Performance of the predator Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) on plastic greenhouse pepper sprayed vs unsprayed pine pollen

From sucking pests, a one of the most known important pest, flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in protected vegetable cultivation in Turkey. The predatory mite, Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) was used to control to suppress the pest population especially on pepper plant in more than 50 countries worldwide since 2005. According the literature on A. swirskii , it can survive on pepper plants sprayed with pine and cattail pollen, where there is no prey. Therefore, it was expected that population of a well-known pollenophagous species, A. swirskii can be increased by spraying pine pollen to peppers. Pollen was diluted in water and sprayed on the plants with backpack sprayer at the dose of 5 kg ha -1 . In both experiments, the thrips populations was less than 2 per flower in the predatory mite released plots (with predators and without pollen and with predators and pine pollen) throughout the experiments. Contrary to our expectation, the provision of pine pollen to peppers did not result in increased number of the predatory mite. Our results clearly show that, the pine pollen was less suitable food source than the pepper own pollen for the predatory mite. Some study on pine pollen as a non-prey food source for A. swirskii with a full analysis of constituents is necessary.


Introduction
Either in open field or protected vegetable cultivation, one of the most important pest group is sucking insects, such as Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), Bemisia spp.Quaintance & Baker (Hemiptera: Aleyrodidae) and Tetranychus urticae Koch (Acarina: Tetranychidae) that have short life span and high reproductive potential.Growers has been used intensively insecticides and acaricides against these pests.Solution of the problems based on sustainable agriculture system especially via biological control tactic is a challenge for researchers and growers in all around the World.In the protected cultivation system, augmentative releases of mass-reared natural enemies to suppress the pest population has been a cleverly chosen as an alternative to the chemical control (van Lenteren and Bueno, 2003).Provision additional food sources, such as pollen to improve biocontrol efficacy in greenhouse has been known by the researchers for a long time.
The Pollen availably have a strong effect on establishing of Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) population in greenhouse crops even before pest are present (Bolckmans et al., 2005).The plants families including Betulaceae and Pinaceae are important pollen providers for generalist predatory mite species in spring, especially when prey abundance was poor (Addison et al., 2000).
A generalist predatory mite, A. swirskii feeds on different insects and mites, however, it is an important biological control agent of the whiteflies, Bemisia tabaci and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) and the Western flower thrips, F. occidentalis (Pergande) (Thysanoptera: Thripidae) (Cock et al., 2010;Gerson and Weintraub, 2012).In pepper grown greenhouse, A. swirskii has effectively provided long term control of western flower thrips (Calvo et al., 2012;Bolckmans et al., 2005).Previous studies carried out by Kütük and Yiğit (2011) and Kumar et al. (2015) found that this predatory mite A. swirskii can survive on pepper plants sprayed with pine and cattail pollen, respectively, where there is no prey.Therefore, we hypothesized that spraying pine pollen with A. swirskii release on the flowering peppers to increase A. swirskii population to a greater extent than the predatory mite releases.So, the effect of the provision of pine pollen on the dynamics of a predatory mite-pollen system was studied under greenhouse conditions.

Cultures
Predatory mite, A. swirskii, population were provided from Koppert prior to this study.A. swirskii was reared on Carpoglyphus lactis (Acari: Acaridae) in a climate room (25°C, 60% RH, 14/10 daylight) at the Biological Control Research Station in Adana, Turkey, according to developed method by Overmeer (1985).

Pollen source
Plants families including Betulaceae and Pinaceae were used to obtain their pollen for the generalist predatory mite in spring (Addison et al., 2000).The collected pollens used in the study from pine (Pinus brutia) plants, where they are at Toros Mountain were dried in the oven for 3 days at 37ºC and kept in a refrigerator at -10ºC.

Plastic greenhouse experiments
A heated (min.10°C during winter months) and an unheated plastic high tunnels (min.0°C during winter months) belongs to the Adana Biological Control Research Institute were used to carry out experiments.Peppers were planted in rows, each with 10 plants, on 16 th of September 2009.The maintenance of the pepper plants was done according to the practices of growers.First, plastic tunnels were separated into three sections, then in each section was separated into 5 subdivisions (having 3 rows).The experiment was designed in a completely randomized block with 3 treatments each replicated 5 times: (A) 50 A. swirskii m 2 + pollen sprayed at 5 kg ha -1 ; (B) 50 A. swirskii m 2 alone, (C) no A. swirskii and all plants were sprayed with water only.
Amblyseius swirskii (nymphs and adults) were released directly on different plants in treatments A and B on 17 th of October 2009 (when the plants started flowering).Five plots treated with "treatment A", plants were first sprayed with pine pollen before releasing the predatory mite.Pollen was diluted in water and sprayed on the plants with backpack sprayer.Pollen spray was repeated three times at 27 October, 7 November, and 17 November.

Sampling started on 6
th of November 2009 and continued weekly to monitor thrips and predators.Totally 28 and 18 sampling were conducted from 6 November 2009 in heated and unheated plastic tunnels, respectively.Nymphal and adult stages of F. occidentalis and all stages of A. swirskii on each sample leaves and flowers (10 leaves and 5 flowers from each section) collected randomly was recorded under a binocular microscope at 30 times magnification in the laboratory.It is provided an average estimation of thrips and predator density per section.HOBO (Onset Computer, Bourne, MA, USA) data loggers were used to monitor temperature and relative humidity during the experiment.Compatible insecticides: chlorantraniliprole (Altacor) and pymetrozine (Plenum) against Spodoptera littoralis and Aphis spp. with A. swirskii were used in the plastic greenhouses used for both experiments.Both insecticides do not negatively affect A. swirskii (Kütük and Karacaoğlu, 2012).

