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Article

Do Cultivar, Watering and Plant Distance Impact Aphids and Their Natural Enemies in Chili (Capsicum chinense Jacq.)?

by
András Lajos Juhász
and
Ágnes Szénási
*
Plant Protection Institute, Department of Integrated Plant Protection, Hungarian University of Agriculture and Life Sciences, 2100 Gödöllő, Hungary
*
Author to whom correspondence should be addressed.
Horticulturae 2024, 10(7), 697; https://doi.org/10.3390/horticulturae10070697 (registering DOI)
Submission received: 9 May 2024 / Revised: 26 June 2024 / Accepted: 27 June 2024 / Published: 2 July 2024
(This article belongs to the Section Insect Pest Management)
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Versions Notes

Abstract

:
Chilies are being increasingly favored worldwide, with an increasing growing area. As limited information is available about the population dynamic of arthropod communities in chilies under field conditions, the aim of our survey was to observe aphids and their natural enemies under various agrotechnological factors to improve IPM for chilies. The Yellow Scotch Bonnet (YSB) and Trinidad Scorpion Butch T (TSBT) chili varieties were investigated. Two plant spacings (30 vs. 40 and 40 vs. 60 cm in YSB and TSBT, respectively) and two watering rates (40 min/day; 20 min every second day) were applied with three replicates. Ten plants per plot/date were checked visually from July to September each year. In 2019, significantly more Chrysopidae eggs and significantly fewer Coccinellidae eggs were found under less watering. The number of Chrysopidae larvae and Coccinellidae pupae and larvae was significantly higher, whereas that of Chrysopidae eggs and Thomisidae individuals was significantly lower in the less-irrigated plots in 2021. In the same year, significantly more Coccinellidae adults were detected in the TSBT cultivar, and the number of Chrysopidae eggs and larvae and Coccinellidae pupae was significantly lower under decreased plant spacing. Predators preferred plots with an increased plant distance and plants with higher aphid pressure.

1. Introduction

Chilies are economically important crops that originated from Middle and South America and were used as herbs in ancient times [1]. They have multiple physiological effects. The vitamin (A, C, E), antioxidant, carotenoid and capsaicin content in their fruit is significant [2,3,4]. Capsaicin has a beneficial effect on the treatment of rheumatoid arthritis [5]. In addition, it is also useful as a painkiller and detoxicant and helps accelerate blood circulation and digestion [6].
Aphids are important pests of different crops worldwide, including chilies [7]. They feed on the juvenile parts of the plants, mostly on foliage, and plant growth is impaired by their damage [8]. Their activity also has a negative impact on flower fertilization [9]. Aphids develop via parthenogenesis with a short generation period, which leads to rapid population growth [10].
Coccinellids, especially larvae, are very voracious [11]. The average consumption of Coccinella septempunctata L. adults is 150 aphids/day. Larvae of this species can prey on 800 aphids during their lifetimes, and this value can reach 4000 in the case of some other ladybird species [12]. Ladybird larvae and adults find their prey randomly. The larvae spot the food by touching, whereas the adults can recognize it from a distance of 7–8 mm. After finding a prey organism, ladybird larvae may search through the whole plant. Ladybird beetles are less persistent; without successful contact, they leave the plant [13].
Green lacewings are important and abundant beneficial insects in agricultural areas all over the world [14]. Chrysopid larvae are also important aphidophagous insects. A single Chrysoperla carnea (Stephens) larva may consume 200–500 aphids during its development. The adults of this species feed on pollen, nectar and honeydew. Chrysopa septempunctata Wesmael larvae can prey on 400–500 aphid adults or up to 1000 younger aphid stages during their life. Adults of this species may destroy up to 40 aphids within 30 min [12].
Spiders are generalist predators and are important regulators of aphids in agro-ecosystems, reducing damage and improving plant health [15,16,17]. Species abundance and the individual number of spiders can be similar in agricultural areas and natural ecosystems [18,19]. The members of the Thomisidae family belong to the most important hunting spiders and prey mostly on insects such as Homoptera, Hemiptera, Thysanoptera, Lepidoptera and Coleoptera species [20].
According to the first principle of integrated pest management, important elements of pest control are adequate cultivation techniques, balanced watering practices and the protection and enhancement of beneficial organisms. The latter can reduce the occurrence of arthropod pests and the seriousness of damage [21].
Drip irrigation is an effective system that enables balanced water and nutrient supply, directly reducing the water deficit [22,23,24]. It is possible to increase the water use efficacy if plants are exposed to a given degree of water deficit in a developmental stage or during the vegetation period. However, this water deficit can directly impact fruit quality and phytonutrient concentration [25]; it can also result in poor plant conditions, which favors different pest organisms.
Chili pepper growth and yield are highly affected by plant and row spacing [26]. The manipulation of plant distance is an agrotechnical method that can be a tool for reducing pests [26]. The relative humidity is higher due to a lower plant distance, which can favor pathogens [27]. Setiawati et al. (2022) [28] observed that thrips damage was reduced by a decreased plant distance. Karungi et al. (2013) [29] found that under closer plant spacing, aphid and whitefly abundances were lower. According to Juhász et al. (2022) [30], plant spacing did not have any impact on the abundance of Thysanoptera and Orius individuals associated with chili flowers.
The research we have undertaken is very timely. Indeed, there is a lack of data concerning the impact of watering on the arthropod abundance and seasonal dynamic in chili. Furthermore, as only limited information is available concerning the population dynamic and density of arthropod communities in chili in temperate climates under different growing conditions, i.e., in the European region, the goal of this survey was to observe aphids and their natural enemies using various agrotechnological factors, to improve the growing practices and integrated pest management for chili in Europe.
Our hypotheses are as follows:
  • More aphids will be found on the cultivar Yellow Scotch Bonnet, as this variety has a bushier habit and yellow fruit. Denser foliage provides a higher humidity and protection for aphids;
  • In the more irrigated areas, more aphids will occur, due to juicier tissues;
  • More aphids will be present in the plots with smaller plant spacing because of the higher humidity and more uniform and denser foliage;
  • Due to the higher aphid pressure, there will be more predators in all of these cases.

