Thrips (Thysanoptera) associated with onion (Allium cepa L.) and Welsh onion (Allium fistulosum L.)

Onions have been consumed for thousands of years in various forms in most cultures of the world. They are most commonly used as an aromatic spice and food supplement, but they are also a valuable source of vitamins, minerals, health-promoting substances and essential oils (Dossa et al., 2018). Nowadays, numerous cultivars of onion (Allium cepa L.) are cultivated, from the most popular yellow to red and white onions, as well as the more exquisite Welsh onion (Allium fistulosum L.). Welsh onion is grown mainly for its chives, although the small bulbs are also edible. The largest producers of A. cepa are China, the United States and India, while the production of A. fistulosum is centred in Japan, Korea, China and Taiwan (Ford-Lloyd and Armstrong, 1993). Among the European Union countries, the leaders in the production and export of onion are Spain, the Netherlands and Poland, while Germany and the Ukraine also have a high onion production (Zaremba, 2015). In Poland, the production of onion amounted to 630,000 and 650,000 tonnes in 2014 and 2016, respectively, while in 2015, due to drought, it fell to 585,000 tonnes. In 2017, the onion production amounted to 667,000 tonnes and was higher compared to next year, when it decreased by 15.6% to 563,000 tonnes in 2018 (Statistics Poland, 2020). In addition to abiotic factors (water deficiency and temperature), which have a significant impact on onion yield, important biotic factors limiting its production include pests and pathogens (Kalbarczyk et al., 2011).

Among the onion pests, one of the most harmful ones is the Thrips tabaci. Larvae and adults of onion thrips live in the leaf sheath and stalk, sucking up the contents of plant cells and causing direct damage, which manifests in the silvering of the leaves and, consequently, inhibited plant growth and reduced bulb weight. In addition, it has indirect effects by promoting the development of fungal and bacterial pathogens as well as the transmission of Iris yellow spot virus (IYSV) (Lewis, 1973). Furthermore, the rapid mass appearance and the high density of thrips on onion crops, particularly during the hot and dry growing seasons, are associated with serious yield loss (Diaz-Montano et al., 2011; Gill et al., 2015). Fournier et al. (1995) demonstrated that in the absence of any control measures, onion thrips infestations of yellow onions resulted in yield losses of 34.5% and 43%. Similarly, Pandey et al. (2011) reported that onion thrips damaged 90% of the onion crop in India and >50% in the United States (Boateng, 2012). It is also one of the major limiting factors affecting yields of leek (Kucharczyk and Legutowska, 2002), cabbage (Fail and Pénzes, 2004; Trdan et al., 2008a), tomato, pepper, cucumber (Riefler and Koschier, 2009; Ssemwogerere et al., 2013) and peas (Pobożniak et al., 2020). The high potential for a rapid population increase of T. tabaci on onion crops is because of a result of their complex lifestyle with a high reproductive rate, a short generation time, a high survival of non-feeding instars (prepupa and pupa), the ability to reproduce without mating (parthenogenesis) and their ability to develop resistance to insecticides (Morse and Hoddle, 2006; Diaz-Montano et al., 2011). Onion thrips do not comprise a homogeneous species and are composed of two distinct reproductive modes: thelytokous and arrhenotokous populations (Nault et al., 2006). The number of generations per year depends on the climatic conditions. In cold areas, from two to three generations may be produced, while in warmer regions, their number can increase up to eight (Gill et al., 2015).

Besides the above-mentioned har mful species T. tabaci, other phytophagous thrips taxa arising from neighbouring crops and wild plants can colonise onion plants. Most of them are not known to cause crop damage (Pobożniak et al., 2007), but their presence on onion plants and sticky traps, which are a useful tool for monitoring onion thrips infestation, can be misleading for farmers. Many authors also observed the presence of Aeolothrips intermedius on onion crops (Pobożniak et al., 2007; Mautino et al., 2014; Pobożniak et al., 2016), and this predatory taxa reduces the densities of other thrips populations and is a predator of 44 species of the Thysanoptera order (Riudavetes, 1995), potentially controlling onion thrips (Trdan et al., 2005). Accurate identification of thrips pests is fundamental to their effective control. Knowledge of this insect pest biology and seasonal dynamics would allow establishing control strategies in a future Integrated Pest Management (IPM) programme.

In this context, this study aimed to determine thrips abundance, species composition and seasonal fluctuation on eight cultivars of A. cepa and one cultivar of A. fistulosum. We also assessed the entity of the autochthonous predator A. intermedius, which is a potential biological control agent of T. tabaci.

