View source for Blackmargined and Yellow pecan aphids

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==Description==
There are two species of "yellow" aphids commonly found on pecan foliage. The nymphs are tiny, yellow, soft-bodied and wingless.  Adults are likewise small (3 - 4 mm) and soft-bodied, but vary somewhat in appearance. The adult of the blackmargined aphid (''monellia caryella'') is generally yellow, but pigmentation often appears as a dark margin on the lateral portions of the abdomen and on the anterior margin of the forewings in winged forms.  At rest, wings are held in a flattened, expanded position and are readily visible.  The adult of ''Monelliopsis pecanisis'' yellow with little pigmentation.  Under magnification, two tiny spots may be visible on opposite sides of the 5th abdominal segment.  At rest, wings are held in a more acute position, with the top portion of the forewings generally facing outward.

==Damage==
Both nymphs and adults cause damage.  Yellow aphids generally feed on the undersides of leaflets and excrete large quantities of honeydew.  The honeydew makes the leaves sticky and frequently supports the growth of a black sooty mold.  This may interfere with the functioning of the leaves.  Aphid feeding may also cause damage appearing as dark areas on some leaflet veins or vague yellow mottling of the leaflet surface.  Heavy infestations of yellow aphids can contribute to tree stress, especially in late season.  They must be controlled before nut quality is affected and before the damage has accumulated to a point where the trees cannot maintain their leaves. 

Aphids are usually noticed first on the lowest tree limbs. As populations increase, they spread throughout the tree.

==Seasonal History==
All aphids on pecans have similar life histories and development. They overwinter as fertilized eggs in crevices in the bark or other protected places on the tree.  Wingless females known as stem-mothers hatch about late March.  These stem-mothers move out to the opening buds and leaves and feed until fully grown.  When grown, they give birth to living young, without mating.  The young are also females.  When mature, they too give birth to living female young.  At some point in the cycle of generations, winged females develop and populations come to be made up almost entirely of winged females.  These winged aphids fly to other parts of the same tree or to different trees.  In the late fall, winged male and wingless female aphids are produced.  They mate and the wingless females lay fertilized overwintering eggs on the tree.  Sixteen to 32 successive aphid generations may occur during the year, depending upon the season. 

Both of these common species of "yellow" aphids are present in orchards whenever pecans are in leaf.  They are normally most numerous in April and May and again in late season (late August through October).

==When to Control==
In early season (prior to July 1), do not treat yellow aphids if they are the only insect problem.  Rely on beneficial insects to suppress early season populations. After July 1, treat if numbers exceed an average of 20 aphids per leaf based on a thorough, random sample, or when honeydew is heavy.
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