Introduction
Peach leaf curl aphid, Brachycaudus helichrysi (Kaltenbach) (Hemiptera: Aphididae), is one of the most destructive pests of regular occurrence and a major limiting factor in the successful cultivation of plum (Sharma and Khokhar, Reference Sharma and Khokhar2018; Singh, Reference Singh2021). It poses a significant threat to plum cultivation in temperate regions of the world, including Himachal Pradesh in India (Arora et al., Reference Arora, Gupta and Bali2009). As a primary pest of stone fruits, this aphid species can cause substantial economic losses by feeding on plant sap and transmitting viral diseases. Its infestation level can surpass 50% if timely control measures are not implemented (Gupta et al., Reference Gupta, Singh, Thakur and Bhatia2017). High incidence of this pest has been reported to cause a significant reduction in leaf area and total chlorophyll content, with a marked decrease in fresh and dry leaf weight (Chandel et al., Reference Chandel, Thakur, Gupta and Kumar2001). Understanding the population dynamics of B. helichrysi on different plum cultivars is crucial for devising effective pest management strategies and ensuring sustainable fruit production.
Previous research has highlighted the seasonal activity patterns and population dynamics of B. helichrysi in temperate fruit orchards (Gupta, Reference Gupta2013). Studies conducted in similar agro-climatic conditions have documented the initiation of aphid activity in early spring, coinciding with the warming weather conditions and vegetative growth stages of fruit trees. Subsequent population growth peaks during the pre- and post-blooming periods, followed by a decline as environmental conditions become less favourable or due to natural biological control mechanisms, have also been documented (Sharma and Khokhar, Reference Sharma and Khokhar2018). The population dynamics of B. helichrysi can vary significantly among plum cultivars, influenced by genetic factors, plant characteristics, and environmental conditions. Life tables provide detailed insect individual and population information for developing integrated pest management strategies and screening insect-resistant plant species (Chi et al., Reference Chi, You, Athhan, Smith, Kavousi, Özgökçe, Güncan, Tuan, Abaei, Athhan, Saska and Gökçe2020; Zhang et al., Reference Zhang, Zhao and Keyhani2024). A higher fecundity rate and shorter developmental duration for an insect are typically observed on suitable host plants. In this context, the present study investigated the population dynamics of B. helichrysi on different plum cultivars in Himachal Pradesh, focusing on the fluctuation of aphid populations over time and its correlation with total phenolic compounds present in different cultivars. Using aphid incidence data alongside phenolic compound measurements, the study aims to characterise infestation severity in various plum cultivars and identify those with phenolic-mediated resistance to B. helichrysi. Drawing on scientific literature and empirical data, this study contributes to a comprehensive understanding of aphid–plant interactions in temperate fruit orchards. The findings will inform integrated pest management strategies tailored to the specific needs of plum cultivation in Himachal Pradesh, thereby promoting sustainable fruit production and ensuring food security in the region. Through this research, we aim to address the knowledge gaps regarding seasonal incidence, aphid population dynamics, and phenolic-mediated resistance in plum cultivars, providing valuable insights for orchard management and pest control in temperate regions.
Material and methods
Developmental and reproductive biology of B. helichrysi life stages reared on different cultivars of Prunus domestica
The present study was conducted at the Biocontrol Research Laboratory, Department of Entomology, Dr. YS Parmar University of Horticulture and Forestry, Nauni, Solan, Himachal Pradesh, India (1275 m above mean sea level; 31.28°N; 76.94°E). All experiments were conducted in an environmentally controlled rearing room maintained at 25 ± 0.5°C, 70 ± 5% relative humidity, and a 14L:10D photoperiod. Six different plum cultivars (Black Amber, Friar, Fortune, Angeleno, Santa Rosa, and Red Beaut) were employed for rearing B. helichrysi. The aphid species were reared on each cultivar separately in cages (43.75 × 43.75 × 50 cm) under laboratory-controlled conditions (26 ± 2°C, 65 ± 5% RH, and L14:D10 photoperiod), and fresh leaves were provided on a daily basis (Khoso et al., Reference Khoso, Khan and Ahmed2019).
Population growth parameters
Life-fertility tables were constructed for B. helichrysi based on daily observations of individual survival, developmental stage transitions, and fecundity across dietary treatments. Demographic or population growth parameters were estimated using the TWO-SEX-MS Chart software (Chi, Reference Chi2022; Chi et al., Reference Chi, Guncan, Kavousi, Gharakhani, Atlihan, Ozgokce, Shirazi, Amir-maafi, Maroufpoor and Taghizadeh2022), which applies the age-stage, two-sex life table theory (Chi and Liu, Reference Chi and Liu1985; Chi, Reference Chi1988; Chi et al., Reference Chi, Guncan, Kavousi, Gharakhani, Atlihan, Ozgokce, Shirazi, Amir-maafi, Maroufpoor and Taghizadeh2022). Means and standard errors (SE) of these parameters across different cohorts were computed through 100,000 bootstrap replications, as implemented within the software (Efron and Tibshirani, Reference Efron and Tibshirani1993; Huang and Chi, Reference Huang and Chi2012; Chi et al., Reference Chi, Guncan, Kavousi, Gharakhani, Atlihan, Ozgokce, Shirazi, Amir-maafi, Maroufpoor and Taghizadeh2022).
