This document summarizes a study on the diversity of insect and arachnid populations in onion fields with barley companion crops. The objectives were to identify 1) which thrips predators and parasites inhabit the barley, 2) what other insects/arachnids live in the barley, and 3) if predator/parasite numbers relate to thrips populations. Onion thrips can transmit Iris Yellow Spot Virus to onions. The study found various beneficial and pest insects present in the barley, with predator numbers sometimes relating to lower thrips counts in fields with the companion crop.

1. Diversity of Insect and Arachnid Populations in Onion Companion Crop
Thaddeus Gourd, Colorado State University Extension, Adams County, Brighton, CO 80601;
Joe Julian, Colorado State University Extension, Douglas County, Castle Rock, CO 80104
Beneficials Found on 6/14/11 Pests Found on 6/14/11
at Companion Crop Field Locations at Companion Crop Field Locations
Abstract: Introduction and Objectives: 15.5
16 120
Onion production across the United States has been impacted by Iris Yellow Spot Virus (IYSV) which is Across the United States, onions are often grown with companion crops such as barley (living mulch) to provide 109
Avg. per 10 foot row insectavac sample
Avg. per 10 foot row insectavac sample
14
vectored by the onion thrips (Thrips tabaci). Reducing thrips populations can sometimes help reduce infection seedling onion plants protection from water and wind erosion (1, 2). Frequently, barley is planted prior to, or 100
12
during the onion seed planting operation. The rapidly emerging barley protects newly sprouted onion plants 10.8
sample
rate of IYSV in onions. In Colorado, companion crops (living mulch) such as barley planted with onions to
sample
10 9.3 80
reduce wind and water erosion has sometimes had an effect on thrips populations. The objectives of this study from wind, sand blasting and occasionally small hail injury that commonly occurs in the early spring along the
Front Range of Colorado. Barley also significantly reduces soil loss in seeded onion fields. Onion producers 8
are to determine 1) which thrips predators and parasites inhabit the barley companion crop; 2) what other 60 55
insectavac
nsectavac
i
51 49
and researchers from many western states have sometimes witnessed a reduction in thrips populations in these 6
insects/arachnids dwell in this living mulch; and 3) if there is a relationship between predator/parasite and thrips 40
companion crop (living mulch) planted fields. 4 28
populations. Three onion field locations were sampled during 2011 that used barley as a companion crop in 1.5
2.8
1.8 17 18.3
2 1.5 1 18
Weld County, Colorado. Four randomly selected areas of each of the three field locations were sampled with the 0.5 0 0.5 0.3 0 0.3 20 15
0 5 4 6 10
insectavac on June 14 and 15. Eight beneficial predator and parasite families were identified from the three field This study was set up to determine if beneficial populations of insects and arachnids found in a barley companion 0 0
1
0
Avg. per 10 foot row
Lady Beetle Braconid Spiders Big Eyed Bug Syrphid Fly
Avg. per 10 foot row
locations sampled. The average of all populations of insects and arachnids at all locations revealed that ladybird crop grown with onions affect thrips populations at various field locations in Colorado. Objectives of this study Larva Wasp Thrips Mites* Leafhoppers Aphids Leaf Beetle
Companion Crop Field Locations Companion Crop Field Locations
beetle larva was the most numerous followed by spiders, braconid wasps, syrphid flies, big eyed bugs, ladybird include: Sakata 1 Arnusch 2 Arnusch 3 Sakata 1 Arnusch 2 Arnusch 3 Figure 4
beetle adults, nabids and lacewings. Six plant feeding insect families and one phytophagous mite family were • Determine which thrips predators and parasites inhabit the barley companion crop. Figure 3
found in the field samples. On July 28, thrips populatiosn ranged from 0.92 to 15.4 thrips per plant. In a non- • Determine what insect/arachnid pests dwell in this living mulch.
companion crop planted field, 20.5 thrips were found per onion plant. No correlation between predator/parasite • Determine if there is a relationship between predator/parasite and thrips populations.
and thrips populations was detected in any companion crop location. Sampling conducted in 2012 confirmed
that predator and parasite populations were significantly greater in onions with living mulch compared to non-
mulched onions.
