Orius laevigatus (Insecta; Heteroptera) local strain, a promising agent in biological control of Frankliniella occidentalis (Insecta; Thysanoptra) in protected pepper crops in Tunisia

  • Mohamed Elimem
  • Ahlem Harbi
  • Essia Limem-Sellemi
  • Soukaina Ben Othmen
  • Brahim Chermiti
Original Paper
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Abstract

Frankliniella occidentalis Pergande (1895) (Thysanoptera; Thripidae) is the most common worldwide western flower thrips. It has a cosmopolitan distribution and a wide host-plant range. The management of F. occidentalis has always been based on chemical and biological methods. However, within the integrated pest management (IPM) concept, beneficial local insects are worth investigating within a biological control approach. This work aims to evaluate and enhance the efficiency of the local thrips predator strains Orius laevigatus (Heteroptera; Anthocoridae) to control F. occidentalis. The study focused on the most convenient dose and release rate of O. laevigatus against F. occidentalis. The minute pirate bugs O. laevigatus were collected on flowers of Chrysanthemum coronarium Linneaus (Asterales; Asteraceae) growing in an uncultivated field in the region of Chott-Mariem (Sousse, Tunisia). Two doses and three predator release frequencies were tested in nine pepper crop greenhouses already infected by F. occidentalis. Preliminary results showed that the O. laevigatus local strain had been successfully installed in all pepper crop greenhouses regardless of doses and release frequencies. Moreover, when released two or three times with a time laps of 1 week at a dose of 1 individual per m2, this predator was able to control thrips populations. In fact, a decrease of F. occidentalis populations was reported 1 week after the first release and very low levels were maintained below the economic threshold. In addition, it turned out that, when employed three times at a dose of 0.5 individual per m2 or just once with a dose of 1 individual per m2, the predatory bug produced a late impact on thrips populations. These results demonstrated the effectiveness of this predatory bug to control F. occidentalis populations and that it may be used as an alternative way to substitute the use of chemical pesticides.

Keywords

Biological control Local strain Predator Thrips Pepper 

Introduction

The Western Flower Thrips (WFT), also known as Frankliniella occidentalis Perande 1895 (Thysanoptera; Thripidae) is a cosmopolitan and phytophagous thrips species that attack numerous host plant species from several botanical families (Lewis 1973; Loomans and van Lenteren 1995). Although F. occidentalis has been reported since the nineteen’s in Tunisia, the species is still considered as a quarantine pest due to its ability to transmit viruses such as the Tomato Spot Wilt Virus (TSWV) and the Impatiens Necrotic Spot Wilt Virus (INSWV) (Belharrath et al. 1994; Kirk 2001; Kirk and Terry 2003; Cloyd 2009). Even though chemical insecticides are the most employed means to control WFT populations, several means are also considered (Grasselly 1996; Shelton et al. 2006). Among the alternatives, the use of beneficial insects has shown to be an efficient biological control agent against WFT. Predators are a promising means of controlling WFT, especially species belonging to the Anthocoridae family such as those of the genus Orius among which O. laevigatus, O. majuscules and O. tristicolor in greenhouses crop particularly cucumber, pepper, sweet pepper, and roses (Loomans and van Lenteren 1995; Parker et al. 1995; Elimem and Chermiti 2012). The predatory bug O. laevigatus is the most used species to control F. occidentalis in pepper crop greenhouses in many Mediterranean and Atlantic countries (Sánchez and Lacasa 2002). The aim of this study is to evaluate the efficiency of the local O. laevigatus strain collected from Chrysanthemum coronarium flowers and released at different doses and frequencies in pepper crop greenhouses.

Materials and methods

This work was carried out in 2011 at nine experimental greenhouses belonging to the Agricultural Support Station of Nebhana in the region of Monastir. Each greenhouse had an area of 500 m2 and contained four rows of plants, each formed by two lines of pepper. The experimental set up in all the greenhouses was a randomized complete block design, with each line divided into eight blocks. Each greenhouse was considered as an experimental unit apart and it was divided into blocks. One pepper plant was randomly chosen from each block and three flowers were taken from the different strata (upper, median and lower), making a total of 96 flowers per greenhouse. The first greenhouse G1 was considered as a control greenhouse where no releases were done to study F. occidentalis population dynamics. Predators of thrips were collected from flowers of C. coronarium that were growing in an uncultivated field at the High Institute of Agronomy of Chott-Mériem, Sousse, Tunisia. C. coronarium flowers were collected on April 27, May 04 and May 10, 2011 (1 day before each release). The flowers were then put into plastic bags to prevent the insects from escaping. In the laboratory, predators were collected using an aspirator and then placed in special vials designed for predator releases. C. coronarium pollen was added to the vials to ensure that the predators had enough food until their release. Polystyrene was also added to the vials to prevent pollen crowding and predator stifling. Predator identification was done according to Pericart (1972)’s identification keys. The release frequencies, applied doses and dates are presented in Table 1.
Table 1

Dates, doses and frequencies of O. Laevigatus releases in the pepper crop greenhouses

Greenhouses

Area (m2)

Releases frequencies

Number of Individual

Doses (individual/m2)

