JMIR Formative Research

Abstract Biological control of invasive thrips is a challenge in many agricultural systems, partly because of a lack of knowledge about their life cycle and interactions with their environment. Thrips parvispinus Karny (Thysanoptera: Thripidae) is an invasive species causing damage to many crops worldwide and on which our knowledge is still limited. We studied the developmental time of T. parvispinus under three different fluctuating temperature regimes, its predatory behaviour against the eggs of a phytoseiid predatory mite and the effect of different food sources on its oviposition rate. We showed that T. parvispinus adult females and L2 larvae can feed on a limited number of Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) eggs and that their predatory behaviour is significantly affected by the nutritional quality of the host plant and the presence of pollen. Additionally, the oviposition rate of T. parvispinus females over six days was not positively affected by the presence of Typha angustifolia pollen, Artemia cysts or prey mites on bean leaves. Finally, we showed that the developmental time of T. parvispinus is relatively fast and comparable to that of the invasive thrips species Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Our study provides further insight into the feeding behaviour of T. parvispinus as an omnivorous pest species and its interactions with its predators. Thrips parvispinus is unlikely to have a negative effect on phytoseiid mite populations and the use of supplementary food to support predatory mites in the crop does not seem to pose a risk of significantly increasing T. parvispinus populations.

Thrips palmi Karny (melon thrips) damages over 200 plant species through direct feeding and vectoring tospoviruses. Excessive use of pesticides has led to melon thrips resistance development, necessitating the exploration of sustainable alternative control options. Entomopathogenic fungi (EPFs) can potentially be an effective alternative biocontrol agent to control melon thrips. In this study, the virulence of nine indigenous EPFs isolates was tested against the second instar larvae and adult melon thrips under laboratory conditions. The promising EPFs were selected and compared to commercial Beauveria bassiana A1 and imidacloprid on susceptible pepper plants infested with melon thrips under greenhouse conditions. The scanning electron microscope (SEM) observation was also performed. The results indicated that, out of the nine EPFs, B. bassiana-NCHU-157 (Bb-NCHU-157) caused the highest mortality in both larval (35%) and adult (98%) thrips at seven days post-inoculation, followed by Metarhizium lepidiotae-NCHU-9 (Ml-NCHU-9), which exhibited 31% larval and 81% adult mortality. Germ tube and appressorium formation were observed under the SEM after 36 h post-inoculation (hpi) for Ml-NCHU-9 and 48 hpi for Bb-NCHU-157 on adult melon thrips, respectively. While all biocontrol treatments were less effective than imidacloprid at suppressing thrips populations, both Bb-NCHU-157 and Ml-NCHU-9 were able to control the thrips population by up to 60% compared to the non-treated control under greenhouse conditions. However, there was no significant difference among Bb-NCHU-157, Ml-NCHU-9, and commercial biopesticide B. bassiana A1 treatments, highlighting the potential of these two indigenous isolates, Bb-NCHU-157 and Ml-NCHU-9, as viable biocontrol agents for melon thrips management.

Clonal invaders can cope with herbivory via clonal integration, but how the impacts of clonal integration are affected by plant-herbivore coevolution history is still poorly understood. Alternanthera philoxeroides (Caryophyllales: Amaranthaceae) is an amphibious clonal invader. The beetle Agasicles hygrophila (Coleoptera: Chrysomelidae) was introduced to control A. philoxeroides, and also feeds on the native Alternanthera sessilis (Caryophyllales: Amaranthaceae) in China. We grew the apical and basal parts of A. philoxeroides and A. sessilis, connected or disconnected with the stolon, and exposed apical parts to A. hygrophila or the native beetle Cassida piperata (Coleoptera: Cassididae) that also feeds on both plants. Both beetles significantly reduced the stem length, belowground biomass and photosynthesis of both plants without clonal integration, and flea beetles had a stronger negative impact on A. philoxeroides than did tortoise beetles. The stem length, stem diameter, belowground and/or aboveground biomass and photosynthetic parameters of apical parts of plants under attack by their corresponding coevolved beetle were 27% ~ 391% higher with clonal integration compared to without. In contrast, when the two plants were attacked by the corresponding beetle without coevolution, the same parameters in either apical or basal parts were unchanged or significantly lower under clonal integration than no integration. These results indicate that artificial disrupting of clonal integration combined with biological control may suppress clonal plants like A. philoxeroides more effectively. Compared with coevolved monophagous herbivores, some oligophagous herbivores in invaded ranges might have a stronger potential to influence the clonal integration capacity of invasive aliens.

