M. S. Ullah

Comparative toxicity of acaricides to Tetranychus merganser Boudreaux and Tetranychus kanzawai Kishida (Acari: Tetranychidae)

ABSTRACT Laboratory bioassays were conducted to determine the toxicity of different acaricides against two strains of Tetranychus merganser Boudreaux and two strains of Tetranychus kanzawai Kishida by probit analysis. The 50% lethal concentration (LC50) value and resistance ratio of the probit-concentration regression was considered to determine the resistance. A laboratory selected susceptible strain of T. kanzawai (Tk-JN) was used to compare the susceptible levels. Adult females of the T. merganser and T. kanzawai strains have little resistance to most of the acaricides. Adult females of the T. merganser Mexican (Tm-MP) strain were resistant to spiromesifen and the T. merganser Thai (Tm-TC) and T. kanzawai Kanaya (Tk-JT) strains were resistant to spirodiclofen and spiromesifen, because their LC50 values were higher than each of the recommended concentrations. For other chemicals, the LC50 values of all strains were lower than each of the recommended concentrations. Eggs of the Tm-MP strain were particularly resistant to bifenazate, cyflumetofen, and fenbutatin oxide, as their LC50 values were higher than each of the recommended concentrations. Eggs of the Tm-TC strain did not show any resistance to any of the acaricides tested. For etoxazole and spirodiclofen, the LC50 values of the Tk-JT strain were higher than the recommended concentrations. The LC50 values of the susceptible Tk-JN strain to cyflumetofen (388 mg/l) and fenbutatin oxide (>10,000 mg/l) were high compared with the recommended concentrations of each acaricide (200 and 240 mg/l, respectively). All other acaricides were effective against all strains. So, several acaricides (chlorfenapyr/tebufenpyrad, cyenopyrafen/cyflumetofen, etoxazole, hexythiazox, and milbemectin) can be considered as candidates for successful control of T. merganser if it invades Japan and cause damages to crops.

Temperature-Dependent Demography of Two Closely Related Predatory Mites Neoseiulus womersleyi and N. longispinosus (Acari: Phytoseiidae)

Temperature has significant effects on the development, survival, and reproduction of ectothermic organisms. In this study, we examined the effect of temperature on the demographic characteristics of two predatory mite species, Neosciulus womersleyi (Schicha) and N. longispinosus (Evans), reared on Tetranychus urticae Koch. The developmental and reproductive traits of both species were examined at 10 constant temperatures between 15 °C and 37.5 °C. The preadult development time of N. womersleyi and N. longispinosus decreased with increasing temperature until 32.5 °C and 35 °C, respectively. The lower developmental threshold (T0) and thermal constant (K) estimated by using a linear model were 11.61 °C and 69.36 DD for N. womersleyi and 11.92 °C and 61.5 DD for N. longispinosus, respectively. Total preoviposition period and total longevity of females and males of N. womersleyi and N. longispinosus decreased with increasing temperature. The mean generation time (T) first decreased with temperature until 32.5 and 35 °C for N. womersleyi and N. longispinosus, respectively, and then increased at higher temperatures. The R0 and r values first increased with temperature until 32.5 and 30 °C for N. womersleyi and N. longispinosus, respectively, and then decreased at higher temperatures. The R0 and r values for N. longispinosus at 37.5 °C were 0.3 offspring and -0.143 d-1, respectively. These results show that N. longispinosus is less fit than N. womersleyi at 37.5 °C.

Interspecific interference in the closely related predatory mites Neoseiulus womersleyi and Neoseiulus longispinosus (Acari: Phytoseiidae)

ABSTRACT Reproductive interference is known to occur in the morphologically similar species Neoseiulus womersleyi and Neoseiulus longispinosus: crosses between N. longispinosus females and N. womersleyi males produce (a few) female offspring, reciprocal crosses produce only male offspring. Details of the interspecific reproduction process remain largely unknown. In this article, we investigated intraspecific and interspecific crosses, spermathecal vesicles and spermatophores in females, and molecular identification of F1 hybrids based on the internal transcribed spacer (ITS) region of nuclear ribosomal RNA (rRNA). The copulation times of interspecific crosses were similar to those of intraspecific crosses, yet interspecific crosses between N. womersleyi females and N. longispinosus males exhibited extremely low fecundity with no female offspring. On the other hand, 1 out of 35 reciprocal crosses produced viable, but sterile female offspring (F1). Intraspecific crosses of N. womersleyi and N. longispinosus showed female-biased offspring sex ratios. Most N. womersleyi females (12 out of 15 females tested) that mated with N. longispinosus males had inflated vesicle(s) and were inseminated. Of the crosses between N. longispinosus females and N. womersleyi males, 14 pairs had neither inflated spermathecal vesicles nor were inseminated, and in only one pair, vesicles were inflated and insemination occurred that enabled the production of female offspring. Polymerase chain reaction products of the ITS region of rRNA gene digested with ClaI exhibited two fragments (361 and 278 bp) for the N. womersleyi and only a single fragment (642 bp) for the N. longispinosus, whereas three fragments for the F1 hybrids (642, 361, and 278 bp), confirming the identification. Our results confirmed the asymmetric reproductive interference between N. womersleyi and N. longispinosus and demonstrated that the F1 female offspring produced were (sterile) hybrids.

