Assessing the Effects of Bt Maize on the Predatory Mite Neoseiulus cucumeris

The investigation of Neoseiulus cucumeris in the context of the ecological risk assessment of insect resistant transgenic plants is of particular interest as this omnivorous predatory mite species is commercially available and considered important for biological control. In a multitrophic feeding experiment we assessed the impact of Bt maize on the performance of N. cucumeris when offered spider mites (Tetranychus urticae) reared on Bt (Bt11, Syngenta) or non-Bt maize (near isogenic line) and Bt or non-Bt maize pollen as a food source. Various parameters including mortality, development time, oviposition rate were measured. Spider mites were used as a prey for N. cucumeris, since these herbivores are known to contain similar levels of Cry1Ab toxin, when reared on Bt maize, as those found in the transgenic leaf material. In contrast, toxin levels in pollen of this transgenic cultivar are very low. No differences in any of the parameters were found when N. cucumeris was fed with spider mites reared on Bt and non-Bt maize. Pollen was shown to be a less suitable food source for this predator as compared to spider mites. Moreover, subtle effects on female N. cucumeris (9% longer development time and 17% reduced fecundity) were measured when fed with pollen originating from Bt maize as compared to non-Bt maize pollen. Our findings indicate that the predatory mite N. cucumeris is not sensitive to the Cry1Ab toxin as no effects could be detected when offered Bt-containing spider mites, and that the effects found when fed with Bt maize pollen can be assigned to differences in nutritional quality of Bt and non-Bt maize pollen. The significance of these findings is discussed with regard to the ecological relevance for risk assessment of transgenic plants.     

Suseptibility of the Predatory Mite,Neoseiulus californicus (Acari: Phytoseiidae), to Seven Insecticides

Susceptibility of the predatory mite, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae), to the field rates of seven commercial insecticides was evaluated in laboratory bioassays. In direct treatments with lufenuron, novaluron, pyrifluquinazon, and sulfoxaflor, 82–88% of N. californicus adult females survived 168 h after exposure. Females exposed to these four insecticides produced 14–19% fewer eggs compared to females in the control group. Eclosion of eggs deposited by treated females was not affected. The percentage of eggs that hatched and larval survival following direct exposure to these four insecticides were not seriously reduced. A total of 72–82% of immature N. californicus survived on leaf discs with residues of lufenuron, novaluron, pyrifluquinazon, and sulfoxaflor matured to adults. Emamectin benzoate, lepimectin and spirotetramat were highly toxic to both N. californicus adult females and larvae. Based on these results, lufenuron, novaluron, pyrifluquinazon and sulfoxaflor are promising candidates for use in integrated pest management programs where N. californicus is a major natural enemy.     

Cloning and Functional Characterization of Two BTB Genes in the Predatory Mite Metaseiulus occidentalis

Proteins containing the BTB (Bric-à-brac, tramtrack, and Broad Complex) domain typically share low sequence similarities and are involved in a wide range of cellular functions. We previously identified two putative and closely related BTB genes, BTB1 and BTB2, in the genome of the predatory mite Metaseiulus occidentalis. In the current study, full-length BTB1 and BTB2 cDNAs were cloned and sequenced. BTB1 and BTB2 encode proteins of 380 and 401 amino acids, respectively. BTB1 and BTB2 proteins each contain an N-terminal BTB domain and no other identifiable domains. Thus, they belong to a large category of BTB-domain proteins that are widely distributed in eukaryotes, yet with largely unknown function(s). BTB1 and BTB2 gene knockdowns in M. occidentalis females using RNAi reduced their fecundity by approximately 40% and 73%, respectively, whereas knockdown had no impact on their survival or the development of their offspring. These findings suggest these two proteins may be involved in processes related to egg production in this predatory mite, expanding the list of functions attributed to these diverse proteins.     

