فصلنامه گیاه پزشکی
سال چهل و هشتم شماره 1 (بهار 1404)

Beet armyworm, Spodoptera exigua (Hübner) is a polyphagous species and an economically important pest that primarily damages various crops, including sugar beet, cotton, corn, and vegetables in Iran. The beet armyworm is known for developing resistance to various insecticides, making management increasingly challenging. The beet armyworm poses a considerable threat to agriculture, requiring ongoing research and adaptive management strategies to mitigate its impact on crops such as sugar beet. In recent years, the damage of the mentioned moth has been observed and reported in the north of Khuzestan. Due to the wide host range of this pest, less attention has been paid to the resistance of cultivars to this pest in sugar beet breeding programs.

In order to evaluate the resistance of 12 sugar beet cultivars (Ratna, Callas, Algar, Bifort, Portal, Sentinel, Brandon, Motor, Homa, Dena, Sharif and 061) to sugar beet armyworm, experiments were carried out in laboratory and experimental fields located at Agriculture and Natural Resources Research and Education Center of Safiabad, Dezful, during 2021-2022. Calculating percentage of preference of beet armyworm larvae to different sugar beet cultivars in the laboratory, and determining damage index of beet armyworm to different cultivars in the field with natural infestation (choice access), with artificial infestation (no-choice access), and percentage of yield (Kg/m2) reduction of the pest in the experimental field conditions included in this study. Damage index of larvae was defined in five groups, namely very sensitive, sensitive, semi-resistant, resistant, and very resistant.

In the evaluations carried out in the field, significant difference was seen between the beet armyworm damage index of experimental cultivars by natural damage. In this experiment, the highest damage index was seen in Ratna cultivar and the lowest in Brandon, Callas, Sentinel, Algar and Homa cultivars. The yield reduction percentage was not significant at the 5% level. Damage compensation in low larval densities and production of new leaves was one of the reasons for the non-significance of yield reduction due to larvae feeding. In laboratory evaluations, the preference percentage of beet armyworm larvae was significant for different sugar beet cultivars. The highest percentage of larvae prevalence was seen in Kalas, Portal, Brandon and Ratna cultivars and the lowest in Dena cultivar. Sentinel, Bifort and Homa cultivars also attracted less larvae after Dena. No significant difference was seen between sugar beet cultivars in terms of decreasing or increasing the survival period of the larvae, but the index of larval feeding on the leaves of the cultivars was significant in the second laboratory tests. The lowest amount of larval feeding was seen in Motor, Dena and Sharif cultivars and the highest amount was seen in 061 and Homa cultivars. The resistance indices/coefficients were calculated based on total evaluations, and according to that, Motor, Kalas and Sentinel cultivars are in the resistant group, Dena and Sharif cultivars are in the semi-resistant group, Algar, Bifort, Portal, Ratna and 061 cultivars are in the semi-resistant group. Brandon and Homa cultivars were grouped in the sensitive group. The calculated resistance index had a significant negative correlation with the damage index of beet armyworms in the field (no-choice test), the percentage of yield reduction by larvae, larval survival period, and the amount of larval feeding on leaves in the laboratory.

The results obtained indicated that, although the sugar beet armyworm is a pest with a very broad host range, the feeding rates and survival percentages of its larvae vary across different sugar beet cultivars. These variations can be utilized to enhance and develop resistant varieties of sugar beet. In further studies, the Sentinel, Motor, and Kalas cultivars, which showed relative resistance in the experiments, along with the Brandon and Homa cultivars, identified as sensitive, can serve as control groups. Additional studies related to the mechanisms of resistance and morphological and biochemical aspects which are effective in the resistance of sugar beet cultivars to the beet armyworm are recommended for use in breeding programs. The use of sugar beet cultivars resistant to the beet armyworm can be effective in reducing the use of pesticides against this pest, managing the resistance of the beet armyworm to pesticides and the integrated management of this pest.

