Functional and Numerical Responses of Three Species of Predatory Phytoseiid Mites (Acari: Phytoseiidae) to Thrips flavidulus (Thysanoptera: Thripidae)

Functional Response of Four Phytoseiid Mites to Eggs and First-Instar Larvae of Western Flower Thrips, Frankliniella occidentalis

The predation capacity and functional responses of adult females of the phytoseiid mites Amblyseius largoensis (Muma), Proprioseiopsis lenis (Corpuz and Rimando), Paraphytoseius cracentis (Corpuz and Rimando), and Amblyseius swirskii (Athias-Henriot) were studied on eggs and first instars of the western flower thrips, Frankliniella occidentalis (Pergande), in the laboratory at 25 °C and 30 °C. At both temperatures, the functional response of all four phytoseiid mites was type II to first instars of the thrips. In contrast, when offered thrips eggs, the functional response was type III. At both temperatures tested, A. swirskii had the highest mean daily consumption of first-instar F. occidentalis, followed by A. largoensis, P. cracentis, and P. lenis. Amblyseius largoensis had the shortest handling time and the highest maximum attack rate when first-instar thrips were the prey. When fed on thrips eggs, A. largoensis had the highest mean daily consumption, followed by A. swirskii, P. cracentis, and P. lenis. On thrips eggs, A. swirskii showed the shortest handling time and highest maximum attack rate. Our findings indicate that all four phytoseiids had a better ability to prey on first-instar larvae of F. occidentalis compared to thrips eggs. At 25 and 30 °C, A. largoensis was the better predator on thrips larvae, whereas A. swirskii was superior in consuming eggs of F. occidentalis. Proprioseiopsis lenis was the inferior predator on both thrips larvae and eggs compared to the other phytoseiids tested.

Implications of Temperature and Prey Density on Predatory Mite Amblyseius swirskii (Acari: Phytoseiidae) Functional Responses

Amblyseius swirskii are predaceous mites that feed on phytophagous mites, pollens, and plant exudates and are known as one of the most potent biological pest management agents. Tetranychus urticae is a global mite that is difficult to manage because of its high population growth rates, necessitating alternative management measures like biological control. Regarding the functional response, the effects of temperature and prey density are some of the essential behaviors of natural enemies. This study investigates the effect of varying temperatures and prey densities on A. swirskii, a biological control agent for T. urticae. The present results demonstrated the change in the functional response estimates when A. swirskii was reared at various temperatures and different prey densities. The results of the estimates regarding the searching efficiency (a') showed the highest value (a' = 0.919) at 26 °C and the lowest value (a' = 0.751) at 14 °C. The handling time per prey item (Th) for the predatory mites changed with the temperature and prey density, showing the shortest handling time at 26 °C (Th = 0.005) and the highest value at 14 °C (Th = 0.015). The functional response curves matched the type II functional response model, demonstrating the inverse dependence of temperatures and prey density with a positive quadratic coefficient. The predation curves for A. swirskii showed a significant difference between the mean numbers of T. urticae consumed at various prey densities and temperatures, illustrating a relationship between A. swirskii and T. urticae. Therefore, the results of this research may be utilized to forecast the behavior of A. swirskii and its usefulness in controlling T. urticae populations.

Numerical responses of the predatory mites, Cheyletus eruditus (Trombidiformes: Cheyletidae) and Cheyletus malaccensis, to Liposcelis decolor (Psocodea: Liposcelididae)

Predatory mites display diverse ecological mechanisms to suppress pest population density below certain thresholds known to cause economic loss. The current study explored the numerical responses of the predatory mites, Cheyletus eruditus (Schrank) (Trombidiformes: Cheyletidae) and Cheyletus malaccensis Oudemans, to Liposcelis decolor (Pearman) (Psocodea: Liposcelididae). The numerical responses of these 2 cheyletid mites to nymphs, adult males, and adult females of L. decolor were determined under laboratory conditions at 24 ± 1 °C, 85 ± 5 RH, and 0:24 (L:D) photoperiod. Oviposition rate, oviposition efficiency, and efficiency of conversion of ingested (ECI) food resources were the key numerical response parameters assessed. The present study revealed a general trend of a strong negative and positive correlation between oviposition rates and increase in prey densities (number of prey per 16.98 cm2) for C. eruditus and C. malaccensis, respectively. The oviposition efficiency was mostly similar for both predatory mites and was inversely related to prey density. Generally, ECI (%) decreased considerably with increasing prey density across different prey types for both predators, however, C. malaccensis was more efficient than C. eruditus in utilizing prey biomass. Given the relatively weak numerical responses, we recommended further assessment of these predatory mites before recommending their use for managing stored-product insect pests in the United States.