Effects of Foraging Experiences on Residence Time of the Predatory Mite <Emphasis Type="BoldItalic">Neoseiulus womersleyi</Emphasis> in a Prey Patch

We investigated the effects of foraging experiences on the residence time of Neoseiulus womersleyi in a currently inhabited prey (Tetranychus urticae) patch. Satiated predators that had experienced starvation stayed longer in a current patch than those that had not experienced starvation. Satiated predators that had experienced a prey-rich patch showed approximately the same residence time in the current patch irrespective of the number of prey therein. By contrast, satiated predators that had experienced a prey-poor patch stayed longer in a current patch of high prey density than in one of low prey density. N. womersleyi appears to determine residence time in the current patch based on foraging experiences together with the quantity of prey in the current patch.     

Genetic Variation in Foraging Traits and Life-History Traits of the Predatory Mite Neoseiulus womersleyi (Acari: Phytoseiidae) among Isofemale Lines

The predatory mite Neoseiulus womersleyi shows a significant correlation between its olfactory response and dispersal tendency in different geographical populations. This study investigated the genetic background of the relationship using isofemale lines. Y-tube olfactometer tests confirmed that there was a genetic component in predator response to herbivore-induced plant volatiles. Wind tunnel tests in the absence of the herbivore-induced plant volatiles revealed that the dispersal tendencies of N. womersleyi exhibited genetic variation among isofemale lines, and other experiments revealed the existence of significant differences in prey consumption rate, fecundity, and developmental time. However, there was no genetic correlation between behavioral traits (olfactory response, innate dispersal) and the other traits, suggesting that the positive correlation between the behavioral traits was not caused by genetic factors.     

Intraguild Interactions Between the Predatory Mites Neoseiulus californicus and Phytoseiulus persimilis

Species at the same trophic level may interact through competition for food, but can also interact through intraguild predation. Intraguild predation is widespread at the second and third trophic level and the effects may cascade down to the plant level. The effects of intraguild predation can be modified by antipredator behaviour in the intraguild prey. We studied intraguild predation and antipredator behaviour in two species of predatory mite, Neoseiulus californicus and Phytoseiulus persimilis, which are both used for control of the two-spotted spider mite in greenhouse and outdoor crops. Using a Y-tube olfactometer, we assessed in particular whether each of the two predators avoids odours emanating from prey patches occupied by the heterospecific predator. Furthermore, we measured the occurrence and rate of intraguild predation of different developmental stages of P. persimilis and N. californicus on bean leaves in absence or in presence of the shared prey. Neither of the two predator species avoided prey patches with the heterospecific competitor, both when inexperienced with the other predator and when experienced with prey patches occupied by the heterospecific predator. Intraguild experiments showed that N. californicus is a potential intraguild predator of P. persimilis. However, P. persimilis did not suffer much from intraguild predation as long as the shared prey was present. This is probably because N. californicus prefers to feed on two-spotted spider mites rather than on its intraguild prey.     

Resource-Dependent Giving-Up Time of the Predatory Mite, Phytoseiulus persimilis

We examined the effect of prey (Tetranychus urticae) egg density on leaving rate of the predatory mite, Phytoseiulus persimilis, from leaf disks using predators with different feeding experiences and levels of external volatile cues related to their prey. Predators stayed longer on disks with prey eggs than on those without prey eggs. However, at each prey egg density predators stayed longer in the absence of prey-related volatiles from an external source. Starved predators stayed longer in a prey patch than those that had not experienced starvation. At each prey density, starved P. persimilis consumed a greater proportion of prey eggs than satiated predators. The total prey consumption of starved predators appears to be related to their longer residence time on source disks compared to satiated predators and also the per capita consumption rate was greater for starved predators compared to satiated predators.     

