Ecology & Evolutionary Biology
Aphids Green Peach Aphid - Myzus persicae
Description: The green peach aphid is a small, (1/32 - 1/16 in.) light green to yellow to pink, pear shaped aphid with red eyes; winged forms with a black patch on the back of the abdomen; tubercles (bumps between antennae) pointing inward. The wingless nymph resembles the larger adult. Damage: Aphids suck plant sap and contaminate the host with honeydew and cast skins. They are also the vectors of a number of plant viruses including tobacco, tomato, lettuce, dahlia, canna, and bee mosaics as well as tuber spindle, rugose mosaic, and leaf roll diseases of potato. Because green peach aphids overwinter on weed hosts, infestations can occur in the greenhouse any time of year. Although damage per aphid is often not serious, these aphids reproduce so rapidly that serious harm can be done in a short time. Life Cycle: In the northern United States, green peach aphids overwinter as eggs, but in the Southeast, no eggs are laid. Female aphids give birth to young
females during the growing season. The reproductive capacity of green peach aphids has been described as "fantastic." High reproductive rate and resistance to pesticides make the green peach aphid a formidable pest in the greenhouse. Up to 30 generations per year may take place. Ladybugs, lacewings, syrphid flies, damsel bugs, wasps, and parasitic fungi tend to regulate green peach aphid populations outdoors. Rain, wind, and mud also help check aphid populations outside. Scouting: Although winged adult aphids will be caught on sticky traps, by the time adults are noted here, there is probably a large population somewhere in the house. Aphids congregate in large groups on the succulent new growth of many species of plants and cast skins are also generally present. Also be alert to the presence of honeydew and the associated sooty mold. Because they reproduce so quickly under greenhouse conditions (in part to the females ability to give birth to live young which are born 'pregnant') infestations can appear seemingly overnight. Note that Encarsia will generally seek out and find aphid populations and that the cast skins of the aphids are much different in appearance than 'aphid mummies' left by the parastoid. The scout should be able to readily tell the difference between the two. |
Aphid Biocontrols
Aphid Parasitoid - Aphidius matricariae 
Description: Aphidius matricariae is a 1/8 inch long, black braconid wasp from Europe, is one of the most common and effective parasites of the green peach aphid.  Life Cycle: The female wasp lays its eggs singly in the abdomen of the aphid. Upon hatching, the wasp larva slowly kills the aphid from within with the aphid turning into a 'mummy' as the wasp pupates. The life-span of the wasp is roughly 2 weeks as an immature, then 2 weeks as adults during which time they can lay 200-300 eggs. Optimum performance is between 64-75F and humidity around 80%. These wasps do not undergo diapause and will continue to be effective in cooler conditions. In addition to killing aphids directly, mechanical disturbance of aphid colonies by the searching behavior of the adult wasps causes many aphids to fall off the plants and die. Scouting: The most obvious signs of the presence of Aphidius wasps is the aphid 'muumies'. Successful development of the parasitoid will result in the aphid swelling and turning a uniform brownish-tan color. Closer inspection may reveal a smoothly cut round hole in the abdomen of the aphid where the parasitoid emerged. Pest scouts should be aware that empty 'mummies' can persist on the plant for quite a length of time and only the presence of 'full' mummies or adult wasps should be used to quantify parasitoid levels. One potential difficulty with Aphidius is the potential for hyper-parasitism, wherein a parasite of the parasitoid is present - most often in late summer. The presence of the hyper-parasite is identified by the exit hole being jagged (rather than smooth) and the flap often remains. Adult Aphidius wasps are also typically easy to spot near aphid outbreaks where they are seen flying about the plant seeking prey. They are easily aspirated into a bottle and relocated to other aphid hot-spots in this fashion. |
