Obsevation on May 11,2013
Location : HL, MO
Insect
Location : HL, MO
Insect
Alfalfa weevil (Hypera postica Gyllenhal)
These insects are estimated to reduce yields by 10 to 15% annually (forage quality not taken into account).
These insects are estimated to reduce yields by 10 to 15% annually (forage quality not taken into account).
Field observation :
1. Alfalfa weevils
In Missouri : The economic threshold is one larva per alfalfa stem, plus 30 percent of plants showing signs of feeding damage.
STEM COUNT DECISION METHOD:
Break off 30 to 50 alfalfa stems at ground level, take care not to dislodge the feeding larvae. Select the stems at random from across the field and shake individually into a deep- sided bucket. Count the stems, determine the average height, and count the larvae so the average number of larvae per stem can be calculated.
1. Alfalfa weevils
In Missouri : The economic threshold is one larva per alfalfa stem, plus 30 percent of plants showing signs of feeding damage.
STEM COUNT DECISION METHOD:
Break off 30 to 50 alfalfa stems at ground level, take care not to dislodge the feeding larvae. Select the stems at random from across the field and shake individually into a deep- sided bucket. Count the stems, determine the average height, and count the larvae so the average number of larvae per stem can be calculated.
- If the alfalfa is 5 inches or shorter and there is less than 1 larvae per stem, no spray is needed and the field should be resampled in 7 days. If there are more than 2 weevils per stem and less than 5 inches tall, spray as soon as possible.
- If there are between 1 and 2 weevils per stem, resample in 3 to 5 days. You may need to spray.
- If the alfalfa is 17 inches tall, and there are 3 weevils per stem, you need to spray. If between 1 ½ and 3 weevils per stem resample in 3 to 5 days. If 17 inches tall and less than 1 ½ weevils per stem, no spray is needed at this time, keep watch.
- If the alfalfa is 20 inches tall and there are 3 or more weevils per stem, it may be best to cut the hay early instead of spraying, and then consider spraying the stubble to protect the regrowth.
To use the economic threshold chart, first determine the control costs in dollars per acre, then estimate the forage value in dollars per ton. Where these two values intersect in the chart is the average number of alfalfa weevil larvae per stem needed to justify chemical control. For example, if control cost is $10 per acre and forage value is $75 dollars per ton, then an average of 3.4 larvae per stem would be needed to justify chemical management.
Biological Control
Parasitic Wasp
Hymenoptera: Ichneumonidae : : Bathyplectes anurus ,B. curculionis
Hymenoptera: Eulophidae:Oomyzus incertus
Hymenoptera: Braconid wasp : Microctonus hyperodae
Entomopathogenic Fungus
Zoophthora (=Erynia, =Entomophthora) phytonomi
Parasitic Wasp
Hymenoptera: Ichneumonidae : : Bathyplectes anurus ,B. curculionis
Hymenoptera: Eulophidae:Oomyzus incertus
Hymenoptera: Braconid wasp : Microctonus hyperodae
Entomopathogenic Fungus
Zoophthora (=Erynia, =Entomophthora) phytonomi
To understand the life cycle of Bathyplectes spp., it is necessary first to understand the life cycle of the alfalfa weevil host.
The alfalfa weevil typically has just one generation per year, with larvae present during the spring. The alfalfa weevil adults emerge from pupae during late spring to early summer, feed for several weeks, and then spend the remainder of the summer "aestivating" in a state of arrested activity and development (diapause). Aestivation is completed by late summer or fall, and the adults become active while the weather remains favorable, then hibernate during the winter and resume feeding and laying eggs the following spring.
The adult flight activity of both Bathyplectes spp. is synchronized with the spring activity period of the alfalfa weevil larvae. The flight lasts up to several weeks, and peak parasitism levels occur 1 to 2 weeks prior to the peak in numbers of weevil larvae. B. anurus, which lays approximately 300 eggs, has just one generation a year, with all parasitoid pupae produced by spring parasitism undergoing diapause, and not emerging as adults until the following spring when weevil larvae are again abundant. B. curculionis, on the other hand, has a partial second generation; many of the parasitoid pupae from spring parasitism are in diapause, but some develop and emerge as adults which then must find and parasitize weevil larvae during the summer. B. curculionis females lay approximately 200 eggs per year.
B. anurus has only one generation per year whereas B. curculionis and O. incertus tend to be multivoltine.
The alfalfa weevil typically has just one generation per year, with larvae present during the spring. The alfalfa weevil adults emerge from pupae during late spring to early summer, feed for several weeks, and then spend the remainder of the summer "aestivating" in a state of arrested activity and development (diapause). Aestivation is completed by late summer or fall, and the adults become active while the weather remains favorable, then hibernate during the winter and resume feeding and laying eggs the following spring.
The adult flight activity of both Bathyplectes spp. is synchronized with the spring activity period of the alfalfa weevil larvae. The flight lasts up to several weeks, and peak parasitism levels occur 1 to 2 weeks prior to the peak in numbers of weevil larvae. B. anurus, which lays approximately 300 eggs, has just one generation a year, with all parasitoid pupae produced by spring parasitism undergoing diapause, and not emerging as adults until the following spring when weevil larvae are again abundant. B. curculionis, on the other hand, has a partial second generation; many of the parasitoid pupae from spring parasitism are in diapause, but some develop and emerge as adults which then must find and parasitize weevil larvae during the summer. B. curculionis females lay approximately 200 eggs per year.
B. anurus has only one generation per year whereas B. curculionis and O. incertus tend to be multivoltine.
Aphid mummie with parasitoid pupa inside.
Comment :
Scouting the number of insect pest and beneficial insects every week. Evaluate the economic damages before make decision.
Scouting the number of insect pest and beneficial insects every week. Evaluate the economic damages before make decision.
Reference: http://www.ipm.iastate.edu/ipm/icm/1997/4-21-1997/aflweevil97.html
http://www.insectimages.org/browse/detail.cfm?imgnum=5365593
http://extension.missouri.edu/extensioninfonet/article.asp?id=6151
http://www.agprofessional.com
/news/alfalfa_weevil_infestations_above_economic_threshold_in_missouri_120103374.html
http://www.biocontrol.entomology.cornell.edu/parasitoids/bathyplectes.html
http://ipmworld.umn.edu/chapters/flanders.htm
http://www.invasive.org/browse/TaxThumb.cfm?fam=70
http://www.drkaae.com/InsectIDPt2/Chapter5WaspsPart2.htm
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9193
http://www.insectimages.org/browse/detail.cfm?imgnum=5365593
http://extension.missouri.edu/extensioninfonet/article.asp?id=6151
http://www.agprofessional.com
/news/alfalfa_weevil_infestations_above_economic_threshold_in_missouri_120103374.html
http://www.biocontrol.entomology.cornell.edu/parasitoids/bathyplectes.html
http://ipmworld.umn.edu/chapters/flanders.htm
http://www.invasive.org/browse/TaxThumb.cfm?fam=70
http://www.drkaae.com/InsectIDPt2/Chapter5WaspsPart2.htm
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9193