Mingxing Jiang

Effects of Cry1Ab Toxin on Propylea japonica (Thunberg) (Coleoptera: Coccinellidae) Through Its Prey, Nilaparvata lugens Stål (Homoptera: Delphacidae), Feeding on Transgenic Bt Rice

Abstract Laboratory feeding experiments using rice plants containing a synthetic cry1Ab gene derived from Bacillus thuringiensis Berliner (Bt) were carried out to study the effects of Bt rice-fed prey on the predator Propylea japonica (Thunberg). Plants were obtained from two homozygous transgenic Bt-cry1Ab expressing rice lines, Kemingdao 1 (KMD1) and Kemingdao 2 (KMD2), and their untransformed parental variety Xiushui 11 (XS11). The herbivorous prey species tested was the brown planthopper, Nilaparvata lugens Stål, one of most serious insect pests of rice and not targeted by KMD1 or KMD2. The concentrations of Cry1Ab toxin expressed in KMD1 and KMD2 plants and that of the toxin transferred to N. lugens feeding on these plants were determined by enzyme immunosorbent assay technique. Development parameters of P. japonica reared on KMD1- or KMD2-fed N. lugens were assessed in the laboratory. The results showed that the concentration of Cry1Ab in rice leaves and stems significantly increased from the booting to grain filling stage and subsequently decreased as the plants matured. Cry1Ab could be detected in nymphs and adults of N. lugens feeding on the Bt rice plants. Development time, pupation, adult eclosion, pupal and adult weight, and male-adult locomotive activity of P. japonica that had preyed on KMD1- or KMD2-fed N. lugens nymphs as larvae were not significantly different from those that preyed on XS11-fed nymphs. In short, our results indicate that the nontarget insect N. lugens and its predator P. japonica are exposed to Cry1Ab toxin from transgenic cry1Ab rice, but development of this predator was not affected by the toxin through tritrophic interactions.

Effects of transgenic cry1Ab rice pollen on fitness of Propylea japonica (Thunberg)

The transgenic rice lines Kemingdao 1 (KMD1) and Kemingdao 2 (KMD2) contain a synthetic cry1Ab gene derived from Bacillus thuringiensis Berliner and are highly resistant to rice stem borers and foliage-feeding lepidopterans. Propylea japonica (Coleoptera: Coccinellidae) is an important predator of rice insect pests; it also uses rice pollen as a food source under natural conditions. In the present study, the effects of KMD1 and KMD2 pollen expressing Cry1Ab protein on the fitness of P. japonica were assessed in the laboratory. P. japonica larvae and adults were provided with the following four diets: KMD1 pollen with the aphid Myzus persicae, KMD2 pollen with M. persicae, nontransgenic Xiushui 11 (parent variety of KMD1 and KMD2) pollen with M. persicae, and M. persicae only (KMD1–pollen, KMD2–pollen, XS11–pollen, and aphid treatments, respectively). The results showed that the longevity of female adults in the KMD1–pollen treatment was significantly lower than that in the XS11–pollen treatment, but was not significantly different from that in the KMD2–pollen and aphid treatments. Newly emerged males in the KMD2–pollen treatment were evidently less vital than those in the XS11–pollen treatment, but not significantly different from those in the KMD1–pollen and aphid treatments. The development, survival and reproduction indices for the three pollen treatments did not differ significantly from one another. In short, Bt toxin expressed in Bt rice pollen had no evident negative impacts on P. japonica fitness when the pollen was used as a food by this beetle.

Identification and Biological Role of the Endosymbionts Wolbachia in Rice Water Weevil (Coleoptera: Curculionidae)

ABSTRACT Wolbachia spp. are obligate intracellular bacteria present in reproductive tissues of many arthropod species. Wolbachia infection status and roles in host reproduction were studied in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera, Curculionidae), an introduced species in China. We examined Wolbachia infection status in five populations in China where it reproduces parthenogenetically, and one native population in Southeast Texas, where it reproduces bisexually. All populations were infected by Wolbachia, and all specimens in each population were infected by Wolbachia of a single strain. Phylogenetic analyses based on multilocus sequence typing system indicated that Wolbachia in non-native L. oryzophilus weevils diverges evidently from those in native weevils. After treatments with tetracycline, parthenogenetic weevils reduced the fecundity significantly and eggs were not viable. Our results suggest that Wolbachia are necessary for oocyte production in L oryzophilus.