The date palm horn beetle, Oryctes elegans (Coleoptera: Scarabaeidae), is a significant wood-boring pest of date palms, causing substantial damage to the tree and fruit through the feeding activity of adults and larvae. This study evaluated the potential of Zarkooh mineral sulfur, a formulation, in mitigating beetle damage and enhancing physiological traits and nutrient absorption in Phoenix dactylifera cv. ‘Piarom’. The research was conducted over 2.5 years (2020–2022) in a randomized complete block design (RCBD) with four treatments and five replications. Treatments included control and three levels of Zarkooh sulfur (below, at, and above the recommended concentration). Results showed no significant effect of sulfur application on pest mortality O. elegans, population reduction (Henderson-Tilton formula), or tree damage across evaluation intervals (9, 20, 51, and 82 days post-treatment). In addition, sulfur did not significantly affect physiological traits (chlorophyll index, electrolyte leakage, relative water content, dry matter percentage, fresh/dry leaf weight) or macro- and micronutrient uptake (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B). These findings suggest that using this fertilizer for pest control in date palm plantations is ineffective, especially when applied without expert guidance, and caution is recommended to avoid excessive or unnecessary applications.

The widespread use of chemical pesticides and fertilizers remains essential in modern agriculture; however, their excessive application poses significant environmental and human health risks. Consequently, alternative pest management strategies, such as host plant resistance and biological control, have gained increasing attention. One promising avenue of research explores the role of plant growth-promoting rhizobacteria (PGPR) fertilizers in integrated pest management (IPM). PGPR fertilizers improve plant quality by improving nutrient availability, facilitating nitrogen fixation, and regulating key signaling pathways. Rhizobacteria contribute to plant defense against herbivorous insects through two primary mechanisms: direct defense, involving the release of insect-deterring proteins, and indirect defense, wherein dilute volatile compounds attract natural enemies of insect pests. Induced systemic resistance (ISR) has been shown to significantly reduce pest populations, reinforcing the role of plant resistance in IPM strategies. Beyond host plant resistance, biological control is widely regarded as a crucial component of IPM programs. Predatory coccinellids have garnered global interest among biological control agents due to their potential in managing diverse populations of sap-sucking pests. The predatory ladybird beetle, Adalia bipunctata L., is a polyphagous species that primarily prey on aphids, with a particular preference for the green peach aphid, Myzus persicae (Sulzer), a highly polyphagous pest responsible for significant damage to numerous field and greenhouse crops. This study aims to assess the demographic parameters of A. bipunctata, a natural predator of M. persicae when reared on bell pepper plants and treated with different plant growth stimulants. The findings could provide valuable insights into the effectiveness of biological control agents as a sustainable strategy for reducing M. persicae populations and mitigating crop damage.

In this study, the effects of zinc sulfate foliar application and the incorporation of organic fertilizer (30% vermicompost) and biological fertilizers (Bacillus subtilis, Pseudomonas fluorescens, Glomus intraradices, G. intraradices × B. subtilis, and G. intraradices × P. fluorescens) into the growth medium of bell pepper plants were investigated. The demographic parameters of the predatory ladybird beetle, Adalia bipunctata, were examined under controlled laboratory conditions at 25 ± 2°C, 65 ± 5% relative humidity, and a 16L:8D photoperiod. The experiment followed a completely randomized design (CRD) with seven treatments and a control. Pairs of male and female A. bipunctata were selected, and 100 eggs were incubated in plastic Petri dishes. The larvae were fed on Myzus persicae and subjected to the respective treatments, with results compared against the control. The developmental parameters of immature stages, including molting, larval growth, pupation, and survival rates, were recorded. After adulthood, beetles were transferred to fresh containers with host plant leaves and aphid prey. Key reproductive and population parameters were analyzed, including oviposition rate, age-specific fecundity, survival rate, life expectancy, and demographic indices. Data were processed using the age-stage, two-sex life table approach. Treatment means were compared using the paired bootstrap test, with statistical analyses performed using TWOSEX-MSChart software.

