Scales, psyllids, and relatives

Scientific name

Order Hemiptera, suborders Sternorrhyncha and Auchenorrhyncha

Other common names

This group includes aphids, mealybugs, psyllids, soft scales, cottony scales, whiteflies, and sharpshooters.

Similar species

True bugs can be mistaken for cockroaches or beetles. Each group is distinguished by antennae type, mouthparts, and wing position at rest.

	Beetles	Cockroaches	True bugs
Antennae	Segmented antennae	Long, filamentous	Bristle-like, thread-like, or stubbed
Mouthparts	Chewing	Chewing	Piercing-sucking
Wing position at rest	Elytra close to create a straight line down the middle of the back	Wings directly overlap on the back	Wings gently overlap on the back or may appear roof-like

Adult aphids, mealybugs, psyllids, scales, whiteflies, and sharpshooters are often confused for one another. Several characteristics can be used to differentiate each group.

	Aphids	Mealybugs	Psyllids	Scales	Whiteflies	Sharpshooters
Body Shape	Pear-shaped with two dark tubes protruding from the rear of the abdomen	Oval or round with laterallateral: with an orientation pertaining to the side appendages	Elongate, oval	Round and plump	Elongate upside-down heart shape with a rounded tip	Pointed projectile shape
Body Covering	Dusty, dried honeydew	Dusty, dried honeydew	Dusty, dried honeydew	Varies - waxy or covered with cotton-like filaments	Dusty, dried honeydew	Dried whitewash cover
Antennae	Thread-like (filiform)	Short, multi-segmented	Short, bristle-like	Short, segmented or reduced to stubs	Thread-like (filiform)	Short, bristle-like
Wings	Translucent and membranous	Membranous membranous: with the same character as a membrane, typically used to refer to structures like wings that are clear and translucent like a membrane and clear	Membranous membranous: with the same character as a membrane, typically used to refer to structures like wings that are clear and translucent like a membrane and either clear or mottled	Membranous membranous: with the same character as a membrane, typically used to refer to structures like wings that are clear and translucent like a membrane and clear	Dusty, membranousmembranous: with the same character as a membrane, typically used to refer to structures like wings that are clear and translucent like a membrane , and matches the body color	Membranous membranous: with the same character as a membrane, typically used to refer to structures like wings that are clear and translucent like a membrane and mostly clear, but partially spotted

Diagnostic characteristics

Adults

• Smallest - 0.09 mm (0.04 in.).
• Largest - 14 mm (0.55 in.).
• Body color varies. Either monochrome from pink to black or multi-colored with a mottled appearance.
• Piercing-sucking mouthparts piercing-sucking mouthparts:
  labium encloses the mandibles and maxillae, which are modified into stylets for piercing and sucking; characteristic of hempiterans
  present. Scales, whiteflies, and aphids have mouthparts arising from between the front legs. Sharpshooters have mouthparts arising from the posteriorposterior:
  orientation pertaining to the rear of the body
  margin of the headhead:
  one of the three main body segments in insects; the anterior-most segment containing the many sensory structures including the eyes, antennae, and mouthparts
  .
• Multi-segmented antennae are either uniform in color, shaded dark at the tips or base, or have alternating dark bands throughout the length. Mealybug and scale antennae are difficult to see without a microscope.
• If winged (alate), psyllids, aphids, and whiteflies have one pair of forewings and hindwings that are held tent-like above the body when at rest.
• When legs are present, scales, whiteflies, psyllids, and aphids have 1- or 2-segmented feet (tarsi). Sharpshooters have 3-segmented tarsi.
• Psyllids have stouter hind legs than front legs. Mealybug and scale legs are difficult to see without a microscope.

Pupae

Hemipterans do not undergo true metamorphosis as characterized by a true pupal phase in between a larval and adult phase. The majority of hemipterans have juveniles termed nymphs that look similar to adults with the only change being external wing development as they mature. However, whiteflies and the males of certain mealybug and scale species do go through a radical developmental change to emerge as winged adults. This inactive developmental stage is termed a pupa.

• Smallest - 0.7 mm
• Largest - 1.5 mm
• Flat, oval, round, or scale-like in shape.
• Mostly uniform in color from black to orange-yellow.
• Pupal edges may be translucent, smooth, or fringed in appearance.

