Population dynamics of cabbage looper [Trichoplusia ni (Hübner, 1803) (Lepidoptera: Noctuidae)] in almond orchards

1 Introduction

Turkey is a gene center, natural distribution, and spread area for most of the fruit species due to its geographical location and diverse climatic conditions (Çelik Oğuz et al., 2021; Ercisli, 2004). Therefore, the southeastern Anatolia region of the country has rich fruit species and varieties (Ozturk et al., 2017; Uzun et al., 2021). Anatolia is one of the homelands of almond [Amygdalus communis L. (Rosales: Rosaceae)] in addition to many other fruit species (Küden, 2011, 1998). Almond has many health benefits as it reduces type-2 diabetes, dysmetabolic syndrome, and oxidative stress (Kamil and Chen, 2012; Mandalari et al., 2008; Rao, 2012).

Turkey is globally ranked 5th in terms of almond production after the USA, Spain, Iran, and Morocco. The annual almond production in Turkey is 100,000 tons (FAO, 2021). Turkey’s most cultivated almond varieties are ‘Ferragnes,’ ‘Ferraduel’, ‘Nonpareil’, ‘Texas’, ‘Drake’, and ‘Cristomorto’ (Isgin and Ak, 2011). The almond orchards in the country have no other fruit trees intercropped. Almond has the highest cultivation area in Şanlıurfa province after pistachio and pomegranate. The annual almond production in the region is ∼6000 tons (TÜİK, 2020).

Almond production in the country suffers from various biotic and abiotic stresses, and numerous difficulties are faced in cultivation and marketing. Numerous insect pests infest almond orchards and significantly reduce production and quality. The most important pest species infesting almond orchards are Tropinota (=Epicometis) hirta Poda (Coleoptera: Scarabaeidae), Anarsia lineatella Zell. (Lepidoptera: Gelechiidae), and Eurytoma amygdali Enderlein (Hymenoptera: Eurytomidae) (Bolu et al., 2005; Tolga and Yoldaş, 2019).

The cabbage looper [Trichoplusia ni (Hübner, 1803) (Lepidoptera: Noctuidae)] is distributed in several areas of Turkey. It has been reported to feed on different conventional and non-conventional hosts. It has emerged as a polyphagous pest in the agricultural regions in Turkey. Keyder (1961) observed that the cabbage looper feeds and incurs economic losses to cabbage. The moths of the pest have been observed in the cotton-growing areas of southeastern Anatolia (Nizamlıoğlu, 1961). Similarly, the pest has been reported to incur heavy economic losses in watermelon production (Giray, 1985). The light traps installed in Şanlıurfa also trapped significant number of cabbage looper adults (Ünlü and Kornoşor, 2003). Likewise, Tezcan et al. (2004) observed the species in thyme production areas of Turgutlu and Salihli districts in Mardin province. However, the pest has been rarely reported from almond orchards in the southeastern Anatolia region of the country.

The cabbage looper usually lays eggs on the lower side of larger leaves (Chow et al., 2005). The larvae are green in color with a white stripe on the side. The eggs turn green after hatching and lose their hair, leaving only a few bristles. Larvae are generally 3–4 cm long and can have four to seven instars within 9–14 days (Capinera, 2020). The cabbage looper larvae initially do not consume much food; however, they increase consumption with time (McEwen and Hervey, 1960).

Although several studies reported that cabbage looper infests various fruit orchards, no study reported it from almond orchards (Karaat et al., 2021; Ünlü and Kornoşor, 2003). Cabbage looper is a medium-sized nocturnal moth that prefers Cruciferae plant species, particularly cabbage (Coapio et al., 2018; Li and Liu, 2015; Liu et al., 1988; Sarfraz et al., 2011). It is a harmful pest for >160 plant species, including tomato and tobacco. The cabbage looper has evolved resistance to many insecticides; hence, several insecticides cannot control the pest (Elsey and Rabb, 1967; Greene, 1972; Greene et al., 1969). This cosmopolitan species is distributed in Africa, Asia, Australia, North and South America, and Europe (Chen et al., 2019; Kiritani, 2006).