Abstract The management of Meloidogyne spp. in tomato crops presents significant challenges for sustainable agriculture. This study evaluates the potential of Nesidiocoris tenuis, Macrolophus pygmaeus, and (Z)-3-hexenyl propanoate—two zoophytophagous mirid species and one of the herbivore-induced plant volatiles (HIPVs) they trigger—to induce systemic resistance against Meloidogyne incognita and M. javanica in tomato plants (cv. Bodar). To this end, we assess the expression of the PIN2 and PR1 genes, related to the jasmonic acid (JA) and salicylic acid (SA) pathways, respectively. Exposure of tomato plants to 15 nymphs of either N. tenuis or M. pygmaeus for 24 or 48 h, and to (Z)-3-hexenyl propanoate for 24 h, before inoculation with 200 second-stage juveniles of the nematodes significantly reduced nematode infectivity and reproduction. Notably, PIN2 gene expression in leaves was upregulated nine- and 14-fold by N. tenuis and M. pygmaeus, respectively, zero days after nematode inoculation (DANI) and was repressed by the nematode seven DANI with a nine-fold decrease, but not when the plants were exposed to M. pygmaeus or N. tenuis, indicating a strong early defense response. However, PR1 expression levels showed no significant changes, suggesting a predominant role of the JA pathway over the SA pathway in the induced resistance. We conclude that induction of systemic resistance in tomato plants by N. tenuis, M. pygmaeus, and (Z)-3-hexenyl propanoate before nematode exposure is a promising strategy for nematode management, at least to suppress nematode infection by the primary inoculum and later reproduction.

The development of cost-effective methods for laboratory and mass rearing of biological control agents necessarily includes the selection of the optimal diet. Experiments with some predatory coccinellids revealed so-called ‘additive effects’: feeding on mixed foods ensures lower mortality, faster larval development and adult maturation, higher fecundity, etc., than feeding on each of the components. These effects were demonstrated for eight of the 11 studied species (although not for all used combinations of foods). Meta-analysis shows that significant additive effect was found in 29.3% of 140 cases resulted from experiments with 11 species of predatory Coccinellidae performed in 21 published studies. However, if (1) one of the two mixed foods was artificial or factitious or if (2) one of the two mixed foods (that of higher quality) was limitedly provided, or if (3) the beneficial effect of mixed foods was estimated by fecundity, rate of maturation, or other indicators of reproductive activity, the probability of detection of a beneficial additive effect increased up to about 50%. These results could be used for the planning of further studies on the selection of optimal diets for laboratory and mass rearing of predatory ladybirds. In particular, a combination of a limited supply of an expensive high quality food with unlimited cheap low quality food could be the most promising and cost-effective approach.

Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae: Caryophyllales) is an aquatic invasive weed from South America with a long history of biological control. The well-studied Agasicles hygrophila Selman & Vogt, 1971 (Coleoptera: Chrysomelidae) successfully controls A. philoxeroides in some parts of its invaded range, but is unsuitable in other areas due to its intolerance to cold temperatures. Amynothrips andersoni O’Neill, 1968 (Thysanoptera: Phlaeothripidae) has shown greater tolerance to cold temperatures, but no research has been conducted to determine its ecological niche with respect to A. philoxeroides. The aim of this study is to predict the environmental niches of A. andersoni and A. hygrophila and their overlap with that of A. philoxeroides in the North and South America under current and future climate scenarios. Accordingly, niche models were constructed in MaxEnt for all three species using environmental variables from the current climate and under two future climate scenarios (SSP1-2.6 and SSP5-8.5) for the year 2040. The niche overlap between the two biological control agents and the host were estimated for all three scenarios. Under both future climate scenarios, the total niche of A. philoxeroides is predicted to decrease by up to 10% whereas niche area is expected to increase by up to 10% for A. andersoni and A. hygrophila. Amynothrips andersoni had a greater niche overlap with A. philoxeroides than did A. hygrophila under all three scenarios, suggesting it is currently more widely suitable for A. philoxeroides biological control and should continue to be in 2040.

