Perennial milkweed, Asclepias perennis, with oleander aphids; notice the brown aphid mummies that have been parasitized. Photo credit: Mary Salinas UF/IFAS Extension.
Milkweeds are appreciated for their beauty, but often we cultivate it for the benefit of the monarch butterflies who lay their eggs only on this plant genus. Avid butterfly gardeners want the monarch caterpillars to eat up the milkweed and become beautiful butterflies. Often instead, thousands of aphids show up and compete for space on the plants. These bright yellow aphids are known as oleander aphids.
Just how do aphids build up their populations so quickly? It seems that one day you have a small number on a few plants and then a few days later, thousands are all over your milkweed. Oleander aphids have a few advantages for quickly building their populations:
All oleander aphids are female and do not need to mate to produce their young
Aphids give birth to live young who immediately start feeding on the plant
Aphids start reproducing when they are 4 to 10 days old and keep reproducing during their one-month life span
When populations get heavy or the plant starts to decline, winged individuals are produced to migrate to new areas and plants.
Parasitic wasp and aphid mummies. Photo credit: University of California.
What can or should you do to control this pest?
One option is to do nothing and let the natural enemies come in and do their job. One of the best is a very tiny wasp that you will likely never see. This parasitoid lays its eggs only inside aphids. The wasp larva feeds on the inside of the aphid and turns it into a round brown ‘mummy’ and then emerges when mature by making a round hole in the top of the aphid. Look closely with a hand lens at some of those brown aphids on your milkweed and you can see this amazing process. Another common predator I see in my own garden is the larvae of the hover fly or syrphid fly. You will have to look hard to see it, but it is usually there. Assassin bugs and lady beetles also commonly feed on aphids. The larvae of lady beetles look nothing like the adults but also are voracious predators of aphids – check out what they look like.
Lady beetle larva feeding on aphid on tobacco. Photo credit: Lenny Wells University of Georgia Bugwood.org.
If you think your situation requires some sort of intervention to control the aphids, first check carefully for monarch eggs and caterpillars, keeping in mind that some may be very small. Remove them, shoo away any beneficial insects, and spray the plant completely with an insecticidal soap product. Recipes that call for dish detergents may harm the waxy coating on the leaves and should be avoided. The solution must contact the insect to kill it. Always follow the label instructions. Soap will also kill the natural enemies if they are contacted. One exception is the developing wasp in the aphid mummies – fortunately, they are protected inside as the soap does not penetrate. Oils derived from plants or petroleum can serve the same purpose as the insecticidal soap.
Syrphid fly larva and oleander aphids. Photo credit: Lyle Buss, University of Florida.
You also can squish the aphids with your fingers and then rinse them off the plant. If you only rinse them off, the little pests can often just crawl back onto the plant.
There are systemic insecticides, like neonicotinoids, that are taken up by plant roots and kill aphids when they start feeding on the plants. However, those products also kill monarch caterpillars munching on the plant and harm adult butterflies, bees, and other pollinators feeding on the nectar. So those products are not an option. Always read the product label as many pesticides are prohibited by law from being applied to blooming plants as pollinators can be harmed.
In the end, consider tolerating some aphids and avoid insecticide use in landscape.
In recent years, not a summer has gone by in which I did not see citrus rust mite (CRM) damage in a garden. I thought this year would be the first. Unfortunately, recently I saw my first rust mite damage of the year.
Unlike the myriad of pests that have been recently introduced into Florida from abroad, the citrus rust mite (Phyllocoptruta oleivora) has been documented as present in Florida since the late 1800s. Along with its companion, pink citrus rust mite (Aculops pelekassi) It can be a major summer pest for satsuma mandarins grown in the Florida Panhandle gardens.
Citrus Rust Mite (CRM) damage manifests itself on fruit in two ways, “sharkskin” and “bronzing“. Sharkskin is caused when mites have fed on developing fruit, and destroyed the top epidermal layer. As the fruit grows, the epidermal layer breaks and as the fruit heals, the brown “sharkskin” look develops. Bronzing occurs when rust mites feed on fruit that’s nearer to mature size. Since the skin is not fractured by growth, the fruits develop a polished bronze look. In both cases, the interior of the fruit may remain undamaged. However, extreme damage can cases cause fruit drop and reduced fruit size. Regardless of the condition of the interior, damaged fruit is not aesthetically pleasing, but fine for slicing or juicing.
