Crop plants exhibit a wide diversity of defensive traits and strategies to protect themselves from damage by herbivorous pests and disease. These defensive traits may be naturally occurring or ...artificially selected through crop breeding, including introduction via genetic engineering. While these traits can have obvious and direct impacts on herbivorous pests, many have profound effects on higher trophic levels, including the natural enemies of herbivores. Multi-trophic effects of host plant resistance have the potential to influence, both positively and negatively, biological control. Plant defense traits can influence both the numerical and functional responses of natural enemies; these interactions can be semiochemically, plant toxin-, plant nutrient-, and/or physically mediated. Case studies involving predators, parasitoids, and pathogens of crop pests will be presented and discussed. These diverse groups of natural enemies may respond differently to crop plant traits based on their own unique biology and the ecological niches they fill. Genetically modified crop plants that have been engineered to express transgenic products affecting herbivorous pests are an additional consideration. For the most part, transgenic plant incorporated protectant (PIP) traits are compatible with biological control due to their selective toxicity to targeted pests and relatively low non-target impacts, although transgenic crops may have indirect effects on higher trophic levels and arthropod communities mediated by lower host or prey number and/or quality. Host plant resistance and biological control are two of the key pillars of integrated pest management; their potential interactions, whether they are synergistic, complementary, or disruptive, are key in understanding and achieving sustainable and effective pest management.
Entomopathogenic nematodes (EPNs) provide economic control of various insect pests. However, field efficacy can be inconsistent. The ability of a nematode to find and infect (invade) a host insect is ...critical to successful pathogenesis. Thus, behaviors including dispersal and infectivity play important roles in improving efficacy. Previously, we discovered that EPN-infected host substances enhance nematode dispersal. Later we found that a mixture of pheromones in the infected host induced dispersal and improved EPN efficacy. In this study, we determined if dispersal-inducing pheromone extracts also increase nematode infectivity (the propensity to invade a host insect). Two nematode species,
and
, and two insect hosts,
and
, were tested. We discovered that conspecific dispersal pheromone extracts of each EPN species enhanced infectivity. These results indicate that the utility of dispersal pheromone extracts for enhancing EPN activity and biocontrol efficacy is improved not only due to increased nematode movement, but also due to increased host infection.
A new strain of Cordyceps javanica (wf GA17) was observed causing widespread epizootics among whiteflies in Southern Georgia in 2017. The tolerance of conidia to environmental factors including ...variable temperature and ultraviolet (UV) light was compared between this strain and three commercial strains of entomopathogenic fungi (Metarhizium brunneum F52, Cordyceps fumosorosea Apopka97, and Beauveria bassiana GHA). Under 10–30 °C, C. javanica wf GA17 responded similarly to other fungi, with the highest virulence against Galleria mellonella at 25 °C, followed by 20, 30, and 15 °C; lowest virulence was observed at 10 °C. At 35 °C and 40 °C, C. javanica wf GA17 had lower tolerance than M. brunneum F52 and B. bassiana GHA, but was superior to C. fumosorosea Apopka97 in conidia viability and post-treatment virulence. After exposure to −20 °C for 56 d, C. javanica wf GA17 exhibited lower germination than M. brunneum F52 and lower virulence than M. brunneum F52 and B. bassiana GHA, but higher germination and virulence than C. fumosorosea Apopka97. Following exposure to strong UV light, viability and virulence of all fungi were reduced with increasing exposure periods. Increased environmental tolerance of C. javanica wf GA17 over C. fumosorosea Apopka97 suggests that the new strain could have applicability for commercial pest management.
The apple maggot,
(Walsh) (Diptera: Tephritidae), is considered a key pest of apples and is native to the eastern United States. The virulence of seven different species of entomopathogenic nematodes ...(EPN) was assessed against pupae of
under laboratory conditions. Nematode species and strains included
(ALL strain),
(SN strain),
(355 strain),
(VS strain),
(VS strain),
(HOM1 strain), and
(UK211 strain). We conducted three bioassays: (i) short-term exposure cup bioassay (7 d), (ii) long-term cup bioassay (30 d), and (iii) pot bioassay (30 d). In the short-term exposure bioassay, all nematode strains (applied at 54 infective juvenile nematodes (IJs) cm
) significantly reduced (range: 42.9-73.8%) insect survival relative to the control, but no differences were observed among the treatments. For the long-term exposure bioassay, using the same EPN application rate as the short exposure assay, all treatments reduced adult
emergence compared with the control.
was the most virulent (28.3% survival), and
and
were the least virulent (53.3% survival). In the pot experiment,
and
(applied at 27 IJs cm
) had the highest virulence (23.3 and 31.7% survival of
, respectively), while
was the least effective (68.33% survival). Our results indicate that
,
, and
have substantial potential to attack
pupae, and their field application under the tree canopy (prior to adult emergence) in the spring when temperatures are conducive might be a good option for successful IPM of apple maggot fly.