2. Materials and Methods

2.1. Study Layout

The experiment was set up at the test area of the Institute of Horticultural Science, Hungarian University of Agriculture and Life Sciences, Gödöllő, Hungary (47.58 N, 19.37 E). There were 24 plots, whose size was arranged by the quantity of seedlings available. The same settings were implemented in both years. Nevertheless, in 2021, as a result of the low number of germinated plants and the unfavorable meteorological conditions in May (near-permanent cloud-covered sky and precipitation), the plot size and experimental field were smaller than in 2019.
The chili pepper (Capsicum chinense Jacq.) cultivars Trinidad Scorpion Butch T and Yellow Scotch Bonnet were planted in plots of 12.96 m2 (3.6 × 3.6 m) in 2019 and 2.16 m2 (1.8 m × 1.2 m) in 2021. Eight combinations of settings were applied, with three replicates. For each cultivar, two plant distances (following their habitual plant heights) and two watering rates were used. The water supply was managed using a drip irrigation system. According to the survey of O’Keefe and Palada (2002) [31], 61 cm was the optimal row distance for chili pepper; therefore, we applied a 60 cm row spacing for each cultivar.
The treatments were coded as follows:
  • C1: Trinidad Scorpion Butch T (TSBT);
  • C2: Yellow Scotch Bonnet (YSB);
  • C1PD1: Plant distance of 60 cm;
  • C1PD2: Plant distance of 40 cm;
  • C2PD1: Plant distance of 40 cm;
  • C2PD2: Plant distance of 30 cm;
  • W1: Watering daily, 40 min (7.33 L/m/day);
  • W2: Watering every second day, 20 min (3.66 L/m/two days).
Table 1 shows the arrangement of the experimental plots with the combinations of the different settings.
Sowing was performed in seedling trays on 12 March 2019 and 7 April 2021. The seeds were dressed with spores of the mycoparasite Pythium oligandrum in both years for the management of soil-borne pathogens.
The planting was conducted on 24 May 2019 and 25 June 2021. The harvest was made on 11–12 September 2019 and 11 October 2021. No pesticides were used during the vegetation periods.

2.2. Weather Data

Meteorological data (daily average, minimum and maximum temperature and rainfall) were derived from Meteoblue AG (Basel, Switzerland) (Figure 1). No statistical analysis of the weather data was made.

2.3. Properties of Investigated Cultivars

The Scoville Heat Unit (SHU) value of the Trinidad Scorpion Butch T ranges from 800,000 to 1,460,000 [32]; therefore, it is among the six hottest chilies worldwide [1]. The Trinidad Scorpion derives from Trinidad and Tobago. ‘Butch T’ refers to the Australian grower, Butch Taylor [33]. This cultivar can reach a 100–200 cm plant height, and it requires only 90–120 days for ripening [34]. Yellow Scotch Bonnet is a very frequent and popular chili in the Caribbean region. Its SHU value ranges from 200,000 to 350,000. It grows slowly, can reach a 50 cm plant height, and it starts to ripen after 160 days [35].