“Sharkskin Damage” to fruit caused by past feeding by the Citrus Rust Mite. Image Credit, Matthew Orwat
If a CRM population is present, they will begin increasing on fresh spring new growth in late April, and usually reach peak levels in June and July. By August the damage has often already been done, but is first noticed due to the increased growth of the fruit. Depending upon weather conditions, CRM can have a resurgence in October and November, just as Satsuma and other citrus is getting ready to be harvested, so careful monitoring is necessary. For more information, check out this publication: Guide to Citrus Rust Mite Identification.
Sun spot resulting from where citrus rust mite avoids feeding on most sun exposed portion of the fruit. Image and Caption courtesy of EDIs publication HS-806
If control of CRM is warranted, there are several miticides available for use, but it is not advisable for home gardeners to use these on their citrus plants since they will also kill beneficial insects. Horticultural oil is an alternative to miticide, which is less damaging to beneficial insects. Several brands of horticultural oil are formulated to smother CRM, but care must be taken to not apply horticultural oil when daytime temperatures will reach 94 degrees Fahrenheit. Application of oils at times when temperatures are at this level or higher will result in leaf and fruit damage.
Although Citrus Rust Mite (CRM) has the potential to be aesthetically unsightly on citrus fruit in the Florida Panhandle, strategies of monitoring and treatment in homeowner citrus production have been successful in mitigating their damage.
Veteran Master Gardener, Les Furr shares an idea he and his wife had to hide an ugly debris pile following Hurricane Michael. He planted a temporary sunflower screen to block something ugly with something beautiful. Sunflowers can be planted along a road or fence, and provide a lovely addition to your property. The seed can be saved and frozen to provide beauty to your property year after year.
Oleander caterpillars, which are active on some oleanders during summer, can provide a number of gardening lessons.
Oleander caterpillar moth on lantana flower. Photo credit: James Castner, UF
The adult moth is striking in appearance. The bluish to purplish moth has white dots on its black wings. The moths resemble wasps as they fly in and around oleander shrubs.
It’s the orange caterpillars with black spots and black hairs that cause problems for some gardeners.
Caterpillars are the larval stage of butterflies and moths. In order to enjoy watching butterflies and moths feeding on the nectar of flowers, some of the caterpillars must survive to become adult butterflies and moths. This is lesson number one.
Oleander caterpillars usually only feed on oleander plants. Oleanders are native to areas of Europe and Asia. This is lesson number two.
Oleander caterpillar, Photo credit: Paul Choate, UF
Oleander caterpillars benefit by us planting their food source in Florida.
This relationship between pest and plant is referred to as the key plant, key pest concept. Some other examples include St. Augustinegrass and chinch bugs, gardenias and whiteflies, crape myrtles and crape myrtle aphids, azaleas and azalea caterpillars, camellias and tea scale, roses and black spot, pecans and pecan scab, squash and squash vine borers.
Understanding this concept can be helpful in designing a “low maintenance” landscape.
When you plant roses, you plant everything that goes with roses, including the time and money required to maintain them. This applies to St. Augustinegrass, pecan trees, squash and oleanders. This is lesson number three.
Oleander caterpillars can temporarily damage the appearance of oleanders. But they cause no long-term damage for the plant. This is lesson number four. The damage is aesthetic. Oleander caterpillars can consume great numbers of leaves. However, if the plant is otherwise healthy, new leaves will be produced and the plant will continue to grow. The damage is temporary; there will be no evidence the plant ever had a problem.
To spray or not to spray for oleander caterpillars has to do with a person’s tolerance level.
If you can’t tolerate having oleander caterpillars around and the temporary aesthetic damage they cause, consider the use of Bacillus thuringiensis. It is sold under a number of brand names and many times is referred to as Bt. This bacterium only controls caterpillars so it is friendlier for the beneficial insects. When using any pesticide, always follow the label directions and precautions.
Here are links to UF/IFAS Extension publications with more info.
I know this is going to come as a shock to some readers, but not all bugs are bad. In fact, while there are over 1 million species of insects worldwide, less than 1% are problem pests! This problem 1%, composed of common garden pests, including aphids, stinkbugs, nuisance caterpillars, and scales, get all the attention and for good reason; they can be extremely destructive to home and commercial crops. However, the good guys, beneficial predatory insects, are out there too, providing valuable pest control day and night and should be considered in part of a quality garden pest management strategy.