Immatures

• Smallest - 0.028 mm (0.001 in.).
• Largest - 9 mm (0.35 in.).
• Typically 3 - 5 nymphal instars.
• Body shape varies between oval and flattened (dorso-ventrally compressed) or round and plump (rotund).
• Mostly uniform in color from translucent to dark brown.

Eggs

• Smallest - 0.3 mm (less than 0.1 in.).
• Largest - 0.32 mm (less than 0.1 in.).
• Opaque, yellow-white.
• Several species of scales and mealybugs do not lay eggs but bear live young called crawlers.
• Scale eggs may be underneath females or in a cotton-like egg sac called an ovisacovisac:
  structure attached to the body that contains eggs; produced by many scale insects
  .
• Smooth, flattened, cigar-shaped (elliptical) or oval.

Hosts

Citrus hosts

Several species of hemipterans can feed on all citrus species and their hybrids, including the cottony cushion scale, Seychelles scale, coffee mealybug, pink hibiscus mealybug, and glassy-winged sharpshooter. See individual fact sheets for more detailed information.

Non-citrus hosts

Hemipterans have a broad host rangehost range:
the range of species that a particular organism can feed on to achieve successful growth and reproduction
that includes weeds as well as vegetables and field and flower crops. See individual fact sheets for more detailed information.

Host damage

Flowers

• Adults and nymphs reduce the number of flowers present by feeding on flowers.

Fruit

• Heavy infestation can lead to fruit pitting or fruit drop.
• Honeydew honeydew:
  the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
  excreted by hemipterans can coat the fruit skin thereby promoting sooty mold fungus growth. Fruit may appear black, moldy, and unattractive.
• Reduced fruiting and production can also occur when pest densities are high.

Leaves

• Honeydew honeydew:
  the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
  excreted by hemipterans can coat leaves and inhibits photosynthesis, which weakens the host planthost plant:
  the plant the provides sustenance for an insect
  .
• Newly infested leaves turn yellow from feeding and may drop.
• Some hemipterans inject toxins during feeding which leaves a yellow spot around feeding areas.

Roots

• Adults and nymphs can infest roots and extract essential nutrients away from the host planthost plant:
  the plant the provides sustenance for an insect
  .

Twigs

• During heavy infestation, twigs and limbs can die back.

Biology

Females either lay eggs or bear live young called crawlers. During the first two instars, crawlers and newly hatched nymphs are mobilemobile:
able to move
and feed on leaves, fruits, and stems by using their piercing-sucking mouthpartspiercing-sucking mouthparts:
labium encloses the mandibles and maxillae, which are modified into stylets for piercing and sucking; characteristic of hempiterans
. After the third instarinstar:
immature stages (larva or nymph) of insects in between molts
, several species of hemipterans become stationary and affix themselves to the leaves and fruit. Aphid, psyllid, and sharpshooter nymphs mature directly into adults. Whiteflies and certain species of scales and mealybugs undergo pupation. Adults emerge, resume feeding, and exude a highly concentrated sugary substance called honeydewhoneydew:
the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
. Ants utilize honeydewhoneydew:
the sugar-rich waste product excreted by aphids, mealybugs, and scales insects as a result of feeding on the phloem of plants
as a food resource. Therefore, populations of these insects are often protected by ants from natural enemies.

Comments

The adult female life stage is typically used for accurate scale and aphid identification.

The pupal life stage is most important for whitefly identification.

References

Davies, F. and L. Jackson. 2009. Pest disease and weed management for the bearing grove, pp. 204-221. In Citrus growing in Florida. 5th ed. University of Florida Press. Gainesville, Florida.

Smith, D., G.A. Beattie, M. Malipatil, D. James, D. Papacek. J. Altmann, A. Green, B. Woods, G. Furness, C. Freebairn, M. Stevens, G. Buchanan, D. Madge, C. Feutrill, J. Kennedy, B. Gallagher, P. Jones, R. Broadley, M. Edwards, G. Baker, S. Dix, P. Burne, B. Frost, J. Watson, M. Pywell. 1997. Citrus pests and their natural enemies: Integrated pest management in Australia. Desert Oak Publishing Services. Brisbane, Australia.

Triplehorn, C. and N. Johnson. 2004. Hemiptera pp. 268- 273. In Borror and DeLong's Introduction to the study of insects. 7th ed. Brooks/Cole Cengage Learning. Belmonte, California.

Authors

Guerrero, S., J.A. Weeks, and A.C. Hodges