatened monarch butterfly by planting more milkweed, the insect's host plant.
Drought, loss of habitat and pesticides have decimated stands of milkweed along the orange-and-black butterfly's migration route from Mexico, through Texas and beyond. Monarchs die without milkweed.
While providing food for the butterfly, well-intended gardeners have discovered that milkweed attracts more than monarchs. Scores of other insects are drawn to the plant mama monarchs use as nurseries. And sometimes it's difficult separating good from "bad" within the complex community.
"Many other insects call the genus Asclepias home, giving rise to the concept of a milkweed village," says Soni Holladay, a horticulturist at the Cockrell Butterfly Center of the Houston Museum of Natural Science. "Milkweed plants produce bitter-tasting toxins called cardiac glycocides, and insects that eat milkweeds have evolved to use these to their advantage, sequestering the toxins in their bodies to protect themselves from predators."
While the yellow-, black- and white-striped monarch caterpillars eat the milkweed foliage, they absorb the toxins that render them and adult butterflies distasteful to birds, lizards and other verterbrate predators.
But wasps, parasitic tachinid flies and other invertebrate predators lurking among the leaves don't mind the toxins. Many gardeners have watched in horror as monarch eggs and caterpillars fall victim to the merciless food chain.
Even some otherwise beneficial insects, such as assassin bug nymphs, eat monarch caterpillars. Compounding the confusion: Assassin bug nymphs, which feed on damaging cabbage loopers, strongly resemble the young of leaf-footed bugs, terrors in a vegetable garden.
So what's a gardener to do?
"It's just a matter of personal choice, I think," Cockrell director Nancy Greig says. "I kill or chase off the leaf-footed bugs that get all over my tomato fruit, but don't usually kill assassin bugs. I figure assassin bugs kill lots of caterpillars, like cutworms and loopers, in addition to the occasional monarch or other desirable insect they get. But some people are very protective of their baby butterflies. I would certainly never use any sort of a chemical control."
Holladay simply flicks assassin bugs off the milkweed.
"I don't really want to kill anything since I feel that it's all pieces of the whole. Leave it to the gardener to decide to collect and squish or let them hunt," she says.
Holladay's milkweed village post at blog.hmns.org helps the public identify who's who in butterfly gardens. Grab a magnifying glass to identify the following more-common residents.
Warning: It's not always a pretty picture.
Yellow oleander aphids (Aphis nerii) congregate on new growth, flowers and developing seed pods and suck sap from the plant.
Ladybug larvae and adults (Hippodamia spp. and others) eat the aphids.
Mealybug destroyers (Cryptolaemus montrouzieri) and scale destroyers (Lindorus lopanthae) are small beetles that eat aphids and other small sap-feeding insects. Their larval stages look like their namesakes, mealybugs and scale, respectively.
Maggotlike larvae of syrphid flies suck aphid bodies dry. Syrphid pupae resemble small brown or tan teardrops. Leave them to ensure another generation of beneficial flies.
Tiny parasitic braconid wasps lay their eggs in aphids' bodies. The wasp larvae feed on the hosts' insides until they pupate, then exit as adult wasps through tiny holes in the aphids' exoskeletons. The remaining brown shells are the aphid mummies. These wasps don't harm monarch caterpillars.
Milkweed leaf beetle (Labidomera clivicollis) is chunky, orange and black, and its larvae feed on milkweed leaves.
Large milkweed bugs (Oncopeltus fasciatus) are oblong-shaped, orange and black sap-sucking true bugs that feed on developing seeds, flowers and nectar. They usually cause only light damage.
White-, black- and yellow-striped monarch butterfly (Danaus plexippus) larvae devour milkweed leaves. Their jewellike chrysalids, or pupae, are jade green with gold lines and spots.
Queen butterfly (Danaus gilippus) caterpillars are quite similar, but they have three pairs of tentacles instead of a monarch's two. Their similar chrysalids are smaller and sometimes a pale pink rather than green.
The gray tachinid fly is about the size of a housefly. Females lay eggs on monarch caterpillars, and when they hatch, the maggots burrow inside and eat the caterpillars' tissues.
Assassin bugs (Zelus spp.), frequent milkweed visitors, stab monarch caterpillars, paralyzing victims and liquefying their insides, making them easier to consume. Assassin nymphs are bright orange-red and have long, skinny legs and more often travel alone. They're similar to undesirable leaf-footed bug nymphs, which tend to be in groups.
Large red wasps (Polistes carolinus) and the smaller yellow and black European paper wasps (Polistes dominulus) hunt caterpillars as food for their own larvae.
"Once a wasp finds a host plant with caterpillars, she will come back regularly to check for more, especially in the summer months when wasps are the most active," Holladay says. "This can be upsetting to butterfly gardeners. To protect your caterpillars from these all-too-efficient predators, place a screen such as a pop up or mesh laundry hamper between them and the wasps."
A hidden concern
In addition to numerous insect predators, protozoan parasites Ophryocystis elektroscirrha, or Oe, threaten monarch and queen butterflies, horticulturist Soni Holladay says.
Infected female monarchs shed dormant Oe spores when laying eggs on milkweed foliage. Once hatched, caterpillars consume the spores on the leaves. Inside the caterpillars' guts, spores become active and reproduce several times. When the butterflies emerge from their pupae, they are covered in dormant Oe spores, facilitating another generation of infected monarchs, Holladay explains.
Initially, butterflies may show no sign of infection, but as Oe levels build up, they eventually cause weakness, deformity and even death.
The annual fall migration to Mexico helps weed out infected butterflies too weak to make the long trip, she says. But some don't migrate and may winter in the Houston area, where their caterpillars may consume Oe spores on the evergreen tropical milkweed, Asclepias curassavica. The cycle produces populations of severely infested monarchs.
"We therefore encourage butterfly gardeners to cut back their tropical milkweed every spring after the first generation of monarchs arrive and eat the milkweed down, and then again in the fall before or during the migration, so that the butterflies will be encouraged to migrate and not overwinter here," Holladay advises.
Holladay says only 5 percent to 10 percent of monarch eggs make it to adulthood. And while natural predators share the blame, humans have done even more damage to monarch populations.
"Planting butterfly-friendly gardens, especially if they include milkweed, can help mitigate this loss of habitat," she says.
Kathy Huber
| 9 years ago. Rating: 6 | |
bustieone
