When a biocontrol agent turns on you, it can be painful. Recently a grower called in asking about an insect that had bit him when he picked it up. It caused a fearsome pain and some swelling. This insect is an assassin bug, one of the numerous predators out there that help keep pest insects in control.
Assassin bugs (family Reduviidae) belong to the order Hemiptera and the suborder Heteroptera, the so called “true bugs.” Altogether, nearly 7,000 species of assassin bugs have been described worldwide, of which about 50 are native to California. All Hemiptera have tubular mouthparts with stylets that help them pierce tissues of plants and other creatures. The stylets may also help them suck blood. Indeed, 140 species of assassin bugs are specialized to feed on blood. Spreaders of Chagas disease, these are the kissing bugs, so named because they frequently bite people on the face around the mouth.
Within insects, they are one of the third biggest groups of predators that mostly feed on other insects. This determines where they are found: many species sit on flowers or leafs, where they stalk or ambush their prey. Others like to hide in special microhabitats, for example, underneath the bark of trees, and feed on insects – such as certain beetle and fly larvae – that live under the bark.
In general, the greatest numbers of assassin bugs are found in wet tropical places around the world, but some also live in subtropical, arid and even temperate places. About 50 species are native to California and the majority of them also occur in Southern California. In California, you can find different species of these bugs from the low deserts to fairly high elevations in the Sierras. Altogether, we have fewer than 190 species recorded from the United States and Canada, but as you get into Central and South America, diversity increases and the species numbers go up.
A common species in California is the leafhopper assassin bug that is frequently found even in backyards around Riverside. It is widely distributed from Canada to Central America. Although it is native to this region, it has been introduced and become established in Chile, Greece and Spain. Leafhopper assassin bugs hang out on various plants and are beneficial – as are many other assassin bugs – because they eat pests that can be a nuisance to crops and ornamental plants.
The smallest are about 3 millimeters long. The largest can be about 1.5 inches in length. As other true bugs, assassin bugs have “divided” wings, meaning that the forewings have a thick leathery texture close to the head and a more membranous structure further back. Assassin bugs can be recognized by the shape of the beak that is typically curved and pretty thick and has three segments. The bug uses this beak to grab and hold on to its prey. There is no need to panic when you see an assassin bug, but since they can inflict rather painful bites it is best not to touch them. Kissing bugs are somewhat unusual amongst assassin bugs in having a fairly slender and straight beak. Although their bite is painless in contrast to the bite of other assassin bugs, they are much more dangerous: their saliva can cause allergic reactions, and they can also spread Chagas disease.
The protozoan that causes Chagas disease, Trypanosoma cruzi, is not transmitted when the kissing bug bites you and sucks your blood. Instead, it is transmitted soon after the kissing bug has stopped feeding blood. When a kissing bug bites you, you don't feel anything at first because the bug injects an anesthetic and the bite will only get itchy shortly thereafter. Now, after its blood meal, the kissing bug defecates. The feces contain the Chagas-disease-causing protozoans. When you scratch, you get the feces into the wound and your blood stream. We have three species of endemic kissing bugs in California. Many of the specimens of our commonest species are to be found in Southern California; about 20-35 percent according to one of our studies, are infected with the protozoan and could serve as carriers. Typically, our native kissing bugs blood-feed on woodrats, but will also try to feed on other vertebrates, given the opportunity. In addition, dogs that sleep outdoors could also get infected with Chagas disease by eating the kissing bugs.
Persons who are bitten should wash and apply antiseptic to the site of the bite. Oral analgesics, such as aspirin or ibuprofen, may be useful to reduce the pain. Treatment by a physician is not usually needed, though Caladryl® or topical corticosteroids may help reduce swelling or itching at the site of the bite. As with any insect sting or bite, the victim should seek medical attention immediately if there is any sign of anaphylactic reaction, such as generalized swelling, itching, hives or difficulty breathing.
- Author: Tunnyalee Martin and Cheryl Wilen
Sometimes an invasive pest takes a while to become invasive. The Invasive Species Council of California defines an invasive species as “non-native organisms which cause economic or environmental harm.” So, until a species not originally from the area actually causes harm, it doesn't get the title of invasive.
Take the Italian white snail, also known as the white garden snail. In San Diego, it caused extensive damage to agricultural plants in the early 1900s but was considered eradicated after a massive control program in the 1920s. However, it was found again in San Diego County in the 1980s but it did not damage agricultural crops or gardens. Instead the snails lived off of weeds in neglected fields. Now it appears to be moving slowly from these fields to fruit tree orchards and avocado groves as well as landscapes. The Italian white snail feeds on decaying organic matter and living plants, damaging leaves, flowers, and fruit. Another fear is it being found in cut flower growing areas or in nurseries where it could become an export issue.