2.4. Monitoring Method

Observations started in early–late July and ended in early–late September, depending on the year. Each year, 10 plants per plot per date were randomly selected and carefully checked by visual observations. Observations were carried out almost, but not always, weekly. In both years, seven observations were recorded over eight weeks. In 2019, observations started on 7 July and ended on 4 September. In 2021, the first observation was conducted on 30 July and the last one on 24 September. The same plants were observed each time. The developmental stages of aphids and aphidophagous taxa were distinguished as follows:
  • Aphididae: individual;
  • Thomisidae: individual;
  • Chrysopidae: egg, larva, pupa, adult;
  • Coccinellidae: egg, larva, pupa, adult.

2.5. Statistical Analysis

The data analysis and aggregation were conducted using R [36] with the Rcmdr package [37]. Generalized linear models were applied to analyze the effect of cultivar, watering rate and plant distance as explanatory variables on the abundance of aphid (Aphididae), ladybird (Coccinellidae), green lacewing (Chrysopidae) and spider (Araneae: Thomisidae) individuals. A backward stepwise model selection was performed with ANOVA on the residuals, and removal of the non-significant explanatory variables. For all the hypothesis tests, a threshold of alpha = 5% was applied to control for a type I error. Nevertheless, the tests with the highest power possible (considering the assumptions) were applied, and thus we were able to eliminate the type II error. Thus, no p-value adjustment was used for multiple comparisons, as the primary comparisons were pre-specified and limited in number. In the event of a low number of individuals, Poisson models, or else Gaussian models, were used. Potential influential data points and assumptions of residual normality and homoscedasticity were tested using basic model diagnostic plots [38], including Q-Q plots and residuals vs. fitted values plots.

3. Results

3.1. Individual Number of Aphids and Their Natural Enemies by Settings

In total, 18,161 Aphididae individuals, 566 Chrysopidae eggs, 366 Chrysopidae larvae, 182 Coccinellidae eggs, 55 Coccinellidae larvae, 673 Coccinellidae pupae, 477 Coccinellidae adults and 1138 Thomisidae individuals were observed on chili plants in the two years. In 2019, Chrysopidae eggs were dominant, while in 2021, aphids, Thomisidae individuals and Coccinellidae pupae were the most abundant taxa (Table S1). The number of Chrysopidae pupae and adults was so small that we did not consider them.

3.1.1. Cultivar

In 2019, slightly more Coccinellidae eggs, larvae and adults and spiders were found on the Red Scorpion Butch T variety (C1); however, there were no significant differences among the cultivars (Figure 2A, Table 2). The numbers of Chrysopidae larvae and aphid individuals were similar on both cultivars (Figure 2B,C). Coccinellidae and Chrysopidae eggs and aphids were the most numerous taxa on the investigated cultivars (Figure 2A–C).
In 2021, Coccinellidae adults and Chrysopidae larvae were more abundant on the Yellow Scotch Bonnet cultivar (C2) (Figure 3A,B); however, the number of Coccinellidae pupa, Thomisidae and aphid individuals was higher on the Red Scorpion Butch T cultivar (C1) (Figure 3A–C). The number of Coccinellidae eggs, larvae and Chrysopidae eggs was very low and was similar on both varieties (Figure 3A,B). The abundances of the studied arthropod taxa did not differ between the cultivars.

3.1.2. Watering

In 2019, significantly more (p < 0.001) Coccinellidae eggs were found in the more watered plots (W1); however, the number of Coccinellidae larvae, pupae and adults was slightly higher under less watering (W2) (Figure 4A, Table 2). The number of Chrysopidae eggs was significantly higher (p < 0.001) in the less watered plots (W2) (Figure 4B, Table 2). More aphid individuals appeared with less watering, but there was no significant difference between the irrigation settings (Figure 4C, Table 2).
In 2021, the number of Coccinellidae eggs and larvae was similar in the watering treatments, although significantly more Coccinellidae pupae (p < 0.001) and adults (p < 0.001) were found with less watering (W2) (Figure 5A, Table 3). The number of Chrysopidae eggs was significantly higher (p < 0.001), and that of Chrysopidae larvae was significantly lower (p = 0.003), in the more irrigated plots (W1) (Figure 5B, Table 3). Aphids were more abundant under less watering (W2), but no significant difference was found between the irrigation treatments (Figure 5C, Table 3).