Field and laboratory research on the determination of composition, abundance and significance of particular thrips species was conducted in the Depar tment of Botany, Physiology and Plant Protection of the University of Agriculture in Krakow, Poland.

Entomological analyses

In the three successive years (2014–2016), the period of entomological analyses lasted from the second decade of June to the end of August. In 2014, analyses were performed at intervals of 14 days, while in 2015 and 2016, analyses were performed weekly, between 10:00 am and 3:00 pm on sunny days. Sampling thrips consisted of two methods: thrips collected with sweeping net and the method composed of plant bagging in plastic bags and then analysis in the laboratory. Thrips landing and spreading on plants were gathered in the net, while the second method allowed collecting of specimens hidden under folded leaves and near the base of the bulb. Thrips were collected from onion leaves using a standard entomological sweeping net (35 cm in diameter). Within each testing plot, 25 sweeps were made, and the sweeping nets and samples were placed individually into plastic bags. In parallel to the sweeping net analysis, 10 randomly selected plants from each plot (40 plants for cultivar) were collected and placed in plastic bags, followed by appropriate labelling. The collected material was transported to the laboratory, where insects were hand-separated using a soft brush and thrips were placed in vials containing 75% ethyl alcohol. Because the species complex of thrips and percentage share from net and direct counting from harvested plants were the same or similar (Tables S1 and S2 in Supplementary Materials), specimens collected by both methods from the same plots and date are shown combined in Tables 1–4 and Figures 1–3.

Table 1

Species composition of thrips (imago and larvae) collected from Allium cepa and Allium fistulosum by sweeping net and directly from plants in 2014

Cultivars		*Alibaba	*Bila	*Karmen	*Kristine	**Kroll	*Niagara F1	*Polanowska	*Tęcza	*Wenta	*Total
Thrips tabaciLindeman, 1889	N	221	179	252	176	99	190	261	273	178	1,829
	(%)	65.38	56.65	78.75	45.60	10.62	61.29	60.70	66.59	51.00	48.25
Frankliniella intonsaTrybom, 1895	N	93	101	51	187	806	84	148	129	141	1740
	(%)	27.51	31.96	15.94	48.45	86.48	27.10	34.42	31.46	40.40	45.90
Aeolothrips intermediusBagnall, 1934	N	14	14	9	13	20	24	11	5	18	128
	(%)	4.14	4.43	2.81	3.37	2.15	7.74	2.56	1.22	5.16	3.38
Thrips flavusSchrank, 1776	N	6	13	1	6	5	6	7	3	3	50
	(%)	1.78	4.11	0.31	1.55	0.54	1.94	1.63	0.73	0.86	1.32
Haplothrips leucantemiSchrank, 1781	N	3	6	6	4	1	4	1	0	5	30
	(%)	0.89	1.90	1.88	1.04	0.11	1.29	0.23	–	1.43	0.79
Haplothrips aculeatusFabricius, 1803	N	1	3	1	–	1	2	2	0	4	14
	(%)	0.30	0.95	0.31	0.00	0.11	0.65	0.47	–	1.15	0.37
Total	N	338	316	320	386	932	310	430	410	349	3,791
Mean (± SE)		84.5 b ± 11.2	79. 0 b ± 13.8	80.0 b ± 22.2	96.5 ab ± 8.9	233.a ± 47.4	77.5 b ± 15.1	107.0 ab ± 20.8	102.5 ab ± 19.2	87.2 b ± 17.3
F											3.531
p											0.006

*

Cultivars of A. cepa.

**

Cultivar of A. fistulosum.

Means marked with different letters are significantly different from each other (multiple Tukey's test p < 0.05).

Table 2

Species composition of thrips (imago and larvae) collected from Allium cepa and Allium fistulosum by sweeping net and directly from plants in 2015.