Interactions between the striped stem borer Chilo suppressalis (Walk.) (Lep., Pyralidae) larvae and rice plants in response to nitrogen fertilization

A screenhouse experiment was conducted to examine the damage and compensation in rice plants when injured by the striped stem borer, Chilo suppressalis (Walker), larvae at tillering stage, as well as larval survival and development of the insect at different nitrogen (N) fertilization levels. Potted plants were fertilized at late seedling stage at the rates 0, 200, 400, 600 and 800 mgN/pot, respectively. More deadheads were caused as fertilization increased. Plants compensated well for injury at the fertilization concentrations of 200 and 400 mgN/pot by producing new tillers, but such compensation did not take place at 600 and 800 mgN/pot. Two weeks after infestation, the highest number of remaining healthy tillers was found in plants fertilized at 400 mgN/pot. Larval survival varied little among the treatments 200 to 800 mgN/pot. Larval weight attainment and/or developmental rate increased with increasing fertilization level from 200 to 600 mgN/pot, but both declined rapidly as fertilization reached 800 mgN/pot, indicating the great dependence of plant suitability on N fertilization levels. Conclusively, both the compensation response of rice plants and their suitability for C. suppressalis larvae could be significantly affected by N fertilization levels.

Complex influence of rice variety, fertilization timing, and insecticide on population dynamics of Sogatella furcifera (Horvath), Nilaparvata lugens (Stål) (Homoptera: Delphacidae) and their natural enemies in rice in Hangzhou, China

The complex influence of rice variety, fertilization timing, and insecticides on the population dynamics of Sogatella furcifera (Horvath) and Nilaparvata lugens (Stål), and their natural enemies was studied in rice in Hangzhou, China. In the early season, S. furcifera adults immigrated to japonica Xiushui 11 (XS11) in a much higher density than to indica-japonica hybrid Xieyou 413 (XY413), which resulted in a higher density of the egg population of successive generations in XS11, while the peak density of the population peak of the 2nd generation in XY413 was higher due to a higher growth rate. In both of the rice varieties, spraying organic phosphorous triazophos in mid-season (during the 1st generation of the planthoppers) induced a population resurgence of the 2nd generations of S. furcifera and N. lugens. The main mechanism for the resurgence was the stimulation of reproduction of the 1st-generation adults and reduction of the density of predators, which in turn increased the survival of the planthoppers. Plots that were fertilized early attracted more N. lugens immigrants, but did not necessarily attract S. furcifera. Reproduction of the S. furcifera immigrants was enhanced by early fertilization of the fields of both rice varieties. The negative correlation between population growth rate from the 1st to the 2nd generation of S. furcifera and the density of spiders during the same period demonstrates the potential of predators in the natural control of rice planthoppers.

Reproductive Biology of Summer/Fall Populations of Rice Water Weevil, Lissorhoptrus oryzophilus Kuschel1, in Southeastern Texas

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Erirhinidae), is one of the most important pests of rice, Oryzae sativa L., in the US, and has emerged as a pest of rice in eastern Asia where it reproduces parthenogenetically. Females were collected from early July to late September 2006 from flooded main crop rice, ratoon crop rice, and a light trap placed in grassy vegetation and fallow fields near Beaumont, TX. Their mating status and ovarian developmental stages were monitored, and their reproductive capacity on rice plants was determined in the laboratory. Sexually reproductive individuals occurred consistently from early July to mid-September, which accounted for more than 50% of the females in most collections. Less than 7% of females seemed to be reproducing parthenogenetically. In the laboratory, 45.1% of females were mated within 9 days after emergence. For females emerging in late July and late August, only 17.4 and 6.1%, respectively, developed to ovipositing and post-ovipositing stages after feeding on rice plants for 4 weeks. These results indicated that in Southeast Texas >80% of summer females entered diapause after emergence, but reproductive females often are abundant later in rice fields. Contributions of summer females to the occurrence and abundance of this insect in subsequent seasons are discussed.

Oogenesis in summer females of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), in southern Zhejiang, China.

