Relationship between leaf vein traits of three dominant Quercus species and ecological factors in the Qinling Mountains, China.

We investigated the inter- and intra-species differences of leaf vein traits of three dominant Quercus species, Q. wutaishanica, Q. aliena var. acutiserrata, and Q. variabilis of Niubeiling (subtropical humid climate) and Taohuagou (warm temperate semi-humid climate), located in the eastern and western Qinling Mountains. The nine examined leaf vein traits included primary leaf vein width, secondary leaf vein width, mean fine vein width, primary vein density, fine vein density, vein areole diameter, areole density, 3D fine vein surface area, and fine vein volume. We further elucidated the influencing mechanisms and regulatory pathways of biotic and abiotic factors on leaf vein traits. The results showed that species identity had significant effects on eight out of nine leaf vein traits except 3D fine vein surface area, while habitat had significant effects on primary leaf vein width, secondary leaf vein width, vein areole diameter, fine vein density, and areole density. Altitude had significant effects on primary vein density, mean fine vein width, vein areole diameter, fine vein density and areole density. Habitat, tree species identity, and altitude had significantly interactive effects on primary leaf vein density, 3D fine vein surface area, and fine vein volume. There were significant differences in primary leaf vein width, mean fine vein width, areole density, 3D fine vein surface area, fine vein volume, primary vein density of Q. wutaishanica between the two studied habitats, but the differences were only found in secondary leaf vein width and areole density of Q. aliena var. acutiserrata and Q. variabilis. The examined leaf vein traits were influenced both by biotic and abiotic factors, with varying effect sizes. Among the biotic factors, petiole length, leaf length and width ratio had strong effect on leaf vein traits. Among the abiotic factors, climatic and soil factors had high effect size on vein traits, with the former being higher than the latter. Leaf vein traits were affected directly by biotic factors, but indirectly by abiotic factors (soil and climatic factors) via regulating biotic factors (leaf stoichiometry and leaf phenotypic traits).

Comparison of species composition and community characteristics of Quercus forests on south and north slopes of Taibai Mountain, China.

We examined species composition, community characteristics, diversity, and community similarity of five Quercus communities composed of three Quercus species (Q. variabilis, Q. aliena var. acutiserrata, Q. wutaishanica) on the altitudinal gradient on the south and north slopes of Taibai Mountain. The results showed that there was an altitudinal transition pattern from Q. variabilis pure forest to Q. variabilis-Q. aliena var. acutiserrata mixed forest, Q. aliena var. acutiserrata pure forest, Q. aliena var. acutiserrata-Q. wutaishanica mixed forest and Q. wutaishanica pure forest on the south and north slopes of Taibai Mountain. The main companion species of Quercus community on the north slope were Pinus armandii, Castanea seguinii, and Sorbus alnifolia, and were Pinus tabuliformis, C. seguinii, Carpinus cordata, and Q. spinosa on the south slope. Species richness, woody plant density, and Quercus species dominance on the north slope of Taibai Mountain were higher than those on the south slope. α diversity of tree layer in Quercus community on the south and north slopes of Taibai Mountain increased first, then decreased and then increased with altitude. α diversity of tree layer was higher in mixed forests than pure forests. α diversity of shrub layer was higher than that of tree layer and herb layer in Quercus community on south and north slopes. ß diversity fluctuated greatly along the altitudinal gradient on the south and north slopes, indicating that species composition changed greatly with altitude. Results of redundancy analysis showed that mean warmest month temperature, altitude and tree height accounted for 79.0% of the community diversity on the north slope, and that soil water content, tree height, canopy density and mean annual temperature accounted for 79.6% of the community diversity on the south slope. Overall, Quercus dominance was higher on the north slope of Taibai Mountain, and the substitution distribution pattern of Quercus species was clearer than that on the south slope. Environmental factors related to temperature and precipitation jointly affected α diversity of Quercus communities.

Parasitism of Two Spodoptera spp. by Microplitis prodeniae (Hymenoptera: Braconidae).

Early instar larvae of the tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae) and the beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae) are recognized hosts of the parasitic wasp Microplitis prodeniae Rao and Kurian (Hymenoptera: Braconidae), although M. prodeniae has previously been regarded as monophagous. In this study, we found the immature period and longevity of M. prodeniae developing in S. exigua was similar to that in S. litura. It was shown that the development time of M. prodeniae in S. exigua was 15.1 ± 0.3 d, not significantly different from 15.0 ± 0.2 d in S. litura. The parasitism rate of M. prodeniae attacking S. exigua was significantly lower than on S. litura (65.48 ± 2.29 and 43.83 ± 2.20%, respectively), whilst the female ratio of the wasp's offspring was not significantly different when developing on the two species. M. prodeniae females prefer to oviposit on the second- and third-instar host larvae of S. exigua, rather than other instars. The effects of development of M. prodeniae on two important lepidopterous pests are discussed.

