Thrips Settling, Oviposition and IYSV Distribution on Onion Foliage

Abstract

Thrips tabaci Lindeman (Thysanoptera: Thripidae) adult and larval settling and oviposition on onion (Allium cepa L.) foliage were investigated in relation to leaf position and leaf length at prebulb plant growth stages under controlled conditions. In the laboratory, four and six adult females of T. tabaci were released on onion plants at three-leaf stage and six-to eight-leaf stage, respectively, and thrips egg, nymph, and adult count data were collected on each of the three inner most leaves at every 2-cm leaf segment. Thrips settling and oviposition parameters were quantified during the light period on the above ground portion of onion plants from the distal end of the bulb or leaf sheath "neck" through the tips of the foliage. Results from studies confirmed that distribution of thrips adults, nymphs, and eggs were skewed toward the base of the plant. The settling distributions of thrips adults and nymphs differed slightly from the egg distribution in that oviposition occurred all the way to the tip of the leaf while adults and nymphs were typically not observed near the tip. In a field study, the foliage was divided into three equal partitions, i.e., top, middle, basal thirds, and thrips adults by species, primarily Frankliniella fusca (Hinds) and T. tabaci, were collected from each partition to determine if there was a similar bias of all adult thrips toward the base of the plant. The results suggested that adults of different species appear to segregate along leaf length. Finally, thrips oviposition on 2-cm segments and Iris yellow spot virus positive leaf segments were quantified in the field, irrespective of thrips species. Both variables demonstrated a very similar pattern of bias toward the base of the plant and were significantly correlated.

Iris Yellow Spot Virus Prolongs the Adult Lifespan of Its Primary Vector, Onion Thrips (Thrips tabaci) (Thysanoptera: Thripidae)

“…Rather, there was an assumption that the thrips would be viruliferous after feeding for 16 h on IYSV-positive plant tissue (Inoue et al 2010, Birithia et al 2013). However, acquisition of tospoviruses by thrips can vary (Bautista et al 1995, Hunter et al 1995, Srinivasan et al 2012, Chitturi et al 2015). Variable virus acquisition may confound experimental results as numbers of nonviruliferous thrips may be underestimated, thereby reducing the likelihood of finding significant differences between treatment groups.…”