White or light tan, the Italian white snail is about the size of a dime or nickel when fully grown. It may or may not have brown markings on the outside of the shell. The inside shell color near the opening is light colored (compared to the milk snail, which looks similar but has a dark inside shell). Italian white snails are most noticeable during the day and when it is hot, because the snails climb up on fence posts, walls, weeds and other vegetation and congregate in large numbers.
In California, the Italian white snail is only officially found in San Diego County. However, it could easily move to new areas because of its small size, which makes it hard to detect, and tendency to attach to many kinds of surfaces such as truck beds. Also, because land snails are hermaphroditic—each snail has both male and female reproductive organs—it only takes any two snails to reproduce!
Californians can help in the fight against invasive species by learning and participating during California Invasive Species Action Week, June 2–10.
Home is where the habitat is: This Earth Day, consider installing insectary plants
—Stephanie Parreira, UC Statewide IPM Program
Help the environment this Earth Day, which falls on Sunday April 22 this year, by installing insectary plants! These plants attract natural enemies such as lady beetles, lacewings, and parasitic wasps. Natural enemies provide biological pest control and can reduce the need for insecticides. Visit the new UC IPM Insectary Plants webpage to learn how to use these plants to your advantage.
The buzz about insectary plants
Biological control, or the use of natural enemies to reduce pests, is an important component of integrated pest management. Fields and orchards may miss out on this control if they do not offer sufficient habitat for natural enemies to thrive. Insectary plants (or insectaries) can change that—they feed and shelter these important insects and make the environment more favorable to them. For instance, sweet alyssum planted near lettuce fields encourages syrphid flies to lay their eggs on crops. More syrphid eggs means more syrphid larvae eating aphids, and perhaps a reduced need for insecticides. Similarly, planting cover crops like buckwheat within vineyards can attract predatory insects, spiders, and parasitic wasps, ultimately keeping leafhoppers and thrips under control.
Flowering insectaries also provide food for bees and other pollinators. There are both greater numbers and more kinds of native bees in fields with an insectary consisting of a row of native shrubs planted along the field edge (called a hedgerow). Native bees also stay in fields with these shrubs longer than they do in fields without them. Therefore, not only do insectaries attract natural enemies, but they can also boost crop pollination and help keep bees healthy.
Insectary plants may attract more pests to your crops, but the benefit is greater than the risk
The possibility of creating more pest problems has been a concern when it comes to installing insectaries. Current research shows that mature hedgerows, in particular, bring more benefits than risks. Hedgerows attract far more natural enemies than insect pests. And despite the fact that birds, rabbits, and mice find refuge in hedgerows, the presence of hedgerows neither increases animal pest problems in the field, nor crop contamination by animal-vectored pathogens. Hedgerow insectaries both benefit wildlife and help to control pests.
How can I install insectary plants?
Visit the Insectary Plants webpage to learn how to establish and manage insectary plants, and determine which types of insectaries may suit your needs and situation. If you need financial assistance to establish insectaries on your farm, consider applying for Conservation Action Plan funds from the Environmental Quality Incentives Program (EQIP) offered by the Natural Resources Conservation Service.
- Flower flies (Syrphidae) and other biological control agents for aphids in vegetable crops. (PDF)
- Good news for hedgerows: no effects on food safety in the field.
- Hedgerow benefits align with food production and sustainability goals.
- Habitat restoration promotes pollinator persistence and colonization in intensively managed agriculture. (PDF)
- Reducing the abundance of leafhoppers and thrips in a northern California organic vineyard through maintenance of full season floral diversity with summer cover crops.
Date growers in the California deserts have many insects to worry about such as carob moth, hibiscus mealybug, and giant palm borer. Now the industry is under threat from another potential pest, the highly damaging and invasive South American palm weevil (SAPW) (Rhynchophorus palmarum). It was first identified by county and state agriculture officials in 2011 in San Ysidro in San Diego. They made the discovery while looking for a closely related palm weevil, R. vulneratus (originally mis-identified as the notorious red palm weevil, R. ferrugineus), which was found in Laguna Beach and declared eradicated in Jan. 2015.SAPW has been reported on at least 35 plant species in 12 families and is especially economically important on plantation crops such as oil and ornamental palms of which date palm, Phoenix dactylifera, is a recorded host (CABI 2016; Dean 1979; Esser and Meredith 1987). SAPW has killed hundreds of Canary Island date palms (P. canariensis) in Tijuana and parts of San Diego County. These large urban infestations pose a significant risk to the multi-million dollar date palm industries (edible fruit and ornamentals) in the Coachella Valley. Losses of ornamental Canary Island date palms in San Diego County, are probably significant and likely now reaching millions of dollars in killed palms, reduced aesthetics, and increase removal costs.
