1Entomology 462Ornamentals Pests:Sucking PestsDavid J. Shetlar, Ph.D.The “BugDoc”The Ohio State University,OARDC & OSU ExtensionColumbus, OH© October, 2004, D.J. Shetlar, all rights reservedWoody Ornamental Pest GroupsSucking PestsThrips (Thysanoptera)True Bugs (Heteroptera)Plant/Leaf bugs, Lace BugsBug-like Insects Leaf/Plant/Tree hoppers, Psyllids, Aphids, Whiteflies, Mealybugs, ScalesMites (Acarina)Spider mites, Eriophyid mites2Notes:We’ve been using a hybrid of plant parts attacked (e.g., foliage, leafminers, roots, etc.) and taxonomic groups (e.g., borers), and we’ll use primarily taxonomic groups to discuss the sucking pests. The tree main groups are the THRIPS (Thysanoptera), the bugs (Hemiptera) and mites (Acari). The bugs can be subdivided into the “true” bugs and the “bug-like” Hemiptera.Remember that the term “thrips” is both singular and plural! We will discuss them in much greater detail in the greenhouse pest section as several species are important vectors of diseases. This group will also be the first one with an incomplete life cycle that diverges a bit from the basic plan of egg to nymphal instars to adult.Several of the bug-like Hemiptera also have highly modified life cycles, especially the whiteflies, mealybugs and scales.Mites technically don’t have sucking mouthparts, but their tiny cheliceratemouthparts produce sucking pest like damage.Notes:Before we discuss the various groups of sucking pests, sucking pest damage symptoms are very useful diagnostic aids.Sucking pests can cause PLANT DISTORTION when they feed on juvenile tissues. Cells are damaged and as the leaves or stems continue to expand, they become distorted. Other sucking pests dissolve tissues within leaves or stems and this results in dead spots, even on expanded plant parts. Salivary secretions can clog vascular bundles, thereby stunting,discoloring or killing plant parts outward from the clogged area.Because sucking pests remove lots of liquids and little nutrients, they produce two types of diagnostic excrement – tar spots and honeydew. Tar spots are dark, shiny spots of resinous-like material. This is typically produced by sucking pests that feed on cell contents. Honeydew is a clear, watery excrement that is produced mainly by insects that feed in plant phloem bundles. Phloem has lots of water and sugars, but little amino acids (for proteins), so this excess is excreted. Honeydew often promotes the growth of sooty molds.Cell feeding often produces tiny spots or speckles of yellow. When extensive, this can cause a general bronzing of browning of foliage.3Woody Ornamental Pest GroupsSucking Pests - SymptomsPlant Distortion -Leaf & stem twisting & curlingDead spotsExcrement Deposits -Tar spots - true bugs, lace bugs, thripsHoneydew & Sooty MoldFoliage Discoloration -Spots & StipplesYellowing & BronzingHoneylocust leaflet distorted.Cuban Laurel (Ficus) thrips leaf distortion.Sooty mold from scale honeydew.Tarspots from lace bugs.4Notes:Thrips are tiny insects that have the mandibles asymmetrically modified so that one mandible is elongated and is used to rasp into plant cells. The cell sap and contents are then sucked in, thereby causing small spots or speckles.Unfortunately, thrips have a complicated life cycle in which the first two nymphal instars are active feeders, but the next two nymphal stages rarely feed. These two instars develop wings and adult features and may remain dormant on the plant or they may drop to the ground to transform into the adult stage. Because of this unique developmental behavior, thripsexperts often call the first two nymphs “larvae,” the third instar is often called a “prepupa” and the fourth instar nymph is often called a “pupa.”Woody Ornamental Pest GroupsSucking Pests - Thripseggs → nymph 1 → nymph 2 → “prepupa” → “pupa” → adult(larva) (larva)• Cause streaking of flowers or spotting of foliage.• Occasionally cause foliage distortion.• Usually produce tiny tar spots.• Have complicated life cycle with non-feeding “prepupa” and “pupal” stages.(Thrips specialists often call the nymphal stages “larvae” which should really be used with insects that have a complete life cycle!)5Notes:There are actually few thrips that are common pests of ornamental plants. The pear thrips occasionally attacks sugar maple in the spring. In this case, overwintered adults insert eggs in the veins of expanding maple leaves. The damage causes the leaves to distort and ragged holes may be formed.Several species of flower thrips cause streaking and spotting of flower petals. These are most noticeable in roses and some perennials.The greenhouse thrips commonly damages a variety of broadleaf evergreens in southern states. Attacks result in bronzed foliage. Upon close inspection, the leaves will be covered with tiny tarspots and numerous speckles where cell contents were removed by the thrips.The privet thrips causes similar damage to privet in northern states. Leaves first appear yellowed and then turn bronze or brown.The Cuban laural thrips causes severe stunting, discoloration and folding of ornamental figs.Pear thrips on maple leaf.Flower thrips on leaf. Note small tarspots and blanching due to cell contents being removed.6Notes:Plant bugs are commonly called leaf bugs and almost all have thetypical bug shape with a pentagonal pronotum, a triangular mesonotum, and a diamond shaped area where the membrane areas of both forewings cross.Almost every plant has its own species of plant bug, but there are several species that are generalists feeders. The tarnished plant bug is common on a variety of woody shrubs, perennials and even annual flowers. The fourlined plant bug is common on smaller shrubs and perennials.Most plant bugs produce irregular damage spots by liquefying leaf tissues with their salivary secretions during feeding. When damage occurs to young, expanding leaves, the leaves can be severely distorted and stunted.The plant bugs produce tarspots rather than honeydew.Controls are rarely necessary, and if needed, applications of contact pesticides should be made before the young nymphs have had sufficient time to cause extensive leaf damage.Woody Ornamental Pest GroupsSucking Pests – Plant/Leaf Bugs• Usually feed by injecting salivary digestive juices into leaf tissues which cause round to irregular necrotic spots.• Adults form “tar spots” with excrement.•