Seasonal incidence of B. helichrysi on the six different cultivars of P. domestica
The studies were carried out at a farmer’s field in Thunag, Mandi, which is located in a temperate zone at an altitude of around 1900 meters (fig. 1). The field studies were carried out in well-managed plum orchards. All the recommended package of practices was followed except for insecticidal application. The experiment was laid out in a randomised block design. The trial was conducted on six main plum cultivars of the region, namely Black Amber, Friar, Fortune, Angeleno, Santa Rosa, and Red Beaut, for the study of seasonal abundance of the peach leaf curl aphid, B. helichrysi (Kaltenbach). Three plum trees per cultivar were randomly selected, and aphid populations were recorded weekly by counting individuals on 10 randomly selected leaves per tree. Leaves were sampled from upper, middle, and lower canopy strata across all cardinal directions to ensure representative coverage. Observations were conducted in situ (in the field) during the peak infestation (February–April 2023), commencing from the first appearance of the pest.
Geographical location of the orchard for the field study of Brachycaudus helichrysi incidence on different cultivars of Prunus domestica.
Figure 1 Long description
The map includes three sections. The main section is a satellite view highlighting the study site with a yellow boundary, located in a forested and agricultural area. The top right section shows a map of India with Himachal Pradesh marked, indicating the broader location of the study site. The bottom right section provides a topographic map of the region, showing elevation and terrain features. The legend identifies the yellow boundary as the 'Location of the study site,' with additional markers for 'Handi' and 'Himachal Pradesh.'.
Determination of phenolic compounds
Fresh leaf samples (100 g) from each cultivar were collected and thoroughly washed. A representative subsample (500 mg) was homogenised using a mortar and pestle with 10 ml of 80% ethanol. The homogenate was centrifuged at 10,000 rpm for 10 minutes, and the supernatant was collected. The residue was re-extracted twice with 80% ethanol, and all supernatants were pooled. The combined extract was evaporated to dryness at room temperature (or under reduced pressure), and the residue was dissolved in a known volume of 80% ethanol for analysis. For phenol estimation, 0.5 ml of the extract was taken in a test tube, and 6.5 ml of distilled water was added. Then, 0.5 ml of Folin–Ciocalteu reagent (previously diluted 1:1 with distilled water) was added and mixed thoroughly. After 5 minutes, 1.0 ml of 10% sodium carbonate solution was added. The reaction mixture was incubated at room temperature for 30–60 minutes for colour development. The absorbance was measured at 765 nm using a spectrophotometer against a reagent blank. Total phenolic content was calculated using a standard calibration curve prepared with gallic acid and expressed as milligrams of gallic acid equivalents (GAE) per gram of fresh weight.
Results
The age-stage-specific survival rate of B. helichrysi on the six different cultivars of P. domestica
The age-stage, two-sex life table allows for the calculation of the probability that B. helichrysi individuals will survive from a specific age (x) and stage (j). The survival rate of B. helichrysi adults on the Fortune cultivar was lower when compared with the other cultivars of plum. The survival rate of B. helichrysi from the first instar nymph to the fourth instar nymph was higher on the Red Beaut cultivar. Female emergence was earliest on Red Beaut and Santa Rosa (6th day), indicating faster development on these cultivars, followed by Black Amber (7th day), Friar, Angeleno (9th day), and lastly on Fortune (10th day). Delayed emergence of females on the Fortune cultivar and less persistence on this cultivar, lasting up to 27 days, suggests uneven and slower development, likely reflecting extended emergence periods on a less suitable cultivar (fig. 2).
Age-stage survival rates (Sxj) of Brachycaudus helichrysi females reared on different Prunus domestica cultivars (Black Amber, Friar, Fortune, Angeleno, Santa Rosa, and Red Beaut).
