Evaluation of efficacy of Neoseiulus cucumeris for control of western flower thrips in spring bedding crops

Western flower thrips, Frankliniella occidentalis (Pergande), is the principal insect pest of spring flower crops grown in the northeastern United States for use as bedding plants. Neoseiulus (=Amblyseius) cucumeris (Oudemans) is a predacious mite reared commercially that is recommended for control of western flower thrips in various vegetable and flower crops at a rate of ca 53 mites/m2/week. Efficacy on spring flower crops, however, is not well demonstrated, reports being either from other crops or extension demonstration trials. In two trials (each replicated), we compared suppression of western flower thrips in spring bedding plants provided by (1) N. cucumeris at the recommended rate, (2) spinosad (at the labeled rate), the most widely used thrips-control pesticide, and (3) both combined. Trial No. 1 was run in mixed bedding plants in commercial greenhouses and Trial No. 2 in impatiens monocultures in University greenhouses. We found that in commercial greenhouses, variation in species composition of crops and movement of plants during crop production made it difficult to detect any significant effects. In an impatiens monoculture (Trial No. 2), we found better evidence of partial suppression of thrips larvae and adults by treatments. Spinosad alone provided the best control, with mites alone usually providing control intermediate to that of spinosad alone and the untreated control. Control from spinosad plus mites was not significantly different from that of spinosad alone (all treatments evaluated as counts of thrips per plant, in flowers). In another University-based trial (Trial No. 3), we compared the commercially recommended rate of N. cucumeris (53 mites/m2/week) to a 3- to 4-fold higher rate (190 mites/m2/week) in impatiens monocultures. This trial was replicated twice in the fall of 2004 and once in spring of 2005 in Amherst, Massachusetts. We found that the higher release rate, while not resulting in statistically significantly more mites per plant (in flowers) than the standard rate, did suppress thrips larvae per plant (in flowers) by 50-75%, a higher level than that achieved by the recommended standard rate. No reductions, however, were found in counts of adult thrips, either as numbers per plant (in flowers) or as numbers caught per yellow sticky card, except for one replication in which thrips counts were lowered compared to controls by mites (at both release rates). We conclude that N. cucumeris, especially at the higher rate, provides partial control of western flower thrips in impatiens bedding plants, but that control from spinosad is better. Biological control of western flower thrips with this predator is not a complete thrips IPM program, but may be used together with spinosad or other materials to prevent development of pesticide resistance. This approach is most likely to be of value in crops grown as continuous relay plantings or a series of different, but thrips-susceptible, crop species.