3.1.3. Plant Distance

As regards aphids and their predators in 2019, we could not find any significant differences between the plant distance settings. The most abundant taxa were Chrysopidae eggs and aphids (Figure 6A–C, Table 2).
In 2021, the number of Coccinellidae eggs and larvae was similar in the plant distance treatments (Figure 7A). The number of Coccinellidae pupae (p < 0.001) (Figure 7A), Chrysopidae eggs (p = 0.016) and larvae (p = 0.011) (Figure 7B) was significantly higher with an enlarged plant distance. In the same plots, more ladybird imagoes, spiders and aphids were found; however, there was no significant difference between treatments (Figure 7A–C, Table 3).
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Figure 7. Average individual numbers (+SE) of aphids and their natural enemies in studied plant distance settings for chili in 2021: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (PD1) Enlarged plant distance (60 vs. 40 cm); (PD2) reduced plant distance (40 vs. 30 cm). * Indicates significant differences between mean values (p < 0.05).
Figure 7. Average individual numbers (+SE) of aphids and their natural enemies in studied plant distance settings for chili in 2021: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (PD1) Enlarged plant distance (60 vs. 40 cm); (PD2) reduced plant distance (40 vs. 30 cm). * Indicates significant differences between mean values (p < 0.05).
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Table 3. Effects of cultivar, watering rate and plant distance on arthropod number in chili in 2021. Residual degrees of freedom were 28 in all tests.
Table 3. Effects of cultivar, watering rate and plant distance on arthropod number in chili in 2021. Residual degrees of freedom were 28 in all tests.
CultivarWateringPlant Distance
ArthropodsEffect
Estimate		Test
Statistics		p ValueEffect
Estimate		Test
Statistics		p ValueEffect
Estimate		Test
Statistics		p Value
Aphid individuals384.10F = 0.3870.538−798.3F = 1.7610.195718.10F = 0.7120.405
Coccinellidae eggs0.267Χ2 = 0.0710.789−0.665χ2 = 0.4450.5061.583χ2 = 2.6350.113
Coccinellidae larvae−0.896χ2 = 0.8050.3701.428χ2 = 2.0950.1530.705χ2 = 0.5020.481
Coccinellidae pupae4.225χ2 = 18.236<0.001−13.430χ2 = 216.970<0.00112.930χ2 = 205.90<0.001
Coccinellidae adults−5.403χ2 = 29.980<0.001−7.559χ2 = 62.160<0.0011.813χ2 = 3.3200.069
Chrysopidae eggs0.036χ2 = 0.0010.9714.374χ2 = 25.080<0.0012.398χ2 = 6.1900.016
Chrysopidae larvae−1.585χ2 = 2.5100.113−2.931χ2 = 8.6900.0032.514χ2 = 6.4100.011
Thomisidae individuals0.449χ2 = 0.2020.6532.205χ2 = 4.8780.0270.245χ2 = 0.0600.806

3.2. Seasonal Dynamics of Aphids and Their Natural Enemies by Settings

3.2.1. Cultivar

In 2019, on 21 August, Coccinellidae individuals were more numerous on the Red Scorpion Butch T cultivar (Figure 8A,B). As for both cultivars, no Chrysopidae larvae were found, except on 21 August; furthermore, the seasonal dynamics of Chrysopidae eggs and Thomisidae individuals were similar during the vegetation period (Figure 8C,D). Coccinellidae eggs, Chrysopidae eggs and spiders were the most abundant on 24 July on both varieties (Figure 8A–D). The aphid population peak occurred on 24 July on the Red Scorpion Butch T cultivar; additionally, in the case of the Yellow Scotch Bonnet cultivar, it occurred on 28 August. At the end of August and at the beginning of September, a little bit more Aphididae individuals appeared on the Yellow Scotch Bonnet plants (Figure 8E,F).
In 2021, the highest abundances of Coccinellidae pupae were found on 11 August in both treatments (Figure 9A,B). Chrysopidae eggs were the most numerous at the end of July (Figure 9C,D), on both cultivars. As for aphids, a population peak was noticed on 4 August, and after that, the number of these pests decreased continuously until the end of the vegetation period, in the case of each variety (Figure 9E,F).

