Four species of aphids attack small grains in Virginia — greenbug, corn leaf aphid, bird cherry-oat aphid, and English grain aphid. In general, these aphids are small pear-shaped insects (1/16 to 1/8 inch long) that are green to nearly black, or sometimes pinkish in colour. Immature aphids look just like adults except smaller.
Both winged and wing-less forms can occur in the same colony. All grain aphids have a pair of conicles, tailpipe-like projections, on the top side of the tail end. Aphids feed singly or in colonies on upper and lower leaf surfaces and stems.
They feed near plant bases when plants are young or during cold weather, and on upper-canopy leaves, stems, and even grain heads later in the season.
Life Cycle and Damage:
All four aphid species overwinter in small grains in Virginia. Winged adult males and females begin moving into early-planted fields in mid-to late October from surrounding wild and cultivated grasses, and can be blown longer distances by wind.
After mating, winged females give birth to wingless females (all wingless aphids of these four species are female), which in turn give birth to more wingless females, in as few as seven days after birth.
Wingless females reproduce without mating and can give birth to 60 to 80 young during their 20- to 30-day reproductive period. Thus, several generations can occur in one season and enormous populations can develop in a short time.
Maximum reproduction and development occurs between 55° and 75° F, but aphids can feed and successfully reproduce at any above-freezing temperatures. Aphids have been observed giving birth at 48° F in eastern Virginia.
Aphid populations are not severely affected by overnight temperatures below 30° F; however, several days of continuous freezing temperatures will dramatically reduce numbers. Aphid populations in Virginia can increase rapidly during periods of warm weather in October through December, are typically very low during January and February, and begin to increase rapidly during warm periods in the spring.
Winged forms can be found throughout the year. The factors that influence the production of winged adult forms are unknown but it is winged adults that leave grain fields after harvest to establish on summer hosts.
Aphids feed by piercing plant tissues with needle like mouth parts, then sucking fluids. The expression of symptoms after aphid feeding depends on whether plant toxins or pathogens are injected during feeding.
The green bug is the only species of the four known to occur in virginia grains that injects plant toxins. Perhaps the biggest aphid-related problem of small grains in Virginia is the potential for transmission or dissemination of barely yellow dwarf virus (BYDV).
Green bug, bird cherry-oat, and English grain aphids are all known BYDV vectors. Some individual aphids carry virus particles in their digestive tracts or saliva. Partides are transmitted to plant tissues during the feeding process.
BYDV causes barley to turn a yellowish colour, and infected plants become stunted and nonproductive, whereas, diseased wheat and oat plants turn a reddish colour and become stunted. BYDV outbreaks have not been common in recent years, with plant samples from only one or two fields being confirmed by diagnostic laboratories.
If they occur, they appear as patches of stunted yellowing or reddening plants scattered throughout the field. Yellowing areas that are in strips or that entirely cover the field are most likely not caused by aphid damage or disease, but rather indicate problems associated with fertility, pH, or cold weather.
Yield losses due to BYDV are more severe when young plants are infected during the fall or early winter.
Information Sourced From:
