Jiale Lv

Amblyseius orientalis Ehara (Acari: Phytoseiidae) is one local predatory mite in China that has high potential for controlling Polyphagotarsonemus latus, a globally important pest to many vegetables and crops. To further evaluate the control potential of A. orientalis on different host plants against P. latus, we selected bean, cucumber, and pepper as host plants to feed P. latus, and then to feed A. orientalis. It was found when the prey P. latus fed on cucumber leaves, development of A. orientalis was the slowest, with the lowest egg production and overall poor biological performance. When A. orientalis was fed with prey hosted on cucumber and the other two plants, there were 119 differentially expressed organic compounds. The differentially metabolites were significantly enriched in the pentose phosphate pathway and carbon metabolism pathway. Further transcriptomic analysis of A. orientalis revealed 36 differentially expressed genes. Among these genes, 20 were annotated in 17 pathways in KEGG, with significant enrichment in hippo signaling pathway-fly and polysaccharide degradation pathways detected. These results indicate that the development and reproduction of A. orientalis are significantly poorer when feeding on P. latus, leading to a marked decline in amino acids, sugars, lipids, and organic compounds in A. orientalis. Additionally, there are 36 genes with consistently different expression patterns in A. orientalis when comparing cucumbers to the other two host plants. This study is an initial attempt to unravel the biological mechanisms of how nutritional substances might affect biology of natural enemies through the food chain.

The brown wheat mite, Petrobia tritici, poses a significant threat to wheat fields. While fertilizers can increase crop productivity, imbalanced application may exacerbate plant susceptibility to pests. This study aimed to evaluate the impact of various NPK fertilization programs on P. tritici infestations over two consecutive cropping seasons. The results revealed significant differences in mite infestation among the treatment groups (p < 0.001). The lowest populations (1.1 and 3.0 mites/leaf) were observed in the treatments sprayed with phosphoric acid (at 0.75 and 1.00 cm/L), where the infestation appeared approximately 120 days after sowing; in contrast, it appeared early at 75 days in the other treatments. Conversely, treatments lacking potassium fertilizer presented the greatest degree of mite injury levels (49.5–57.7 mites/leaf). Although these treatments provided moderate leaf nutrition and crop yield, the highest nutritional content and total yield (10.49 and 9.71 1 t/ha for the two years) were observed in the treatment that received 224:70:100 kg fad⁻¹ commercial fertilizers (=178:25:114 kg ha⁻¹ NPK units) as soil fertilization, which was followed by the treatment with a foliar application of phosphoric acid (1.00 cm/L) with a total yield of 9.34 and 8.53 1 t/ha for the two years. In this treatment, the P. tritici density was moderately high at 9.40 and 6.32 mites/leaf over the two years, respectively. The consistency of P. tritici density and total yield ranking across both years indicated reliable estimates of the impact of fertilization. This study suggests that potassium sulfate application is crucial for reducing P. tritici density and that foliar phosphoric acid application instead of soil application reduces the number of P. tritici and delays its occurrence.

The broad mite, Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae), is a cosmopolitan pest that infests many greenhouse crops. Biological control is an important way to control P. latus, with predatory mites being the most widely used natural enemies of this pest. The purpose of this study is to evaluate the capabilities of three native phytoseiids in China (Neoseiulus californicus, Neoseiulus barkeri and Amblyseius orientalis) in controlling P. latus, using Amblyseius swirskii as a control, a commercial biocontrol agent of this pest widely used in Europe. Consumption, development, and reproduction of the four species when fed with P. latus were assessed, and their life table parameters were estimated and compared. Among the three native species, A. orientalis has the highest consumption rate of P. latus (29.0 per day), the shortest developmental duration (5.3 days), and the highest cumulative fecundity (13.5 eggs/female). Overall, its intrinsic rate of increase (r_m) is 0.12, comparable to that of A. swirskii. Among the three candidates, A. orientalis is the only one whose population increase might be expected when fed with P. latus. Therefore, we propose A. orientalis to be a potential biocontrol agent for this pest in China.

Phytoseiulus persimilis is a specialist predator of spider mites, with promising control effects. Its population generally has a stable sex ratio. Under appropriate conditions, the proportion of female offspring can reach 80%. But the mechanisms of sex determination in P. persimilis is still unclear. Sex-lethal (sxl) is an important gene in studying sex regulation mechanisms in insects. In the model organism Drosophila melanogaster, it has been proved to be a switch controlling sex determination. Herein, we screened one sex-lethal gene ortholog in the genome of P. persimilis (Ppsxl). We separated male and female offspring successfully based on the order of the egg laid, and found Ppsxl is expressed in both sexes at different stages. The expression peak was found in females 10 h after mating, and it was also highly expressed in eggs that developed into males. RNA interference was used to study the function of Ppsxl. When Ppsxl was interfered, all female individuals remained fertile. However, their cumulative fecundity decreased by 18.0%, daily fecundity decreased by 13.4%, and the proportion of female offspring decreased by 22.7%. This study showed that Ppsxl gene has a certain influence on the reproduction of P. persimilis, but its influence on sex determination may not be as critical as that in D. melanogaster. The regulation of sxl on P. persimilis was different from that in D. melanogaster.

Transformer-2 (tra-2) is an important sex-determining gene in insects. It also plays a role in the reproduction of phytoseiid mites. We performed bioinformatic analyses for the tra-2 ortholog in Phytoseiulus persimilis (termed Pptra-2), measured its expression at different stages and quantitatively identified its function in reproduction. This gene encodes 288 amino acids with a conserved RRM domain. The peak of its expression was observed in adult females, especially ca. 5 days after mating. In addition, expression is also higher in eggs than in other stages and adult males. When Pptra-2 was silenced through RNA interference with oral delivery of dsRNA, 56% of the females had their egg hatching rates decreased in the first 5 days, from ca. 100% to ca. 20%, and maintained at low levels during the rest of the oviposition period. To detect other genes functionally related to Pptra-2, transcriptome analyses were performed on day 5 after mating. We compared mRNA expressions among interfered females with significantly reduced egg hatching rate, interfered females without significant hatching rate and CK. In total 403 differential genes were identified, of which 42 functional genes involved in the regulation of female reproduction and embryonic development were screened and discussed.

Phytoseiulus persimilis is a specialist predator of spider mites, with promising control effects. Its population generally has stable sex ratio. Under appropriate conditions, the proportion of female offspring can reach 80%. But the mechanism of sex determination in P. persimilis is still unclear. Sex-lethal (sxl) is an important gene in studying sex regulation mechanisms in insects. In the model organism Drosophila melanogaster, it has been proved to control sex determination and dose compensation. Herein, we screened one sex-lethal gene ortholog in the transcriptome of each stage of P. persimilis that fed with spider mites (Ppsxl). It contains three highly conservative RRM domains. The expression pattern and function of Ppsxl were analyzed using real-time quantitative PCR and RNA interference. Ppsxl expressed in P. persimilis males and females at different developmental stages: the expression peaked 10 h after mating in females, and it was also highly expressed in eggs that developed into males (the first egg). The adult females, 5 hours after mating, were interfered through soaking in a mixed system of dsRNA and nanomaterials Star Polycation (dsRNA and SPc were 1:1 mixed, the concentration was 500 ng/μl). When Ppsxl was interfered, the expression of Ppsxl decreased by 47%. All female individuals after interference were fertile, and the first eggs still always developed into males. However, the daily fecundity per female decreased by 13.4%, and the proportion of female offspring decreased by 22.7%. This study showed that Ppsxl gene had a certain influence on reproduction of P. persimilis, but its influence on sex determination may not be as critical as that of D. melanogaster.

RNA interference (RNAi) is one of the most widely used techniques to study gene functions. There is still a lack of RNAi techniques that can be applied in Phytoseiidae conveniently and efficiently. Star Polycation is a new nanomaterial commonly used as a carrier of dsRNA in RNAi. Five genes of P. persimilis (PpATPb, PpATPd, PpRpL11, PpRpS2, and Pptra-2) were selected to verify whether SPc promotes the delivery of dsRNA into P. persimilis through soaking. When each of the five genes were interfered using SPc-mediated dsRNA, the total number of success offspring produced per female in six days decreased by ca. 92%, 92%, 91%, 96%, and 64%. When PpATPb, PpATPd, PpRpL11, or PpRpS2 was interfered, both the fecundity and egg hatching rate decreased. In contrast, when Pptra-2 was interfered, reduction in the reproductive capability was mainly the result of the decreased egg hatching rate. Correspondingly, when the target gene was interfered, P. persimilis expression of PpRpL11 reduced by 63.95%, while that of the other four genes reduced by at least 80%. Our studies showed that nanomaterials, such as SPc, have the potential to be used in RNA interference of phytoseiid mites.

Vitellogenin (Vg) is an important factor that impacts oocyte maturation, egg formation and embryonic development in Arthropoda. Two orthologs of Vg gene were obtained from the genome of Phytoseiulus persimilis and termed as PpVg1 and PpVg2. Both orthologs belong to the large lipid transfer protein superfamily. The expression of PpVg1 and PpVg2 was low in immatures and male adults, and increased rapidly in female adults after mating, and reached a peak before the first egg was laid (168× and 20.5× the level in virgin females, respectively). When PpVg1 and PpVg2 were interfered with dsRNA, the relative expression decreased by 81.0 and 30.9%, respectively, and 7.8 and 31.4% interfered individuals died within 24 h. Among surviving individuals, ca. 51.1 and 44.8% are infertile. Factors that might be related to expression of Vg genes are also discussed.