The peachtree borer, Synanthedon exitiosa (Say) (Lepidoptera: Sesiidae), is a major pest of stone fruits including the peach Prunus persica (L.) Batsch. The entomopathogenic nematode, Steinernema ...carpocapsae, was previously shown to be an effective tool for controlling S. exitiosa. In orchards where irrigation is not available, a sprayable gel (Barricade®) can be used to maintain soil moisture which can facilitate nematode efficacy. However, rates of nematode and Barricade® application had not been optimized for their maximum economic and biocontrol efficiency. Therefore, our objective was to compare rates of S. carpocapsae and Barricade® in field trials. Nematodes were tested at per-tree application rates of 1.5 million, 1 million and 0.5 million infective juveniles. The sprayable gel was used at two rates, 4% and 2%. A reduction in the used nematodes from 1.5 million to 0.5 million per tree showed no difference in efficacy. Similarly, using the gel at half rate also did not impact the efficacy, and treatments containing nematodes controlled the S. exitiosa better than the chlorpyrifos control in several of the tests (p < 0.05). As an added benefit, the nematode treatments were also able to reduce the prevalence of weevil (Coleoptera: Curculionidae) populations as secondary pests of the peach trees. The lower rates of grower inputs will reduce costs, making the nematode biocontrol of the peachtree borer more likely to be adopted by commercial growers of peach.
Abstract
Entomopathogenic nematodes in the genera Steinernema and Heterorhabditis, produced through in vitro or in vivo methods, are effective insect biological control agents. In vivo production ...yields good-quality nematodes, but the costs associated with obtaining insects and labor make this production system have a low economy of scale. Conceivably, if growers can produce their own nematodes, then the cost could be reduced. Grower-based production systems described to-date are not sustainable because they rely on outside sources to obtain or calibrate inoculum. Here, we describe a self-sufficient grower-based system where the grower can produce in-house nematodes after obtaining the initial inoculum from a reliable source. We validated our approach in 2 experiments comparing in vivo nematode production from standard White traps and a grower-based approach using polyacrylamide gel. For both tested species, Steinernema carpocapsae (Weiser) and Heterorhabditis bacteriophora Poinar, the grower-based approach produced equal to or more nematodes than the standard method. For example, when comparing the average yield of S. carpocapsae-infective juveniles per Galleria mellonella cadaver (n = 30), the standard White trap method produced 159,114 ± 9,669, whereas the grower-based approach produced 244,029 ± 16,241. The sustainable system described herein has promise for wide adoption by growers.
Display omitted
•Pheromone treated EPNs exhibited enhanced dispersal in soil columns.•Pecan weevils, and black soldier flies had lowest survival with pheromone treated EPNs.•Pheromones increase EPN ...dispersal and host mortality.
Inconsistency in entomopathogenic nematode (EPN) efficacy is still one of the biggest challenges for the wider adoption of EPNs as biocontrol agents. Previous studies demonstrated that extracts from EPN-infected hosts enhance dispersal and efficacy, two key factors in success of EPNs. Some active components in the insect host cadavers responsible for dispersal, ascarosides, have been identified as nematode pheromones. We hypothesized that pheromone extracts increase dispersal of EPN infective juveniles (IJs) leading to increased efficacy. First, we determined whether pheromone extracts improved IJ movement/dispersal in soil columns baited with Tenebrio molitor larvae. We found that pheromone extracts induced higher numbers of Steinernema carpocapsae and Steinernema feltiae IJs to move towards T. molitor larvae in the bottom of the column compared to IJs treated with infected cadaver macerate and water, positive and negative controls, respectively. Furthermore, the number of S. carpocapsae IJs that invaded T. molitor larvae was higher for the pheromone extract treatment than the controls. S. feltiae IJs that were pretreated with pheromone extracts and macerate (positive control) infected T. molitor at the same rate but invasion was superior to IJs that were treated with water. Consistent with the soil column tests, both S. carpocapsae and S. feltiae IJs treated with pheromone extracts performed better in killing larvae of two economically important insect larvae, pecan weevil, Curculio caryae, and black soldier fly, Hermetia illucens, in greenhouse tests compared to IJs treated with water. We demonstrated pheromone-mediated behavioral manipulation of a biological control agent to enhance pest control potential. Conceivably, nematodes can be exposed to efficacy-enhancing pheromones prior to field application.