3.2.2. Watering

In 2019, the population dynamics of the different developmental stages of Coccinellidae were similar, and from the end of August, the number of adults stagnated under both watering rates. At the beginning of July, mostly adults appeared; furthermore, the largest number of Coccinellidae eggs and adults occurred on 27 July in both watering settings (Figure 10A,B). The seasonal dynamics of Chrysopidae eggs and Thomisidae individuals were similar at both watering rates (Figure 10C,D). Except for one single date, the number of aphids was a little bit greater during the whole vegetation period in the less watered plots (Figure 10E,F).
In 2021, the highest abundance of Coccinellidae pupae and adults was found on 18 August under more watering, and on 11 August with less watering, respectively. Subsequently, a decrease in the number of these taxa was observed in both watering treatments. Coccinellidae imagoes were more numerous at each date and setting than larvae (Figure 11A,B). Until 11 August, the abundance of Chrysopidae larvae and Thomisidae individuals was similar with more frequent watering (Figure 11C). During the experiment, the aphid number was very low in the more watered plots in the whole growing season, and aphids constituted the most numerous organisms at a lower watering rate (Figure 11E,F).

3.2.3. Plant Distance

In 2019, by early August, the number of Coccinellidae eggs decreased in both treatments; however, by the beginning of September, it started to increase again in the plots with an enlarged plant distance (Figure 12A,B). The abundance of Chrysopidae eggs and Thomisidae individuals had a peak on 24 July (Figure 12C,D); furthermore, the number of aphids was similar in the vegetation period under the plant spacing settings (Figure 12E,F).
In 2021, for the plant spacing settings, the population dynamics of Coccinellidae pupae were fluctuating; additionally, more Coccinellidae adults were found than larvae (Figure 13A,B). On each date, Chrysopidae larvae were more abundant than eggs. From 18 August until the end of the growing season, spiders were dominant in both treatments (Figure 13C,D). In early August, the number of aphids was much higher at an enlarged plant distance, and after that, a decrease in the number of individuals was observed in the settings (Figure 13E,F).