SAPW has a long rostrum (this is the beetle's snout) and is large often up to 1 ½ inches to 2 inches in length (CDFA 2018). SAPW is now California's biggest weevil species! Inside the palm crown, weevil larvae feed on the meristematic tissue and it is this feeding that kills the palm crown which results in palm death. Larvae pupate inside 3-inch cocoons made of palm fibers. The pupal stage typically lasts two to three weeks. Adult weevils emerge from these protective cocoons, mate, and they are capable of flying significant distances, perhaps as far as 15 miles in a single day, to find new palm hosts. Female weevils use their snout to chew holes in the apical regions of the palm and they lay eggs in these holes. Larvae that hatch from eggs burrow into the palm crown and feed turning the meristem tissue in a fermenting “mash”. Feeding wounds that result in fermenting damage in association with aggregation pheromone released by male weevils create a highly attractive airborne cocktail of odors that weevils fly too. Adult weevils can live for at least 40 days, often longer (CDFA, 2018).
A single infected palm can result in the production of hundreds of weevils and detection of weevil infested palms at the early stages of attack can be difficult to identify because larvae live inside their host trees. The first obvious symptom of attack is a crown that is starting to collapse. Unless palms are treated within systemic insecticides at the early stages of attack, infested palms will ultimately die in as little as 2-3 months once visual symptoms become apparent.
In addition to direct physical damage SAPW inflict via feeding, it is a primary vector of the nematode that causes red ring disease (RRD), a fatal wilt disease of palms. Fortunately, RRD has not yet been detected in SAPWs or palms attacked in San Diego (Hoddle et. al. 2016). Removal of infected trees is necessary not only to remove breeding weevil populations from the environment, but also to minimize risk of harm to people, pets, and property from crown and frond drop.
More information on the SAPW invasion and to report suspect palms please visit this website: http://cisr.ucr.edu/palmarum.html
The following is the abstract of a recent article highlighting the occurrence of the invasive shot hole borer that is found in California and described in our blog site:
Invasive species are a problem world-wide and this is an example of how invasives can arrive in multiple countries at the same time and/or how possibly they might move from somewhere like California to another far away country like South Africa. People are the usual agents for carrying these pests around the world.
The polyphagous shot hole borer (PSHB) and its fungal symbiontFusarium euwallaceae: a new invasion in South Africa
The polyphagous shot hole borer (PSHB), an ambrosia beetle (Coleoptera: Curculeonidae: Scolytinae) native to Asia, together with its fungal symbiont Fusarium euwallaceae, has emerged as an important invasive pest killing avocado and other trees in Israel and the United States. The PSHB is one of three cryptic species in the Euwallacea fornicatusspecies complex, the taxonomy of which remains to be resolved. The surge in the global spread of invasive forest pests such as the PSHB has led to the development of programs utilizing sentinel tree plantings to record new host-pest interactions. During routine surveys of tree health in botanical gardens of South Africa undertaken as part of a sentinel project, an ambrosia beetle/fungal associate was detected damaging Platanus x acerifolia(London Plane) in the KwaZulu-Natal National Botanical Gardens, Pietermaritzburg.
Identification of the beetle by sequencing part of the mitochondrial cytochrome oxidase c subunit 1 (COI) gene confirmed its identity as PSHB, and specifically one of the invasive haplotypes of the beetle. The associated fungus F. euwallaceaewas identified based on phylogenetic analysis of elongation factor (EF 1-α) sequences. Koch's postulates have confirmed the pathogenicity of fungal isolates toP. x acerifolia. This is the first report of PSHB and its fungal symbiont causing Fusarium dieback in South Africa. This report also represents the first verified case of a damaging invasive forest pest detected in a sentinel planting project, highlighting the importance of such studies. Given the potential impact these species present to urban trees, native biodiversity and agriculture, both the PSHB and its fungal symbiont should be included in invasive species regulations in South Africa.
The full paper is at:
Photo: Infected sycamore which is related to London plane tree.