Onion cultivars		*Alibaba	*Bila	*Karmen	*Kristine	**Kroll	*Niagara F1	*Polanowska	*Tęcza	*Wenta	Total
Thrips tabaciLindeman, 1889	N	1,312	1,241	1,672	1,157	1,781	1,403	1,024	1,059	1,389	12,038
	(%)	68.58	69.68	68.55	66.53	39.26	68.31	69.42	64.97	73.77	61.89
Frankliniella intonsaTrybom, 1895	N	557	474	705	523	2687	584	417	543	457	6,947
	(%)	29.12	26.61	28.91	30.07	59.24	28.43	28.27	33.31	24.27	35.72
Aeolothrips intermediusBagnall, 1934	N	38	36	55	50	40	58	29	28	34	368
	(%)	1.99	2.02	2.26	2.88	0.88	2.82	1.97	1.72	1.81	1.89
Haplothrips nigerOsborn, 1883	N	3	6	0	3	12	3	3	0	0	30
	(%)	0.16	0.34	–	0.17	0.26	0.15	0.20	–	–	0.15
Chirothrips hamatusTrybom, 1895	N	2	4	2	3	10	2	1	0	2	26
	(%)	0.10	0.22	0.08	0.17	0.22	0.10	0.07	–	0.11	0.13
Thrips fuscipenisHaliday, 1836	N	0	6	5	2	3	2	0	0	0	18
	(%)	–	0.34	0.21	0.12	0.07	0.10	–	–	–	0.09
Thrips flavusSchrank, 1776	N	0	13	0	0	0	1	0	0	0	14
	(%)	–	0.73	–	–	–	0.05	–	–	–	0.07
Haplothrips aculeatusFabricius, 1803	N	1	1	0	0	3	1	1	0	1	8
	(%)	0.05	0.06	–	–	0.07	0.05	0.07	–	0.05	0.04
Haplothrips leucantemiSchrank, 1781	N	0	0	0	1	0	0	0	0	0	1
	(%)	–	–	–	0.06	–	–	–	–	–	0.01
Total	N	1,913	1,781	2,439	1,739	4,536	2,054	1,475	1,630	1,883	19,450
Mean (± SE)		478.2 bc ± 52.8	445.2 bc ± 64.8	609.7 b ± 45.7	434.7 bc ± 41.4	1134.0 a ± 150.4	513.5 bc ± 44.9	368.7 c ± 23.7	407.5 bc ± 32.1	470.7 b ± 51.3
F											9.995
p											0.000

*

Explanations: see Table 1.

Table 3

Species composition of thrips (imago and larvae) collected from Allium cepa and Allium fistulosum by sweeping net and directly from plants in 2016.

Onion cultivars		*Alibaba	*Bila	*Karmen	*Kristine	**Kroll	*Niagara F1	*Polanowska	*Tęcza	*Wenta	Total
Thrips tabaciLindeman, 1889	N	723	494	578	639	1,084	579	848	232	616	5,793
	(%)	58.92	64.74	64.22	63.77	44.10	64.12	69.28	80.28	58.17	58.96
Frankliniella intonsaTrybom, 1895	N	320	177	207	240	1043	214	247	29	298	2775
	(%)	26.08	23.20	23.00	23.95	42.43	23.70	20.18	10.03	28.14	28.24
Aeolothrips intermediusBagnall, 1934	N	137	68	86	101	137	88	84	28	94	823
	(%)	11.17	8.91	9.56	10.08	5.57	9.75	6.86	9.69	8.88	8.38
Haplothrips aculeatusFabricius, 1803	N	9	4	12	8	77	6	12	0	13	141
	(%)	0.73	0.52	1.33	0.80	3.13	0.66	0.98	–	1.23	1.44
Thrips fuscipenisHaliday, 1836	N	10	4	11	8	74	6	9	0	12	134
	(%)	0.81	0.52	1.22	0.80	3.01	0.66	0.74	–	1.13	1.36
Chirothrips hamatusTrybom, 1895	N	22	9	4	1	23	7	20	0	12	98
	(%)	1.79	1.18	0.44	0.10	0.94	0.78	1.63	–	1.13	1.00
Chirothrips manicatusHaliday, 1836	N	4	6	1	4	14	3	1	0	10	43
	(%)	0.33	0.79	0.11	0.40	0.57	0.33	0.08	–	0.94	0.44
Haplothrips leucantemiSchrank, 1781	N	2	0	1	1	5	0	3	0	4	16
	(%)	0.16	–	0.11	0.10	0.20	–	0.25	–	0.38	0.16
Thrips flavusSchrank, 1776	N	0	1	0	0	1	0	0	0	0	2
	(%)	–	0.13	–	–	0.04	–	–	–	–	0.02
Total	N	1,227	763	900	1,002	2,458	903	1,224	289	1,059	9,825
Mean (± SE)		306.7 b ± 21.2	160.7 b ± 15.3	225.0 b ± 29.4	250.5 b ± 42.1	614.5 a ± 55.6	225.7 b ± 28.0	306.0 b ± 20.7	72.2 c ± 15.2	264.7 b ± 29.0
F											21.671
p											0.000

*

Explanations: see Table 1.