Figure 2 Long description
Age stage survival rate (Sxj) Legend: Red Beaut; Santa Rosa; Black Amber; Friar; Angeleno; Fortune; Females. Lines are distinguished by separate legend entries and distinct marker and line styles. Horizontal axis label: Age (days) (x). Range: 0 to 50. Vertical axis label: Age stage survival rate (Sxj). Range: 0 to 1. Data points as coordinate pairs. Red Beaut: (7, 0), (8, 0.1), (9, 0.3), (10, 0.6), (11, 0.7), (12, 0.7), (13, 0.7), (14, 0.7), (15, 0.7), (16, 0.7), (17, 0.7), (18, 0.7), (19, 0.7), (20, 0.7), (21, 0.7), (22, 0.7), (23, 0.7), (24, 0.7), (25, 0.7), (26, 0.7), (27, 0.7), (28, 0.7), (29, 0.7), (30, 0.7), (31, 0.7), (32, 0.7), (33, 0.7), (34, 0.7), (35, 0.7), (36, 0.7), (37, 0.7), (38, 0.7), (39, 0.7), (40, 0.7), (41, 0.7), (42, 0.7), (43, 0.7), (44, 0.3), (45, 0). Santa Rosa: (5, 0), (6, 0.1), (7, 0.4), (8, 0.8), (9, 0.8), (10, 0.8), (11, 0.8), (12, 0.8), (13, 0.8), (14, 0.8), (15, 0.8), (16, 0.8), (17, 0.8), (18, 0.8), (19, 0.8), (20, 0.8), (21, 0.8), (22, 0.8), (23, 0.8), (24, 0.8), (25, 0.8), (26, 0.8), (27, 0.8), (28, 0.8), (29, 0.8), (30, 0.8), (31, 0.8), (32, 0.8), (33, 0.8), (34, 0.8), (35, 0.8), (36, 0.8), (37, 0.8), (38, 0.8), (39, 0.8), (40, 0.8), (41, 0.8), (42, 0.8), (43, 0.8), (44, 0.8), (45, 0.8), (46, 0.8), (47, 0.8). Black Amber: (5, 0), (6, 0.1), (7, 0.5), (8, 0.8), (9, 0.8), (10, 0.8), (11, 0.8), (12, 0.8), (13, 0.8), (14, 0.8), (15, 0.8), (16, 0.8), (17, 0.8), (18, 0.8), (19, 0.8), (20, 0.8), (21, 0.8), (22, 0.8), (23, 0.8), (24, 0.8), (25, 0.8), (26, 0.8), (27, 0.8), (28, 0.8), (29, 0.8), (30, 0.8), (31, 0.8), (32, 0.8), (33, 0.8), (34, 0.8), (35, 0.8), (36, 0.8), (37, 0.8), (38, 0.8), (39, 0.8), (40, 0.8), (41, 0.8), (42, 0.8), (43, 0.8), (44, 0.8), (45, 0.8), (46, 0.8), (47, 0.8). Friar: (6, 0), (7, 0.1), (8, 0.3), (9, 0.6), (10, 0.7), (11, 0.7), (12, 0.7), (13, 0.7), (14, 0.7), (15, 0.7), (16, 0.7), (17, 0.7), (18, 0.7), (19, 0.7), (20, 0.7), (21, 0.7), (22, 0.7), (23, 0.7), (24, 0.7), (25, 0.7), (26, 0.7), (27, 0.7), (28, 0.7), (29, 0.7), (30, 0.7), (31, 0.7), (32, 0.7), (33, 0.7), (34, 0.7), (35, 0.7), (36, 0.7), (37, 0.7), (38, 0.7), (39, 0.7), (40, 0.7), (41, 0.6), (42, 0.2), (43, 0). Angeleno: (7, 0), (8, 0.1), (9, 0.3), (10, 0.6), (11, 0.7), (12, 0.7), (13, 0.7), (14, 0.7), (15, 0.7), (16, 0.7), (17, 0.7), (18, 0.7), (19, 0.7), (20, 0.7), (21, 0.7), (22, 0.7), (23, 0.7), (24, 0.7), (25, 0.7), (26, 0.7), (27, 0.7), (28, 0.7), (29, 0.7), (30, 0.7), (31, 0.7), (32, 0.7), (33, 0.7), (34, 0.7), (35, 0.7), (36, 0.7), (37, 0.5), (38, 0.2), (39, 0). Fortune: (8, 0), (9, 0.1), (10, 0.2), (11, 0.4), (12, 0.6), (13, 0.7), (14, 0.7), (15, 0.7), (16, 0.7), (17, 0.7), (18, 0.7), (19, 0.7), (20, 0.7), (21, 0.7), (22, 0.7), (23, 0.7), (24, 0.7), (25, 0.7), (26, 0.7), (27, 0.7), (28, 0.7), (29, 0.7), (30, 0.7), (31, 0.7), (32, 0.7), (33, 0.7), (34, 0.7), (35, 0.6), (36, 0.3), (37, 0.2), (38, 0.1), (39, 0), (40, 0). Key values and comparisons from the plotted coordinates. Santa Rosa reaches 0.8 at age 8 and remains at 0.8 through age 47. Black Amber reaches 0.8 at age 8 and remains at 0.8 through age 47. Red Beaut reaches 0.7 at age 11 and remains at 0.7 through age 43, then drops to 0.3 at age 44 and 0 at age 45. Friar reaches 0.7 at age 10 and remains at 0.7 through age 40, then drops to 0.6 at age 41, 0.2 at age 42 and 0 at age 43. Angeleno reaches 0.7 at age 11 and remains at 0.7 through age 36, then drops to 0.5 at age 37, 0.2 at age 38 and 0 at age 39. Fortune reaches 0.7 at age 13 and remains at 0.7 through age 34, then drops to 0.6 at age 35, 0.3 at age 36, 0.2 at age 37, 0.1 at age 38 and 0 at age 39 and age 40.
