|Crop Knowledge Master|
Siphanta acuta (Walker)
Ronald F.L. Mau, Extension Entomologist
Jayma L. Martin Kessing, Educational Specilaist
Department of Entomology
This bug is considered a pest of banana, citrus, coffee, guava, macadamia, and many ornamentals. Other hosts include Acaia, Cheirodendron, Coprosma, Eucalyptus, Metrosideros, Moraea iridoides, Rubus, Styphelia, sumac, Myrsine, and Tetraplasandra (Zimmerman, 1948).
Originally from Australia, this species has spread with the unintentional help of man. It was established in Hawaii sometime before 1898 and is present on all major islands (Zimmerman, 1948).
In the early 1900's this flatid was prevalent in the forest of Oahu and destroyed large numbers of certain native trees. It also attacked coffee and other cultivated crops (Fullaway and Krauss, 1945).
Like most homopteran insects such as aphids, mealybugs and scales, plant hoppers produce honeydew. The honeydew of the torpedo bug is a dark bluish-green, sweetish, transparent liquid. Its color is influenced by its host plant. A black fungus, sooty mold, grows quickly on the exuded honeydew which, in heavy infestations, blackens the leaf, decreases photosynthesis activity, decreases vigor and often causes disfigurement of the host.
Eggs are approximately 1/25 inch (1.2 mm) long. Masses of more than a 100 eggs are laid in a sub-circular pattern about 1/5 inch (5 mm) in diameter with a maximum thickness of 1/25 inch (1 mm) on the stems or leaves of plants (Myers, 1922). Eggs on the margin of the clutch are laid flat while eggs in the center of the clutch are more upright giving the egg mass a dome-like shape. The egg mass is glued together and partially covered by a dark, semi-transparent cement produced by the adult female (Zimmerman, 1948). Eggs hatch in 10 to 20 days (Kershaw, 1913).
This bug has five nymphal stages, called instars, that are each separated by molts. Molting usually occurs at night or in the early morning. Myers (1922) gives detailed descriptions and drawings of each nymphal stage and the general descriptions below are adapted from his study.
First instars are pale green, about 1/10 inch (2.4 mm) long with white, waxy filaments extending from the last two abdominal segments. The second instars are slightly greener with six black spots located on the middle sections of the body (mesonotum and metanotum), have white waxy filaments on the last abdominal segments, and are about 1/8 inch (3 mm) long. The first two nymphal instars are covered with a white powder or dust.
Compared to the first and second nymphal stages, the third instars are much wider in proportion. They are slightly longer (approximately 7/50 inch) (3.6 mm) and have more intensified and enlarged black spots as well as a bright yellow streak across the thorax and a red spot on the abdomen. The rest of the body is pale green and has less of a white powdery coating than the younger stages.
The fourth nymphal instars are yellowish-green marked with red, black and pink marking. Wing pads, or incompletely developed wings are present on the 4/25 inch (4 mm) long body. Legs are pink. About half way through this stage, a striking change occurs in the appearance of the instars. The new red markings found in the earlier portion of this stage fade to yellow-green, paler than the rest of the insect body such that the insect changes from mostly red to green. It takes about 2 weeks for this color change to occur.
The fifth, and last, instars are about 1/5 inch (5 mm) in length and 3/20 inch (3.75 mm) at greatest width. Instars are devoid of the white powdery covering. For the first three days of this stage the instars are mostly a pale green with some black markings, eyes are green, and legs are pink (spines black), there is no trace of red. Like the fourth instars, the fifth instars also go through a color change. On the fourth day of this stage, instars begin to turn reddish in color reaching a maximum intensity of red on the seventh or eighth day. Thereafter, the instars gradually turn a uniform green, more vivid than the first three days of this stage. The abdomen lengthens and swells and the white filaments on the last two segments are significantly reduced (Myers, 1922).
The moderately large (1 inch wing-expanse), vivid green bugs are triangular in shape with pink eyes and a pointed head. The forewings, called tegmina, cover the body like the sides of a sloping roof when the insect is at rest. Adults live for about two months (Myers, 1922).
Young nymphs prefer to feed on leaves and older ones prefer stems.
These bugs will remain inactive for hours while feeding. Occasionally, their abdomens will start to vibrate and move up and down before they exude a droplet of honeydew almost as large as the width of their abdomen. The process ends with a jerky movement by the bug. This process is not as intense in the younger instars (Myers, 1922).
Nymphs have a characteristic movement of swaying rhythmically from side to side when they are either stationary or walking. The movement in which the body swings clear of the surface is very distinct from the abdominal movements prior to the excretion of honeydew.
This bug acquires its common name, "torpedo bug", from its great leaping power. First nymphal instars usually remain near the empty egg mass. If they are disturbed, they hop away vigorously. The fifth nymphal instar can leap as far as 2 feet. Adults rarely hop and usually spread their wings when they do (Myers, 1922).
Several predators and parasites of this flatid pest are present in Hawaii. An egg-parasite, Aphanomerus pusillus Perkins (Hymenoptera: Scelionidae), introduced in 1904 is very effective at controlling this pest in many areas throughout the state. Chrysopa microphya McLachlan (Neuroptera) preys on the flatid nymphs. Nesomimesa antennata (Smith) (Hymenoptera: Mimesidae) stores its nest with paralyzed flatid individuals (Zimmerman, 1948). Several coccinellid beetles feed upon torpedo bug eggs. In wet localities, this pest is controlled by a parasitic fungus (Kirkaldy, 1908).
Information not available.
Fullaway, D.T. and N.L.H. Krauss. 1945. Siphanta acuta (Walker). pp. 57. In: Common Insects of Hawaii. Tongg Publishing Company; Honolulu, Hawaii. 228 pages.
Kirkaldy, G.W. 1908. Proc. Hawaiian Entomol. Soc. 1: 161.
Myers, J.G. 1922. Life-History of Siphanta acuta (Walk.), the Large Green Plant-Hopper. New Zealand J. Sci. Tech. 5: 256-263.
Zimmerman, E.C. 1948. Siphanta acuta (Walker). pp. 249-251. In: Insects of Hawaii Volume 4: Homoptera: Flatidae. University of Hawaii Press: Honolulu. 268 pages.