Honeydew feeding in the solitary bee Osmia bicornis as affected by aphid species and nectar availability

Like honey bees (Apis mellifera), non-Apis bees could exploit honeydew as a carbohydrate source. In addition to providing carbohydrates, this may expose them to potentially harmful plant products secreted in honeydew. However, knowledge on honeydew feeding by solitary bees is very scarce. Here we determine whether the polylectic solitary bee Osmia bicornis (=O. rufa) collects honeydew under semi-field conditions, and whether this is affected by aphid species and presence of floral nectar. Bees were provided with oilseed rape plants containing flowers and/or colonies of either Myzus persicae or Brevicoryne brassicae. We used the total sugar level of the bee crop as a measure of the individual's nutritional state and the oligosaccharide erlose as indicator for honeydew consumption. Erlose was present in honeydews from both aphid species, while absent in oilseed rape nectar, nor being synthesized by O. bicornis. When bees were confined to a single honeydew type as the only carbohydrate source, consumption of M. persicae honeydew was confirmed for 47% of the bees and consumption of B. brassicae honeydew for only 3%. Increased mortality in the latter treatment provided further evidence that B. brassicae honeydew is an unsuitable food source for O. bicornis. All bees that were given the choice between honeydew and floral nectar showed significantly increased total sugar levels. However, the fact that no erlose was detected in these bees indicates that honeydew was not consumed when suitable floral nectar was available. This study demonstrates that honeydew exploitation by O. bicornis is dependent on honeydew type and the presence of floral nectar.     

Survival, growth, and reproduction of two aphid species on sucrose solutions containing host or non-host honeydews

Aphids, like most phloem-feeding insects, commonly exhibit a high degree of host specificity. Plant-specific chemical compounds are likely to serve as important host selection cues for monophagous aphids and such substances could be present in aphid honeydew. Apterous virginoparae ofMyzus persicae (Sulzer) andPhorodon humuli (Schrank) were reared on a buffered sucrose solution containing various aphid honeydews or a mixture of amino acids. In two separate experiments, the host-specificP. humuli (hop aphid) could grow and reproduce only on diets containing honeydew collected from hop (Humulus lupulus L.).M. persicae (the green peach aphid, GPA) did not perform well on diets containing hop honeydew, perhaps because hop is a poor GPA host. Honeydew collected from preferred GPA host plants rape,Brassica napus L., and jimsonweed,Datura stramonium L., allowed GPA growth and reproduction. Hop aphids, however, performed poorly on rape and jimsonweed honeydew diets. Bell pepper,Capsicum annuum L., honeydew supported neither the hop aphid nor GPA. The study of aphid honeydew components may contribute towards a more complete understanding of host preference and selection phenomena in aphids.     

Osmoregulation by the aphid Myzus persicae: A physiological role for honeydew oligosaccharides

The dry matter content of honeydew produced by Myzus persicae feeding on artificial diets increased with increasing sucrose concentrations of the diet. Whereas the diet osmolalities ranged from 828 to 1800 milliosmolal, the honeydew osmolality was relatively constant (about 500 milliosmolal). This osmoregulatory capacity is achieved largely by variations in the mean molecular weight of glucose-containing honeydew oligosaccharides.     