A Place to Grow? Host Choice and Larval Performance of Microplitis similis (Hymenoptera: Braconidae) in the Host Spodoptera litura (Lepidoptera: Noctuidae).

Host selection is a key stage in the lifecycle of parasitoids, and is critical to both their function in control and to the maintenance of their population. The solitary endoparasitoid Microplitis similis (Hymenoptera: Braconidae) is a potential biological control agent of Spodoptera litura (F.) larvae (Lepidoptera: Noctuidae). In this study, we examined the preference M. similis exhibits for different instars of the host, host instar effects on parasitoid development, and the weight gain and food consumption of different instars of parasitized larvae. In no-choice tests, parasitization rates were highest in second- and early third-instar larvae, and no fourth- or fifth-instar hosts were parasitized. When provided with a choice of first- to late third-instar host larvae, M. similis preferred to parasitize early third-instar host larvae (41%) with a selection coefficient of 0.37. All morphometric features of wasp offspring increased with increasing age of the host at parasitization. A lower proportion of females emerged from first-instar larvae than any other instar. Parasitized S. litura larvae showed a pronounced reduction in food consumption and weight gain. Microplitis similis may have the potential to significantly suppress population growth and the damage caused by S. litura.

Imperfection works: Survival, transmission and persistence in the system of Heliothis virescens ascovirus 3h (HvAV-3h), Microplitis similis and Spodoptera exigua.

Ascoviruses are insect-specific large DNA viruses that mainly infect noctuid larvae, and are transmitted by parasitoids in the fields. Heliothis virescens ascovirus 3h (HvAV-3h) has been recently isolated from Spodoptera exigua, without parasitoid vector identified previously. Here we report that Microplitis similis, a solitary endoparasitoid wasp, could transmit HvAV-3h between S. exigua larvae in the laboratory. When the female parasitoid wasp acquired the virus and served as a vector, the period of virion viability on the ovipositor was 4.1 ± 1.4 days. Infected host larvae were still acceptable for egg laying by parasitoids, and the parasitoids thereafter transmitted virus to healthy hosts. Virus acquisition occurred only from donor hosts between 3 and 9 days post infection. The peak of virus acquisition (80.9 ± 6.3%) was found when M. similis wasps oviposited in larvae that had been inoculated with the virus 7 days previously. When virus infection of the host took place during the life cycle of the parasitoid wasp, it caused 1- to 4-day-old immature parasitoids death in the host, whilst a small proportion of 5- to 6-day-old and the majority of 7-day-old parasitoids larvae survived from the virus-infected hosts. Viral contamination did not reduce the life span or fecundity of female M. similis.

A comparison of growth and development of three major agricultural insect pests infected with Heliothis virescens ascovirus 3h (HvAV-3h).

Ascoviruses are double-stranded DNA viruses that are pathogenic to lepidopteran hosts, particularly noctuid larvae. Infection of a larva is characterized by retarded growth, reduced feeding and yellowish body color. In this paper, we reported the growth and development of three major agricultural noctuid insect pests, Helicoverpa armigera (Hübner), Spodoptera exigua (Hübner) and Spodoptera litura (Fabricius), infected with Heliothis virescens ascovirus 3h (HvAV-3h). Using 10-fold serial dilutions (0 to 7) of HvAV-3h-containing hemolymph to infect S. litura larvae, we found no significant difference in larval mortalities from 0 to 10(3)-fold dilutions; however, significant differences were observed at 10(4)-fold dilution and above. Using a 10-fold dilution of HvAV-3h-containing hemolymph to infect H. armigera, S. exigua and S. litura larvae, we found that the growth and development were significantly affected. All infected larvae could not pupate; the survival times of treated H. armigera, S. litura and S. exigua larvae were significantly longer than untreated control larvae. Body weight showed significant difference between treated and untreated control group from day 1 after inoculation in H. armigera and S. exigua, but day 2 in S. litura. Additionally, food intake also showed significant difference between treated and untreated control group from day 2 after inoculation in H. armigera and S. litura, but day 3 in S. exigua.