In recent years, synthetic microbial communities (SMC) have garnered significant attention as a promising approach to harness the collective capabilities of multiple microbial species across diverse applications, including plant disease management. Advances in omics technologies have provided deeper insights into the complex interactions between plant microbiomes and their surrounding environments. Notably, significant progress has been made in the design and engineering of SMC that exhibit synergistic interactions, demonstrating great potential in managing phytopathogens. Novel tools, such as automated design and artificial intelligence, are increasingly being integrated to enhance the precision and efficiency of SMC engineering. Given the complexity of natural and agricultural plant-associated systems, along with the multitude of variables that influence SMC performance, developing a universal rationale for engineering SMC for biocontrol application remains challenging. This review discusses the design perspective of SMC for biocontrol application, their underlying design principles, critical considerations, and current research endeavors. Additionally, it briefly contemplates the challenges and prospects of SMC application in plant disease management.

Fusarium verticillioides (Hypocreales: Nectriaceae) infects maize, causing stalk rot disease and producing toxins that accumulate in grains. The antifungal activity of seven strains of Paenibacillus polymyxa (Bacillales: Paenibacillaceae) against F. verticillioides was evaluated in vitro using the microbiological growth media potato dextrose agar, malt extract agar, and crushed maize grains. The strain LIS03, which demonstrated the strongest antagonistic activity, was selected for further investigation based on its ability to reduce the severity of stalk rot disease and induce plant-defense enzymes in maize. In the greenhouse, seed inoculation and plant spraying (V4 phenological stage) with LIS03 prior to F. verticillioides injection in the stem were evaluated regarding the activity of phenylalanine ammonia-lyase (PAL) and glutathione reductase (GR) in maize leaves. PAL activity significantly increased in plants inoculated with LIS03 at three and nine days post-inoculation (dpi). In contrast, plants simultaneously inoculated with LIS03 and the pathogen showed an increase of 82% in GR activity 12 dpi. Higher GR activity was correlated with reduced stalk rot severity at 6 dpi (r = − 0.53). In the field, the combination of seed inoculation followed by plant spraying, as well as plant spraying alone, resulted in a 33% reduction in disease severity. Only seed inoculation led to an 18.7% decrease. Although the grains did not show symptoms of fungal diseases in the field experiment, a culture-based blotter test revealed a high incidence of F. verticillioides. The blotter test also showed that grains from silks sprayed with LIS03 presented a reduction of 16% and 25% in the incidence of F. verticillioides in naturally infected and artificially inoculated plants, respectively. These results with P. polymyxa provide a promising avenue for developing biological control strategies for controlling maize diseases caused by F. verticillioides.

Ants tending aphid colonies may reduce the effectiveness of aphid natural enemies, which can result in additional plant damage. However, their mutualistic interaction is complex, and depending on the quantity and quality of the sugar that aphids produce, it may change to a predator–prey interaction. This study aims to test this hypothesis by providing ants with a high-quality sugar supply with the prediction that ants with an extra sugar source should more often prey on aphids and, therefore, the abundance of aphids on plants should decrease. We carried out an experiment on pepper plants infested with Aphis gossypii Glover (Hemiptera: Aphididae) in greenhouses with naturally occurring Tapinoma ibericum Santschi (Hymenoptera: Formicidae) in three different periods. Results showed a significant reduction in aphid abundance and greater aphid predation by ants in plants with an artificial sugar supply. However, the expected effects varied among greenhouses and seasons. A negative effect on aphid abundance was mainly detected in autumn, whereas the largest effect on aphid predation by ants was detected in summer when lower ant activity on the plants occurred. Although our results show that artificial sugar supply changes ant behavior from tending to preying on aphids, the large variation observed indicates that other unconsidered factors influence its effectiveness. Future research should focus on understanding factors driving variations across locations and seasons. Additionally, the effect of sugar feeders and their disruption of the ant-aphid mutualism may improve the access of biological control agents to aphid colonies, which is worth testing.