Influence of elevated CO2 on interspecific interactions at higher trophic levels

Abstract We report the results of a study investigating the influence of elevated CO₂ on species interactions across three trophic levels: a plant (Brassica oleracea), two aphid herbivores (the generalist Myzus persicae and the specialist Brevicoryne brassicae), and two natural enemies (the coccinellid Hippodamia convergens (ladybird) and the parasitoid wasp Diaeretiella rapae). Brassica oleracea plants reared under elevated CO₂ conditions (650 ppmv vs. 350 ppmv) were larger and had decreased water and nitrogen content. Brevicoryne brassicae reared on plants grown in elevated CO₂ were larger and accumulated more fat, while there was no change in M. persicae traits. Fecundity of individual aphids appeared to be increased when reared on plants grown in elevated CO₂. However, these differences were generally lost when aphids were reared in colonies, suggesting that such changes in plant quality will have subtle effects on aphid intraspecific interactions. Nevertheless, CO₂ treatment did influence aphid distribution on plants, with significantly fewer M. persicae found on the shoots, and B. brassicae was only found on senescing leaves, when colonies were reared on plants grown in elevated CO₂. We reared B. brassicae and M. persicae in competition on plants grown at both the CO₂ concentration treatments. We found a significantly lower ratio of M. persicae: B. brassicae on plants grown under elevated CO₂ conditions, strongly suggesting that increasing CO₂ concentrations can alter the outcome of competition among insect herbivores. This was also reflected in the distribution of the aphids on the plants. While the CO₂ treatment did not influence where B. brassicae were found, fewer M. persicae were present on senescing leaves under elevated CO₂ conditions. Changes in plant quality resulting from the CO₂ treatments did not appear to alter aphid quality as prey species, as the number consumed by the ladybird H. convergens, and the number parasitised by the parasitoid wasp D. rapae, did not change. To our knowledge, this study provides the first empirical evidence that changes in host plant quality mediated by increasing levels of CO₂ can alter the outcome of interspecific competition among insect herbivores.     

The effects of azadirachtin-treated diets on the feeding behaviour and fecundity of the peach-potato aphid,Myzus persicae

Adult apterousMyzus persicae, which had fed for 26 h on diet containing azadirachtin at concentrations of 25–100 ppm, produced nymphs at less than half the rate of aphids on control diets. After 50 h on azadirachtin-treated diets nymph production had virtually ceased. After this period, any nymphs produced by adults that had fed on azadirachtin-treated diets were born dead with undeveloped appendages. Honeydew production on azadirachtin-treated diets was unaffected during the first 26 h period but was approximately three times less than on control diets during the subsequent 24 h period.     

Efficacy of Beauveria bassiana (Blas.) Vuill. against cabbage aphid Brevicoryne brassicae L. (Hem.: Aphididae) in laboratory condition

In order to replace the conventional chemical pesticides, extensive researches have been done on entomopathogenic fungi. Entomopathogenic fungus Beauveria bassiana is an important biocontrol agent against major economic pests and is being employed in Integrated pest management (IPM) along with synthetic pesticides. Cabbage aphid Brevicoryne brassicae L. is one of the important pests of Brassicaceae family. Therefore, in this research, the virulence isolate of B. brassicae (IRAN 429C) was investigated on adults of cabbage aphid under laboratory conditions. The experiments were conducted at 25 ± 2 °C, 60 ± 10 R. H. and a photoperiod of 16:8 (L: D). After preliminary experiments, the adult aphids were treated with fungal concentrations of 1 × 10³ to 1 × 10⁷ spores/ml. Probit analysis was conducted to calculate LC₅₀ and LC₉₅ values for the isolate. Positive correlation was observed between concentrations and pest mortality. LC₅₀ and LC₉₅ values calculated for IRAN 429C isolate are 2.04 × 10⁵ and 1.82 × 10⁸, respectively. The mortality was counted one day after the treatment and then continued for 14 days. Cumulative mortality for 14 days after treatment varied from 54% for IRAN 429C at low concentration (10³ conidia/ml) to 83% at high concentration (10⁷ conidia/ml). The lowest LT₅₀ was obtained at 7.67 days for IRAN 429C isolate at concentration 1 × 10⁷ spore/ml. According to the insecticidal activity of mentioned fungi on cabbage aphid, it can be used in biocontrol programmes of B. brassicae.     

Population growth parameters of the cabbage aphid,Brevicoryne brassicae (L.) (Hemiptera: Aphididae), exposed to sublethal doses of thiacloprid

The cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae) is a major pest of cabbage in the world. In this study, the influence of thiacloprid on population growth parameters of B. brassicae using demographic toxicology by leaf spray method was determined. The LC₅₀ values and confidence limits for thiacloprid were 274.89?ppm (185.22–479.22), respectively. To evaluate the sublethal effect of this insecticide on population growth parameters of cabbage aphid, LC₂₅ and LC₁₀ concentrations of thiacloprid were used at 76.44 and 23.52?ppm, respectively. Also The LC₅₀ value of this insecticide on the life table estimates was measured. Experiments were carried out in the laboratory at 23?±?1?°C, 60?±?5% RH and 16:8 (L:D) photoperiod on cabbage seedlings, Brassica oleracea, var. capitata L. Intrinsic rates of increase (r_m) were lower in thiacloprid treatment than in controls. The mean generation time and doubling time were also lower in populations treated with insecticide than in controls. There was a considerable reduction in the average numbers of nymphs reproduced per female as compared with the control. The average longevity of female adults in the control was significantly different (p?<?0.05) from those treated with thiacloprid. According obtained results, thiacloprid is a good choice for control of the B. brassicae.     

Prey‐mediated effects of glucosinolates on aphid predators

1. Plant resistance against herbivores can act directly (e.g. by producing toxins) and indirectly (e.g. by attracting natural enemies of herbivores). If plant secondary metabolites that cause direct resistance against herbivores, such as glucosinolates, negatively influence natural enemies, this may result in a conflict between direct and indirect plant resistance. 2. Our objectives were (i) to test herbivore‐mediated effects of glucosinolates on the performance of two generalist predators, the marmalade hoverfly (Episyrphus balteatus) and the common green lacewing (Chrysoperla carnea) and (ii) to test whether intraspecific plant variation affects predator performance. 3. Predators were fed either Brevicoryne brassicae, a glucosinolate‐sequestering specialist aphid that contains aphid‐specific myrosinases, or Myzus persicae, a non‐sequestering generalist aphid that excretes glucosinolates in the honeydew, reared on four different white cabbage cultivars. Predator performance and glucosinolate concentrations and profiles in B. brassicae and host‐plant phloem were measured, a novel approach as previous studies often measured glucosinolate concentrations only in total leaf material. 4. Interestingly, the specialist aphid B. brassicae selectively sequestered glucosinolates from its host plant. The performance of predators fed this aphid species was lower than when fed M. persicae. When fed B. brassicae reared on different cultivars, differences in predator performance matched differences in glucosinolate profiles among the aphids. 5. We show that not only the prey species, but also the plant cultivar can have an effect on the performance of predators. Our results suggest that in the tritrophic system tested, there might be a conflict between direct and indirect plant resistance.     

Insecticidal Potential of α-Pinene and β-Caryophyllene against <i>Myzus persicae</i> and Their Impacts on Gene Expression

Myzus persicae (M. persicae) is now considered a threat to agricultural crops due to economic losses. Numerous synthetic insecticides applied every year against M. persicae, are reported to be unsafe for environment, humans, and beneficial insects. Furthermore, several species of Myzus have been found to develop resistance due to over application of these insecticides. Therefore, it is required to find some novel insecticide that would be safe for the environment as well as for humans. In the current study, two major pure constituents α-pinene and β-caryophyllene were evaluated for their insecticidal potential against M. persicae using a fumigant toxicity assay. Furthermore, impact of α-pinene and β-caryophyllene on expression of five different genes, e.g., HSP 60, FPPS I, OSD, TOL and ANT responsible for reproduction, dispersion, and growth of M. persicae has also been investigated. To perform fumigant toxicity assay, five different concentrations (3.5, 4, 4.5, 5 and 6 μL L⁻¹) of α-pinene and β-caryophyllene were prepared. Lethal concentration (LC) was calculated, and gene expression studies were executed through qRT PCR at LC₃₀ of α-pinene and β-caryophyllene. Both constituents demonstrated excellent fumigant toxicity effects against M. persicae at all five concentrations. However, α-pinene shows significantly better results (98%) as compared to β-caryophyllene (80%) after 72 h at 6 μL L⁻¹ of dose. The highest upregulation in expression was demonstrated at LC₃₀ dose of α-pinene in five in three out of five genes understudy (TOL, ANT, and FPPS I). Conversely, two genes HSP 60 and OSD demonstrated downregulation at LC₃₀ dose of β-caryophyllene. Conclusively, our results highlighted the promising insecticidal potential of both compounds α-pinene and β-caryophylleneby interfering with the reproduction and development related processes in M. persicae, allowing us to recommend the phytoconstituents under investigation as an ecofriendly alternative to synthetic insecticides.     

