By Oscar Shilliebo

Mealybugs in Kenya were original pests that attacked the coffee plants in the eighties but as the flower and rose growing industry begun to thrive, the pests found a new host and were transferred through to roses from the coffee bushes through coffee stakes that were used to hold the rose beds together and as well through grafted roses.

Before the onset of IPM and use of biological methods to manage especially the red spider mites in roses, Mealybugs were not a major pest in rose growing. The reason being that most Miticides used to manage the spider mites were also controlling the mealy bugs and other pests on the rose crop. But as the pest management practices shifted more towards IPM and biological control especially for the spider mites which use to account for more than 40% of the total chemical cost the attentions then shifted and other pests begun to be of importance. One such pest is the Mealy bug.

The mealybugs that attack roses in Kenya are scientifically known as Planococcus kenyae the coffee mealybug. Close relatives of scales, mealybugs are small insects that grow to about 2/3 inch. Adult females can lay up to 600 eggs and look like small cotton balls. They’ve got an oval body outline, and functional legs allow them to be mobile in their immature stage. Some mealybugs are more ornate than others, having filaments around the edge of their bodies or even “tails.” Immature males and females look similar, but they’re very different as adults: The adult male looks like a gnat with one pair of wings. (Only the adult males fly) Female crawlers go through four developmental stages until they reach maturity. The male goes through five. On average, within six to 14 days, the eggs start to hatch, and immature scale crawlers emerge. This stage varies with plant species and indoor temperature. When it does occur, it’s the time when dispersal to new plant parts or new plant hosts occurs. So in other words: This is when you want to target treatment!

In addition to sooty mold, mealybugs damage plants with their toxic saliva, causing leaves to drop, inhibiting plant growth and creating yellow spots. Mealybugs can be difficult to treat because they hide in crevices where stems meet leaves and can reach damaging population levels rather quickly.

They are normally located on the underside of plant leaves and stems, and populate many outdoor plants such annuals, bushes and shrubs. Mealybugs will heavily infest almost any plants in greenhouses, homes or businesses. They feed by forcing their needle-like piercing mouthparts into the plant and use a sucking action to remove the plant juices. Mealybugs attract ants by excreting honeydew, a sticky, sweet substance that the ants feed on. Plants infested with mealybugs usually have leaves that turn yellow and wilt, and if the infestation is not eliminated, the plant may eventually die.

Mealybugs Damage

Once the crawler selects a feeding site, it inserts its mouthpart (called a stylet) and begins feeding on plant sap. While eating, a sticky waste substance is excreted by the insect (commonly called honeydew). This liquid adheres to leaves and provides a medium for sooty mold to colonize and grow. Sooty mold is black and eventually covers leaves and stems. This mold inhibits infected portions of the plant from photo synthesizing and causes aesthetic damage.

In addition to the sooty mold, plant damage is caused by the mealybugs sucking plant sap and the pests’ toxic saliva, both resulting in distorted plant growth and premature leaf drop. Plant leaves also develop yellow chlorotic spots.

Management and Control of Mealybugs.

It’s important to always inspect any plant before you bring it home. Not doing so is how most people get pest problems. Because of the woolly nature of mealybugs and cotton like webs they form around them, mealybugs are proving very difficult to control. If mealybugs do find their way to your plants, there are a few control methods you can try.

Yellow sticky cards can be used to trap the flying adult males, preventing them from mating. Insecticidal soaps and horticultural oils work great in controlling this pest. The tricky part is mealybugs tend to hide very well where leaves attach to the stem, so make sure you get coverage there. Horticultural soaps and oils don’t have systemic properties, which means when spraying, the product must come in contact with the pest. So know where your pest is on the plant.

A word of warning: You can burn leaves with horticultural soaps and Oils. These products need to be applied when the air temperature is cool. Make sure your plants were watered well the day before you apply your control – never spray wilted plants. Following labeled rates also reduces the risk of leaf damage. More is not better. Also, make sure beneficial insects are not present when you spray. (Insecticides can kill the good guys, too.)

Biological Control: There are a few beneficial insects that can help you with mealybug treatment, too. Green lacewings (Chrysoperla sp.) Feed on the crawler stage of almost any mealybug, where some others are more specialized – like the mealybug destroyer (Cryptolaemus montrouzieri). This beneficial insect is a type of ladybug that loves to feed on most mealybug species (although it doesn’t do well on the long tail mealybug). There is also a parasite specific to the citrus mealybug that’s commercially available. All these are available through the Internet.

Mealybugs can be controlled if you catch them early and time your treatment correctly. Crawlers are the easiest to kill, so time your spray right, and you can win the war against mealybugs.

