Search

Obstacles in different tissue layers of leaves can influence aphid feeding behavior and host preference. In this study, we examined the feeding behaviors of cabbage aphids Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae) on the five oilseed rape cultivars with varied levels of aphid susceptibility using the electropenetrography (EPG) technique. The leaf anatomical structures of the five oilseed rape cultivars were also analyzed using the microscopical observations. The results showed that the cabbage aphid feeding behaviors varied among the five cultivars. On ‘Dehezayou8’ which had the highest aphid population in the field, the cabbage aphids showed significantly shorter non-probing time to the first phloem contact, shorter duration of the no phloematic phase, and longer average probing duration than those on ‘Zhongyou821’ which showed the least aphid population. In the mesophyll of ‘Dehezayou8,’ the cabbage aphids made significantly fewer brief probes and spent a shorter time in penetrating the mesophyll cells than on ‘Zhongyou821.’ In the phloem, the aphids on ‘Dehezayou8’ secreted less saliva and ingested more sap than those on ‘Zhongyou821.’ On ‘Dehezayou8,’ the aphids took the shortest time to first penetration than they did on the other cultivars. ‘Dehezayou8’ had relatively thin upper epidermis and rare short trichomes, which might have facilitated the aphid infestation. Our results suggested that the leaf tissue characteristics of oilseed rape cultivars, such as epidermis thickness, trichomes, and the factors from mesophyll and phloem could be associated with aphid feeding preference and therefore aphid population in the field.

Background Strongyllodes variegatus (Fairmaire) is a major insect pest of oilseed rape in China. Despite its economic importance, the contribution of its population genetics in the development of any suitable protection control strategy for the management of oilseed rape crops is poorly studied. It is a much urgent need to prevent its spread to the rest of the world. Results Using the sequences of mitochondrial DNA cytochrome c oxidase subunit I (COI) and cytochrome b (Cytb) as genetic markers, we analyzed the population genetic diversity and structure of 437 individuals collected from 15 S. variegatus populations located in different oilseed rape production areas in China. In addition, we estimated the demographic history using neutrality test and mismatch distribution analysis. The high level of genetic diversity was detected among the COI and Cytb sequences of S. variegatus. The population structure analyses strongly suggested three distinct genetic and geographical regions in China with limited gene flow. The Mantel test showed that the genetic distance was greatly influenced by the geographical distance. The demographic analyses showed that S. variegatus had experienced population fluctuation during the Pleistocene Epoch, which was likely to be related to the climatic changes. Conclusion Overall, these results demonstrate that the strong genetic structure of S. variegatus populations in China, which is attributed by the isolation through the geographical distance among populations, their weak flight capacity and subsequent adaptation to the regional ecological conditions.

Background : Strongyllodes variegatus (Fairmaire) is a major insect pest of oilseed rape in China. Despite its economic importance, the population genetics of this pest contributing to the development of suitable management and control strategies is poorly known. To understand the population genetics and assess the geographical patterns and genetic structure of S. variegates in China. Using mitochondrial DNA cytochrome c oxidase subunit I and cytochrome b region sequences as genetic markers, we analyzed population genetic diversity and structure from 437 individuals collected in 15 S. variegates populations located in different oilseed rape production areas in China. In addition, we estimated the demographic history using neutrality test and mismatch distribution analysis. Results : The high level of genetic diversity was detected among the mtDNA region sequences of S. variegates . The population structure analysis strongly suggested that three genetic and geographical regions occur with limited gene flow. The Mantel test showed that the genetic distance was greatly influenced by geographical distance. The demographic analyses showed that S. variegates experienced population fluctuation during the Pleistocene, which was likely to be related to the climatic changes. Conclusion : Overall, these results demonstrated that the strong population genetic structure of this beetle may attribute to the geographical barriers and subsequently adapt to the regional ecological conditions for the distribution of S. variegates in China. Keywords : Gene flow, Genetic differentiation, Haplotype, Oilseed rape, Population genetic pattern, Strongyllodes variegates

Plant resistance to aphids might be present in different plant tissues, such as the epidermis, mesophyll and phloem, but not all of them play a key role in determining the feeding preference of aphids. In this study, electrically recorded feeding behaviors of cabbage aphids were combined with choice tests and microscopic observations to understand the feeding preference of cabbage aphids on oilseed rape cultivars. The choice tests showed that more cabbage aphids survived on &lsquo, Qianyou18&rsquo, and less on &lsquo, Zhongshuang11&rsquo, compared with the other cultivars. The results of the choice tests were paradoxical with the results analyzed from the general and mesophyll-associated variables. The thick upper epidermis with bushy long trichomes on the leaves of &lsquo, delayed the first probe of the cabbage aphids. The duration of phloem-feeding was similar among the four cultivars although there were differences in the hindrance of the mesophyll. However, salivation was increased when the aphids fed on &lsquo, further indicating that the leaf&rsquo, s physical properties could be important for aphid feeding preference on the four cultivars.

