Selection and validation of optimal reference genes for RT-qPCR analyses in Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae)

Aphidoletes aphidimyza is a predator that is an important biological agent used to control agricultural and forestry aphids. Although many studies have investigated its biological and ecological characteristics, few molecular studies have been reported. The current study was performed to identify suitable reference genes to facilitate future gene expression and function analyses via quantitative reverse transcription PCR. Eight reference genes glyceraldehyde-3-phosphate dehydrogenase (GAPDH), RPS13, RPL8, RPS3, α-Tub, β-actin, RPL32, and elongation factor 1 alpha (EF1-α) were selected. Their expression levels were determined under four different experimental conditions (developmental stages, adult tissues, sugar treatment, and starvation treatment) using qRT-PCR technology. The stability was evaluated with five methods (Ct value, geNorm, NormFinder, BestKeeper, and RefFinder). The results showed that GAPDH, RPL32, and EF1-α were ranked as the best reference gene combinations for measuring gene expression levels among different developing stages and in various starvation treatments. RPL8 and RPS3 were recommended to normalize the gene expression levels among different adult tissues. RPL32, β-actin, and EF1-α were recommended sugar-feeding conditions. To validate the utility of the selected reference pair, RPL8, and RPS3, we estimated the tissue-biased expression level of a chemosensory protein gene (AaphCSP1). As expected, AaphCSP1 is highly expressed in the antennae and lowly expressed in the abdomen. These findings will lay the foundation for future research on the molecular physiology and biochemistry of A. aphidimyza.

Myzus persicae Management through Combined Use of Beneficial Insects and Thiacloprid in Pepper Seedlings

Simple Summary

Myzus persicae is a worldwide pest causing significant economic loss, especially to vegetables. However, the mainly applied insecticides were not effective, whilst also endangering the safety of pollinators. Harmonia axyridis and Aphidoletes aphidimyza are predators of aphids, but they are costly and affected by temperature and insecticides. We conducted toxicity tests and greenhouse trails to make an effective combination of neonicotinoid insecticides and predators. Both H. axyridis and A. aphidimyza effectively controlled aphids whether combined with thiacloprid or not, at above 20 °C temperature condition. Our results indicated that it is it is necessary to choose H. axyridis or A. aphidimyza to control aphids based on economic and thermal considerations. Practically, thiacloprid could be used either as an emergency option to control aphids’ abundance alone or in combination with natural enemies.

Abstract

Excessive insecticide application has posed a threat to pollinators and has also increased insecticide resistance of Myzus persicae Sulzer. Therefore, it is urgent to develop an economical and effective strategy, especially for greenhouse vegetables. Firstly, we selected a neonicotinoid insecticide that is specifically fatal to M. persicae but relatively safe to predators and bumblebees by laboratory toxicity tests and risk assessments. Then, we tested the effectiveness of the neonicotinoid insecticide under different temperature conditions. According to the LC₅₀ values and the hazard quotients, thiacloprid met the requirements. Greenhouse trails indicated that thiacloprid was quite efficient, while control dropped to 80% without the application of thiacloprid. As for biological control, Harmonia axyridis effectively controlled 90% of aphids with thiacloprid or not. However, Aphidoletes aphidimyza performed better above 20 °C. Our results indicated that it is cost-effective to control M. persicae with A. aphidimyza in suitable temperature conditions and H. axyridis was more effective at low temperatures. Practically, thiacloprid could be used either as an emergency option to control aphids’ abundance alone or in combination with natural enemies.

Variable effects of mycorrhizal fungi on predator-prey dynamics under field conditions