Dow AgroSciences has recently registered and will be launching in the recent future in Kenya a new chemistry product that is systemic and targeted at managing mealybugs and other sap sucking pests on many crops. Closer 240SC is powered by IsoclastTM active (sulfoxaflor), discovered by and proprietary to Dow AgroSciences, currently is the sole member of a new chemical class of insecticides, the sulfoximines. Isoclast has been developed globally for use in major crop groups, including roses, carnations, cotton, leafy and fruiting vegetables, apples, soybeans, rice (outside of the U.S.), Cereals, citrus, colecrops, grapes, and other crops. Isoclast controls economically important and difficult-to control sap-feeding insect pests including most species of aphids, jassids, leafhoppers, mealybugs, plant bugs, plant hoppers, stink bugs, and whiteflies, and certain species of psyllids and scales.

Noteworthy Features

• Effective at low use rates

• Excellent knockdown and residual control

• Excellent translaminar and systemic activity

• Effective against insect pest populations resistant to other insecticides

• Valuable rotation partner with other chemistries

• Minimal impact on beneficial insects, including bees and natural enemies, when applicators follow label directions for use.

Mode of Action and Resistance Management

Available data indicate Isoclast™ active exhibits complex and unique interactions with insect nicotinic acetylcholine receptors (nAChR) that are distinct from those observed with neonicotinoids. Isoclast is a high efficacy nAChR agonist with low affinity for the imidacloprid binding site. Numerous studies have been conducted to determine whether insects resistant to other insecticides are cross resistant to Isoclast. Available data for Isoclast indicate a broad lack of cross-resistance in many sap-feeding insect strains resistant to other insecticides. In several field studies, Isoclast controlled insect populations known to be resistant to neonicotinoids and to insecticides with other modes of action (e.g., carbamates, organophosphates, pyrethroids). The broad lack of cross-resistance between Isoclast and neonicotinoids is due primarily to differences in metabolism by monooxygenase enzymes, which are the predominant mechanism of insecticide resistance in the field. Laboratory studies have demonstrated a monooxygenase that degrades neonicotinoids has no effect on Isoclast. The novel chemistry of Isoclast and the lack of cross-resistance suggest that efficacy of Isoclast will be retained even in the presence of sap-feeding insect strains that are resistant to other insecticides, including neonicotinoids. For reasons indicated in the preceding paragraphs, sulfoxaflor* was classified as a Group 4, Subgroup 4Cinsecticide in the Insecticide Resistance Action Committee Mode of Action Classification Scheme (Version7.2, April 2012, http://www.irac-online.org). Sulfoxaflor is the sole member of this subgroup. Neonicotinoids insecticides are classified in Group 4, Subgroup 4A in the IRAC Mode of Action Classification Scheme. Because of its unique properties and broad lack of cross-resistance, Isoclast will be a useful rotation partner with other insecticide chemistries, enhancing insect resistance management (IRM) strategies.

How Isoclast™ Active Kills Insect Pests

Isoclast™ active kills insect pests both on contact and through ingestion to provide both knockdown and residual control. Isoclast displays translaminar movement (moves to the opposite leaf surface) when applied to foliage and is xylem-mobile.

Biological Activity

Background

Sap-feeding insects, especially those in the sub-orders Hemiptera and Homoptera, are among the most destructive insect pests in the world, annually causing economic losses in both row crops and horticultural crops. Management of sap-feeding insects often requires diverse and intensive control tactics, including the use of insecticides. Consequently, populations of sap-feeding insects have developed resistance to many insecticides representing a wide range of insecticide modes of action. Isoclast’s efficacy and unique mode of action suggest that it will be a key tool for controlling economically important pests and a useful rotation partner in IRM programs.

Efficacy of Isoclast Against Insect Pests

Isoclast provides excellent efficacy against target pests at low use rates. Proposed application rates of Isoclast range from approximately 12 to 150 grams of active ingredient per hectare depending on the target pest and the crop. Field efficacy trials with Isoclast have been conducted worldwide on many crops against a wide range of sap feeding insects. Results from these trials have revealed that Isoclast provides excellent control of many species of sap-feeding insects, including tarnished plant bug (Lyguslineolaris) and western tarnished plant bug (Lygushesperus) in cotton; cotton/melon aphid (Aphis gossypii) in cotton and cucurbits; several species of aphids in cereal crops; soybean aphid (Aphis glycines) and stink bugs in soybean; green peach aphid (Myzuspersicae) and whiteflies (Bemisia species) in multiple crops; Asian citrus psyllid (Diaphorinacitri), citrus thrips (Scirtothripscitri), and several species of scales in citrus; woolly apple aphid (Eriosomalanigerum) and other aphids in pome fruits; brown plant hopper (Nilaparvatalugens) and other plant hoppers in rice; black margined aphid (Monelliacaryella), grape leafhoppers (Erythroneura species), and several other sap-feeding species in tree nuts and vines; cabbage aphid (Brevicorynebrassicae) in cole crops; and lettuce aphid (Nasonoviaribisnigri) and other aphids in leafy vegetables. Isoclast does not control lepidopteran and coleopteran pests.