Data analysis
Differences in the number of thrips were calculated by analysis of variance and means were separated using Duncan's multiple comparison test (P≤0.05)at each sampling date.Average numbers of thrips (leaf+flowers) and numbers of predatory mite (leaf + flowers) were subjected to Student's test (P≤0.05)presence or absence of pollen as factors.

Heated plastic greenhouse
Thrips densities were significantly different in the 3 treatments (without predatory mite and pollen; with predatory mite and without pollen and with predatory mite and pine pollen) at some dates (Table 1).Thrips, F. occidentalis, densities remained very low in release plots (with predatory mite and without pollen; with predatory mite and pine pollen) during the autumn and winter months.However, average thrips density increased rapidly on 30 th of November in the control plot.On 14 th of December, thrips density reached a peak level of 3.60 active stages per flower.This value exceeds the action threshold of 3 thrips per flower (Yücel et al., 2011;Keçeci and Gürkan, 2017).The thrips level then decreased to 2.40 thrips per flower on 4 th of January, after which a steadily decline in population occurred.The number of thrips per flower averaged 1-1.5 during February 1 to March 23 (Table 1).A very small increase was seen in thrips populations on 12 th of April, but they declined on 3 th of May due to the presence of naturally occurring Orius species in the flowers.The number of A. swirskii (all stages) recorded on plants with pollen (treatment A) was not significantly different than plants without pollen (Treatment B) (Figure 1; t (49) =-0.789;P= 0.434).

Unheated plastic greenhouse
Thrips densities were significantly different in the 3 treatments (without predatory mite and pollen, with predatory mite and without pollen and with predatory mite and pine pollen) at some date (Table 2).Predator densities were not significantly different between plants treated with pollen than those without pollen (Figure 2; t (43) =-0.1;P= 0.921).Also, there was no significant differences in thrips density between plants with pollen (treatment A) and without pollen (treatment B), (Figure 2; t (14) =-0.999;P= 0.335).
Thrips populations, which was less than 2 per flower throughout the experiments in the release plots (with predatory mite and without pollen and with predatory mite and pine pollen) incidence with an increase in predatory mite density in both experiment.These results show that thrips can be effectively controlled by predatory mite, A. swirskii on greenhouse grown peppers in the eastern Mediterranean region of Turkey.It has been known that A. swirskii effectively control F. occidentalis in greenhouse grown peppers (Calvo et al., 2012;Kutuk et al., 2011)).However, we would expect that spraying pine pollen with A. swirskii release on flowering peppers to increase the number of A. swirskii to a greater extent than predatory mite releases without pine pollen in both experiments.Contrary to our expectation, the provision of pine pollen to peppers did not result in increased number of the predatory mite.This predator is a well-known pollenophagous species, feeds on different insects and mites (Ragusa and Swirski, 1975;Goleva and Zebitz, 2013).The previous studies carried out by Kütük and Yiğit (2011) and Kumar et al. (2015) found this predatory mite was able to survive in the absence of prey on pepper plants sprayed with pine and cattail pollen, respectively.Figure 2. Effects of spraying pine pollen on the numbers of predatory mite, Amblyseius swirskii in unheated plastic greenhouse experiment.
Additionally, Bolckmans et al. (2005) suggested that A. swirskii is able to establish on flowering pepper in greenhouse without prey.When collaborated result of this study with the previous study carried by Kütük and Yiğit (2011), Kumar et al. (2015) and Bolckmans et al. (2005), pine pollen was less suitable food source than pollen own pepper plants for A. swirskii.Goleva and Zebitz (2013) suggested that A. swirskii can feed exclusively on pollen, but the nutritional value of pollens is significantly important for the performance of this predatory mite.However, the nutritional suitability of different pollens for A. swirskii is not sufficiently known yet.

Conclusion
Considering all these results, pollen own peppers is suitable food source to establish for A. swirskii in greenhouse grown pepper, additional pollen provision is not necessary.On the other hand, to obtain a better knowledge, the nutritional value of pine pollen as food source for A. swirskii with a full analysis of pine pollen constituents and the correlation of lifetable is necessary.

Table 1 .
Population dynamics of Frankliniella occidentalis on peppers treated with Amblyseius swirskii on pepper sprayed vs unsprayed pine pollen and control in heated plastic tunnel experiment *Means in rows followed by different small letters indicate significant differences among treatments at P ≤ 5% (ANOVA) Figure1.Effects of spraying pine pollen on the numbers of predatory mite, Amblyseius swirskii in heated plastic greenhouse experiment

Table 2 .
Population dynamics of Frankliniella occidentalis on peppers treated with Amblyseius swirskii on pepper sprayed vs unsprayed pine pollen and control in unheated plastic greenhouse experiment *Means in rows followed by different small letters indicate significant differences among treatments at P ≤ 5% (ANOVA)