Within-Plant Distribution of Onion Thrips (Thysanoptera: Thripidae) in Onions

Abstract

Two aspects of the within-plant distribution of Thrips tabaci Lindeman (Thysanoptera: Thripidae) on onion, Allium cepa L., plants were investigated: 1) diurnal variations in the distribution of adults and larvae between basal and upper sections of onion leaves, and 2) between-leaf and within-leaf distribution of the eggs. The diurnal investigations showed that higher proportions of larvae than of adults congregated at the basal sections of plants, particularly when plants were young and thrips density was low. As plants matured and thrips density increased, the larvae became more dispersed. Regardless of plant size, there were always more adults in the upper than basal plant sections. There were no clear time-windows during the 24-h diurnal cycle when more thrips were in the upper plant parts. T. tabaci eggs were laid everywhere in the plant. Leaves of intermediate ages had more eggs than older or younger leaves. Within leaves, the white leaf sheath received the least eggs and leaf tips received slightly more eggs than leaf sheaths. The highest egg density was found between the green leaf base and the leaf tips. Regardless of plant size, more than half of all eggs were laid above the basal sections. The percentage increased to >95% in mature plants. Except when plants were small the outer leaves were preferred over inner leaves and upper leaf sections preferred over lower leaf sections as egg-laying sites by adults. Implications of the results in the management of T. tabaci are discussed.

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

“…Both plant beating and plant dissection showed a strong relationship with visual inspection, so the regression equations can be used in practice to adjust the number of thrips per plant recorded with the two proposed methods. This is particularly useful in estimating the real number of larvae by beating plants because, with this method, larvae are only partly captured, most of them remaining among the leaves at the base of the plant 37. 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.…”

Biological parameters of onion thrips, Thrips tabaci Lindeman on onion cultivars

“…The morphological characteristics might involve thickness and rigidity of the cellular walls, the amount of epicuticular waxes, and the wider central angle between the leaves. Th ese features increase the diffi culty of attack by onion thrips on onion plants (Martin and Workman 2006;Mo et al 2008;Morsello et al 2008;Diaz-Montano et al 2010;Silva et al 2015). Chemical substances and the nutritional composition of onion plants infl uence the feeding rate, the development and reproduction of T. tabaci, resulting in plant resistance by antibiosis and antixenosis (Riefl er and Koschier 2009).…”

<b>Morphological and chemical characteristics of onion plants (<i>Allium cepa</i> L.) associated with resistance to onion thrips

“…Alfa São Francisco and Sirius showed a significantly smaller angle between the central leaves than Alfa São Francisco RT (Table 2). Cultivars with a wider central angle and more round leaves in horizontal cuts suffer fewer infestations by T. tabaci due to the non-preference of the insects for these leaves due to the smaller contact surface of the leaves with one another compared to more flattened leaves (FREI et al, 2003;MARTIN;WORKMAN, 2006;MO et al, 2008;MORSELLO et al, 2008). Loges et al (2004) observed a relationship between the plant height and thrips density because taller pants have heavier leaves and therefore a wider angle between the central leaves.…”

“…tabaci is controlled mainly by means of chemical products, but their efficiency in the control of thrips is low, and high amounts of insecticides are required because the insects have a high escape capacity, high reproductive rate, fast development rate and low sensitivity to the insecticides (BACCI et al, 2008;MO et al, 2008). Some populations of T. tabaci have acquired resistance to the insecticides used in several regions of the world due to the Acta Scientiarum.…”

“…The morphological factors responsible for resistance are the thickness and the rigidity of the cellular wall, the distribution and the size of stomata, the rugosity of the leaf surface, the composition and amount of wax accumulated on the surface of the leaves, the leaf shape and, the most investigated, the central angle between the leaves, once, all these features make it difficult for pests and microorganisms to attack the plant. (CUARTERO et al, 1999;FREI et al, 2003;MARTIN;WORKMAN, 2006;MO et al, 2008;MORSELLO et al, 2008;VOORRIPS et al, 2008).…”