Biological Control Potential and Drawbacks of Three Zoophytophagous Mirid Predators against Bemisia tabaci in the United States

Begomovirus Transmission to Tomato Plants Is Not Hampered by Plant Defenses Induced by Dicyphus hesperus Knight

Plants can respond to insect infestation and virus infection by inducing plant defenses, generally mediated by phytohormones. Moreover, plant defenses alter host quality for insect vectors with consequences for the spread of viruses. In agricultural settings, other organisms commonly interact with plants, thereby inducing plant defenses that could affect plant-virus-vector interactions. For example, plant defenses induced by omnivorous insects can modulate insect behavior. This study focused on tomato yellow leaf curl virus (TYLCV), a plant virus of the family Geminiviridae and genus Begomovirus. It is transmitted in a persistent circulative manner by the whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), posing a global threat to tomato production. Mirids (Hemiptera: Miridae) are effective biological control agents of B. tabaci, but there is a possibility that their omnivorous nature could also interfere with the process of virus transmission. To test this hypothesis, this study first addressed to what extent the mirid bug Dicyphus hesperus Knight induces plant defenses in tomato. Subsequently, the impact of this plant-omnivore interaction on the transmission of TYLCV was evaluated. Controlled cage experiments were performed in a greenhouse setting to evaluate the impact of mirids on virus transmission and vector acquisition by B. tabaci. While we observed a reduced number of whiteflies settling on plants exposed to D. hesperus, the plant defenses induced by the mirid bug did not affect TYLCV transmission and accumulation. Additionally, whiteflies were able to acquire comparable amounts of TYLCV on mirid-exposed plants and control plants. Overall, the induction of plant defenses by D. hesperus did not influence TYLCV transmission by whiteflies on tomato.

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.

Biological traits of the zoophytophagous predatory mirid Nesidiocoris poppiusi (Heteroptera: Miridae), a candidate biocontrol agent in China

Mirid predators are increasingly used in biological control of multiple greenhouse crops pests. However, due to great morphological similarity and tiny body size, some mirid predators have been largely confused with their allied species. Nesidiocoris tenuis Reuter as a commercial mirid predator was confused largely with Nesidiocoris poppiusi Carvalho in China. To evaluate the biocontrol potential of N. poppiusi, its biological traits and the functional response to Bemisia tabaci Gennadius were studied compared with N. tenuis under laboratory conditions. The results showed that no significant differences of the developmental times from the first instar to adult stages between the 2 mirids fed on Corcyra cephalonica Stainton eggs were observed, while N. poppiusi had better population growth parameters than N. tenuis. Under the condition with prey, both female and male of N. poppiusi lived significantly longer than those of N. tenuis. It could lay 74.0 eggs, which was significantly higher than that of N. tenuis (30.2 eggs). Under the condition without prey, both N. poppiusi and N. tenuis couldn't complete development to adulthood on tomato, tobacco, muskmelon, and cabbage leaves, however, tobacco and tomato were more suitable than the other 2 plants. A type II functional response was observed for both males and females of the 2 predators. Nesidiocoris poppiusi females consumed significantly more B. tabaci pupae than N. tenuis when prey densities were large than 30. Our results indicated that N. poppiusi could be a promising candidate for biological control of B. tabaci.

Do releases of the mirid predator Macrolophus basicornis (Hemiptera: Miridae) together with the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) improve biological control of Tuta absoluta (Lepidoptera: Gelechiidae) in tomato?

During the past decade, the use of predatory mirids alone or combined with releases of egg parasitoids of the genus Trichogramma have been tested in Europe for biological control of the worldwide invasive pest, Tuta absoluta (Meyrick). Here, we evaluated the control of this pest by the release of the Neotropical mirid Macrolophus basicornis (Stal), the Neotropic/Nearctic parasitoid Trichogramma pretiosum Riley, and by combined releases of the predator and the parasitoid. Tests were conducted in greenhouse compartments during the summer and fall season. Each compartment contained 10 tomato plants in which only the pest was released or the pest with 1 or 2 natural enemies. Plant damage, and pest and natural enemy densities were checked weekly on one apical, medium, and bottom leaf of 5 plants. Both M. basicornis and T. pretiosum significantly reduced T. absoluta density when released alone. Combined releases resulted in a 10% higher reduction during the summer season, but not during the fall season. The damage caused by T. absoluta was significantly higher in control treatments than in all natural enemy treatments: at the end of the summer trial leaves were completely damaged in the control treatment, whereas only up to 25% leaf damage occurred in the natural enemy treatments. Combined releases did not result in lower damage than with releases of either M. basicornis or T. pretiosum. Practical aspects of single and combined releases are discussed.

