Monitoring onion (Allium cepa) crops for onion thrips (Thrips tabaci) (Thysanoptera: Thripidae): Testing a commercial protocol

Abstract

Onion thrips (Thrips tabaci) is the main insect pest on New Zealand onions (Allium cepa). Insecticide applications are triggered by thrips numbers exceeding action thresholds. A new crop monitoring protocol that involves sampling a minimum of 100 plants (up to 4 ha) or 25 plants/ ha, was tested in 10 young or mature onion crops. Two people independently sampled each crop by zigzagging up and down groups of onion beds defined by pairs of sprayer wheel tracks and selecting a plant at random at predetermined intervals along the crop beds. The number of thrips adults and larvae per plant was recorded. A strong relationship was found between total numbers of thrips and the percentage of plants infested. If the onion industry raised its spray action threshold from 0.1 thrips/plant to 2 or 3 thrips/plant (c. 50% plants infested), it could adopt presence-absence sampling that would be faster than counting all thrips. The time to monitor a crop was affected by field size, and only increased slightly with higher levels of infestation. The new H08042; guidelines could also be used for monitoring disease and weeds.

Integrated management of Thrips tabaci (Thysanoptera: Thripidae) on onion in north‐western Italy: basic approaches for supervised control

“…Nonetheless, plant beating is the most suitable sampling method for preserving commercial crops and a more feasible routine practice for growers than counting insects leaf by leaf, directly in the field or after plant dissection. The number of onion plants to be inspected for a correct population estimate is also very important: five plants each in ten different areas of a field for a total of 50 plants per field is ideal;38 even fewer plants can be examined when they are selected by stratified random sampling 29…”

“…In Piedmont, the current action threshold suggested on onion against T. tabaci is fixed at around 20 thrips plant −1 . The action thresholds recorded in the literature range from 0.1 to 2 thrips plant −1 in New Zealand,29 and from 4 to 30 thrips plant −1 , depending on onion plant growth stage, in Canada,8 the United States5, 38, 39 and Honduras 40. Lower action thresholds are often recommended for thrips‐susceptible varieties and during the bulbing stage, whereas higher action thresholds are recommended for moderately tolerant varieties (such as ‘Derek’), young plants or plants near maturity.…”

“…Independently of the employed chemical, a supervised control based on action thresholds or tolerance levels is one of the major aspects of integrated pest management 5, 22, 29. As a consequence, a reliable sampling method that is fast and easily adoptable is needed for correct monitoring of T. tabaci on onion crops.…”

Population dynamics and integrated pest management of Thrips tabaci on leek under field conditions in northwest Italy

“…(1999) employed an action threshold of 50% of infested plants, which is what was also proposed for onion thrips on onion in New Zealand (Martin et al., 2008). In the present study, when 50% of plants were infested, the average density was approximately one thrips per plant, which was comparable to other studies with the same method on leek (Theunissen & Legutowska, 1991a; Richter et al., 1999), and slightly lower than densities calculated on onion (Martin et al., 2008). Although this number may be underestimated due to under‐sampling of larvae, it is much too low for an action threshold.…”

Kairomone and Camera Trapping New Zealand Flower Thrips, Thrips obscuratus

“…Such labor-intensive work is less frequently reported but camera traps might be tool that can offer a palatable substitute. Initially, direct crop sampling for some pests may have advantages for setting action thresholds, as in onion thrips Thrips tabaci [ 33 ], but with the increasing development of lures and traps this could change.…”