Plant resistance to aphids might be present in different plant tissues, such as the epidermis, mesophyll and phloem, but not all of them play a key role in determining the feeding preference of aphids. In this study, electrically recorded feeding behaviors of cabbage aphids were combined with choice tests and microscopic observations to understand the feeding preference of cabbage aphids on oilseed rape cultivars. The choice tests showed that more cabbage aphids survived on ‘Qianyou18’, and less on ‘Zhongshuang11’, compared with the other cultivars. The results of the choice tests were paradoxical with the results analyzed from the general and mesophyll-associated variables. The thick upper epidermis with bushy long trichomes on the leaves of ‘Zhongshuang11’ delayed the first probe of the cabbage aphids. The duration of phloem-feeding was similar among the four cultivars although there were differences in the hindrance of the mesophyll. However, salivation was increased when the aphids fed on ‘Zhongshuang11’, further indicating that the leaf’s physical properties could be important for aphid feeding preference on the four cultivars.

Seed treatments with the neonicotinoid insecticides imidacloprid and thiamethoxam were evaluated to determine whether the chemicals at effective concentrations for aphid control would influence the germination and early growth of oilseed rape, Brassica napus. Treatment with imidacloprid or thiamethoxam did not affect the cumulative germination rate, but significantly inhibited establishment potential by suppressing root system development in the cotyledon stage. However, these alterations in seedling development in the thiamethoxam-treated seeds appeared not to be detrimental as leaves developed; in contrast, for the seedlings with imidacloprid as seed treatment agent, a significantly decreased shoot/root ratio was still evident at the late two-leaf stage. After two leaves developed, chlorophyll content per leaf in the thiamethoxam treatment was significantly higher than that of the control, while chlorophyll content per leaf in the imidacloprid treatment remained close to that in the control. Most other parameters, i.e., height, leaf area, weight of stem, leaf or root, and other growth indexes, between the treatments and the control showed no significant difference. Additionally, it was found that storage time of the treated seeds had a significant effect on cumulative germination rate. Treatment 30 d before planting significantly reduced germination relative to that of the control. All of the plants treated with neonicotinoids were shown to have significant anti-aphid characteristics that persisted until the end of the trial.

Most insects must accumulate certain metabolites before entering diapause by virtue of photoperiodic regulation. Photoperiods influence diapause beyond the maternal generation in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), which is one of the most important larval endoparasitoid of Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). The accumulation of metabolites in the non-diapausing prepupae, adults, and eggs (before and after oviposition) in progeny from C. vestalis cultures reared at 25°C under three photoperiods (8:16, 12:12, and 16:8 (L:D) hr), along with diapausing prepupae were measured to investigate the effects of photoperiod on the accumulation of metabolites during diapause induction. Compared with those of non-diapausing prepupae, free water, trehalose, total lipid titer, and total polyol contents in diapausing prepupae showed no significant differences; but weight, bound water, total sugar, glycogen, triglyceride, and protein contents were significantly higher. Und...

Imidacloprid application, as a seed coating agent on oilseed rape, is recommended to control mustard aphid, Lipaphis erysimi (Kaltenbach) (Hemiptera: Aphididae). In this study, responses of L. erysimi were investigated, including survival, feeding behavior, and detoxifying enzymes, on the oilseed rape seedlings grown from seeds coated with imidacloprid at rates of 6, 12, or 18 g active ingredient (a.i.)/kg seed. The results showed that the aphids&rsquo, survival rate, together with that of the progeny of the survivors, on the seed-treated seedlings significantly decreased. This indicates that the aphid population in fields can be suppressed effectively. The electrical penetration graph (EPG) technique was used to record aphid feeding behaviors on two-, four-, and six-leaf stages of oilseed rape seedlings that had been seed-coated with imidacloprid, and individual responses were revealed during the aphid feeding behavior. On the plants at the two-leaf stage, aphid feeding behaviors were influenced, showing decreased frequency of stylet penetration into the leaf (probe) or into the mesophyll cells (potential drops, pds for short), and shortened duration of stylet event in the leaf (probe) or in the phloem. On the plants at the four- and six-leaf stages, these impacts of imidacloprid were weakened, however, the saliva secretion duration in phloem was shortened to less than 5 min in all imidacloprid treatments. The activity of mixed-function oxidase in aphids maintained on the treated seedlings with imidacloprid was elevated. In conclusion, imidacloprid could be used as a seed coating agent for aphid control, but chemical resistance in aphids should not be ignored.