A cuticle-degrading protease (CDEP-1) of Beauveria bassiana enhances virulence

In order to investigate virulence enhancement of entomopathogenic fungi, a Beauveria bassiana-sourced Pr1 protease (CDEP-1) was expressed by a methylotrophic yeast Pichia pastoris and then used as an additive to three gradient sprays of B. bassiana strain (Bb0062) onto apterous green peach aphid Myzus persicae adults in six bioassays. The resultant data fit well to a time–concentration–mortality model. Generally, the LC₅₀ estimates of the fungal pathogen against the aphid species decreased with increasing CDEP-1 concentrations from 0 to 100 µg mL^?1. The LC₅₀s on days 5–7 after spray were reduced by 1.5–2.5-fold at the concentrations of 20–100 µg mL^?1. However, sprays of 20–100 µg CDEP-1 mL^?1 aqueous solution alone had no significant effect on aphid mortality compared to water spray only. Neither did inclusion of inactivated CDEP-1 at a concentration of 50 µg mL^?1 affect significantly the fungal virulence to aphids. Our results confirm for the first time that the cuticle-degrading protease CDEP-1 enhanced fungal virulence due to acceleration of conidial germination and cuticle penetration. This suggests a new approach to utilising the protease in microbial control.     

A comparison of the reproduction of Brevicoryne brassicae and Myzus persicae in relation to soluble nitrogen concentration and leaf age (leaf position) in the brussels sprout plant

Wide variations in total soluble nitrogen occurred in different leaves of Brussels sprout plants. These variations were partly the result of leaf age (leaf position) and partly the result of different fertiliser application to the plants. The fecundity of Brevicoryne brassicae and Myzus persicae caged on such leaves also varied greatly and was correlated with total soluble nitrogen within leaves of the same age, but not between leaves of different ages. The value of total soluble nitrogen concentrations, based on analysis of leaf tissue, for indicating plant suitability for aphids is discussed as well as the difference in response of the two aphid species to experimental conditions favouring proteolysis in the leaf.

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Ein vergleich der vermehrung von Brevicoryne brassicae und Myzus persicae in beziehung zum gehalt löslichen stickstoffs und dem blattalter von rosenkohlpflanzen

Zusammenfassung Brevicoryne brassicae (L.) und Myzus persicae (Sulz.) wurden an Kohlblättern gekäfigt, die infolge verschiedener physiologischer Ursachen sehr unterschiedliche Mengen löslichen Stickstoffs enthielten. Den Pflanzen wurden zwei Düngerstoffe ((NH₄)₂SO₄ und KCL) verabreicht und die Blattläuse auf jungen, mittelalten und alten Blättern gekäfigt. Dadurch wurde der Gehalt löslichen Stickstoffs in den Blättern zwischen 0,543% und 1,286% variiert. Die Nachkommenzahl der Blattläuse bei diesen Düngungen und auf verschiedenaltrigen Blättern war sehr unterschiedlich (zwischen 7,3 und 30,2 bei B. brassicae; 17,6 und 59,4 bei M. persicae) und konnte in jedem Blattalter mit dem Stickstoffgehalt korreliert werden. Der Befund, daß die Korrelationen zwischen Blattlausnachkommenzahl und Stickstoffgehalt nicht unabhängig vom Blattalter waren, deutet darauf hin, daß der Stickstoffgehalt in physiologisch aktiven Blattgeweben nicht relativ mit dem der Siebröhren übereinstimmt. M. persicae vermochte in höherem Maße als B. brassicae Blätter auszunützen, in denen der Eiweißabbau durch Düngung oder Alter begünstigt war. Dieser Unterschied zwischen den beiden Arten steht möglicherweise mit ihren verschiedenen Nährstoffbedürfnissen in Zusammenhang.