Beneficials come in many shapes and sizes. Some are commonly known predators, such as spiders, Lady Beetles and Praying Mantids, while others are lesser known pest nemeses, like Paper Wasps, Pirate Bugs, and Lacewings. Regardless, gardeners should do their homework and be able to identify beneficials when they see them and allow them to do their jobs. The presence, or not, of a handful of Lady Beetles or Lacewings on the attack can be the difference between needing to treat with insecticides for an aphid outbreak or just letting nature take its course. Studies have shown that just one individual Lady Beetle in the larval stage can consume as many as 500 aphids; adult Lady Beetles are even hungrier aphid eaters! Paper Wasps, you know the ones who make the large “papery” nests around eaves of house and other structures, play an important beneficial role, frequently preying on caterpillars. If their nests aren’t near highly trafficked areas around your home and you don’t have family members allergic to wasp stings, your garden will thank you for leaving a few paper wasp colonies as caterpillar insurance!
Lacewing eggs on a Jade plant in close proximity to the author’s vegetable garden.
In many instances, beneficial insects can keep pest insect infestations at bay, allowing gardeners to spot treat outbreaks when they get out of hand or even prevent the problem from needing chemical intervention altogether.
As helpful as they are, beneficial insects in the garden won’t totally negate the need for chemical treatment entirely. From time to time, garden pest populations outpace the beneficials’ abilities to kill them and intervention from humans is needed. In these times, it is advisable to use a couple of best practices to limit exposure to beneficial insects. First, try to use selective insecticides that only target specific pests and are nontoxic to other bugs, like the product Bt for caterpillar pests (sold under many brands like Dipel, Garden Safe Bt Worm and Caterpillar Killer, Thuricide, etc). However, if a nonselective, general insecticide, like the Pyrethroids (many common homeowner insecticide brands) and carbamates (Sevin and others), is needed, timing these broad spectrum sprays for early in the morning and late in the evening when many beneficials are not very active can help reduce friendly fire casualties. Care should also be taken to only spot treat infested plants and not the entire garden, this helps reduce beneficial exposure to these broadly toxic pesticides.
Every gardener should have a plan for pest control and beneficials can play an important role in this overall strategy. Gardeners can help ensure that nature pulls its weight in controlling problem pests by taking a little time to scout for beneficial insect populations, keeping a close eye on developing pest outbreaks, using selective insecticides when you can, and only spraying broad spectrum products as spot treatments when necessary and timing those applications for very early or late in the day. If you have a question about whether or not a garden insect is a good guy or a pest or want more information on garden pest control strategies, contact your local UF/IFAS County Extension Office! Happy Gardening!
The following resources were used in the development of this article:
On a daily basis, it is not unusual for our Extension Office to get calls, emails, and walk-ins with questions about insect identification. Sometimes we even get questions about imaginary insects! The overwhelming opinion by our clientele is that the insects in question are harmful to their landscapes and gardens. This is not always the case since there are more than 100,000 species of insects found in the United States, but less than 1% are harmful.
Recently I received a call about an abundance of bugs in a client’s newly installed sod. He was concerned that the insects were taking over his yard. Luckily, he was able to submit some good quality photos so the University of Florida/IFAS Extension Service could help him identify the insects.
An adult ground beetle (Mochtherus tetraspilotus). Photo Credit: Michael C. Thomas, Florida Department of Agriculture & Consumer Services
The photos were sent to a University of Florida Entomologist for identification verification. It turns out the insects were ground beetles (family Carabidae). Adult ground beetles are slender and range between 1/4″ and 3/8″ in length. Their head and thorax are much narrower than their abdomens. Ground beetles are beneficial insects that feed on moth eggs and larvae. They are known predators of soybean loopers, cabbage loopers, and velvetbean caterpillars. It is suspected that the beetles found by the client came from the sod farm and were living in the thatch layer of the sod. They were possibly feeding on sod webworms or other moth larvae.
Accurate identification is the first step of integrated pest management (IPM). In this case, the insect found wasn’t a pest at all. If you need help identifying an insect, feel free to contact your local Extension Agent. For more information on beneficial insects, visit these publications found at edis.ifas.ufl.edu.