There is no study on the population dynamics of cabbage looper in almond orchards globally. The current study determined population dynamics of cabbage looper with sexual pheromone traps in almond orchards. Population dynamics parameters such as first adult flight, population density, peak population periods, last adult flight, and estimated number of progenies under natural conditions were determined through this study. The study will provide valuable insights for producers regarding managing cabbage looper in almond orchards.

2 Materials and Methods

2.2

2.2 Experimental treatments

The population development of cabbage looper was monitored with delta-type sexual pheromone traps (5.0 mg E5 Decenyl acetate and 1.0 mg E5 Decenol). We selected one almond orchard in ach district, and sexual pheromone traps were installed in the orchards. Different background information on the almond orchards is given in Table 1. The climatic data of the studied orchards are presented in Fig. 1.

Table 1 Background information on the almond orchards selected for the current study in Şanlıurfa province, Turkey.

District	Village	Variety	Age	Area (ha)	Number of trees	Geographic coordinates	Altitude (m)
Haliliye	İncirli	Ferragnes Ferraduel	12	2.5	1000	N 37° 09′ 10′' E 39° 02′ 05″	472
Eyyübiye	Günbalı	Ferragnes Ferraduel	15	8.0	3200	N 37° 05′ 19″ E 38° 58′ 55″	426
Karaköprü	Dağeteği	Ferragnes Ferraduel	30	2.0	600	N 37° 09′ 47″ E 38° 51′01″	491

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Fig. 1

Average monthly temperature and relative humidity in Şanlıurfa province, Turkey. The red lines represent relative humidity, whereas the blue lines indicate temperature.

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Sexual attractive pheromone traps were installed in each orchard at 1.5–2 m height from the ground towards the southern side of trees on April 4, 2019. The traps were observed twice a week until the first adult emerged and followed once a week afterward. The pheromone capsules were changed after every 4–5 weeks. The adhesive plates in the traps were replaced with new ones at appropriate times, depending on their adhesiveness.

3 Results

The first adult flight of cabbage looper in Şanlıurfa was recorded during the first week of April, whereas the first adult flight in Haliliye district was noted on April 6 and 14 adults were trap (Fig. 2). The peak population development (40 adults/trap) of cabbage looper was recorded in Haliliye district on April 27. Population density decreased after the peak and reached to zero during mid-June. No adults were observed in the traps until end October. However, the traps caught 5 adults/trap on November 9 and no adult flight was observed afterwards (Fig. 2).

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Fig. 2

Population dynamics of cabbage looper in almond orchards of Haliliye district Şanlıurfa, Turkey.

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The first adult flight of cabbage looper in Karaköprü district was observed on April 13 and 32 adults/trap were captured during the first flight (Fig. 3). One week after this date, peak pest population was recorded with 43 adults/trap in Karaköprü district. Population density of cabbage looper declined after the peak development period. Although the traps caught one adult/trap during some weeks in summer months, population density of cabbage looper was not significantly high. The last adult flight was recorded on October 5 in almond orchards of Karaköprü district (Fig. 3).

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Fig. 3

Population dynamics of cabbage looper in almond orchards of Karaköprü district Şanlıurfa, Turkey.

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The first adult flight of cabbage looper was recorded during the first week of April in almond orchards of Eyyübiye district. The first adult flight was recorded on April 6 with 25 adults/trap and peak density was noted on April 13 (Fig. 4). After this date, population density decreased like in other districts. From mid-June to mid-September adults were not recorded in the pheromone traps located in Eyyübiye district. At the end of the season, 8, 10 and 4 adults/traps were recorded on September 28, November 2, and November 16, respectively, and adult flight ended on November 23. The population declined after peaks formed in all three districts. The pest did not form a population from the second half of June until September. It is thought that summers are very hot in Şanlıurfa province and the pest switches to diapause during these months (Fig. 4).