Scotophase interruption with LEDs and OLEDs to inhibit photoperiodic induction of diapause in Tetranychus urticae and T. kanzawai (Acari: Tetranychidae)

Abstract Tetranychus urticae Koch and T. kanzawai Kishida enter facultative diapause in response to short-day photoperiods. To determine the effect of various colors of light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs) on diapause induction, both species were reared under different photoperiods at 18°C and 2.0 W m-2 light intensity, in which photon flux density (PFD) was 7.9–11.0 µmol m-2 s-1 depending on light quality. Under blue, green, and white LEDs, critical photoperiods were ca. 13.5:10.5 h L: D for T. urticae and ca. 12.5: 11.5 h L: D for T. kanzawai, but no diapause was induced in either species under red LEDs. Under blue, green, orange, and white OLEDs, the critical light phases were ca. 13.3–13.5 h for T. urticae and ca. 12.5 h for T. kanzawai. The inhibitory effects of the duration, quality, and intensity of scotophase-interrupting lights on diapause induction in both species were tested under an 8:16 h L: D photoperiod. In T. urticae females, diapause induction was prevented by interrupting the scotophase with 1 h of light from all colors of LEDs or OLEDs except red LEDs. However, in T. kanzawai females, diapause was fully induced with 1-h scotophase interruption of all light colors and types, even when the PFD was as high as 20 µmol m-2 s-1. Interrupting the scotophase with 3 h of 20 µmol m-2 s-1 light from blue, green, and white LEDs, and from blue, green, orange, and white OLEDs completely inhibited diapause induction in both species. When interrupting the dark phase with 3 h of light at the lowest intensity tested (0.2 µmol m-2 s-1), blue and green inhibited diapause induction in T. urticae, whereas only blue light inhibited diapause induction in T. kanzawai. Therefore, blue LED and OLED performed best to inhibit diapause of T. urticae and T. kanzawai at 3-h scotophase interruption even at low light intensity.

Pesticide-mediated displacement of a phytoseiid predator, Neoseiulus womersleyi, by another phytoseiid predator, N. californicus (Acari: Phytoseiidae).

Neoseiulus womersleyi and N. californicus are two predators that are frequently used to control spider mites in fruit-tree orchards. Neoseiulus womersleyi used to be the dominant predator species in Japan, but since the 1990s in central and southwestern Japan, N. californicus populations have been increasing and have displaced populations of N. womersleyi. We previously observed the same phenomenon under laboratory conditions when these species were released at a 1:1 ratio, and attributed the displacement to asymmetrical intraguild predation. However, the ratio in fruit-tree orchards could be different from 1:1. Therefore, we hypothesized that differential susceptibilities to pesticides might accelerate species displacement of N. womersleyi by N. californicus, even if the ratio between these two species was extremely skewed in favor of N. womersleyi and no species displacement occurred otherwise. We examined the effects of 21 pesticides on egg-to-adult and adult survivorship in N. womersleyi and N. californicus. Among these pesticides, two neonicotinoids (acetamiprid and imidacloprid) had much severer effects on N. womersleyi than on N. californicus and thus could possibly account for the species displacement. When the two species were released onto leaf arenas at an N. californicus: N. womersleyi ratio of 1:9 in the absence of insecticide, no displacement was observed. However, just after acetamiprid or imidacloprid application, the proportion of N. californicus increased, causing N. californicus to displace N. womersleyi. Our results indicate that displacement in predator complexes of fruit-tree orchards could be due to different degrees of pesticide susceptibility.

Different responses to hypobaria between spider mites and a predatory mite

ABSTRACT Spider mites are a quarantine pest for different agricultural products imported to Japan, which may require phytosanitary treatments. To develop an environmental-friendly physical method to control agricultural pests, with minimal harm to natural enemies, we evaluated the effect of hypobaria (reduced atmospheric pressure) on three pest spider mites (Tetranychus urticae, T. kanzawai, Panonychus citri) and their natural enemy, the predatory mite Neoseiulus californicus. None of the spider mite eggs hatched when exposed to 17 kPa (lower partial pressure of oxygen, pO2 ≈ 3.5 kPa) at 25°C or 30°C for 24 h. The hatchability of N. californicus eggs was slightly reduced when the eggs were exposed to hypobaria at 30°C for 24 h. However, N. californicus adult females were more susceptible to hypobaria than females of the three species of spider mites. Adult survival of T. urticae and P. citri was significantly reduced by exposure to hypobaria at 30°C for 12 or 24 h, while adult survival of N. californicus was significantly reduced at 20°C, 25°C, and 30°C for ≥12, ≥12, and ≥6 h, respectively. For most species in most of the exposures, the adult survivabilities could be recovered by supplying water during the treatment. The exception was N. californicus when exposed to hypobaria at 30°C for 24 h. These results suggest that hypobaric-induced desiccation rather than hypoxia (pO2 ≈ 3.5 kPa) causes the mortality of adult females and that hypobaric treatments can be useful for selectively controlling spider mite eggs for phytosanitary treatment of several commercially important fresh commodities.