The results indicate that the shortest oviposition period was observed in the vermicompost (30%), zinc sulfate, and control treatments, whereas the longest was recorded in the B. subtilis treatment. Life expectancy was highest in the B. subtilis treatment and lowest in the vermicompost (30%) treatment. Similarly, the net reproductive rate (R0) of A. bipunctata reached its highest value in the B. subtilis treatment and its lowest in the vermicompost (30%) treatment. The intrinsic rate of increase (r) was lowest in the vermicompost (30%) treatment, while the highest values were recorded in the B. subtilis, zinc sulfate, G. intraradices × B. subtilis, and P. fluorescens treatments.

The B. subtilis and P. fluorescens treatments were the most beneficial for the two-spotted ladybird beetle, Adalia bipunctata, suggesting enhanced nutritional quality. These PGPRs interact with insects through multiple mechanisms, such as inducing resistance against herbivores or attracting natural predators. Our analysis demonstrated that different fertilizer treatments significantly impacted the population growth parameters and the biological traits of A. bipunctata. Notably, soil treatment with biological fertilizers (B. subtilis and P. fluorescens) positively and significantly affected the population dynamics of the predatory insects. These findings suggest that biological fertilizers could be integrated with biological control agents in IPM programs to improve green peach aphid (Myzus persicae) management in greenhouse environments.

Filenchus is one of the most diverse genera of the family Tylenchidae, with various feeding habits. The members of this genus feed on fungi in the soil and the epidermal cells of plant roots. A species belonging to Filenchus was recovered and identified during a survey on the fauna of the plant-parasitic nematodes from the soil around the roots of corn in the north of Khuzestan province (Dezful city). This study aimed to characterize the recovered population based on the morphological and morphometric characters and reconstruct its phylogenetic affinities using 18S rDNA and D2-D3 expansion segments of the 28S rDNA sequences. Additionally, the phylogenetic relationships of the Iranian population with other populations of the species and other species of Filenchus were investigated.

Several soil samples were collected around the roots of corn fields in the north of Khuzestan province. The centrifugal-floatation and tray methods were used to extract the nematodes from the soil samples. The collected specimens were fixed, transferred to pure glycerin, and mounted on permanent microscopic slides. The species was recognized using an Olympus CX31 light microscope equipped with a drawing tube based on the morphological and morphometric characteristics, and valid keys. The nematode specimens were photographed using an Olympus BX51 microscope with a Tucsen Michrome 20 digital camera. The morphological and morphometric characters of the population were compared with other reported populations of the species. For molecular analyses, DNA was extracted from the studied nematodes. The DNA samples were stored at –20°C until used as a PCR template. Primers for amplification of 18S rDNA were forward SSUF22 and reverse SSUR13. Primers for D2-D3 expansion segments of the 28S rDNA amplification were forward D2Ab and reverse D3B. The polymerase chain reactions (PCRs) were performed to amplify the abovementioned loci. Amplification success was evaluated with electrophoresis on 1% agarose gel. The PCR products were subjected to sequencing. The newly obtained sequences of the studied species were deposited into the GenBank database (PQ803453-PQ803455). The molecular phylogenetic analyses were performed using a partial sequence of the 18S rDNA and D2-D3 expansion segments of the 28S rDNA based on the Bayesian inference under the GTR + G + I model.

A population of Filenchus was recovered in the present study. The morphological, morphometric, and molecular studies based on the 18S rDNA and D2-D3 expansion segments of the 28S rDNA indicated that the recovered population belongs to F. vulgaris. This population has females with a length of 630 to 722 µm, lateral field with four incisures, and stylet 10.5 to 11.2 µm long. Males were observed in fewer numbers than females, with spicules of 17.0 to 18.5 µm. In the phylogenetic tree inferred using the 18S rDNA sequences, the newly generated sequences of the Iranian population of F. vulgaris formed a clade with other sequences of F. vulgaris and sequences of other species of Filenchus and species of Tylenchus and Neopsilenchus genera. The newly generated sequence of the Iranian population formed a maximally supported clade with other sequences of the species in the phylogenetic tree inferred using the 28S rDNA gene. This clade included sequences of other species of Filenchus and species of the two genera Tylenchus and Irantylenchus. The molecular data of the Iranian population of the species were presented for the first time in this study.