Results:
The time required to vacuum each sample site was approximately one minute. Placing the sample in a gallon-
sized bag added another minute of time. The actual process of examining just one sample for insects and
Table 1. Average number of beneficial insects and arachnids per 10 foot row
arachnids required approximately two hours. Eight beneficial predator and parasite families were identified from
(25 square feet) Locations 1 and 2 sampled on 6/14/2011; Location 3 on 6/15/2011 the three field locations. The average of all populations of insects and arachnids at all locations revealed that
ladybird beetle larva (Coccinellidae) was the most numerous, followed by spiders, braconid wasps (Diaeretiella),
Beneficial Sakata Farm Arnusch Farm Arnusch Farm Avg. syrphid flies (Syrphidae), big eyed bugs (Geocoridae), ladybird beetle adults (Coccinellidae), damsel bugs
Arthropods Location 1 Location 2 Location 3 (Nabidae), and green lacewing adults (Chrysopidae) (Table 1 and Figure 3). No statistical differences were seen
between beneficial populations at any location. Six plant feeding insect families and one phytophagous mite
Lady Bird Beetle 0 1 0 0.33
family were found in the field samples. The average of all populations of insects and arachnids at all locations
Adult
revealed that phytophagous mites were the most numerous, followed by aphids (Aphidae), thrips (Thripidae),
Lady Bird Beetle 10.75 15.5 9.25 11.83 leafhoppers (Cicadellidae), leaf beetles (Chrysomelidae), miscellaneous flies, one grasshopper and one boxelder
Larvae bug adult (Table 2 and Figure 4). Other than the thrips, these insects and mites would normally be found
Braconid Wasp .25 1.5 1.5 1.08 feeding in barley and not in onions.
Syrphid Flies adults 0 1.75 .25 0.67
Thrips populations were evaluated on July 28 by sampling 100 plants from each of four locations in the four
Spiders 2.75 1 .75 15.0 fields. Numbers ranged from 1.0 to 15.4 thrips per plant in companion crop planted fields. In one non-
Big Eyed Bugs .5 0 1 0.50 companion crop planted field (Arnusch 5) located near a test location, 20.5 thrips were found per onion plant.
Nabid 0 .5 0 0.17 This was significantly higher than all other onion companion crop field locations (Figure 5). Because the thrips
evaluation on July 28 occurred after a number of insecticide applications were made to the onion crop, no
Lacewing Adult 0 .25 0 0.08 correlation between the companion crop (living mulch) fields thrips population compared to a non-companion
crop planted field, could be drawn. This thrips evaluation only showed efficacy of the previously applied
insecticides.
Little to no IYSV was found at any field locations sampled in 2011. Populations sampled on June 14 and 15
showed no correlation between beneficials and thrips. However, this study did document that eight beneficial
predator/parasite families, six plant feeding insect families, and one phytophagous mite family inhabited one or
more companion crop onion field locations in Weld County in 2011.
Results of predator and parasite insect populations sampled in May 2012 confirmed the results seen in 2011.
Table 2. Average number of insects and arachnids per 10 foot row Significantly more beneficial insect populations were found in onions that had living mulch compared to non-
(25 square feet) Locations 1 and 2 sampled on 6/14/2011; Location 3 on 6/15/2011 mulched onions (Figure 6).
Phytophagous Sakata Farm Arnusch Farm Arnusch Farm Avg. References:
Arthropods Location 1 Location 2 Location 3 1. Zandstra, Bernard, Michigan State University, Horticulture, “Time to kill barley cover crops in barley,”
Thrips 5.25 50.75 27.75 27.92 Integrated Pest Management Resources, Vegetable Crop Advisory Team Alert, Current news articles for
Figure 1 - Sampling Equipment vegetable production, 5/12/2010.
Stihl gas powered BG56 Shredder / Vacuum Mites 109 4.25 16.75 43.33 2. Stivers, Lee, Crop Profile: Onions in New York, Cornell Cooperative Extension, 249 Highland Ave.,
Leafhoppers 5.5 10 15 10.17 Rochester, NY 14620.