The developmental duration of B. helichrysi on the six different cultivars of P. domestica
Nymphal development of B. helichrysi was significantly faster on Red Beaut (7.38 days) and Santa Rosa (7.44 days), both of which were at par, followed by Black Amber (8.50 days), Friar (10.57 days), Angeleno (10.79 days), and Fortune (11.43 days), with all pairwise differences being highly significant (P < 0.00001). The developmental duration and longevity of B. helichrysi on the different plum cultivars varied significantly (P < 0.05). The longevity of B. helichrysi in Red Beaut was the longest at 35.31 days. However, the female longevity of B. helichrysi was 22.20, 24.16, 28.30, 30.15, and 33.00 days on Fortune, Angeleno, Friar, Black Amber, and Santa Rosa, respectively; these durations of B. helichrysi were significantly shorter than that on Red Beaut (table 1).
Developmental and reproductive biology (mean ± SE) of B. helichrysi life stages reared on different plum cultivars
Table 1 Long description
Mean duration in days, with standard errors, is reported for four nymph stages (N1 to N4), total pre-adult time, and female longevity of B. helichrysi on six plum cultivars. Pre-adult development is longest on Fortune at 11.86 days and shortest on Red Beaut at 7.38 days, with Santa Rosa similarly low at 7.44 days. Across individual nymph stages, Fortune generally has the longest durations (about 2.86 to 3.00 days), while Santa Rosa and Red Beaut are typically shortest (about 1.75 to 2.00 days). Black Amber is intermediate for nymph stages (about 2.05 to 2.12 days) and has a pre-adult time of 8.50 days. Female longevity increases from Fortune at 22.20 days through Angeleno at 24.16 and Friar at 28.30 to Black Amber at 30.15, Santa Rosa at 33.0, and peaks on Red Beaut at 35.31 days. Overall, cultivars associated with shorter immature development also tend to be associated with longer adult female lifespan, though the table reports means with standard errors and does not indicate statistical significance.
Age-specific life table parameters of B. helichrysi on the six different cultivars of P. domestica
In B. helichrysi, age-specific survival rate (lx) remained 1.0 up to day 3 on Red Beaut, Santa Rosa, and Black Friar, 5 on Friar and Angeleno, and 6 on Fortune, and after these ages, mortality began, occurring earliest on Red Beaut, Santa Rosa, and Black Friar, possibly due to faster progression through developmental stages. In contrast to other cultivars, a sharp decline in lx on Fortune between days 32 and 37 (0.55–0.10) indicated abrupt reductions in cohort survival. Among the cultivars, ‘Fortune’ exhibited the earliest drop of lx to zero on day 38, while in ‘Red Beaut’, this point was reached on day 45, reflecting differences in developmental rate and life-cycle completion across cultivars. The age-stage-specific fecundity (fx) and age-specific fecundity (mx) appeared earliest in Red Beaut (8th day), indicating faster reproductive maturity at the population level than in Santa Rosa (9th day), Black Amber (9th day), Friar and Angeleno (12th day), and lastly in Fortune (13th day). The fx and mx of B. helichrysi varied across hosts, with both remaining non-zero for most days on Red Beaut (12 days), indicating a broader population-level reproductive window and more sustained egg laying across individuals. Although Santa Rosa exhibited the highest peaks for fx and mx, the duration of fx and mx expression was shorter, reflecting a narrow reproductive window with high output. Overall, Red Beaut supported prolonged survival and stable fecundity across populations, as captured by lx, fx, mx, and lxmx patterns (fig. 3A–D).
Age-specific life table parameters of Brachycaudus helichrysi reared on Black Amber, Friar, Fortune, Angeleno, Santa Rosa, and Red Beaut. (A) age-specific survival rate (lx), (B) age-specific fecundity (mx), (C) age-stage-specific fecundity (fx), and (D) age-specific maternity (lxmx).