Table 4

Sex ratio index of the most numerous species of thrips (imago) collected from Allium cepa and Allium fistulosum by sweeping net and directly from plants in 2015 and 2016.

Onion cultivars	Thrips tabaci			Aeolothrips intermedius			Frankliniella intonsa
	Male	Female	Sex ratio	Male	Female	Sex ratio	Male	Female	Sex ratio
2015
Alibaba	1	1,311	99.9	1	37	97.4	15	542	97.3
Bila	14	1,227	98.9	0	36	100.0	11	463	97.7
Karmen	20	1,652	98.8	4	51	92.7	15	690	97.9
Kristine	2	1,155	99.8	0	50	100.0	12	511	97.7
Kroll**	12	1,769	99.3	5	35	87.5	81	2606	97.0
Niagara F1	15	1,388	98.9	0	58	100.0	21	563	96.4
Polanowska	0	1,024	100.0	2	27	93.1	14	403	96.6
Tęcza	0	1,059	100.0	0	28	100.0	0	543	100.0
Wenta	0	1,389	100.0	3	31	91.2	5	452	98.9
2016
Alibaba	0	723	100.0	33	104	75.9	3	317	99.1
Bila	0	494	100.0	18	50	73.5	2	175	98.9
Karmen	1	577	99.8	18	68	79.1	1	206	99.5
Kristine	1	638	99.8	22	79	78.2	2	238	99.2
Kroll**	0	1,084	100.0	21	116	84.7	21	1,022	98.0
Niagara F1	1	578	99.8	25	63	71.6	0	214	100.0
Polanowska	2	846	99.8	18	66	78.6	1	246	99.6
Tęcza	0	232	100.0	0	28	100.0	0	29	100.0
Wenta	0	616	100.0	23	71	75.5	7	291	97.7

**

Cultivar of A. fistulosum, other cultivars are the A. cepa.

Figure 1

Figure 2

Figure 3

The obtained results indicate that A. fistulosum and A. cepa plants are colonised by six to nine thrips species throughout the growing season, primarily by the suborder Terebrantia and the family Thripidae. Two herbivorous (T. tabaci and F. intonsa) and one predatory (A. intermedius) species together accounted for over 97% of the material collected from onion and Welsh onion plants throughout 3 years. T. tabaci was the most abundant species on all tested cultivars of onion, the second most numerous was F. intonsa, while the opposite ratio was noticed on Welsh onion. The participation of thrips species differed by years and both species of Allium. The mean share of T. tabaci in the total collection of sampled thrips from A. cepa ranged from 60.5% to 68.8%, while for F. intonsa it was lower and accounted from 23.5% to 32.7%. In turn, in material collected from A. fistulosum, the share of onion thrips ranged from 10.6% to 44.1%, while for flower thrips it accounted from 42.4% to 86.4%. Also, Pobożniak et al. (2016) found that the population of T. tabaci in onion crops may vary depending on the year, and the share of this species on onions crops can range from 34% to 68%, while for F. intonsa, it can range from 29.8% to 58.0%. Onion thrips predominated, accounting for 82.6% to 84.9% of the thrips on onion in Colorado (USA) (Mahaffey and Cranshaw, 2010). In Texas (USA), according to Bender and Morrison (1989) and Doederlein and Sites (1993), the species composition of thrips on onion is dominated by the western flower thrips (Frankliniella occidentalis Pergande) and by onion thrips. Sparks et al. (2011) reported that key arthropod pests on onions in Georgia (USA) are tobacco thrips (Frankliniella fusca Hinds), western flower trips and onion thrips, which represented 49.9% of all detected thrips. The species T. tabaci is a major pest and predominant on onion fields in Europe (Hudák and Pénzes, 2004; Diaz–Montano et al., 2011; Gill et al., 2015; Pobożniak et al., 2016), the United States (Macintyre-Allen et al., 2005, Smith et al., 2016), Asia (Pandey et al., 2011; Reitz et al., 2011; Li et al., 2014), Australia (Herron et al., 2008), New Zealand (Martin et al., 2006) and Africa (Maniania et al., 2003). In addition to onion, onion thrips may attack garlic and leek (Afifi and Haydar, 1990; Theunissen and Schelling, 1998; Duchovskienė, 2006; Akhtari et al., 2014) and other vegetables, such as cauliflower, cabbage, pea, cucumber and carrot (Farrugia, 1997; Pourian et al., 2009; Li et al., 2014, Pobożniak et al., 2020; Silva et al., 2020). Notably, the extent and frequency by which onion thrips damage crops vary across plant species, but onion is its preferred host and the most damaged crop. Also, F. intonsa has been determined in Poland on the onion by Pobożniak et al. (2016) and on leek by Legutowska and Theunissen (2003). This species is mainly associated with flowering plants and is the dominant species in legume field crops such as peas, beans, soybeans, lentils and lupine in Poland (Pobożniak, 2011; Hurej et al., 2014; 2015). There is no information in the literature on the possibility of F. intonsa feeding on onion plants. The author's own observations, however, suggest that this species is not likely to feed on onion, and the presence of F. intonsa specimens on onion at least partially may be due to the presence of many flowering plants in the vicinity of the experimental plots. However, Hazir et al. (2011) discussed the possibility of this species feeding on organs other than the flowers. The authors report that F. intonsa feeding on ovary tissue caused brown blemishes and scars on nectarine fruit, and feeding on mature fruit caused whitish skin patches called silvering. Also, Murai (1988) noted that swollen white spots were produced as a result of this species feeding on tomato fruits. Moreover, Molnár et al. (2008) observed that in addition to T. tabaci and F. occidentalis also F. intonsa feeds on pepper and can also spread the tomato spotted wilt virus (TSWV) with the same efficacy as the other two species. The very high abundance of F. intonsa on onion and the observations of the cited authors indicate a potential possibility of this species feeding also on onions, but this issue requires further clarification.