     

Host plant recognition in monophagous weevils: Specialization ofCeutorhynchus inaffectatus to glucosinolates from its host plantHesperis matronalis

Several aphid honeydews were incorporated into sucrose solutions and presented to hop aphids, Phorodon humuli (Schrank), as artificial diets in free-choice bioassays. Small additions of honeydew collected from two species of aphid feeding on hop, Humulus lupulus L., arrested the searching behavior of the hop aphid and appeared to stimulate prolonged periods of ingestion. This effect was more dependent on the host plant honeydew source than the species of aphid that produced the honeydew. Aphid honeydews collected from plants other than hop (non-hosts to P. humuli) contained hop aphid phagostimulants that were less effective. Our results indicate that analysis of aphid honeydew could help describe chemical cues involved in the recognition of appropriate host plants by aphid species.     

On the effect of the food ofMyzus persicae Sulz. on the hymenopterous parasiteAphelinus asychis Walker

Summary The effect of different synthetic diets of the hostMyzus persicae on the parasiteAphelinus asychis was tested. Deficient diets were prepared by reducing sucrose or iron concentration: sucrose concentration was reduced from 15% in the complete diet (D.I.) to 7.5% in D. II and 3.75% in D. III; that of iron from 0.0023% in D. I to 0.0011% in D. IV and 0% in D.V.The development of the immature stages ofA. asychis in aphids fed on the deficient diets was delayed (especially on D. V). The size of the emerging adults was small, which corresponds with the reduced size of the host. The percentage of the male parasites was found to be higher on the deficient diets than on the full one. The lowest average longevity of the females was found among those reared on aphids on D. III and D.V.If honeydew fromM. persicae was offered to the females, a marked reduction in the longevity of these parasites was observed on D. II and D. III. On the other hand, on honeydew from aphids on D. IV and D.V,A. asychis lived as long as on honeydew from those fed on D.I.The fecundity of the females ofA. asychis was found to be dependent on the food composition of the hosts during larval development as well as during adult life.     

Interactions among the entomopathogenic fungus, Beauveria bassiana (Ascomycota: Hypocreales), the parasitoid, Aphidius matricariae (Hymenoptera: Braconidae), and its host, Myzus persicae (Homoptera: Aphididae)

The effect of the entomopathogenic fungus Beauveria bassiana on the biological characteristics and life table of Aphidius matricariae, a parasitoid of the green peach aphid, Myzus persicae, was studied under laboratory conditions. Aphids were first infected with twice the LC₉₅ of B. bassiana for third-instar M. persicae (2 × 10⁸ conidia/ml). Subsequently, at different intervals they were exposed to 1-day-old mated parasitoid females for 24 h. The number of mummies produced per female and the percentage emergence of the F1 generation differed significantly as a function of the time interval between application of the fungus and exposure to the parasitoid. The interference of B. bassiana on parasitoid development was also studied by first exposing the aphid hosts to the parasitoid for 24 h and subsequently applying B. bassiana. The number of mummies produced by a female A. matricariae varied from 11.8 to 24.8 and was significantly different when the aphids were first exposed to the parasitoids and then treated with B. bassiana 24, 48, 72, and 96 h after exposure. There were no significantly different effects of B. bassiana on net reproductive rate (R₀), mean generation time (T), intrinsic rate (r_m) and the finite rate of increase (λ) of A. matricariae as a result of development in hosts exposed to low or high conidial concentrations (1 × 10², 2 × 10⁸ conidia/ml). The parasitoids developed in infected hosts had lower r_m, λ, T and DT (doubling time) values compared with those that developed in uninfected hosts but no differences were observed in R₀ values. With proper timing, A. matricariae and B. bassiana can be used in combination in the successful biological control of M. persicae.     