Figure 3 Long description
The image contains four multi-line graphs labeled 2(a), 2(b), 2(c) and 2(d), each representing different age-specific life table parameters for Brachycaudus helichrysi across six cultivars: Red Beaut, Santa Rosa, Black Amber, Friar, Angeleno and Fortune. Graph 2(a) shows age-specific survival rate (lx) with the x-axis labeled 'Age (days)' ranging from 0 to 50 and the y-axis labeled 'Age-specific survival rate (lx)' ranging from 0 to 1.0. Red Beaut, Santa Rosa and Black Amber show a sharp decline after day 3, while Friar and Angeleno decline after day 5 and Fortune after day 6. Graph 2(b) displays age-specific fecundity (mx) with the x-axis labeled 'Age (days)' from 0 to 50 and the y-axis labeled 'Age-specific fecundity (mx)' ranging from 0 to 10. Peaks occur earliest in Red Beaut around day 8, followed by Santa Rosa and Black Amber around day 9, Friar and Angeleno around day 12 and Fortune around day 13. Graph 2(c) illustrates age-stage specific fecundity (fx) with the x-axis labeled 'Age (days)' from 0 to 50 and the y-axis labeled 'Age-stage specific fecundity (fx)' ranging from 0 to 10. Red Beaut shows sustained fecundity over 12 days, while Santa Rosa has the highest peaks but shorter duration. Graph 2(d) represents age-specific maternity (lxmx) with the x-axis labeled 'Age (days)' from 0 to 50 and the y-axis labeled 'Age-specific maternity (lxmx)' ranging from 0 to 10. Red Beaut supports prolonged survival and stable fecundity, while Santa Rosa exhibits high output but narrow reproductive window. Each cultivar is distinguished by different line styles and markers, allowing comparison of survival, fecundity and maternity trends across cultivars. Key observations include Red Beaut's prolonged survival and early fecundity and Fortune's earliest drop in survival rate.
The reproductive parameters of B. helichrysi on the six different cultivars of P. domestica
The reproductive parameters of B. helichrysi on all the cultivars are shown in table 2. The intrinsic rate of increase of B. helichrysi was highest on Red Beaut. The net reproductive rate of B. helichrysi on Red Beaut was higher and 1.5-fold than that on Fortune. The fecundity of B. helichrysi was lower, and the doubling time was higher on the Fortune cultivar. B. helichrysi fed on Fortune had the smallest r value (0.17). Therefore, the cultivar Fortune was found to be more resistant to aphid populations.
Population parameters of Brachycaudus helichrysi on different plum cultivars
Table 2 Long description
The table reports mean values with standard errors for aphid population growth and reproduction metrics across six plum cultivars: Fortune, Angeleno, Friar, Black Amber, Santa Rosa, and Red Beaut. Intrinsic and finite rates of increase rise from Fortune and Angeleno to Red Beaut, with intrinsic rate increasing from 0.17 to 0.23 and finite rate from 1.19 to 1.26. Net reproduction rate also increases across cultivars, from 42.54 on Fortune to 65.30 on Red Beaut. Mean generation time declines from 21.33 days on Fortune to 17.83 days on Red Beaut, indicating faster turnover on the latter cultivars. Fecundity is lowest on Fortune at 60.29 and highest on Red Beaut at 81.62, with Santa Rosa also high at 74.38. Doubling time shortens from 3.95 on Fortune to 2.92 on Red Beaut, consistent with faster population growth. Differences should be interpreted with the reported standard errors in mind, as some values are close between neighboring cultivars.