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, has two generations in southern Zhejiang, China. To determine oogenesis in first-generation females (summer females) and its relations to temperature, females were collected from a rice field in early and mid-July and reared on young rice plants at 28, 31 and 34°C in the laboratory. Percentage of females having oocytes, number of oocytes of different stages (stage-I, from early previtellogenesis to middle vitellogenesis; stage-II, late vitellogenesis; and mature-oocyte stage), and length of ovarioles were determined every 10 d of feeding. At each temperature, oogenesis took place in over 40% of females after 20–40 d of feeding, but 0.0–3.3 stage-I, 0.0–0.8 stage-II and 0.0–1.1 mature oocytes were observed at each observation date. Temperature had significant effect on number of stage-I oocytes but not on number of stage-II and mature oocytes in early July females; temperature had no significant effect on number of oocytes of either stage in mid-July females. Conclusively, in southern Zhejiang, summer L. oryzophilus females have great potential to become reproductive on rice, but their oogenesis activity is very low, with the overall procedures little affected by temperature.

Elytral Color Dimorphism in Rice Water Weevil (Coleoptera: Curculionidae): Occurrence in Spring Populations and Relationship to Female Reproductive Development

Abstract Adults of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), were collected from three sources: 1) overwintering sites near rice, Oryza sativa L.; 2) a light trap placed in grassy vegetation and fallow fields; and 3) flooded rice plots near Beaumont, TX, from mid-April to late May 2005. Their color morph and reproductive status were surveyed. Frequency of the dark morph (36.0, 45.8, and 31.6% at each collection source, respectively) was significantly lower than that of the light morph (64.0, 54.2, and 68.4% respectively). Dark males accounted for only 3.5–7.4% of the populations, significantly less abundant than light males (28.8–32.0%) in each collection source. The morph frequency changed significantly with season in females, but not in males. Female-biased sex ratios were observed with the proportion of females to males being 1.5, 2.1, and 1.9 at each collection source, respectively. In most collections, ovarian development and mating status were similar between the females of different morphs, suggesting that elytral morph in this weevil might not be related to female reproductive development.

Rice water weevil females of different elytral color morphs: comparisons of locomotor activity, mating success, and reproductive capacity.

Abstract Females and males of the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Erirhinidae), have two elytral color morphs in Texas: the central pattern of their elytra is black (dark morph) or gray (light morph). In southeast Texas, the dark and light females exhibited similar proportions (28.6 and 32.0%, respectively) in populations collected during the spring. In this study, females of the two morphs were collected near rice fields in southeast Texas during April and May 2005. In the laboratory, light females were more active than dark ones. They mated equally successfully with males, irrespective of morph. For females supplied with males for 2 d or kept solitary, and then reared on rice seedlings for 48 d, no significant differences were found between the two morphs in oviposition period, number of eggs deposited, and survival rate. In both morphs, a proportion of mated females did not oviposit throughout the rearing period, implying that a mating experience might be necessary before reproductive development can be initiated. However, oviposition occurred in a proportion of females in which no mating experience could be detected, and their eggs produced larvae, which suggests the probability of existing parthenogenetic females in southeast Texas.

Culture-Independent Analysis of Bacterial Communities in the Gut of Rice Water Weevil (Coleoptera: Curculionidae)

ABSTRACT Gut bacteria play important roles in the biology of insects. In this study, gut bacterial communities were investigated in the rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), which is a serious pest in rice growing-areas of the United States and some Asian countries. Overwintered female adults were collected from rice plants in five geographic locations: Beaumont, TX; Colt, AR; and Biggs, CA; in the United States, and Tanghai of Hebei and Yueqing of Zhejiang in China. Using polymerase chain reaction, bacterial 16S rRNA clone libraries were constructed. From the libraries, we identified 19 bacterial phylotypes (operational taxonomic units, OTUs). Of them, only 3–5 OTUs were identified in each population, except in the Beaumont weevils, which had 10 OTUs. The OTUs were affiliated with the bacteria in six classes of four phyla: &agr;-, &bgr;-, &ggr;-proteobacteria, Bacilli, Sphingobacteria, and Actinobacteria, with the &ggr;-proteobacteria being the richest. Bacteria of the genera Pantoea and Wolbachia were detected in all weevil populations examined. There were also some bacteria that were specifically detected in certain locations but had a high relative abundance, such as the ones matched to Enterobacter oryzae, Lactococcus lactis, and Rickettsia felis. Geographic variations were found among bacterial communities in their richness, diversity, and evenness. This was the first study depicting a detailed profile of bacterial communities in L. oryzophilus, and the results provide important information for future studies on the bacterial functions, mutual interactions, and use for developing a biocontrol technique against this weevil.