Effects of Manduca sexta allatostatin and an analogue on the peach-potato aphid Myzus persicae (hemiptera: aphididae) and degradation by enzymes in the aphid gut

The oral toxicity of the C‐type allatostatin, Manduca sexta allatostatin (Manse‐AS) and the analogue δR³δR⁵Manse‐AS, where R residues were replaced by their D‐isomers, were tested against the peach‐potato aphid Myzus persicae by incorporation into an artificial diet. Both peptides had significant dose‐dependent effects on mortality, growth, and fecundity compared with control insects. The analogue, δR³δR⁵Manse‐AS, had an estimated LC₅₀ of 0.31 µg/µl diet and was more potent than Manse‐AS (estimated LC₅₀ of 0.58 µg/µl diet). At a dose of 0.35 µg δR³δR⁵Manse‐AS/µl diet, 76% of the aphids were dead after 6 days and all were dead after 10 days. In comparison, three times the dose of Manse‐AS was required to achieve 74% mortality after 8 days and 98% mortality after 16 days. The degradation of both peptides by extracts prepared from the gut of M. persicae was investigated. The estimated half‐life of Manse‐AS, when incubated with the gut extract from M. persicae, was 31 min. Degradation was due to a cathepsin L‐like cysteine protease, carboxypeptidase‐like activity, endoprotease activity with glutamine specificity, pyroglutamate aminopeptidase activity, and possibly trypsin‐like proteases. The half‐life of the δR³δR⁵ Manse‐AS analogue was enhanced (73 min) with the D‐isomers of R appearing to prevent cleavage around the R residues by cathepsin L‐like cysteine proteases or from trypsin‐like proteases. The greater stability of the analogue may explain its increased potency in M. persicae. This work demonstrates the potential use of Manse‐AS and analogues, with greater resistance to enzymatic attack, in aphid control strategies. © 2010 Wiley Periodicals, Inc.     

Seasonal changes in aphid populations on Brussels sprouts

Populations of Brevicoryne brassicae (L.) and Myzus persicae (Sulz.) were assessed weekly on Brussels sprouts at Wellesbourne, from July onwards in each of 3 years. A peak of B. brassicae numbers occurred every year about the end of July, and in 1968 and 1970 this was larger than the September peak. Some alates were produced in the generation born to the June immigrants and the dispersal of those produced at the end of July consistently brought a decline in B. brassicae populations in early August. In 1968 and 1970, however, outbreaks of entomogenous fungi which followed rain, added considerably to this decline. Records of predators and parasites indicated that these natural enemies had only a minor effect on aphid numbers. M. persicae colonized sprouts slightly earlier than B. brassicae; in 1969 and 1970 its numbers in July were low and some persisted after the first week of August in 1968 only. In each year the first eggs of B. brassicae were laid at the beginning of October, but viviparae were still numerous for a further 7 to 10 weeks.     

Time and concentration dependent interactions of Beauveria bassiana with sublethal rates of imidacloprid against the aphid pests Macrosiphoniellasanborni and Myzus persicae

A series of laboratory bioassays with each consisting of low, medium and high concentration treatments of the fungal biocontrol agent Beauveria bassiana alone or supplemented with an increasing sublethal rate of imidacloprid were conducted to quantify the fungal and chemical interactions on chrysanthemum aphid Macrosiphoniella sanborni (0.01‐0.05 a.i. μg mL^?1) and green peach aphid Myzus persicae (0.05‐0.5 a.i. μg mL^?1). During one week after exposure to a 1 mL spray onto a 95 cm² area in a Potter Spray Tower, M. sanborni was either more susceptible to B. bassiana or more sensitive to imidacloprid than M. persicae. The time–concentration–mortality (TCM) responses of each aphid species in each of five bioassays fit well to a TCM model, indicating a strong dependence of the fungal and chemical interactions on both concentration and post‐spray time. Adding imidacloprid to B. bassiana sprays at the rates of 0.025–0.05 μg mL^?1 against M. sanborni or 0.1–0.5 μg mL^?1 against M. persicae significantly enhanced or accelerated the fungal action. Based on the LC₅₀ or LC₉₀ estimates and their variances determined by the fitted TCM relationships for each aphid species, the relative potencies of an imidacloprid‐inclusive bioassay over those with B. bassiana alone or together with a lower sublethal rate ranged from a few to hundreds of times and varied over days after spray. These results suggest an alternative tactic for practical control of the aphid pests by a combined formulation or application of B. bassiana and imidacloprid and manage aphid resistance to the chemical insecticide.     