Effects of short-term extreme temperature treatment on the development and reproductive capacity of Encarsia formosa

Encarsia formosa is a natural enemy of the invasive pest Bemisia tabaci and is known to be a dominant parasitic. The frequency and magnitude of climate extremes, particularly temperature extremes, have increased, which has put insect populations at risk. However, the effects of temperature extremes on E. formosa are not well understood. To examine the impact of short-term extreme temperature exposure on the development and reproduction of E. formosa, eggs, larvae, pupae, and adults were exposed to high/low temperature treatments (HLT₂₅, HLT₅₀, LLT₂₅, and LLT₅₀). Our findings indicate that the pupal stage of E. formosa exhibited the strongest tolerance to both heat and cold, while adults exhibited a weaker tolerance. The shortest egg-to-adult development period of 12.65 days was observed in E. formosa exposed to HLT₅₀ treatment during the egg-larval stage. The parasitism peak of the adult stage was delayed by 1-6 days after exposure to extreme temperatures during the egg-larval stage. Conversely, the parasitism peak was advanced by 1-3 days after exposure to extreme temperatures during the pupal and adult stages. The eclosion rate, total parasitism, eclosion rate of the F₁ generation, and adult longevity of the F₁ generation were lower in the treatment groups than in the control groups. The F₁ generation's development period was prolonged to 15.49 and 15.19 days after exposure to HLT₂₅ and HLT₅₀ treatments, respectively, during the egg-larval stage. The F₁ generation's development period was shortened to 13.33 days after exposure to LLT₅₀ treatment during the pupal stage. Male individuals appeared in the F₁ generation after exposure to HLT₅₀ treatment during the pupal stage, with females accounting for only 56.38%. Our results demonstrate that short-term exposure to extreme temperatures has detrimental effects on the growth and reproduction of E. formosa. In field biocontrol against E. formosa, the release of E. formosa should be avoided as much as possible when the ambient temperature is higher than 35°C or lower than 0°C. During extreme temperature conditions, timely supplementation and release of E. formosa population, along with ventilation and cooling in greenhouse facilities during summer, are necessary for better pest control efficacy.

Sesame as an Alternative Host Plant to Establish and Retain Predatory Mirids in Open-Field Tomatoes

The silverleaf whitefly (Bemisia tabaci) and the South America tomato pinworm (Tuta absoluta) are two of the most destructive pests of tomato. Open-field tomato production frequently relies on chemical treatments, which has been shown to lead to pesticide resistance. The integration of biological control using predatory mirid bugs is an effective alternative method for managing these pests. However, methods to establish and maintain populations of zoophytophagous mirids are not adequately described. We explored the potential use of two mirids naturally occurring in Florida, Nesidiocoris tenuis and Macrolophus praeclarus. We conducted 6 field experiments over 4 consecutive years to develop a strategy to maintain the mirids. Pre-plant inoculation of tomato plants did not lead to their establishment, likely due to the low prevalence of prey. We explored the use of sesame (Sesamum indicum) to retain the mirids. Intercropping sesame maintained the populations of N. tenuis throughout the duration of the crop. Macrolophus praeclarus never established in any of the open-field experiments. Nesidiocoris tenuis damage was minimal (<1 necrotic ring/plant) and mirid damage was reduced in the presence of sesame. Our results show that intercropping sesame may provide a means to utilize mirids to manage B. tabaci, an established pest, and provide options to tomato growers should T. absoluta invade USA.

Half Friend, Half Enemy? Comparative Phytophagy between Two Dicyphini Species (Hemiptera: Miridae)

Despite their importance as biological control agents, zoophytophagous dicyphine mirids can produce economically important damage. We evaluated the phytophagy and potential impact on tomato plants of Dicyphus cerastii and Nesidiocoris tenuis. We developed a study in three parts: (i) a semi-field trial to characterize the type of plant damage produced by these species on caged tomato plants; (ii) a laboratory experiment to assess the effect of fruit ripeness, mirid age, and prey availability on feeding injuries on fruit; and (iii) a laboratory assay to compare the position of both species on either fruit or plants, over time. Both species produced plant damage, however, although both species produced scar punctures on leaves and necrotic patches on petioles, only N. tenuis produced necrotic rings. Both species caused flower abortion at a similar level. Overall, N. tenuis females produced more damage to tomato fruit than D. cerastii. There was an increased frequency of D. cerastii females found on the plants over time, which did not happen with N. tenuis. Our results suggested that, although D. cerastii caused less damage to fruit than N. tenuis, it still fed on them and could cause floral abortion, which requires field evaluation and caution in its use in biological control strategies.

Biological traits of the predatory mirid Macrolophus praeclarus, a candidate biocontrol agent for the Neotropical region

The predatory mirid Macrolophus praeclarus is widely distributed throughout the Americas, and is reported to prey upon several horticultural pest species. However, little is known about its biology, thermal requirements, crop odour preferences, phytophagy, and capability to induce defensive responses in plants. When five temperatures studied (20, 25, 30, 33 and 35°C) were tested and Ephestia kuehniella was used as prey, the developmental time from egg to adult on tomato, was longest at 20°C (56.3 d) and shortest at 33°C (22.7 d). The ability of nymphs to develop to adults decreased as the temperature increased, with the highest number of nymphs reaching the adult stage at 20°C (78.0%) and lowest at 35°C (0%). The lower and upper developmental thresholds were estimated at 11.2° and 35.3°C, respectively. The maximum developmental rate occurred at 31.7°C and the thermal constant was 454.0 ± 8.1 degree days. The highest predation rate of E. kuehniella eggs was obtained at 30°C. In Y-tube olfactory choice tests, M. praeclarus selected tomato, sweet pepper and eggplant odours more frequently than no plant control treatment. Macrolophus praeclarus feeding did not damage tomato plants compared to another zoophytophagous mirid, Nesidiocoris tenuis, which caused necrotic rings. The phytophagy of M. praeclarus induced defensive responses in tomato plants through the upregulation of the jasmonic acid metabolic pathway. The implications of the findings for using M. praeclarus in tomato biological control programmes in the Americas are discussed.