The predatory A. intermedius was a less abundant species and accounting for about 4.5% of all species on A. cepa and 2.9% on A. fistulosum. Similarly, Pobożniak et al. (2016) found about 5% of A. intermedius on Allium sp. The appearance of this predatory thrips species was noticed on A. fistulosum in Ljubljana (Trdan et al., 2005). In turn, Ábrahám (2012) observed about 9% of this taxon on alfalfa, and Pobożniak et al. (2020) registered about 8.6% on peas, with the first maximum appearance during the flowering and the second during forming pods phases, when the number of potential victim, onion thrips, was the highest. The occurrence of A. intermedius in the flowers of many plants may be due to the fact that pollen can be used as an alternative source of food by this species (Trdan et al., 2005; Conti, 2009). In Europe, A. intermedius has usually been mentioned as a predator of onion thrips (Franco et al., 1999). In our experiment, the percentage share of predatory thrips increased on the onion plants from mid-July. In our opinion, A. intermedius certainly limited the number of onion thrips on onion plants. However, despite its presence, the numbers of herbivorous onion thrips were so high that they caused damage to the onion leaves. Also, Pobożniak et al. (2020) and Ábrahám (2008) noted that the number of A. intermedius was insufficient to reduce the population of phytophagous thrips in pea and soybean. Other species associated with flowers (Thrips flavus, Thrips fuscipenis, Haplothrips leucantemi and Haplothrips niger) and mainly with grasses (Chirothrips hamatus, Chirothrips manicatus and Haplothrips aculeatus) were observed on A. cepa and A. fistulosum in a small numbers. They have also been found in small amounts on onion by Pobożniak et al. (2007), on leek by Legutowska and Theunissen (2003) and on cabbage by Fail and Pénzes (2004) and their presence was accidental and resulted from the neighbourhood of flowering plants and cereals.

The species T. tabaci can reproduce asexually (parthenogenesis) and sexually. The most common reproductive mode is thelytoky, a parthenogenesis in which females are produced from unfertilised eggs. Onion thrips also reproduce via arrhenotoky, a parthenogenesis in which males are produced from unfertilised eggs and females from fertilised eggs. Onion thrips that reproduce via thelytoky differ genetically and ecologically from those that reproduce via arrhenotoky (Toda and Murai, 2007). According to Kobayashi et al. (2013), in some instances, arrhenotokous and thelytokous onion thrips populations can coexist in the same field, but it is difficult to distinguish between thelytokous and arrhenotokous female adults morphologically (Jenser and Szénási, 2004). On onion, arrhenotokous T. tabaci performed better than thelytokous form and produced more progenies, while on cabbage, the opposite occurred (Li et al., 2014). In our experiment, both females and males of T. tabaci were found on A. cepa and A. fistulosum, and the average sex ratio on all tested onion cultivars was about 99.5% and 99.9% in 2015 and 2016, respectively, and 99.3% and 100% on Welsh onion in subsequent years. Different sex ratios on onions crops, garlic and leeks have also been confirmed by Torres-Vila et al. (1994) in Spain. Both females and males of T. tabaci were found also by Bosco and Tavella (2010) on leek under field conditions in northwest Italy. In the Netherlands, the male/female ratio of onion thrips on leek was 1:26 (Vierbergen and Ester, 2000). In turn, in Ontario (USA), Macintyre-Allen et al. (2005) did not notice the presence of T. tabaci males on onion crops. According to Jenser and Szénási (2004), the rare occurrence or absence of male T. tabaci is associated with the geographical area from which the host plants originate, including onions and leeks. Their area of origin is Central Asia and the eastern Mediterranean region; T. tabaci has been introduced in moderate climate zones, which is likely to explain the absence of males (Jenser and Szénási 2004).