Seasonal incidence of B. helichrysi on the six different cultivars of P. domestica
The study investigated the population dynamics of aphids across various months and plum varieties. The data presented in table 3 illustrate fluctuations in aphid populations over time and among different varieties. The results on the incidence of peach leaf curl aphid, B. helichrysi, on plum revealed that the activity of the pest commenced in February and continued to increase in the pre- and post-blooming periods with increasing warming of the weather. Across the months of February–May, a significant variation in aphid populations was observed. The initial mean population of aphids recorded per 10 leaves in the first week of February (6th standard week) was 30.17 aphids/10 leaves. Notably, there was a general increasing trend in aphid populations from February to March across all varieties, with a monthly average of 43.68 aphids/10 leaves in February. March marked a substantial rise in aphid populations across all cultivars, with a peak observed in the fourth week of March (13th standard week) with 156.97 aphids/10 leaves. This surge in aphid populations may be attributed to favourable environmental conditions or intrinsic biological factors. April witnessed mixed patterns in aphid populations among different cultivars, with some experiencing declines compared to March, while others saw increases, indicating variations in susceptibility to aphid infestation among peach cultivars. In May, a notable decrease in aphid populations was observed across all cultivars, with mean populations ranging from 9.40 to 24.20 aphids/10 leaves. This reduction could be attributed to seasonal factors such as temperature rise or natural biological control mechanisms. The annual mean aphid population per 10 leaves ranged from 39.53 to 103.12 across cultivars. The annual mean aphid population ranged from 39.53 to 103.12 aphids/10 leaves across cultivars. It was maximum in the Red Beaut cultivar (103.12 aphids/10 leaves), followed by Santa Rosa (96.04 aphids/10 leaves), with both being statistically at par. Black Amber (87.80 aphids/10 leaves) and Friar (80.28 aphids/10 leaves) had intermediate populations, significantly lower than Red Beaut and Santa Rosa, showing moderate susceptibility. The minimum aphid population was recorded in the Fortune plum cultivar with 39.53 aphids per 10 leaves throughout the period of 20 standard weeks closely followed by Angeleno with 44.37 aphids per 10 leaves in the total activity period of aphid recorded, being significantly superior to all other cultivars, indicating relative resistance or tolerance. The interaction of cultivar and week was also significant, showing that the population differences among cultivars were most pronounced during the peak weeks of March. Red Beaut and Santa Rosa consistently recorded higher aphid numbers during these peak periods, whereas Angelino and Fortune remained comparatively low, suggesting inherent cultivar resistance.
Seasonal incidence of Brachycaudus helichrysi on different plum cultivars
Table 3 Long description
Weekly counts of aphids per 10 leaves are listed for six plum cultivars from early February through early May, with a weekly mean across cultivars and monthly average totals. Populations rose from moderate levels in February (weekly means about 30 to 51) to a sharp peak in late March, when the weekly mean reached about 157 in the fourth week and about 153 in the fifth week. The highest single-cultivar value occurred on Red Beaut in the second week of March (about 230), and Santa Rosa also reached very high levels in late March (about 206 in the fourth week). Angelino and Fortune consistently had the lowest counts, generally below about 80 even during the March peak, while Red Beaut, Santa Rosa, Black Amber, and Friar were higher and more variable. After March, the weekly mean dropped through April (about 128 in the first week down to about 29 by the fifth week) and reached the lowest weekly mean in the first week of May (about 17). Overall mean aphid populations across the season were highest on Red Beaut (about 103) and Santa Rosa (about 96), intermediate on Black Amber (about 88) and Friar (about 80), and lowest on Angelino (about 44) and Fortune (about 40). Some values include transformed numbers in parentheses and letter groupings indicating statistical comparisons, so small differences may not be meaningful.
Values in parenthesis are square-root transformed values. Means followed by common letters do not differ significantly at P = 0.05. CD (Critical Difference) 0.05: 1.35 (cultivars); 2.05 (weeks); 3.34 (interaction). SEm (Standard Error of Mean): 0.48 (varieties); 0.72 (weeks).
This suggests differences in aphid susceptibility among plum cultivars, possibly influenced by genetic factors or plant characteristics affecting aphid preference and colonisation.
Total phenolic compounds in six different cultivars of P. domestica
Furthermore, table 4 indicates the phenolic compounds of each plum cultivar. The results revealed variations in phenolic compounds among cultivars, with Fortune, Angeleno, and Friar exhibiting higher phenolic compounds (15.82, 15.72, and 15.70 mg GAE per gram dry weight, respectively) compared to other cultivars with minimum phenolic compounds in the Red Beaut and Black Amber cultivars (8.23 and 8.30 mg GAE per gram dry weight, respectively). The correlation between phenolic compounds and aphid incidence in plum cultivars holds significant scientific interest due to its implications for plant–insect interactions and agricultural pest management. Our study examined this relationship by analysing the phenolic compounds, measured as GAE per gram dry weight, and aphid incidence per 10 plants across six plum cultivars and revealed that a correlation coefficient between these factors was 0.780 and a coefficient of determination based on regression analysis of phenolic compounds and aphid incidence per 10 plants was 0.510, which implies that 51.0% of variation in the aphid incidence per 10 plants on plum trees was defined by phenolic compounds present in the plum variety. Our findings revealed a significant variation in both phenolic compounds and aphid incidence among the tested cultivars. Red Beaut exhibited the highest aphid incidence, followed by Santa Rosa, while Angeleno and Fortune displayed lower aphid populations. The negative correlation observed between phenolic compounds and aphid incidence suggests a potential role of phenolic compounds in mediating plant resistance to aphids. Higher phenolic compounds, particularly in cultivars such as Angeleno and Fortune, may confer greater resistance to aphid infestation by acting as feeding deterrents or anti-nutritional factors, thus reducing aphid fitness and survival.