Interactions between herbivores and their predators are shaped, in part, by plant phenotype. Consequently, ubiquitous symbionts of plants below-ground, such as arbuscular mycorrhizal fungi (AMF), may influence interactions above-ground between predators and their prey by altering plant phenotype. However, the ecological relevance of below-ground organisms on predator-prey interactions under field conditions remains unclear. We assessed how AMF influence herbivore-predator interactions through a field experiment. We planted two milkweed species (Asclepias curassavica and Asclepias incarnata) provided with different amounts of AMF inoculum (zero, medium, and high) in a randomized block design. We added aphids to plants and reduced predator pressure weekly for 5 weeks to evaluate effects of AMF on predator recruitment. We then allowed herbivore-predator interactions to re-establish naturally for the remainder of the season to examine whether AMF-mediated variation in predator recruitment influenced the suppression of aphid populations. Arbuscular mycorrhizal fungi availability in soils mediated interactions between predaceous aphid midge flies Aphidoletes aphidimyza and their aphid prey Aphis nerii, but the effects were plant species-specific. On A. curassavica, by mid-season, midges were recruited most strongly on plants under medium AMF availability and least on plants under high AMF availability. In contrast, each midge killed fewer aphids with increasing aphid density on medium AMF plants, but killed more aphids with increasing aphid density on high AMF plants. In combination, aphid mortality rates imposed by midges were greatest on medium AMF plants, followed by high and zero AMF plants. By comparison, on A. incarnata, the recruitment of midges was strongest on high AMF plants and weakest on medium AMF plants. AMF had no effect on the number of aphids killed per midge, relative to aphid density, so mortality rates of aphids imposed by midges mirrored recruitment. Rates of decline in aphid populations following predator recolonization were associated with midge densities, as well as lacewing and syrphid densities, which were unaffected by AMF availability. Therefore, the effects of AMF on aphid population decline were not a simple function of AMF-midge interactions. Our findings demonstrate that the availability of AMF in soils has pervasive, but complex, effects on predator-herbivore dynamics in the field.

Leucopis glyphinivora Tanasijtshuk (Diptera: Chamaemyiidae), a new aphidophagous biocontrol agent; development, survival and comparison with Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae)

The silver fly Leucopis glyphinivora Tanasijtshuk (Diptera: Chamaemyiidae) is an aphidophagous predator during its larval stage. Our study describes the life cycle of L. glyphinivora and evaluates its potential as a biocontrol agent. The development, survival and longevity of L. glyphinivora were observed and compared with those of the aphid gall midge Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae). Tests were conducted under laboratory conditions in Petri dishes with the green peach aphid Myzus persicae Sulzer (Hemiptera: Aphididae) on potato leaves. Leucopis glyphinivora has a 42% longer life cycle than A. aphidimyza. Larval development was 27% longer in L. glyphinivora than in A. aphidimyza. Egg hatch rate and pupal emergence rate were similar in both species, but larval survival was 20% lower for L. glyphinivora than for A. aphidimyza. Sex ratio was approximately 50% in both species. A longer development time for L. glyphinivora in the larval stage could be an advantage for biocontrol by providing more time to exert predation pressure against aphids. However, this may be offset by the lower survival rate found in the silver fly larvae.

The Quality of Nonprey Food Affects Cannibalism, Intraguild Predation, and Hyperpredation in Two Species of Phytoseiid Mites

Generalist arthropod predators not only prey on herbivores but also may engage in competitive interactions by attacking and consuming conspecifics (cannibalism) or other predators (intraguild predation [IGP] and hyperpredation). These types of interactions are quite common among predators used in biological control. Although there is evidence that nonprey food relaxes cannibalism and IGP, there is little information regarding the impact of the quality of the nonprey food. Herein, we examined how pollen of different nutritional quality (pine, narrow-leaf cattail, or apple) impacted 1) the cannibalism by females of Euseius stipulatus (Athias-Henriot) (Acari: Phytoseiidae) on conspecific larvae, 2) the reciprocal predation between gravid females of E. stipulatus or Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) and heterospecific larvae, and 3) the predation of E. stipulatus on the eggs of the aphid predator Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). E. stipulatus cannibalism was significantly reduced in the cattail pollen treatment, whereas in the pine pollen it did not significantly differ from control (no food). Predation between I. degenerans and E. stipulatus was significantly reduced in the cattail pollen treatment as compared to the control treatment. Finally, predation of E. stipulatus on A. aphidimyza eggs was significantly reduced when cattail or apple pollen was provided compared to the pine pollen or control treatments. These results suggest that cattail or apple pollen is suitable for mitigating negative interactions among generalist predatory mites used in biological control.

