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Yellow orchid aphidOn this page: Identification & Distribution Other aphids on the same host Damage & Control
Identification & Distribution
Adult apterae of Sitobion luteum (see foreground of first picture below) are bright yellow to pale yellowish green, with a large black oval sclerotic area extending over tergites I-V, with only small marginal indentations (cf. Sitobion indicum, which has a dorsal abdominal patch with a very irregular outline and large intersegmental indentations). There is a narrow cross bar on the metathorax (the hind thoracic segment), small marginal spots on tergites I-IV, and rather large postsiphuncular sclerites. The antennal tubercles are well developed, with the median frontal tubercle distinct but rather small. Antennae are black except at the bases and bear 1-4 secondary rhinaria on segment III. They are 1.2-1.5 times the body length, with the terminal process about 5.5 times the base of antennal segment VI. Antennal hairs on segment III are 0.3-0.4 times the basal diameter of that segment. The apical rostral segment (RIV+V) is slightly longer than the second hind tarsal segment (HTII). The siphunculi are black and rather thick, 1.4-2.0 times the length of the yellow cauda with reticulation on the apical part (cf. Sitobion orchidacearum, which has siphunculi 1.1-1.3 times the caudal length). The cauda is not constricted, rather pointed, with 6-8 hairs (cf. Sitobion indicum, which has 9-13 hairs on the cauda). The body length of adult apterae is 1.3-2.4 mm. Immature Sitobion luteum are similar to the adult aptera, with yellow body and black siphunculi, but they lack the black sclerotic patch on the dorsum.
The alate Sitobion luteum (not pictured) has the head and thorax rather dark, and the abdomen yellow with dark narrow intersegmental markings instead of a patch. Antennal segment III bears 10-19 rather large secondary rhinaria. The siphunculi are slightly shorter than in the apterous vivipara. The cauda is more or less constricted with 7-9 hairs. The body length of the alate is about 2.3 mm.
The yellow orchid aphid feeds on a wide range of orchid genera (including Dendrobium, Epidendrum, Laelia, Oncidium). It appears to be wholly anholocyclic, no sexual morphs having been recorded. Sitobion luteum has a world-wide distribution including Madagascar, Mauritius, India, Singapore, Java, New Guinea, Australia, Fiji, Tahiti, central and South America, and under glass in Europe and USA.
Other aphids on the same host
Sitobion luteum has been recorded on 9 Dendrobium species (Dendrobium aemulum, Dendrobium bigibbum, Dendrobium densiflorum, Dendrobium heterocarpum, Dendrobium jonesii, Dendrobium kingianum, Dendrobium longicornu, Dendrobium moschatum, Dendrobium mutabile).
Sitobion luteum has been recorded on 2 Epidendrum species (Epidendrum diforme, Epidendrum ellipticum).
Damage and control
On orchids aphids are found feeding on the buds and flowers, and also on other succulent new and growing tissues such as the leaves, sheaths, and flower parts. Plant damage is done by repeated insertion and probing, as well as by nutrient removal. Feeding debilitates the plant and can cause generalized yellowing, and distorted leaves and flowers. As well as direct feeding damage, aphids can also transmit plant viruses, although this is not thought to be a serious problem for orchids. A wide range of insecticides are available for aphid control, but where conditions are manipulated as in greenhouses, biological or integrated control offer the best options. For more on controlling aphids on orchids see St Augustine Orchid Society.