Blister blight, caused by the fungus Exobasidium vexans, is a major disease affecting tea plants. This study aimed to isolate and evaluate the efficacy of endophytic bacterial strains as potential biocontrol agents against the disease. Thirteen endophytic bacterial strains were isolated from healthy tea plants collected in Thach That, Hanoi, Vietnam. Six of these strains exhibited antagonistic effects against E. vexans, with strains R8 and S2 showing the highest inhibition. Heat-treated bacterial supernatants lost their antifungal activity, indicating that the inhibitory compounds were protein-based. Strain R8, identified as Bacillus subtilis, also demonstrated plant growth-promoting traits, including the production of Indole-3-acetic acid (IAA) and phosphate solubilization. Greenhouse trials showed that both chemical fungicides and antagonistic bacteria significantly reduced disease incidence, with the preventative application of chemical fungicide being the most effective (control efficacy of about 91.05%), followed by preventative inoculation with antagonistic bacteria (82.77%). Additionally, treated plots yielded significantly more fresh tea shoots, with an increase of 19.02% and 21.17% for antagonistic bacteria and chemical fungicide treatments, respectively, compared to the control. These findings suggest that B. subtilis R8 holds promise as a biocontrol agent, providing both disease suppression and yield enhancement in tea cultivation.

Cassava mosaic disease causes major losses of cassava crops in Southeast Asia. The disease is caused by the cassava mosaic virus, which is primarily transmitted by the tobacco whitefly (Bemisia tabaci). Chemical insecticides are widely used to control whitefly populations. However, their effectiveness is limited by environmental issues and whitefly resistance. Biocontrol agents such as entomopathogenic fungi are alternatives to chemical insecticides. We conducted two cassava field trials of the entomopathogenic fungus Beauveria bassiana for the control of whitefly populations. Comparison between plants treated with B. bassiana, buprofezin, or a combination of B. bassiana-buprofezin or B. bassiana-neem oil adjuvant, were tested in the same field. The whitefly adult populations were lowest in the B. bassiana/neem oil treatment group, with up to 86% reduction compared with the control six months after application. Natural enemies of insect pests were unaffected in the B. bassiana/neem oil and B. bassiana-only treatments. Our study revealed that integrated pest management using B. bassiana and neem oil was effective for controlling whiteflies and maintaining the natural balance of insects in cassava fields.

The predatory mites (Phytoseiidae) tested to date cannot effectively control the mite pest Aculops lycopersici (Acari: Eriophyidae) due to the unfavorable characteristics of tomato leaves and stems. However, recent studies show that the phytoseiid, Typhlodromus (Anthoseius) recki, can feed on this pest. Because T. (A.) recki is naturally present in high densities on Mentha suaveolens and Phlomis fruticosa, we performed preliminary studies using these species as banker plants in laboratory and greenhouse conditions. In laboratory conditions, we analyzed the effect of banker plants inoculated with T. (A.) recki and co-planted with tomato plants (infested or not with A. lycopersici) at two banker to tomato plants ratios. T. (A.) recki dispersed and established on tomato plants. Higher predator densities were observed on infested plants when M. suaveolens was used as a banker plant with a ratio of one banker plant to two tomato plants. In greenhouse conditions, predators were introduced on tomato plants (infested with A. lycopersici) via branches of banker plants at two densities. T. (A.) recki significantly reduced the length and intensity of stem russeting and A. lycopersici densities. The number of T. (A.) recki on tomato plants was the highest using branches of M. suaveolens at the higher densities released. These results underscore the efficacy of T. (A.) recki in controlling A. lycopersici and open new avenues for the use of M. suaveolens as a reservoir of this predator.

Barley intercropping is an effective strategy for managing multiple insect pests in cabbage fields. We hypothesized that combining barley with flowering plants can increase pest suppression by enhancing parasitism and predation effects in cabbage fields. This study aimed to evaluate whether the spatial arrangements of flowering plants in a cabbage–barley intercropping system can enhance pest control. We also assessed the roles of predation by ground-dwelling predators, such as carabid beetles, and flight disruption, using Pieris rapae crucivora Boisduval (Lepidoptera: Pieridae) as the target pest. Over two years, planting flowering plants (buckwheat, lacy phacelia, and coriander) around barley-intercropped cabbage showed inconsistent pest suppression compared with those around barley intercropping alone. However, a significant increase in multiple pest suppression and parasitism by two species of parasitoid wasps was observed when cabbage was intercropped with a mixture of barley and buckwheat. This suggests that the proximity of cabbage, barley, and flowering plants plays a key role in pest control. In planter experiments, the carabid beetle Chlaenius micans (Fabricius) (Coleoptera: Carabidae) was able to prey on larval P. rapae crucivora on cabbage plants. Additionally, the flight activity of P. rapae crucivora seemed to be disturbed by the intercropped barley in cabbage fields. These findings highlight the importance of both top-down and bottom-up effects in suppressing pest populations in cabbage–barley–buckwheat intercropping systems.