Correlation between Olfactory Responses, Dispersal Tendencies, and Life-history Traits of the Predatory Mite Neoseiulus Womersleyi (Acari: Phytoseiidae) of Eight Local Populations

To investigate the relationship between foraging behavior and life-history traits of the predatory mite Neoseiulus womersleyi, the olfactory responses, dispersal ratios from a prey patch, predation rates, fecundity, and developmental times in eight local populations of N. womersleyi were investigated. Significant differences among local populations were found in all these traits except fecundity. None of the life-history traits correlated with foraging behavior. A significant positive correlation was found only between the olfactory response and the dispersal ratio. These results suggested that predatory mites with low olfactory responses would stay in a prey patch longer than predatory mites with high olfactory responses.     

Species and Strain Identification of the Predatory Mite Euseius Finlandicus by RAPD-PCR and ITS Sequences

The variation within and between Finnish Euseius finlandicus populations was investigated by RAPD-PCR and ITS sequence analyses. Resin DNA extraction was found to be a suitable method for samples of single mites used in PCR. The banding patterns from 24 RAPD primers and 10 primer pairs were very similar and reproducible in all specimens of the predatory mite studied. However, the E. finlandicus K-strain could be distinguished from organophosphate-resistant predatory mites (R-strain), since almost all of them produced a 1,400 bp RAPD-PCR product, which was missing or very rare in other strains studied. Another RAPD band of ca. 680 bp was in turn much more common in other mites of E. finlandicus than in the K-strain mites. Mite specific primers were designed and used to follow the survival of the R-strain released on apple trees. The 680 bp band obtained with specific primers was specific to the species E. finlandicus mites studied, including those that had been negative with RAPD primers. The 1,400 bp specific primers could be used as a marker for following the survival of R-strain mites on apple trees. At the species level it was possible to distinguish adults and eggs of E. finlandicus from Anthoseius rhenanus and Phytonemus pallidus by RAPD-PCR. In addition, a band at 480bp was found to correspond to DNA of the predatory mite Phytoseius macropilis, when both specific primer pairs were used together. It was not possible to amplify the ITS region of E. finlandicus rDNA using several primer pairs that work in other mites and aphids. However, a basidiomycete rDNA sequence was amplified with one of these ITS primer pairs in K-strain mites. Finally, it was found that fungal rDNA-specific primers amplified an ITS region of ca. 650 bp in several strains of E. finlandicus. Internal primers, designed to amplify the central part of the 650 bp product, successfully amplified this product from all the mites.     

截形叶螨对胡瓜钝绥螨的吸引作用

室内测定表明,截形叶螨不同螨态对胡瓜钝绥螨均有显著的吸引作用,均达到极显著水平,而胡瓜钝绥螨对截形叶螨的排泄物没有明显的反应。截形叶螨对胡瓜钝绥螨的这种吸引作用说明胡瓜钝绥螨具有自动搜索截形叶螨的能力,表明胡瓜钝绥螨可以用于截形叶螨的生物防治。     

An Entomopathogenic Strain of Beauveria bassiana against Frankliniella occidentalis with no Detrimental Effect on the Predatory Mite Neoseiulus barkeri: Evidence from Laboratory Bioassay and Scanning Electron Microscopic Observation

Among 28 isolates of Beauveria bassiana tested for virulence against F. occidentalis in laboratory bioassays, we found strain SZ-26 as the most potent, causing 96% mortality in adults at 1×10⁷ mL⁻¹conidia after 4 days. The effect of the strain SZ-26 on survival, longevity and fecundity of the predatory mite Neoseiulus (Amblyseius) barkeri Hughes were studied under laboratory conditions. The bioassay results showed that the corrected mortalities were less than 4 and 8% at 10 days following inoculation of the adult and the larvae of the predator, respectively, with 1×10⁷ conidia mL⁻¹ of SZ-26. Furthermore, no fungal hyphae were found in dead predators. The oviposition and postoviposition durations, longevity, and fecundity displayed no significant differences after inoculation with SZ-26 using first-instar larvae of F. occidentalis as prey in comparison with untreated predator. In contrast, the preoviposition durations were significantly longer. Observations with a scanning electron microscope, revealed that many conidia were attached to the cuticles of F. occidentalis at 2 h after treatment with germ tubes oriented toward cuticle at 24 h, penetration of the insect cuticle at 36 h, and finally, fungal colonization of the whole insect body at 60 h. In contrast, we never observed penetration of the predator''s cuticle and conidia were shed gradually from the body, further demonstrating that B. bassiana strain SZ-26 show high toxicity against F. occidentalis but no pathogenicity to predatory mite.     