The identification of most of the species of the genus Filenchus was based only on morphological and morphometric characteristics. Multiple phylogenetic analyses have shown that the genus Filenchus is polyphyletic. In the phylogenetic trees, the sequences of some populations of F. vulgaris are relatively far from each other and even in two different clades. With the increase of sequences of various species of the genus, especially from different populations that belong to different geographical regions, the grouping of populations and species may change, and the phylogenetic relationships between them might be more specific.

The ability of predators to feed, develop, and reproduce on non-prey food sources, such as pollen, is a desirable trait for biological agents to maintain their populations in the event of prey scarcity. Additionally, this trait is valuable for rearing predators in laboratories or mass-rearing purposes before release. Research has shown that pollen as a dietary supplement may increase the establishment of generalist predatory mites, thereby improving pest control by these mites. Pollen provides essential nutrients, including proteins, carbohydrates, lipids, amino acids, vitamins, flavonoids, and minerals; however, pollen's nutritional value can vary among plant species. In addition, phytoseiid mite species vary in their ability to utilize pollen. Studies have shown that food sources, particularly those containing high percentages of protein and carbohydrates, are nutritionally valuable for rearing predators. Thus, our study aimed to compare the nutritional value of a powdered sugar diet (contains high carbohydrates) and saffron and the mixture of almond and maize pollen grains (contains high protein) for Neoseiulus californicus McGregor (Acari: Phytoseiidae) performance to optimize its mass-rearing.

In this research, we evaluated the nutritional value of powdered sugar (sugar dust), saffron pollen, and a mixture of almond and maize (almond+maize( pollen in mass-rearing of the predatory mite N. californicus. Life table studies were conducted under laboratory conditions at 25 ± 1°C, 60 ± 5% RH, and a photoperiod of 16:8 (L:D) h. Data analysis and population parameters (r, 𝜆, GRR, R0, and T) were calculated using the TWOSEX-MSChart program. The means and standard errors of all parameters (duration of different life stages, fecundity, reproductive periods, longevities, and population growth parameters), were calculated by the bootstrap procedure. To obtain stable estimates, 100,000 bootstraps were used. Mean comparisons of the parameters were performed using the paired bootstrap test based on confidence interval.

Individuals of N. californicus successfully developed from larva to adult when fed all tested diets. However, the pre-adult duration was significantly longer on the powdered sugar diet compared to the pollen diet. The individuals fed saffron pollen had the shortest pre-adult duration (6.70 days). The adult longevity of males and females fed on the pollen diets was longer than those fed on powdered sugar. Females lived longer than males on all the treatments. The highest average lifespan was for the individuals fed saffron pollen (58.33 days). However, the longest life span belonged to one of the female individuals fed on the almond+maize pollen (90 days). Although individuals fed on powdered sugar exhibited high survival rates and long lifespans, they had no fecundity. However, the average fecundity on saffron and almond+maize pollens was 43.19 and 37.59 eggs/female, respectively. The values of the intrinsic rate of increase (r), finite rate of increase (λ), gross reproductive rate (GRR), net reproductive rate (R0) and mean generation time (T) on saffron pollen and almond+maize pollen were 0.195 versus 0.183 day-1, 1.215 versus 1.201 day-1, 32.15 versus 31.48 offspring, 29.85 versus 25.36 offspring and 17.41 versus 17.68 days, respectively, without any significant differences. The probability of newly laid eggs reaching the adult stage was 100%, 100%, and 91% on the saffron pollen, almond+maize pollen, and powdered sugar diet, respectively.

Our results indicate that saffron and almond+maize pollens can be effectively used for the mass-rearing and conservation of the predatory mite N. californicus in biological programs. Although the reproductive efficiency of the predatory mite on the powdered sugar diet was poor (with no fecundity), this diet is suitable for the long-term survival of the predatory mite and can be used to maintain populations during periods of low demand or limited supply. The long lifespan of the powdered sugar diet may be related to its high carbohydrate content; however, the lack of fertility on this diet is due to its deficiency in protein and other essential nutrients. The protein content of pollen is believed to be one of the best indicators of nutritive quality as it is closely linked to the reproductive performance of consumers. The high efficiency of the predator on the saffron and almond+maize pollens is probably due to their high protein content.