In the case of F. intonsa, the average sex ratio on onion cultivars and Welsh onion was nearly the same and accounted for 97.8% and 97.0% on A. cepa and 97.0% and 98.0% on A. fistulosum in 2015 and 2016, respectively (Table 4). In a population of F. intonsa in flowers of food legume plants, participation of males was even higher, with a sex ratio of over 79% Pobożniak (2011). Hurej et al. (2015), in their analysis of thrips settlement on both forms of Andean lupine, pointed out that in the case of flower thrips, the morphological form of the plant did not affect the occurrence of male thrips, and the calculated sex ratio was 86.2%.

Mautino et al. (2014) noted that the adult population of A. intermedius consists of both female and male zoophages. In our experiment, the sex ratio of this species on A. cepa and A. fistulosum was about 96.8% and 79.0% on onion and about 87.5% and 84.7% on Welsh onion in 2015 and 2016, respectively (Table 4). Hurej et al. (2017) reported that the sex ratio of A. intermedius on linseed ranged from 61.5% to 77.1%, but never exceeded 80%. In turn, on peas, beans, lentil, French beans or soya beans, the percentage of males in the population of A. intermedius was lower, and the sex ratio ranged from 82.4% to 89.6% (Pobożniak, 2011).

The relationship bet ween populations of the most numerous species T. tabaci, F. intonsa and A. intermedius changed in the subsequent months of the growing season. In June 2014 and 2015, only T. tabaci and F. intonsa occurred on onion plants, while in 2016, also a small number of the predatory A. intermedius was observed. From July, the percentage shares of F. intonsa and predatory A. intermedius in the thrips populations on many onion cultivars increased, most likely because of the presence of many flowering plants near the experimental plots and the growing population of T. tabaci on onion plants, potential A. intermedius prey. Pobożniak et al. (2007; 2016) reported that the peak flight activity of thrips on onion crops in South Poland took place from the beginning of July to the beginning of August and was slightly earlier than that reported for Germany (Richter et al., 1999). In turn, in North Italy, the peak population of onion thrips was reached in September (Bosco and Tavella, 2010), while in South Texas (USA), it peaked in April (Liu, 2004).

Differences in the infestation levels of thrips between the all tested onion cultivars were observed in successive years. In all 3 years of the study, the cultivar most populated by thrips specimens was cv. Kroll (A. fistulosum), on which the number of F. intonsa was 8 and 1.5 times as high compared to T. tabaci in 2014 and 2015, respectively, while the numbers of both species in 2016 were similar. The number of thrips caught from the A. cepa cultivars was about from 2 to 3 times lower compared to the thrips population on Welsh onion (cv. Kroll). However, the number of T. tabaci on cultivars of A. cepa was always higher than that of F. intonsa. In the case of some cultivars, the number of T. tabaci was even about 3, 5 or 8 times as high compared to F. intonsa or was almost the same. In turn, Pobożniak et al. (2016) found that in some years, onion thrips inhabited Welsh onion more frequently compared to onion cultivars. The tested onion cultivars demonstrated varying degrees of attractiveness to thrips species and underwent changes in the subsequent years. The level of attractiveness of onion cultivars related to T. tabaci, which is reported as a main pest of onion, varied depending on the year and cultivar. The differences in thrips infestation of the studied cultivars are caused by a number of factors, and clarifying them requires further research. Presumably, factors affecting the colonisation of cultivars by T. tabaci were their biochemical and morphological features, influencing the vision, taste and smell senses of thrips, and could be responsible for antixenosis and antibiosis (Smith, 2005; Trdan et al., 2008b; Diaz-Montano et al., 2012; Silva et al., 2014).