Integrated Management of Two-spotted Spider Mite Tetranychus urticae on Hops using Hop ß-acids as an Antifeedant Together with the Predatory Mite Phytoseiulus persimilis

The effects on population development of two-spotted spider mite Tetranychus urticae by sprays of hop β-acids, a repellent and antifeedant of T. urticae, together with an inoculative release of the predatory mite Phytoseiulus persimilis were compared on tall and dwarf hops. The combination of the semiochemical with the predator was more effective than either factor singly on both hop types. The highest numbers of spider mites and their eggs were recorded on untreated plots. The sprays of β-acids slowed the rate of increase of the pest and contributed more to the effect of the combined treatment early in the season when the predator was establishing itself on the crop. By harvest time, the predator was the more influential of the two factors.     

Bioinsecticide-Predator Interactions: Azadirachtin Behavioral and Reproductive Impairment of the Coconut Mite Predator Neoseiulus baraki

Synthetic pesticide use has been the dominant form of pest control since the 1940s. However, biopesticides are emerging as sustainable pest control alternatives, with prevailing use in organic agricultural production systems. Foremost among botanical biopesticides is the limonoid azadirachtin, whose perceived environmental safety has come under debate and scrutiny in recent years. Coconut production, particularly organic coconut production, is one of the agricultural systems in which azadirachtin is used as a primary method of pest control for the management of the invasive coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae). The management of this mite species also greatly benefits from predation by Neoseiulus baraki (Athias-Henriot) (Acari: Phytoseiidae). Here, we assessed the potential behavioral impacts of azadirachtin on the coconut mite predator, N. baraki. We explored the effects of this biopesticide on overall predator activity, female searching time, and mating behavior and fecundity. Azadirachtin impairs the overall activity of the predator, reducing it to nearly half; however, female searching was not affected. In contrast, mating behavior was compromised by azadirachtin exposure particularly when male predators were exposed to the biopesticide. Consequently, predator fecundity was also compromised by azadirachtin, furthering doubts about its environmental safety and selectivity towards biological control agents.     

Biocontrol of Two-spotted Spider Mite Tetranychus urticae on Dwarf Hops by the Phytoseiid Mites Phytoseiulus persimilis and Neoseiulus californicus

Two female Phytoseiulus persimilis and their offspring eliminated two-spotted spider mite Tetranychus urticae from hop leaf discs faster than two female Neoseiulus californicus and their offspring at 25°C. A combination of one female of each species and their offspring eliminated spider mites faster than the N. californicus alone, but slower than P. persimilis alone. Air relative humidities of 55% and 93% had no effect on predation. Both predator species cannibalised eggs and juveniles when spider mite numbers were low. In field experiments in 1996, fewer spider mites were recorded where P. persimilis was released, irrespective of the presence of N. californicus. Pest numbers on cv. 'First Gold' were lower than on cv. 'Herald'. No differences were recorded between the numbers of spider mite eggs in predator release treatments on 'First Gold', but fewer active stages of spider mites were recorded on plots with P. persimilis than controls soon after the time of peak pest population densities. On 'Herald', fewer spider mite active stages and eggs were recorded where predators were released than on untreated controls.     

