Effects of Beauveria bassiana on predation and behavior of the predatory mite Phytoseiulus persimilis

Lethal and Sub-Lethal Effects of Organic-Production-Approved Insecticides and Fungicides on the Predator Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae)

In this study, the effects of paraffin oil, copper hydroxide, copper oxychloride, wettable sulfur, Beauveria bassiana and deltamethrin, as a toxic reference treatment, on the survival and predation rate of M. pygmaeus were investigated. In each treatment, the prey were classified as slightly, partially or fully consumed. The mortality rate after contact exposure was high (66.6%) when nymphs were treated with copper hydroxide but much lower after residual exposure (6.6%). B. bassiana caused 53.3% and 46.6% mortality via contact and residual exposure, respectively. The total prey consumption was significantly lower in the pyrethroid reference treatment control and B. bassiana treatments. The highest percentage of slightly consumed prey was recorded in the toxic reference and B. bassiana treatments, that of partially consumed prey in the copper hydroxide treatment and, finally, that of fully consumed prey in the paraffin oil treatment. Therefore, assessing the sub-lethal effects by separating the prey killed into slightly, partially and fully consumed is a sensitive approach to detect impacts which otherwise may remain unnoticed. The results provide information for the most appropriate use of M. pygmaeus in IPM programs and introduce more sensitive approaches in the detection of side-effects of pesticides on M. pygmaeus and other hemipteran predators.

Acaricide exposure impairs predatory behavior of the phytoseiid mite Neoseiulus idaeus (Acari: Phytoseiidae)

Predation is an important interaction that can change the structure of arthropod communities across both temporal and spatial scales. In agricultural systems predation can reduce the population levels of several arthropod pest species of a community. This predator-prey interaction involves the predator searching and handling behaviors. Several factors can affect this interaction, such as pesticide exposure, which is a frequent feature in agroecosystems. Thus, the hypothesis of our study is that the predatory behavior of the phytoseiid mite Neoseiulus idaeus Denmark & Muma, an important natural enemy of spider mites, is affected by acaricide exposure. To test that hypothesis, the predatory mite was exposed to the acaricides abamectin, fenpyroximate, and azadirachtin in 4 exposure scenarios. The predatory behavior of N. idaeus was negatively affected by acaricide exposure when the leaf surface containing both prey and predator was sprayed leading to a reduction in the frequency of transitions between predator walking and meeting preys. Prey handling and consumption were also compromised by acaricide exposure through contaminated leaf surface and prey, and contaminated leaf surface, prey, and predator. Abamectin compromised predation regardless of the exposure scenario. Acaricide-exposure reduced the number of prey found, number of attacks, and number prey killed by N. idaeus. Moreover, partial prey consumption was observed with acaricide-exposed mites. Thus, caution is necessary while attempting to integrate acaricide applications and mass release of N. idaeus for spider mite management.

Phytoseiid predatory mites can disperse entomopathogenic fungi to prey patches

Recent studies have shown that predatory mites used as biocontrol agents can be loaded with entomopathogenic fungal conidia to increase infection rates in pest populations. Under laboratory conditions, we determined the capacity of two phytoseiid mites, Amblyseius swirskii and Neoseiulus cucumeris to deliver the entomopathogenic fungus Beauveria bassiana to their prey, Frankliniella occidentalis. Predatory mites were loaded with conidia and released on plants that had been previously infested with first instar prey clustered on a bean leaf. We examined each plant section to characterize the spatial distribution of each interacting organism. Our results showed that A. swirskii delivered high numbers of conidia to thrips infested leaves, thereby increasing the proportion of thrips that came into contact with the fungus. The effect was larger when thrips infestation occurred on young leaves than on old leaves. Neoseiulus cucumeris delivered less conidia to the thrips infested leaves. These patterns result from differences in foraging activity between predatory mite species. Amblyseius swirskii stayed longer on plants, especially within thrips colonies, and had a stronger suppressing effect on thrips than N. cucumeris. Our study suggests that loading certain predatory mite species with fungal conidia can increase their capacity to suppress thrips populations by combining predation and dispersing pathogens.

Beauveria bassiana (Ascomycota: Hypocreales)-treated Diamondback Moth (Lepidoptera: Plutellidae) Larvae Mediate the Preference and Functional Response of Euborellia annulipes (Dermaptera: Anisolabididae) Nymphs

Biological control is one of the strategies to reduce populations of diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), the major pest of brassica. Entomopathogen-based biopesticides are recommended and used for its control, reducing the constant use of chemical pesticides. Predators and/or fungal entomopathogens have an increasing interest to be used against diamondback moth, and the compatibility of these control agents in the field is important for pest management. Here we experimentally investigate the effects of diamondback moth larvae treated with a biopesticidal formulation of Beauveria bassiana (Balsamo) Vuillemin in the feeding preference and functional response of the ring-legged earwig. We used untreated and B. bassiana-treated diamondback moth fourth instars (over a 24-h period of exposure) and Euborellia annulipes (Lucas) fifth instars. The nymphs were included in choice condition tests and different larval densities to the analysis of feeding preference and functional responses, respectively. Euborellia annulipes nymphs exhibited no feeding preference under choice conditions but presented different types of functional response: Type II on untreated and type III on fungus-treated diamondback moth larvae. The interaction between E. annulipes and B. bassiana observed in our study contributes to the understanding of the predator-prey-pathogen relationships with implications for P. xylostella integrated management strategies.

Influence of pathogenic fungi on the life history and predation rate of mites attacking a psyllid pest

The two biological control agents, predatory mite Amblydromalus limonicus Garman & McGregor (Acari: Phytoseiidae) and entomopathogenic fungi (EPF) Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae), have the potential to independently suppress the invasive tomato potato psyllid (TPP), Bactericera cockerelli (Šulc), in New Zealand. The integrated strategy of combining the release of predatory mites and EPF may further promote biocontrol of pests. To examine the compatibility of A. limonicus and B. bassiana, we tested the lethal effects of B. bassiana on A. limonicus females on B. cockerelli and calculated the sublethal concentrations of B. bassiana. The effects of sublethal concentrations (LC₁₀ and LC₃₀) of EPF on predatory mite females were assessed on the reproduction parameters of the parental generation (F₀). We also evaluated the transgenerational effects of EPF on life table parameters and predation rates of the offspring generation (F₁) that was fed on the psyllids. Our results showed that A. limonicus females were susceptible to B. bassiana and the LC₅₀ was 2.2 × 10⁵ conidia mL^-1. Sublethal concentrations of EPF (LC₃₀) significantly reduced the fecundity, longevity, oviposition period and predation rates of F₀ predatory mite females. However, life table and predation rates of F₁ predatory mites were not influenced by sublethal concentrations (LC₃₀), except for the reduction of the preadult and total pre-oviposition period, and the predation rate of F₁ males. Also, F₁ population parameters including the intrinsic rate of increase (r_m), finite rate of increase (λ), gross reproduction rate (GRR), and net reproduction rate (R₀) were not significantly influenced by sublethal concentrations (LC₁₀ and LC₃₀). This result suggests that the transgenerational effects of entomopathogenic fungi cannot be carried over to F₁. In conclusion, the simultaneous application of both biological control agents does have the potential to control TPP at appropriate intervals during the crop season. Further evaluation in the field will be needed to confirm the viability of this approach to control TPP.