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Fig. 4

Population dynamics of cabbage looper in almond orchards of Eyyuübiye district Şanlıurfa, Turkey.

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The chord diagrams indicated that April and May were the most contributing months in terms of total number of adults (Fig. 5) and percentage of the adults (Fig. 6) recorded during the whole monitoring season. This can be linked with the peak development period of cabbage looper during April. The population declined after April; thus, contribution of remaining sampling dates was low compared to sampling dates in the month of April and May.

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Fig. 5

Chord diagram indicating the contribution of different sampling dates towards total number of adults trapped by pheromone traps installed in different almond orchards. The only dates where infestation was observed were included in the analysis.

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Fig. 6

Chord diagram indicating the relative percentage contribution of different sampling dates towards total number of adults trapped by pheromone traps installed in different almond orchards. The only dates where infestation was observed were included in the analysis.

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4 Discussion

Studying population dynamics of different pests infesting non-target crops provide empirical information for their timely management. Although cabbage looper infests vegetables, this study identified that it could establish significant population in almond orchards. This study determined population development of cabbage looper in almond orchards for the first time. Although it was hypothesized that the orchards will differ for population development, this hypothesis proved wrong since almost similar population of cabbage looper was recorded in all orchards.

Several studies have reported that some of the pest species spend hot summer in temporary diapause (Mamay et al., 2014; Summers and Price, 1961). The peak population development of cabbage looper was recorded during April in all studied orchards. Cabbage looper again developed small populations at the end of September and during first week of November. The total number of adults trapped by pheromone traps in almond orchards situated in Eyyübiye, Haliliye and Karaköprü were 156, 181 and 117 adults/traps, respectively. It was recorded that cabbage looper adults remain active for at least 7 months from the beginning of April to the beginning of November in almond orchards in Turkey (Figs. 3–5).

Several earlier studies have reported that cabbage looper infests cabbage, watermelon, thyme and salvia in Turkey (Giray, 1985; Keyder, 1961; Nizamlıoğlu, 1961; Tezcan et al., 2004; ünlü and Kornoşor, 2003; Zarkani and Turanli, 2019). This study revealed that cabbage looper has started to establish population in almond orchards of Turkey. However, economic damages caused cabbage looper were not determined through this study. Therefore, it is recommended that future studies should determine the economic damages and develop effective management practices to halt the further spread of cabbage looper in almond orchards.

Early detection and rapid response are effective management strategies for new pest species infesting non-native areas or non-conventional hosts (Farooq et al., 2015; Jabran et al., 2015; Onen and Farooq, 2015). The newly recorded species are difficult to manage once they establish population after their introduction (Ozaslan et al., 2016; Özaslan et al., 2016). Therefore, early warnings should be issued through effective monitoring and detection of the species in new areas or non-conventional crops. These systems have been effective for the management of invasive species at regional and global scales (Sari et al., 2016; Welch et al., 2014). Therefore, it is recommended that an early detection and rapid response system should be developed for cabbage looper to suppress its population in almond orchards of Turkey.

The studies relating to pest risk analysis of cabbage are also needed to infer whether pest can be of potential risk in almond production. Nonetheless, a modelling study relating to the potential spread of the pest in almond production areas could determine the potential global risks related to the species.

5 Conclusion

This study determined the population development of cabbage looper for the first time in almond orchards. The total number of adults trapped by pheromone traps from almond orchards situated in Eyyübiye, Haliliye and Karaköprü distrcits were 156, 181 and 117 adults/trap, respectively. It is concluded that cabbage looper adults remain active for at least 7 months from the beginning of April to the beginning of November in almond orchards. The studies relating to pest risk analysis are needed to infer whether cabbage looper can be of potential risk in almond production. Nonetheless, a modelling study relating to the potential spread of the pest in almond production areas of the world could determine the risks related to the species.