Phenolic compounds of different plum cultivars
Table 4 Long description
The table compares six plum varieties by mean aphid incidence, reported as average number of aphids per 10 leaves, and phenol content, reported as milligrams per gram dry weight as gallic acid. Red Beaut has the highest aphid incidence at 103.12, followed by Santa Rosa at 96.04. Fortune and Angeleno have the lowest aphid incidence at 39.53 and 44.37, and they also have high phenol content at 15.82 and 15.72. Friar shows relatively high aphid incidence at 80.28 while also having high phenol content at 15.70. Black Amber and Red Beaut have the lowest phenol content, 8.30 and 8.23, and both have high aphid incidence at 87.8 and 103.12. Overall, lower phenol content often aligns with higher aphid incidence, but Friar is an exception, so the pattern is not consistent across all varieties.
Discussion
Influence of host plant quality on aphid life table parameters
Host plant characteristics play a decisive role in shaping the oviposition choice, developmental performance, and population growth of herbivorous insects. Traits commonly used to evaluate insect performance include growth, fecundity, survival, parasitism or predation, developmental rate, consumption rate, and population growth parameters derived from life table analyses. Fecundity, in particular, is a key determinant of reproductive capacity and is strongly influenced by host plant quality during larval development (Awmack and Leather, Reference Awmack and Leather2002). In the present investigation, B. helichrysi exhibited higher fecundity and a greater intrinsic rate of increase on the Red Beaut cultivar, suggesting that this variety provides a superior nutritional environment for aphid proliferation. We suspect that the lower total gallic acid content in Red Beaut leaves contributes to its susceptibility. In contrast, aphids reared on Fortune, Angeleno, and Friar displayed reduced longevity, fecundity, intrinsic rate of increase, finite rate of increase, and net reproductive rate. According to the principle that female insects reduce reproductive output when encountering poor-quality hosts (Awmack and Leather, Reference Awmack and Leather2002), this pattern indicates that these cultivars possess deterrent or inhibitory traits. Previous studies have shown that structural plant defences – such as thicker cuticles, trichomes, and surface waxes – can impede insect feeding and reduce performance (Kariyat et al., Reference Kariyat, Raya, Chavana, Cantu, Guzman and Sasidharan2019; Kaur and Kariyat, Reference Kaur and Kariyat2023). However, these traits were not directly assessed in the present study; therefore, their role in influencing cultivar for B. helichrysi remains to be elucidated.
Role of phenolic compounds in mediating resistance
Phenolic compounds are widely recognised for their defensive functions against herbivores. Several studies have demonstrated enhanced insect resistance in cultivars with elevated phenolic levels. Zhou et al. (Reference Zhou, Wang, Yu, Tan, Cheng, Zhang and Li2013) reported greater resistance to woolly apple aphid in phenolic-rich cultivars. Similarly, Wojcicka (Reference Wojcicka2016) found higher nymph mortality on waxy triticale plants, which also possessed higher flavonoid content, suggesting that flavonoids are a key biochemical resistance factor. Our findings align with these reports: cultivars with higher phenolic content (Fortune, Angeleno) supported lower aphid population growth. The negative correlation between phenolics and aphid performance underscores the potential role of these compounds as deterrents or growth inhibitors. Comparable outcomes have been documented for Myzus persicae and Rhopalosiphum padi, where phenolic acid mixtures prolonged prereproductive periods, suppressed fecundity, and reduced intrinsic rates of increase (Chrzanowski et al., Reference Chrzanowski, Leszczyński, Czerniewicz, Sytykiewicz, Matok, Krzyżanowski and Sempruch2012; Czerniewicz et al., Reference Czerniewicz, Chrzanowski, Sytykiewicz, Sprawka and Leszczyński2016). Phenolics are known allelochemicals that affect feeding behaviour, enzyme activity, nutrient assimilation, and developmental processes (Chrzanowski et al., Reference Chrzanowski, Leszczyński, Czerniewicz, Sytykiewicz, Matok, Krzyżanowski and Sempruch2012; Rehman et al., Reference Rehman, Khan, Badruddin, Khemani, Srivastava and Srivastava2012; Czerniewicz et al., Reference Czerniewicz, Chrzanowski, Sytykiewicz, Sprawka and Leszczyński2016). Their biosynthesis via the shikimic and malonic acid pathways results in structurally diverse compounds such as flavonoids, tannins, and phenolic acids, each contributing uniquely to plant defence (Saltveit, Reference Saltveit and Heuvelink2018; Karantzi et al., Reference Karantzi, Kafkaletou, Christopoulos and Tsantili2021).
Seasonal incidence and environmental influence on population dynamics
The field component of this study demonstrated peak aphid abundance during March, followed by a decline in April and a steep reduction in May. Similar observations were made by Arora et al. (Reference Arora, Gupta and Bali2009), who attributed seasonal population surges in aphids to favourable combinations of temperature and relative humidity. Such environmental conditions can trigger the production of winged morphs, enabling dispersal to alternative hosts, as observed in our study.