Aphids 18.25 49.25 54.5 40.67 3. Ellington, J.J., Kiser, K., Cardenas, M., Duttle, J., and Lopez, Y. 1984. The insectavac: A high-clearance,
high-volume arthropod vacuuming platform for agricultural ecosystems, Environmental Entomology 13 (1),
Leaf Beetles 0 18.25 1 6.42
259-265.
Grasshoppers 0 .25 0 0.08
Boxelder Bugs 0 .25 0 0.08 Acknowledgements: A special thank you goes out to Robert and Bob Sakata and to Marc Arnusch for allowing
Misc. Flies 1.75 0 10 3.92 the use of their onion fields for this study. Funding for this project came from the Colorado Onion Association.
Methods:
Three onion field locations were identified that used barley as a companion crop (living mulch), along with one
field with no companion crop. Sakata Farm Location 1 used sprinkler irrigation. Barley was planted on March 3,
2011, and the onions were planted on March 10. Arnusch Farm Location 2 used furrow irrigation. Here, barley
was planted on March 2, and the onions were planted on March 23. Arnusch Farm Location 3 used sprinkler Figure 2 - Sample Prep and Counting Organisms
irrigation. Here, barley was planted on March 12, and the onions were planted on March 26. Arnusch Farm
Location 5 had no companion crop, used flood irrigation and was planted on March 23. Thrips Populations on 7/28/11 Predator & Parasites Found per 10 Row Feet in Living
Mulched and Non Mulched Onions on 5/16/12
Each location had four randomly selected areas sampled with an insect vacuum. Field Locations 1 and 2 were
)
25 20.5 (a)
Avg. per 10 foot row insectavac sample
10 9.4
sampled on June 4, and Location 3 was sampled on June 15. Sample size was one row (2.5 feet) wide by 10 feet 20 15.4 (b) 9
sampled
long. The onions had three to four true leaves at the time of the sampling. 8 7.5
7
15 7
plants
9.2 (c)
6
A Stihl gas powered BG56 Shredder/Vacuum with an insect screen liner (192 micron polyethylene monofilament 10 5
5
Non Mulched
181 x 181 mesh) attached to the suction tube by rubber bands (Figure 1) was used to collect samples. The liner 5 1 (d) 4
Living Mulch
captured plant parts and arthropods inhabiting the barley and onions. An insect vacuum (insectavac) was created 3 2.5
per plant (100
0 2
in the late 1970s by J. Ellington, New Mexico State University (3) and modified by Colorado State University Companion Crop and Non-Companion Crop Field Locations 1.25
Avg.
1 0.625 0.625 0.625
Extension entomologist, Bob Hammon [Traditional hand-net samples catch only 8% of total insects, and the Sakata 1 0
0
insectavac catch-efficiency ranges from 14 to 64%, with an average of 32.6% (3)]. The fine mesh bags were Arnusch 2 Lady Bird Nabid Big Eyed Braconid Syrphid Flies
Larvae Bug wasp
emptied into one-gallon zip lock freezer bags and placed in a cooler. Ten-foot plot samples were taken and Arnusch 3
examined in the lab using a Nikon SM2800 dissecting microscope with 6.3 x 10 magnification. Fine-meshed Arnusch 5 Non-Conpanion Crop Location Figure 5
7 Collected on 5/16/12 at Sakata Farm Location. Data represents the average of four replicates.
Specimens were collected using an Insectvac. Figure 6 8
Figure
screens were used to separate insects and arachnids from soil debris and plant material (Figure 2).
A thrips population evaluation determined the number of thrips per plant on June 28 at the three companion
crop (living mulch) locations and at one field location where no companion crop was used. One hundred plants
were randomly sampled at each location and checked for all stages of thrips. Data was analyzed using Analysis of
Variance and the Tukey HSD All Pairwise Comparisons Test.
For comparison, a similar experiment was set up in May 2012 on onions in one field, both with and without a
living mulch, and sampled on May 16 with an insectavac.