Tobacco thrips, Frankliniella fusca (Hinds) is an economically significant pest. Entomopathogenic nematodes (EPNs) have shown promise as biocontrol agents against certain thrips species, but they ...have not been explored for suppression of F. fusca. We investigated the potential of EPNs to manage F. fusca by conducting three different bioassays: 1) a small cup dose–response bioassay (25, 50, and 100 IJs cm–2) with four EPN species, 2) a broad virulence bioassay with eight EPN species at 100 IJs cm–2, and 3) a potted soil bioassay testing with four EPN species (100 IJs cm–2). In the dose–response bioassay, all treatments showed relatively lower adult emergence when compared with the control group, but the minimum adult emergence (30%) was observed at 7 d post-treatment when Heterorhabditis bacteriophora (FL1-1) was applied at the highest rate (100 IJs cm–2). In the broad virulence study, all EPN treatments caused significant reductions in F. fusca adult emergence (18.3–75.0%) in comparison with the control. H. bacteriophora (Fl1-1) was more virulent than other nematode treatments but statistically not different from Steinernema feltiae and Steinernema riobrave, while Steinernema rarum was the least virulent. In the potted soil bioassay, the lowest emergence (10.6%) was observed in H. bacteriophora (Fl1-1) treatment, followed by S. feltiae (SN), S. riobrave (355), and Heterorhabditis indica (HOM1) treatments. These results indicate that EPNs have the ability to suppress the soil dwelling stage of F. fusca and should be explored further under greenhouse and field conditions for biocontrol potential within an integrated pest management (IPM) context.
The objectives of this study were to quantify the virulence of four entomopathogenic fungal species to pupae of Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) and to determine the potential to ...combine entomopathogenic fungi (EPFs) and entomopathogenic nematodes (EPNs) for biological control of this pest. The four species of EPFs included Beauveria bassiana (strain GHA), Metarhizium brunneum (strain F52), Isaria javanica (wf GA17), and Isaria fumosorosea (Apopka 97 strain). In laboratory assays, all fungi reduced adult emergence but there were no differences between fungal species. Isaria javanica and M. brunneum were examined further in a EPFs and EPNs bioassay that also included the EPNs Steinernema carpocapsae (ALL strain) and S. riobrave (355 strain). All nematodes and fungi were applied either alone or in combination (fungus + nematode). There were no differences between species within the same entomopathogen group (fungi and nematodes). However, the treatment with S. riobrave resulted in lower R. pomonella emergence than either fungal species. The combination of S. riobrave and I. javanica resulted in the lowest R. pomonella emergence (3%) at fourth-week interval, which was significantly lower than any of the single-agent applications, yet virulence of the other three combination treatments was not different from their respective nematode treatments applied alone. Additive interactions were detected for all fungus–nematode combinations. This study suggests that application of entomopathogenic nematodes and fungi could be an effective option to suppress R. pomonella populations.
•Grandevo (Chromobacterium subtsugae) reduced pecan aphid populations in a pecan orchard.•Populations of lady beetles and green lacewings were conserved with Grandevo.•Chemical insecticides ...controlled aphids, but reduced natural enemy populations.
The pecan weevil, Curculio caryae (Horn) (Coleoptera: Curculionidae), and the pecan aphid (Hemiptera: Aphididae) complex: black pecan aphid, Melanocallis caryaefoliae (Davis), blackmargined aphid, Monellia caryella (Fitch), and yellow pecan aphid, Monelliopsis pecanis Bissell are major pests of pecan production. Management is primarily based on chemical insecticides, and alternative control methods need to be explored. Prior field tests showed that the microbial insecticide Grandevo® (based on Chromobacterium subtsugae) can suppress C. caryae at similar rates to insecticides, and a laboratory test showed that Grandevo is toxic to M. caryaefoliae. However, it was unknown if Grandevo applications targeted towards C. caryae also impact the pecan aphid complex and aphid natural enemies. Hence, we initiated a field study to determine the impact of two rates of Grandevo (2.24 and 3.36 kg/ha) on aphid, Coccinellidae (Coleoptera) and Chrysopidae (Neuroptera) populations. Both Grandevo rates, in both years of the study, suppressed M. caryaefoliae in comparison to the negative control. Only the standard chemical insecticide regimen suppressed M. caryella and M. pecanis combined populations during both years of the experiment. In 2016, both Grandevo rates had more abundant natural enemy populations compared with the chemical insecticide regimen, and the higher Grandevo rate (3.36 kg/ha) had more natural enemies than the non-treated control. In 2017, all treatments had comparable populations of natural enemies. These findings suggest that a microbial insecticide can manage multiple insect pests while preserving the natural enemy community.
PDF