4. Discussion

In contrast with our hypothesis, in both years, aphids preferred Trinidad Scorpion Butch T plants. Regarding the occurrence of aphids and Coccinellidae eggs, we found that in each growing season, the female ladybirds laid more eggs on the plants of the Trinidad Scorpion Butch T cultivar, which was more infected with aphids. As for Chrysopidae females, we observed this phenomenon only in 2021. However, spiders were more abundant on this cultivar, in both years. We thought that more aphids would occur on the Yellow Scotch Bonnet cultivar, which has yellow fruit, because it is known that these insects prefer the color yellow [9]. According to our results, the chili cultivars investigated had no effect on the abundances of aphids and of their natural enemies. Therefore, it is necessary to prioritize other characteristics of cultivation and market demand when choosing a chili cultivar.
We hypothesized that in the more irrigated areas, more aphids would occur, due to juicier tissues. Quite the opposite, aphid pressure was always higher in the less watered plots. Accordingly, Hluchý et al. (2007) [39] reported that dry growing areas are favorable for the occurrence and damage of aphid species such as Aphis grossulariae Kaltenbach, Aphis schneideri (Börner), Aphis idaei v.d. Goot and Cryptomyzus ribis L. Similarly with our results, Juhász et al. (2022) [30] observed that other sucking insects, namely, phytophagous thrips adults, were also more numerous under less irrigation in 2019. In contrast, González-Zamora et al. (2021) [40] found no influence of irrigation on the population of Hyalopterus amygdali (Blanchard) in almond.
Regarding the population dynamics of aphids and the amount of precipitation in 2019, it rained for several days in the middle of July, and after that the number of aphids decreased. There was longer rain at the end of July and at the beginning of August, and presumably as a result, the abundance of aphids went down in the first decade of August. In 2021, at the beginning of August, the number of aphids increased because of the decreasing temperature before the rain, and then dropped as a result of the heavy rain. In contrast, Blanchard et al. (2019) [41] observed that an increase in average temperature enhanced the abundance of many aphid species.
Significantly more Chrysopidae eggs were found in 2019 under less watering and in 2021 under more watering. Additionally, in 2019, the number of Coccinellidae eggs was significantly higher in the more watered plots. Consequently, in both years, the irrigation setting affected Chrysopidae females, and, in 2019, it affected Coccinellidae females during oviposition. In 2021, watering had an impact on the occurrence of Chrysopidae larvae and Coccinellidae pupae and adults, because their numbers were significantly higher with less watering. As for spiders, they preferred the more watered plants both years, but no significant difference was found between the watering treatments.
No coherence was found between the number of Chrysopidae eggs and aphid individuals, while both years, more Chrysopidae larvae were detected in the less watered plots, where more aphids were present. Similarly, Juhász et al. (2022) [30] observed that predatory thrips adults and their prey also preferred less irrigation. In contrast, González-Zamora et al. (2021) [40] did not detect any influence of irrigation treatment on Chrysopidae. In both years, more Coccinellidae larvae and adults occurred in the less watered plots, in which the aphid pressure was higher. In contrast, Pérez-Fuertes et al. (2015) [42] found significantly more Aphididae and Coccinellidae individuals in an irrigated wheat field compared to fields without irrigation.
According to our hypothesis, more aphids were present in the plots with smaller plant spacing, but only in 2019. However, in this year, almost all predators were more numerous under an enlarged plant spacing. A smaller plant spacing provides a higher humidity, and the optimal relative air humidity for aphids ranges from 75% to 85% [43]. In 2021, the plant distance setting affected the occurrence of Chrysopidae eggs and larvae and Coccinellidae pupae. Consequently, their numbers were significantly higher in the plots with an enlarged plant distance.
In 2021, regarding plant distance, we found more ladybird eggs, in addition to a higher number of aphids. Female ladybirds lay their eggs near aphid colonies; thus, the larvae can feed shortly after hatching [44]. In parallel with this, in our trials, Coccinellidae females preferred plants with a higher abundance of aphids. More ladybird pupae were detected in both years in those treatments, in which the aphid infestation was higher. Similarly, Thangjam et al. (2020) [45] found that the peak of the Coccinellidae population coincided with the maximum number of aphids in Capsicum chinense.
Plots with larger plant distances were chosen for egg laying by Chrysopidae females, whereas Nasreen et al. (2000) [46] reported that more lacewing eggs were observed under reduced plant spacing in cotton.
In both years, Thomisidae individuals preferred plots with a higher plant distance. With regards to the population dynamics of the spiders, we concluded that their abundance fluctuated throughout the experiment, but it was stable. This supports the observation that polyphagous predators are less affected by a rapid decline in prey numbers than specialist predators [47].
Coccinellids may indirectly reduce the number of aphids; their presence pressures these pests to leave the plant. For instance, C. septempunctata reduced the aphid number on the plant not only by predation but simply by its presence [48]. The effectiveness of ladybirds can be reduced by two factors. The development of Coccinellids is disrupted by a limited quantity of food. This can occur if the oviposition of the female ladybirds is too late, compared to the appearance of aphid colonies. The other case is when there are too many coccinellid larvae. Due to the presence of many larvae, the number of aphids can easily drop to such an extent that a lack of food can occur [49].
According to the observations of Altieri et al. (2001) [50] and Tscharntke et al. (2012) [51], in smaller cultivated areas, farmers with more diverse economies rely more on natural enemies, biological pest control methods and the opportunities that arise from them, while in large-scale, monoculture farming systems, growers rely more on chemical pest control methods.
The originality of our effort is that such research about aphids and their natural enemies in chili had not been previously investigated in the European region. Little is known about the density and population dynamics of these organisms associated with chilies; furthermore, the literature data on different water rates and plant distances concerning chilies are also limited.
In the following years, the impact of predatory insects on natural habitats and agricultural crops should receive increasing attention [52]. The biological diversity of agroecosystems promotes the success of pest control, which can significantly reduce the reliance on chemical insecticides [53,54]. However, further studies on other cultivars and growing conditions should also be assessed, based on different environmental conditions, seasons and soil types.

5. Conclusions

The natural enemies of aphids clearly preferred the plots with a higher plant distance. To promote these organisms, a higher plant spacing can be recommended. Predators visited plants with a higher aphid pressure. Accordingly, this phenomenon does not depend on the irrigation frequency but on the location of the prey organisms.
This study was conducted over two years. It is obvious that such a short period constitutes specific constraints, both in the research operation itself and in the interpretation of the results. The difficulty is nearly insurmountable when, as this is the case, divergent, or even some apparently contradictory, results are obtained. The research team is conscious of the problem induced by the scarcity of the time. An additional one-year research period could lead to some new findings, whose analysis could permit some well-founded conclusions regarding correlations between aphids and their natural enemies. In the future, it may be worth investigating the influence of the weather.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae10070697/s1, Table S1: Aggregated individual numbers of arthropods occurring on chili pepper in Hungary during cultivation periods.