Gene cloning and difference analysis of vitellogenin in Neoseiulus barkeri (Hughes)

Neoseiulus barkeri (HUGHES) is the natural enemy of spider mites, whiteflies and thrips. Screening for chemically-resistant predatory mites is a practical way to balance the contradiction between the pesticide using and biological control. In this study, the number of eggs laid by fenpropathrin-susceptible and resistant strains of N. barkeri was compared. Additionally, we cloned three N. barkeri vitellogenin (Vg) genes and used quantitative real-time polymerase chain reaction to quantify Vg expression in susceptible and resistant strains. The total number of eggs significantly increased in the fenpropathrin-resistant strain. The full-length cDNA cloning of three N. barkeri Vg genes (NbVg1, NbVg2 and NbVg3) revealed that the open reading frames of NbVg1, NbVg2 and NbVg3 were 5571, 5532 and 4728 bp, encoding 1856, 1843 and 1575 amino acids, respectively. The three N. barkeri Vg possessed the Vitellogenin-N domain (or lipoprotein N-terminal domain (LPD_N)), von Willebrand factor type D domain (VWD) and the domain with unknown function 1943 (DUF1943). The NbVg1 and NbVg2 expression levels were significantly higher in the resistant strain than in the susceptible strain, while the NbVg3 expression level was lower in the resistant strain. Thus, we speculate that the increased number of eggs laid by the fenpropathrin-resistant strain of N. barkeri may be a consequence of changes in Vg gene expression.

Functional Response and Prey Preference of Neoseiulus bicaudus (Mesostigmata: Phytoseiidae) to Three Important Pests in Xinjiang, China

Knowledge about the prey preference of polyphagous predators is important for determining their ability to suppress pest insects. Tetranychus truncatus (Tetranychidae), Tetranychus turkestani (Tetranychidae), and Thrips tabaci (Thripidae) often coexist in crops. Neoseiulus bicaudus (Wainstein) is a native predatory mite that was recently observed in the Xinjiang Uygur Autonomous Region of northwest China. The objective of this study was to assess the potential of N. bicaudus as a bio-control agent against the three pest species mentioned above. The results showed that N. bicaudus protonymphs, deutonymphs, and adults can be effective biological control agents for the three pest species. Neoseiulus bicaudus at all three developmental stages exhibited a Holling's Type II (convex) functional response to the prey. Neoseiulus bicaudus exhibited no preference between T. truncatus adults and T. turkestani adults, irrespective of the prey ratio. In comparison, N. bicaudus clearly preferred first-instar T. tabaci larvae to T. turkestani adults. The results of this study suggest that N. bicaudus could help control T. truncatus, T. turkestani, and T. tabaci. Among these pests, N. bicaudus may be most effective for first-instar T. tabaci.

Complete Mitochondrial Genome of Euseius nicholsi (Ehara et Lee) (Acari:Phytoseiidae)

In this study, the complete mitochondrial genome (mitogenome) sequence of Euseius nicholsi (Acarinae: Phytoseiidae) was determined by long PCR and primer walking methods. The complete mitochondrial genome is 15,561 bp in length and contains 13 protein-coding genes, 2 ribosomal RNA genes, 21 transfer RNA genes. The overall base composition of the genome is A (34.69%), T (43.14%), C (8.06%) and G (14.10%). Stop codon was missed for the COXIII gene in E.nicholsi. The mitogenome would contribute to resolving phylogenetic position and interrelationships of Euseius.