Clathrin Heavy Chain Is Important for Viability,Oviposition, Embryogenesis and,Possibly, Systemic RNAi Response in the Predatory Mite Metaseiulus occidentalis

Clathrin heavy chain has been shown to be important for viability, embryogenesis, and RNA interference (RNAi) in arthropods such as Drosophila melanogaster. However, the functional roles of clathrin heavy chain in chelicerate arthropods, such as the predatory mite Metaseiulus occidentalis, remain unknown. We previously showed that dsRNA ingestion, followed by feeding on spider mites, induced systemic and robust RNAi in M. occidentalis females. In the current study, we performed a loss-of-function analysis of the clathrin heavy chain gene in M. occidentalis using RNAi. We showed that ingestion of clathrin heavy chain dsRNA by M. occidentalis females resulted in gene knockdown and reduced longevity. In addition, clathrin heavy chain dsRNA treatment almost completely abolished oviposition by M. occidentalis females and the few eggs produced did not hatch. Finally, we demonstrated that clathrin heavy chain gene knockdown in M. occidentalis females significantly reduced a subsequent RNAi response induced by ingestion of cathepsin L dsRNA. The last finding suggests that clathrin heavy chain may be involved in systemic RNAi responses mediated by orally delivered dsRNAs in M. occidentalis.     

Food deprivation exposes sex‐specific trade‐offs between stress tolerance and life span in the copepod Tigriopus californicus

Long life is standardly assumed to be associated with high stress tolerance. Previous work shows that the copepod Tigriopus californicus breaks this rule, with longer life span under benign conditions found in males, the sex with lower stress tolerance. Here, we extended this previous work, raising animals from the same families in food‐replete conditions until adulthood and then transferring them to food‐limited conditions until all animals perished. As in previous work, survivorship under food‐replete conditions favored males. However, under food deprivation life span strongly favored females in all crosses. Compared to benign conditions, average life span under nutritional stress was reduced by 47% in males but only 32% in females. Further, the sex‐specific mitonuclear effects previously found under benign conditions were erased under food limited conditions. Results thus demonstrate that sex‐specific life span, including mitonuclear interactions, are highly dependent on nutritional environment.     

A Sexually Conditioned Switch of Chemosensory Behavior in C. elegans

In sexually reproducing animals, mating is essential for transmitting genetic information to the next generation and therefore animals have evolved mechanisms for optimizing the chance of successful mate location. In the soil nematode C. elegans, males approach hermaphrodites via the ascaroside pheromones, recognize hermaphrodites when their tails contact the hermaphrodites'' body, and eventually mate with them. These processes are mediated by sensory signals specialized for sexual communication, but other mechanisms may also be used to optimize mate location. Here we describe associative learning whereby males use sodium chloride as a cue for hermaphrodite location. Both males and hermaphrodites normally avoid sodium chloride after associative conditioning with salt and starvation. However, we found that males become attracted to sodium chloride after conditioning with salt and starvation if hermaphrodites are present during conditioning. For this conditioning, which we call sexual conditioning, hermaphrodites are detected by males through pheromonal signaling and additional cue(s). Sex transformation experiments suggest that neuronal sex of males is essential for sexual conditioning. Altogether, these results suggest that C. elegans males integrate environmental, internal and social signals to determine the optimal strategy for mate location.     

Distribution of the Predatory Mite Typhlodromus pyri (Acari: Phytoseiidae) on Different Apple Cultivars

The effect of apple cultivar on the distribution of the predatory mite Typhlodromus pyri was studied in an experimental orchard where spider mites occurred at negligible densities. Seven apple scab-resistant cultivars, showing some differences in their leaf morphology, were considered. In particular, their leaf blade was classified according to four levels of pubescence. The distribution of T. pyri along the shoots was also studied. In the first experimental year the colonization of different cultivars by T. pyri showed definite patterns, sometimes influenced by the occurrence of eriophyids. One year later, T. pyri abundance again showed some differences among cultivars in conditions of prey scarcity. In both years large phytoseiid populations were recorded on the cultivar N.Y. 18491, despite the low eriophyid occurrence, probably because of its highly pubescent leaf undersurfaces. In contrast, Prima and TSR 29T219, characterized by slightly pubescent leaf undersurfaces, supported low phytoseiid densities independently of prey availability.