Author Contributions

Conceptualization, Á.S. and A.L.J.; methodology, Á.S. and A.L.J.; investigation, A.L.J.; data curation, A.L.J.; writing—original draft preparation, Á.S. and A.L.J.; writing—review and editing, Á.S. and A.L.J.; visualization, A.L.J. and Á.S.; supervision, Á.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Acknowledgments

We kindly thank all the people involved for their contributions to the data collection.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Daily average (Av.), minimum (Min.) and maximum (Max.) air temperature and rainfall (RF) data for cultivation periods 2019 and 2021.
Figure 1. Daily average (Av.), minimum (Min.) and maximum (Max.) air temperature and rainfall (RF) data for cultivation periods 2019 and 2021.
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Figure 2. Average individual numbers (+SE) of aphids and their natural enemies on studied chili cultivars in 2019: (A) Coccinellidae. (B). Chrysopidae and Thomisidae. (C) Aphididae. (C1) Trinidad Scorpion Butch T; (C2) Yellow Scotch Bonnet.
Figure 2. Average individual numbers (+SE) of aphids and their natural enemies on studied chili cultivars in 2019: (A) Coccinellidae. (B). Chrysopidae and Thomisidae. (C) Aphididae. (C1) Trinidad Scorpion Butch T; (C2) Yellow Scotch Bonnet.
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Figure 3. Average individual numbers (+ SE) of aphids and their natural enemies on studied chili cultivars in 2021: (A) Coccinellidae. (B). Chrysopidae and Thomisidae. (C) Aphididae. (C1) Trinidad Scorpion Butch T; (C2) Yellow Scotch Bonnet.
Figure 3. Average individual numbers (+ SE) of aphids and their natural enemies on studied chili cultivars in 2021: (A) Coccinellidae. (B). Chrysopidae and Thomisidae. (C) Aphididae. (C1) Trinidad Scorpion Butch T; (C2) Yellow Scotch Bonnet.
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Figure 4. Average individual numbers (+SE) of aphids and their natural enemies in studied watering settings for chili in 2019: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (W1) Watering daily, 40 min; (W2) watering every second day, 20 min. * Indicates significant differences between mean values (p < 0.05).
Figure 4. Average individual numbers (+SE) of aphids and their natural enemies in studied watering settings for chili in 2019: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (W1) Watering daily, 40 min; (W2) watering every second day, 20 min. * Indicates significant differences between mean values (p < 0.05).
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Figure 5. Average individual numbers (+SE) of aphids and their natural enemies in studied watering settings for chili in 2021: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (W1) Watering daily, 40 min; (W2) watering every second day, 20 min. * Indicates significant differences between mean values (p < 0.05).
Figure 5. Average individual numbers (+SE) of aphids and their natural enemies in studied watering settings for chili in 2021: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (W1) Watering daily, 40 min; (W2) watering every second day, 20 min. * Indicates significant differences between mean values (p < 0.05).
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Figure 6. Average individual numbers (+SE) of aphids and their natural enemies in studied plant distance settings for chili in 2019: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (PD1) Enlarged plant distance (60 vs. 40 cm); (PD2) reduced plant distance (40 vs. 30 cm).
Figure 6. Average individual numbers (+SE) of aphids and their natural enemies in studied plant distance settings for chili in 2019: (A) Coccinellidae. (B) Chrysopidae and Thomisidae. (C) Aphididae. (PD1) Enlarged plant distance (60 vs. 40 cm); (PD2) reduced plant distance (40 vs. 30 cm).
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Figure 8. Seasonal dynamics of aphids and their natural enemies for studied chili cultivars in 2019. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae.
Figure 8. Seasonal dynamics of aphids and their natural enemies for studied chili cultivars in 2019. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae.
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Figure 9. Seasonal dynamics of aphids and their natural enemies for studied chili cultivars in 2021. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae.
Figure 9. Seasonal dynamics of aphids and their natural enemies for studied chili cultivars in 2021. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae.