Interactions among the Predatory Midge Aphidoletes aphidimyza (Diptera: Cecidomyiidae), the Fungal Pathogen Metarhizium brunneum (Ascomycota: Hypocreales), and Maize-Infesting Aphids in Greenhouse Mesocosms

The generalist entomopathogenic fungus, Metarhizium brunneum, has proved to have great potential as a versatile biological pest control agent. The gall midge Aphidoletes aphidimyza is a specialist predator that occurs naturally in Europe and has been successfully used for aphid suppression. However, the interaction between these two biological control organisms and how it may affect the biological control of aphids awaits further investigation. As part of the EU-supported project INBIOSOIL, this study was conducted in greenhouse conditions to assess the possible effects of combining both biological control agents. In a randomized complete block design, sweet corn (Zea mays var. saccharata) plants were grown in large pots filled with natural soil or natural soil inoculated with M. brunneum. At the third leaf stage, before being individually caged, plants were infested with Rhopalosiphum padi and A. aphidimyza pupae were introduced in the soil. Aphidoletes aphidimyza midge emergence, number of living midges and number of aphids were recorded daily. The presence of conidia in the soil and on leaves was assessed during the experiment. At the conclusion of the experiment, the number of live aphids and their developmental stage, consumed aphids, and A. aphidimyza eggs was assessed under stereomicroscope. This study’s findings showed that the presence of M. brunneum did not affect A. aphidimyza midge emergence. However, longevity was significantly affected. As the study progressed, significantly fewer predatory midges were found in cages treated with M. brunneum compared to untreated cages. Furthermore, by the end of the study, the number of predatory midges found in the Metarhizium-treated cages was four times lower than in the untreated cages. Both daily and final count of aphids were significantly affected by treatment. Aphidoletes aphidimyza applied alone suppressed the aphid population more effectively than M. brunneum applied alone. Additionally, the aphid population was most suppressed when both agents were combined, though the suppression was less than additive.

Does insect mother know under what conditions it will make their offspring live?

According to the optimal oviposition theory, the larval success of insects depends on the oviposition site selection by females. Females are expected to choose a site with many resources and few competitors or predators to allow the best performance for their progeny, assuming that "mother knows best." However, this is not systematically observed. The Aphidoletes aphidimyza larvae are generalist aphid predators and females consequently lay their eggs near or inside aphid colonies. The goal of this study was to investigate the impact of intraspecific competition on oviposition behavior of A. aphidimyza females. First, we counted the number of eggs laid by a female on a leaf with 20 aphids, in the presence of 0, 2, 4, or 6 conspecific eggs or in the absence of eggs but in presence of 3 virgin females. The same experiment was also performed under choice condition with 2 oviposition sites. Our results show that the presence of low densities of conspecific eggs, or the presence of conspecific females, have no significant impact on the number of eggs laid by A. aphidimyza females. One of the hypotheses advanced to explain these results is the advantages of conspecifics presence. At low densities, the presence of eggs on an oviposition site can indicate the suitability of the site for the females. The conspecific presence can also insure a dilution effect against predator and increase the presence of potential mating partners for this monogenic species.

Impact of Humidity on the Biological Development of Aphidoletes aphidimyza (Diptera: Cecidomyiidae)

Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae) is one of the most important predators used in the augmentative biological control of aphids worldwide. However, due to its particular life history, mass rearing A. aphidimyza remains difficult. Our results show that a high relative humidity level during pupation optimizes the development of A. aphidimyza . By improving humidity levels during pupae storage, we improved the production efficiency and nearly achieved a 100% adult emergence rate. These results allow us to suggest a new rearing method for the aphid predator A. aphidimyza .

Target Host Finding by Steinernema feltiae and Heterorhabditis bacteriophora in the Presence of a Non-Target Insect Host

The ability of Steinernema feltiae or Heterorhabditis bacteriophora infective juveniles (IJ), when applied to the soil surface, to infect a Galleria mellonella larva at the base of a soil-filled cup (276 cm(3)) was evaluated in the presence and absence of 100 larvae of a non-target insect, the aphid midge Aphidoletes aphidimyza, near the soil surface. In all four trials with either S. feltiae or H. bacteriophora, A. aphidimyza presence did not affect the number of IJ finding and infecting a G. mellonella larva. Steinernema feltiae and H. bacteriophora IJ movement (as measured by the percentage of IJ aggregating on either side of an experimental arena) in the presence of one or many A. aphidimyza larvae was evaluated in agar- and soil-filled petri dishes, respectively. Infective juvenile movement in the presence of A. aphidimyza did not differ from random, indicating that IJ were not attracted to A. aphidimyza. It is suggested, therefore, that A. aphidimyza does not reduce IJ efficacy when these two forms of biological control agent are present together in a field situation even though it is known that A. aphidimyza is susceptible to IJ of these species.