Impact of Isoclast™ Active on Natural Enemies of Insect Pests

Field studies have been conducted to measure the impact of Isoclast™ active on several predatory and parasitic arthropods (natural enemies): assassin bugs, big-eyed bugs, braconid wasps, green lacewings, lady beetles, minute pirate bugs (including Orius insidious ), and spiders. When applied at field-use rates in these studies, Isoclast had no significant impact on population levels of any of the natural enemies measured.

In addition, Isoclast has had no impact on beneficial mite species. Based on the results from these studies, as well as on observations from other field trials, use of Isoclast is not expected to cause outbreaks of secondary insect pests (often referred to as “flaring”).

Crop Tolerance

Tolerance of formulations of Isoclast is high for the many major crop species that have been tested. At labelled use rates, Isoclast exhibited no phytotoxicity in seedling emergence and vegetative vigor tests in ten crop species. No crop injury has been observed in any field trials over a range of environmental conditions, and no differences in varietal sensitivity have been observed. Since being registered in multiple countries, Dow AgroSciences has received no reports of any negative plant responses or phytotoxicity from application of Isoclast.

Isoclast™ Active and Non-Target Organisms

Isoclast™ active does not persist in the terrestrial environment and degrades rapidly to products that exhibit low toxicity to non-target organisms. Consequently, when Isoclast is used according to label directions, exposure of non-target organisms to Isoclast is expected to be minimal. Based on available data, use of Isoclast in the manner consistent with label directions will not cause any unreasonable adverse effects in the environment.

Isoclast and Bees

The effects of Isoclast on honey bees (Apismellifera) and bumble bees (Bombusterrestris) have been studied in laboratory experiments and in tunnel tests that simulate field conditions. In laboratory studies, Isoclast exhibits acute toxicity to bees when consumed by or applied directly to bees. However, in tests designed to mimic use conditions, toxicity of Isoclast to bees was significantly reduced after the spray droplets had dried.

Acute Toxicity (Laboratory Studies). Under laboratory conditions, Isoclast exhibited acute toxicity to bees when the bees were exposed by oral or contact routes of administration. Isoclast technical and formulated products had similar toxicities to honey bees. The primary metabolite was not toxic to honey bees. The following table shows available acute toxicity data.

Test material Oral toxicity Contact toxicity

Honey bee (Apismellifera)

Isoclast technical (95.6% a.i.) 48-hr LD50 = 0.146 μg a.i./Bee 72-hr LD50 = 0.379 μg a.i./Bee

SC formulation of Isoclast 48-hr LD50 = 0.0515 μg a.i./Bee 48-hr LD50 = 0.130 μg a.i./Bee

WG formulation of Isoclast 48-hr LD50 = 0.08 μg a.i./Bee 48-hr LD50 = 0.244 μg a.i./Bee

Bumble bee (Bombusterrestris)

SC formulation of Isoclast 72-hr LD50 = 0.027 μg a.i./Bee 72-hr LD50 = 7.554 μg a.i./Bee

Based on data for technical materials reported in the US EPA Pesticide Ecological Effects Database (http://www.ipmcenters.org/ecotox), the laboratory Contact toxicity of Isoclast is in the middle of the range of reported contact toxicity values for insecticides used to control sap-feeding insects. Semi-Field and Tunnel Studies on Isoclast. Isoclast does not exhibit Extended Residual Toxicity on foliage.

In semi-field studies during which honeybees were exposed to dried residues of Isoclast on alfalfa foliage that had been field-aged for 3, 6, and 24 hours, mortality rates of bees were significantly reduced at all three observation times. In tunnel tests in which honey bees from small colonies were allowed to forage among plants (Phaceliatanacetifolia) in plots treated with Isoclast™ active and commercially available insecticides, foraging activity by honey bees in Isoclast-treated plots was similar to foraging activity by bees in the non-treated controls. For aging activity in plots treated with two commercially available insecticides in these same studies essentially ceased for several days. Based on available data for Isoclast, no longterm effects on brood development have been observed.

Summary

At the time of publication of this bulletin, the findings from all of the completed studies suggest that although Isoclast is acutely toxic to bees in laboratory studies, the risk of adverse effects on bees should be low under field conditions when applicators follow label directions for use. Because potential exposures to honeybees may vary among crops and field conditions at the time of application, it is important to read and follow all label directions regarding honey bees.