G1

500

G2

500

3

500

1

G3

500

3

500

1

G4

500

2

500

1

G5

500

2

500

1

G6

500

1

500

1

G7

500

1

500

1

G8

500

3

250

0.5

G9

500

3

250

0.5

Results

The obtained results in control greenhouse G1 showed a typical WFT population dynamic. Thrips number tended to increase progressively approaching the hot season to reach a mean number of 4.43 and 5.82 thrips per flower, respectively, on June 02 and 09, 2011 (Fig. 1). In greenhouses G2 and G3, where O. laevigatus was released three times at a dose of 1 individual per m2, the WFT populations increased progressively from the beginning of the study till the end of April. However, 1 week after the first release, thrips number in both greenhouses decreased. This decline was maintained after the second and third release to reach 0.08 and 0.04 on June 09, 2011, respectively, in G2 and G3. Regarding predator, a continuous increase in both greenhouses from the first week after the first release till the end of study has been reported (Figs. 2, 3). Regarding greenhouses G4 and G5, where 1 individual per m2 was released twice, thrips population decreased 1 week after the first release till reaching 0.04 and 0.06 thrips per flower on June 09, 2011, respectively, in G4 and G5. O. laevigatus populations showed a continuous increase starting with their first release till the end of the study (Figs. 4, 5). Concerning greenhouses G6 and G7, where one individual per m2 was released once, thrips population decreased 3 weeks after the first release in G6. In G7, WFT showed a decline 1 week after the first release and it increased later. However, it dropped again 4 weeks after the first release. The other greenhouses, O. laevigatus populations increased slowly at first and then they reached a mean numbers around 0.3 predator per flower on June 09, 2011 (Figs. 6,  7).
Fig. 1

Thrips populations in the control greenhouse G1

Fig. 2

Thrips and O. laevigatus populations in greenhouse G2 (R1: 1st release, R2: 2nd release, R3: 3rd release)

Fig. 3

Thrips and O. laevigatus populations in greenhouse G3 (R1: 1st release, R2: 2nd release, R3: 3rd release)

Fig. 4

Thrips and O. laevigatus populations in greenhouse G4 (R1: 1st release, R2: 2nd release)

Fig. 5

Thrips and O. laevigatus populations in greenhouse G5 (R1: 1st release, R2: 2nd release)

Fig. 6

Thrips and O. laevigatus populations in greenhouse G6 (R1: 1st release)

Fig. 7

Thrips and O. laevigatus populations in greenhouse G7 (R1: 1st release)

In greenhouses G8 and G9, where half a dose of the predator was applied, results showed that the F. occidentalis population did not decrease 1 week after the first release. However, abundances started to decline 1 week after the third release. As for the development of predator populations, O. laevigatus appeared 1 week after the first release with low mean numbers and it continued to increase slowly till reaching values surrounding 0.3 individuals per m2 in both greenhouses (Figs. 8, 9).
Fig. 8

Thrips and O. laevigatus populations in greenhouse G8 (R1: 1st release, R2: 2nd release, R3: 3rd release)

Fig. 9

Thrips and O. laevigatus populations in greenhouse G9 (R1: 1st release, R2: 2nd release, R3: 3rd release)

Discussion

Monitoring of O. laevigatus local strain in all greenhouses showed a progressive increase of the population after each release. In fact, this proves that this local strain was successfully installed in all greenhouses regardless of doses or frequencies. Tommasini and Maini (2002) indicated that the appearance of the predator after each release confirms the establishment of the species. In addition, predator population did not stop increasing continually. In G2 and G3 where three releases were applied with a dose of 1 individual per m2 and G4 and G5 where two releases were done with the same dose, similar results were obtained with the same impact on F. occidentalis populations. This shows that two releases with 1 individual per m2 are enough to control thrips populations in pepper greenhouses. These results are consistent with those previously mentioned by Sanchez et al. (1997), showing that O. laevigatus must be released twice with a dose of 1 individual per m2 to guarantee its installation in the greenhouses and the control of the WFT. The same authors mentioned that the first release has an impact on thrips population causing thus its decrease, while the second release is recommended to improve predator installation in the greenhouse. Sanchez et al. (1997) indicated that the release of O. laevigatus twice causes its installation which is then improved by the second release. In fact, this concords with results found in greenhouses G8 and G9. It is recommended to substitute the use of pesticides by the release of the predator that may reduce thrips populations to very low amounts.

Within the same context, Tommasini and Maini (2002) reported that in the case of use of Orius species local strains such as O. laevigatus at a dose of 1 individual per m2, the predator number was higher in pepper flowers than those of the WFT. In fact, this was observed in greenhouses G2, G3, G4 and G5. These results prove the effectiveness of the local strain and its ability to control the WFT populations. Chambers et al. (1993) found that the release of 1 individual of O. laevigatus per pepper plant may guarantee thrips population’s control. Weintraub et al. (2011) indicated that O. laevigatus was able to reduce thrips populations with no differences between the doses of 2 and 6 individuals per m2 and that it is able to control the WFT with very low doses. On the other hand, it must be noted that different releases and doses employed during this study did not only make WFT populations decrease but they maintained it under low mean values. Comparison between this biological means of control and other ones such as the use of chemical pesticides or natural pesticides showed that thrips populations increase later after products’ application. Elimem and Chermiti (2011) mentioned that F. occidentalis populations increase again just 1 week after natural and chemical pesticides application. Wang et al. (2001) obtained similar results. They found that WFT populations decrease immediately after chemical pesticide applications and increase later, while greenhouses treated by O. strigicollis showed a progressive decrease of thrips number without increasing again.

Notes

Acknowledgements

The authors would like to thank the staff and directors of the Agricultural Support Station of Nebhana in the region of Monastir who kindly accepted to conduct the study in their greenhouses.

Compliance with ethical standards

Conflict of interest

The authors whose names are listed certify that they have no affiliations with or involvement in any organization or entity with any financial or non-financial interest in the subject matter or materials discussed in this manuscript.

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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  • Mohamed Elimem
    • 1
  • Ahlem Harbi
    • 2
  • Essia Limem-Sellemi
    • 2
  • Soukaina Ben Othmen
    • 2
  • Brahim Chermiti
    • 2
  1. 1.Ecole Supérieur D’Agriculture de MograneMograneTunisia
  2. 2.Institut Supérieur Agronomique de Chott-MariemChott-MariemTunisia

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