Posts Tagged ‘thrips’

Thrips counting

This past week I’ve been out in the field a lot, looking at a lot of onions.  And good news for the growers, I haven’t found very many thrips.  In integrative pest management, counting and sampling has quite an important role.  Courses of action are based on thresholds established for certain pests and certain crops.  These are economic thresholds and economic injury levels.

The economic injury level (EIL) is defined as the lowest pest population density that will cause economic damage.  If a pest populations reaches the EIL, economic damage will be sustained.  To prevent such damage, action can be taken at the determined economic threshold (ET).  The ET is the point at which action should be taken to prevent further damage, and prevent pest densities from reaching the EIL.  The ET is also called the action threshold, which is more descriptive.  More information about EILs and ETs can be found here.

In New York State, the ET for onion thrips is 3 thrips per green leaf.  When sampling, it is important to examine multiple plants in different areas of the field.  Some growers sample up to 50 plants to evaluate thrips populations  The calculation to determine whether or not the ET has been reached is:

(# of thrips counted)/(# of leaves counted)

Of course, it is also important to assess damage, for thrips as well as other pest species.  For onion thrips on onion, this is the characteristic damage:

Different growers have differing levels of acceptable damage, depending on whether it is direct or indirect damage, or may have different thresholds at different points in the season.  To spray or not to spray, that may still be the question.


I love TED.  Someday, I would love to attend the conference, even an independent TEDx event.  Until then, I will just be satisfied by watching TED talks.  Like this one about biological control!  He even talks about thrips 🙂

One ray of sunshine

We’ve gotten a lot of wet weather the past few weeks which has greatly affected the vegetable growers in the region.  Soil preparations and field plantings have been delayed, putting everything a couple weeks behind schedule.  With the delays in crop host establishment, it seems like pests may also be delayed in the colonizing of crop fields.  One way of determining whether this is the case is to use degree day models.

In pest management, degree days are a measure of heat which can be used to track development or manage insect pests.  Organisms have development temperature thresholds, below and above which development is arrested.  For example, with San Jose scales Quadraspidiotus perniciosus the lower threshold is 51ºF and the upper threshold is 90º.  As long as the ambient temperature is between these two thresholds, San Jose scales continue to develop.  For onion thrips, the lower threshold is 52.7ºF.

Degree days are the accumulated product of time and temperature between temperature thresholds.  One degree days is one 24 hour period in which the temperature is one degree above the lower development threshold.  Of course, temperature varies throughout a 24 hour period in field situations. This is taken into account when constructing a degree day model.  Degree days can also be accumulated throughout a growing season, which is how emergence predictions are calculated.

In the simplest model, the equation for a degree day calculation for one 24 hour period looks something like this:

(min temp +max temp)/2 – (min threshold)

Summing the above term for the number of days would give you the degree day accumulation.  Other calculations model temperature fluctuation in more complicated ways, which may provide closer estimates of actual degree days accumulated.

So let’s check on onion thrips in Elba, NY.  Cornell has degree day information here, with 147.6 degree days accumulated since Jan 1.  This calculation is based on 50ºF as the minimum threshold.  The UC IPM site states 140.4 degree day accumulations are necessary for egg development.  Given that onion thrips have a slightly higher threshold than the Cornell model, they’re not hatching.  In Penn Yan, degree day accumulation is 182.0.  Slightly higher, which is better for onion thrips.  But on account of the rain, which demolishes thrips populations, I still didn’t see any thrips out and about when I was in the field yesterday.  So until we get some sun and it warms up, I may just be sitting pretty.


As a graduate student writing about entomology and agriculture, it’s inevitable that my own research will come up.  So I would like to share a little bit about what I do, especially as I begin my first field season.

My research interests are focused on sustainable pest management of agricultural systems, specifically biological control of insect pests.  Currently I’m working on management of onion thrips in onion production systems of New York.  Onions are one of the most valuable vegetable crops in the state, grossing $45 million in 2009.  Most of the crop is grown for fresh market or storage, indicating a low tolerance for insect damage that reduce bulb size, quality, or both.

Onion thrips (Thrips tabaci) are a major pest in New York onion production.  They hide in leaf folds and feed on green leaves, reducing photosynthetic capacity of the plant and overall yield. Furthermore, onion thrips can can transmit Iris yellow spot vitus (IYSV) a Tospovirus which can further damage plants and cause complete yield loss.

Photo courtesy of Thrips of California

Current management practices rely heavily on foliar broad spectrum insecticide sprays with multiple sprays per season to control onion thrips.  However, efficiency may not be adequate as thrips often hide between leaves, protecting themselves from spray droplets.  Furthermore, the possibility of insecticide resistance development is high due to the nature of thrips reproduction.  Newer selective insecticides have shown to be effective in thrips management and fortunately may be compatible with biological control agents such as predators and parasitoids.

I’m interested in natural enemies that may potentially impact thrips populations.  This season, I am lucky to have multiple research sites with a mix of growers to complete my research.  I’m so excited to be doing field work out in the sunshine!