Mechanistic basis of phenolic-mediated resistance
Accumulation of phenolic compounds is often induced in response to herbivory. Florencio-Ortiz et al. (Reference Florencio-Ortiz, Gruz and Casas2021) reported elevated phenolic content in plants exposed to low initial aphid densities, while high-density infestations led to the accumulation of specific phenolic acids such as caffeic, p-coumaric, sinapic, p-hydroxybenzoic, and salicylic acids, all of which contribute to defence. Gantner et al. (Reference Gantner, Najda and Piesik2019) found that hazelnut cultivars with high phenolic acid concentrations (notably gallic and caffeic acids) were less acceptable to aphids, whereas susceptible cultivars contained significantly lower levels. Similar roles of defensive metabolites have been reported in peach, where resistant genotypes emitted defence-related volatile organic compounds (VOCs) such as methyl salicylate upon aphid attack (Staudt et al., Reference Staudt, Jackson, El-aouni, Buatois, Lacroze, Poessel and Sauge2010). Metabolite profiling by Poessel et al. (Reference Poessel, Sauge, Staudt, Dufour, Deborde, Rahbé and Moing2011) further indicated that phenolic compounds directly affect aphid performance, with resistance factors localised at prephloem and phloem levels (Verdugo et al., Reference Verdugo, Sauge, Lacroze, Francis and Ramirez2015). Our results corroborate these findings: cultivars with higher phenolic profiles were less susceptible to B. helichrysi. However, the specific phenolic compounds responsible for antibiosis or antixenosis require further investigation. Plant–insect interactions are multifaceted, influenced by environmental variables, plant phenology, and the dynamic nature of secondary metabolite expression (Pincebourde et al., Reference Pincebourde, van Baaren, Rasmann, Rasmont, Rodet, Martinet and Calatayud2017). Verghese et al. (Reference Verghese, Soumya, Shivashankar, Manivannan and Krishnamurthy2012) similarly demonstrated that mango varieties with higher phenolic concentrations exhibited increased resistance to fruit fly herbivory, reinforcing the idea that phenolics serve as a broad-spectrum defence mechanism across crops. Chrzanowski et al. (Reference Chrzanowski, Leszczyński, Czerniewicz, Sytykiewicz, Matok, Krzyżanowski and Sempruch2012) highlighted the potential of phenolic acid mixtures as botanical pesticides within IPM programs. Leal (Reference Leal2012) also reported strong antixenosis effects in peach cultivars associated with elevated phenolic content.
Implications for integrated pest management
The collective evidence from our study and prior literature indicates that phenolic-rich plum cultivars offer a promising avenue for managing B. helichrysi through host plant resistance. However, it is essential to evaluate the ecological consequences of phenolic-based resistance, particularly with respect to non-target organisms and broader ecosystem function. Integrated pest management strategies incorporating resistant cultivars, biological control, cultural practices, and judicious chemical interventions remain crucial for sustainable aphid suppression (Bashyal et al., Reference Bashyal, Poudel and Gautam2022). Enhancing phenolic levels through breeding or agronomic manipulation may strengthen plant resilience, but should be complemented with these integrated approaches to ensure long-term sustainability.
Conclusion
Our study demonstrated significant variations in aphid population dynamics across different months and plum cultivars, reflecting the combined influences of host plant traits and environmental conditions. Aphid population increased from February to March, followed by variable trends in April and a decline in May. Differences in phenolic content among cultivars, particularly higher levels in Angelino and Fortune, were negatively associated with aphid incidence, suggesting a potential role of phenolic compounds in host plant resistance. These findings highlight the importance of integrating host plant resistance with seasonal monitoring for effective pest management. Future research should focus on elucidating the mechanistic basis of phenolic-mediated resistance and its interaction with natural enemies. Importantly, the identification of less susceptible cultivars provides a practical basis for incorporating host plant resistance into integrated pest management programs for suitable plum production.
Author contributions
All authors contributed to the study conception and design. Idea conceptualisation: D.S. and R.T. Methodology, design and material preparation, and data collection: D.S. and R.T. Formal analysis and investigations: D.S., A.B., S.S., and D.K. Manuscript writing: D.S. and A.B. Review and editing: All the authors.
Financial support
The authors have no relevant financial or non-financial interests to disclose, and the authors declare that no funds, grants, or other support was received during the preparation of this manuscript.
Competing interests
The authors declare that they have no conflict of interest.
Data availability statement
The data supporting the findings of this study are available upon request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Additional datasets generated or analysed during the current study are available from the corresponding author on reasonable request.