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Figure 10. Seasonal dynamics of aphids and their natural enemies in the studied watering settings for chili in 2019. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (More watering) Watering daily, 40 min; (Less Watering) watering every second day, 20 min.
Figure 10. Seasonal dynamics of aphids and their natural enemies in the studied watering settings for chili in 2019. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (More watering) Watering daily, 40 min; (Less Watering) watering every second day, 20 min.
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Figure 11. Seasonal dynamics of aphids and their natural enemies in studied watering settings for chili in 2021. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (More Watering) Watering daily, 40 min; (Less Watering) watering every second day, 20 min.
Figure 11. Seasonal dynamics of aphids and their natural enemies in studied watering settings for chili in 2021. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (More Watering) Watering daily, 40 min; (Less Watering) watering every second day, 20 min.
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Figure 12. Seasonal dynamics of aphids and their natural enemies in studied plant distance settings for chili in 2019. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (Enlarged Plant Distance) 60 vs. 40 cm; (Reduced Plant Distance) 40 vs. 30 cm.
Figure 12. Seasonal dynamics of aphids and their natural enemies in studied plant distance settings for chili in 2019. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (Enlarged Plant Distance) 60 vs. 40 cm; (Reduced Plant Distance) 40 vs. 30 cm.
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Figure 13. Seasonal dynamics of aphids and their natural enemies in studied plant distance settings for chili in 2021. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (Enlarged Plant Distance) 60 vs. 40 cm; (Reduced Plant Distance) 40 vs. 30 cm.
Figure 13. Seasonal dynamics of aphids and their natural enemies in studied plant distance settings for chili in 2021. (A,B) Coccinellidae. (C,D) Chrysopidae and Thomisidae. (E,F) Aphididae. (Enlarged Plant Distance) 60 vs. 40 cm; (Reduced Plant Distance) 40 vs. 30 cm.
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Table 1. A study map with the arrangement of the experimental plots for chili in 2019 and 2021.
Table 1. A study map with the arrangement of the experimental plots for chili in 2019 and 2021.
C1PD1W1C2PD1W1C1PD1W1C1PD2W1C2PD1W1C1PD2W1
C1PD1W1C1PD2W1C2PD2W1C2PD1W1C2PD2W1C2PD2W1
C2PD2W2C2PD1W2C1PD2W2C1PD1W2C1PD2W2C1PD1W2
C1PD2W2C2PD1W2C1PD1W2C2PD1W2C2PD2W2C2PD2W2
Note: Trinidad Scorpion Butch T (C1), Yellow Scotch Bonnet (C2), enlarged plant spacing (PD1) reduced plant spacing (PD2), irrigation daily, 40 min (W1), irrigation every second day, 20 min (W2).
Table 2. Effects of cultivar, watering rate and plant distance on arthropod number in chili in 2019. Residual degrees of freedom were 26 in all tests.
Table 2. Effects of cultivar, watering rate and plant distance on arthropod number in chili in 2019. Residual degrees of freedom were 26 in all tests.
CultivarWateringPlant Distance
ArthropodsEffect
Estimate		Test
Statistics		p ValueEffect
Estimate		Test
Statistics		p ValueEffect
Estimate		Test
Statistics		p Value
Aphid individuals0.071F = 0.00050.982−4.429F = 2.0470.164−0.646F = 0.0400.84
Coccinellidae eggs0.296Χ2 = 0.0900.7674.359χ2 = 20.450<0.001−0.286χ2 = 0.0900.767
Coccinellidae larvae1.197χ2 = 1.5290.231−1.462χ2 = 2.3060.1430.286χ2 = 0.0810.775
Coccinellidae pupae−1.368χ2 = 2.3820.171−0.444χ2 = 0.2010.656−0.287χ2 = 0.0830.773
Coccinellidae adults1.185χ2 = 1.4250.236−1.19χ2 = 1.4270.2340.334χ2 = 0.1110.738
Chrysopidae eggs−0.995χ2 = 0.9900.320−3.090χ2 = 9.6400.0020.197χ2 = 0.0400.844
Chrysopidae larvae−0.143χ2 = 0.0200.886−0.005χ2 = 5.5450.9960.143χ2 = 0.0200.886
Thomisidae individuals−1.075χ2 = 1.1940.282−0.277χ2 = 0.0770.7817−0.573χ2 = 0.3350.566
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Juhász, A.L.; Szénási, Á. Do Cultivar, Watering and Plant Distance Impact Aphids and Their Natural Enemies in Chili (Capsicum chinense Jacq.)? Horticulturae 2024, 10, 697. https://doi.org/10.3390/horticulturae10070697

AMA Style

Juhász AL, Szénási Á. Do Cultivar, Watering and Plant Distance Impact Aphids and Their Natural Enemies in Chili (Capsicum chinense Jacq.)? Horticulturae. 2024; 10(7):697. https://doi.org/10.3390/horticulturae10070697

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Juhász, András Lajos, and Ágnes Szénási. 2024. "Do Cultivar, Watering and Plant Distance Impact Aphids and Their Natural Enemies in Chili (Capsicum chinense Jacq.)?" Horticulturae 10, no. 7: 697. https://doi.org/10.3390/horticulturae10070697

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