Photoperiods influence diapause beyond the maternal generation in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae). The sizes, 20-hydroxyecdysone (20E), and juvenile hormone III (JH III) contents in the G1 diapausing prepupae, G0 nondiapausing prepupae, adults, and G1 eggs from C. vestalis cultures reared under three photoperiods (8:16 hours light:dark, 12:12 hours light:dark, and 16:8 hours light:dark) were measured to investigate the hormones’ roles on maternal information transmission and diapause regulation. Results showed that the body size of G1 diapausing prepupae was significantly larger than that of G0 nondiapausing prepupae. The sizes of G0 prepupae, female abdomens, and G1 eggs under eight-hour light were significantly larger than those under 16-hour light. The 20E content in diapausing prepupae was significantly lower than that in nondiapausing prepupae, whereas JH III content did not show significantly difference under the same photoperiod. The 20E content in maternal prepupae, mated females and G1 eggs decreased as the light period was reduced. Juvenile hormone III contents in G0-mated females and G1 eggs (after oviposition) under three photoperiods showed no significant differences. These findings suggest that 20E may play a critical role in diapause regulation of C. vestalis, and be used as a maternal environmental message to be transmitted to the next generation.

Most insects must accumulate glycogen before entering diapause. Photoperiod influences diapause beyond the maternal generation in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae). In this study, we measured glycogen content and the activity and messenger RNA (mRNA) expression of glycogen synthase and glycogen phosphorylase at different G0 (25 °C under light:dark photoperiods of 8L:16D, 12L:12D, and 16L:8D) and G1 life stages (13 °C under 8L:16D). Glycogen content in G0 and G1 increased with shorter light periods, except for G0 adult males, which showed no significant difference under the three photoperiods. Compared with those under 16 h, in those under 8 h light, glycogen synthase activity was significantly higher at all tested stages, except for G0 pupa and adult male, for which it was identical; mRNA expression was higher at G0 larva and prepupa, lower at pupa, and identical at rest stages. Glycogen phosphorylase activity was significantly higher for G1 egg, lower at G1 prepupa, and identical at all other stages; mRNA expression was higher at G0 and G1 larval stages, and similar at rest stages. These findings suggest that glycogen, being regulated by the two enzymes, may be a consequential factor in the transmission of maternal information and diapause induction of C. vestalis.

Hydrogen peroxide is a toxic metabolite of oxidative metabolism, but may also serve as a broad spectrum signaling molecule controlling a variety of essential physiological processes. Photoperiod influences diapause beyond the maternal generation in Cotesia vestalis and we speculated that intracellular hydrogen peroxide was a possible signal mediating this generational effect. To investigate the signaling functions of hydrogen peroxide in diapause induction in C. vestalis, hydrogen peroxide and activities of the antioxidant enzymes superoxide dismutase, peroxidase, and catalase were measured at diapause, and in maternal non-diapausing prepupa, adult, and offspring egg stages form the cultures reared at 25°C under the photoperiods of 8∶16, 12∶12, and 16∶8 (L∶D) h. The hydrogen peroxide contents and activities of superoxide dismutase and peroxidase in maternal non-diapausing prepupae and adults declined as the light period was reduced, whereas catalase activity increased significantly. Compared to d...

Effects of maternal photoperiod on the diapause trait of Cotesia plutellae in two populations, one from Hangzhou (30°14′ N), Zhejiang Province, and the other from Changchun (43°52′ N), Jilin Province, China, were examined in the laboratory by exposing the mother generation (G0) to 3 day-lengths (8L-16D, 12L-12D, and 16L-8D) at 25°C, and exposing their offspring (G1) to 2 day-lengths (8L-16D, 11L-13D) at 4 temperatures (13, 15, 17, 20°C). All three diapause-inducing factors had a significant influence on the incidence of diapause. Both populations could be induced to enter diapause under pertinent conditions. Long day length in G0 decreased the incidence of diapause and lowered the critical temperature for diapause-induction in G1. There were significant differences in the incidence of diapause between the two populations in almost all combinations. Compared to the southern Hangzhou population, the northern Changchun population produced a higher proportion of diapause individuals, and had higher critical temperatures for diapause-induction in all 6 photoperiod combinations used in G0 and G1 except for the one in which short day length (8L-16D) was used in both generations.