Sub-lethal effects of tiametoxam on life table parameters of the cabbage aphid,Brevicoryne brassicae (L.) (Hemiptera: Aphididae) under laboratory conditions

Efficiency of tiametoxam was determined on population growth parameters of cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae) using demographic toxicology by leaf spray method. At first, bioassay was performed. The LC₅₀ values and confidence limits for thiamethoxam were 169.05?ppm (92.61–342.51). To evaluate, the sub-lethal effect of this insecticide on population growth parameters of cabbage aphid, LC₂₅ and LC₁₀ concentrations of tiametoxam were used at 58.8 and 22.05?ppm, respectively. Also, the LC₅₀ value of insecticide on the life table estimates was measured. Experiments were carried out in the laboratory at 23?±?1?°C, 60?±?5% RH and 16:8 (L:D) photoperiod on cabbage seedlings, Brassica oleracea, var. capitata L. Net fecundity rate decreased in insecticide-treated populations. Intrinsic rates of increase (r_m) were lower in tiametoxam treatment than in controls. There was a relative increase in intrinsic death rates of treated populations. The mean generation time and doubling time were also lower in population treated with insecticide than the control. There was a considerable reduction in the average numbers of nymphs reproduced per female as compared with the control. The average longevity of female adults in the control was significantly different (p?<?0.05) from those treated with thiamethoxam.     

3种酰胺类稻田除草剂对克氏原螯虾的急性毒性

[目的] 研究稻虾共作模式条件下,稻田封闭除草剂对克氏原螯虾产生的急性毒性。[方法] 采用半静态试验方法,研究3种酰胺类除草剂（乙草胺、丙草胺和丁草胺）对克氏原螯虾的急性毒性,计算3种酰胺类除草剂对克氏原螯虾的安全浓度,并分析其LC₅₀衰减规律。[结果] 随着暴露时间和除草剂浓度的增加,虾体侧躺,步行足和游泳足活动频率降低,最终死亡。乙草胺对克氏原螯虾的96 h半致死浓度（LC₅₀）和安全浓度（SC）分别为0.0707和0.0146 mL·L^-1;丙草胺对克氏原螯虾的96 h LC₅₀和SC分别为0.0119和0.0021 mL·L^-1;丁草胺对克氏原螯虾的96h LC₅₀和SC分别为0.0073和0.0014 mL·L^-1。乙草胺、丙草胺及丁草胺除草剂LC₅₀随着暴露时间延长呈下降趋势,符合双曲线衰减模型,回归方程分别为：① y₁=2.0840x^-0.7380（R²=0.9973）;② y₂=0.1106x^-0.4930（R²=0.9872）;③ y₃=0.2236x^-0.7480（R²=0.9990）。克氏原螯虾对3种除草剂的敏感性由高到低依次为：丁草胺 > 丙草胺 > 乙草胺。[结论] 乙草胺和丙草胺可在稻田综合种养生产过程中按常规剂量使用,而丁草胺按常规剂量使用可能存在较大的风险。     

Feeding response of the cotton aphid,Aphis gossypii,to sublethal rates of flonicamid and imidacloprid

The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is an important sap‐sucking pest of many plants, including melons and peppers. This study was conducted to determine the effects of sublethal exposure to flonicamid and imidacloprid and the mechanisms by which these insecticides affect the feeding behavior of A. gossypii. The median lethal concentrations (LC₅₀) of flonicamid and imidacloprid for adult A. gossypii were 2.40 and 1.92 mg l^?1, respectively. The lower lethal concentrations of flonicamid were 1.01 mg l^?1 (LC₃₀) and 0.29 mg l^?1 (LC₁₀), and those of imidacloprid were 0.82 mg l^?1 (LC₃₀) and 0.24 mg l^?1 (LC₁₀). The developmental period of A. gossypii nymphs at LC₃₀ was 3.6 days for both insecticides, which was shorter than that of the untreated controls (4.2 days). Longevity and total fecundity of A. gossypii adults were decreased at the sublethal concentrations of both insecticides. The lowest net reproductive rate was observed in A. gossypii treated with the LC₃₀ of flonicamid. Feeding behavior analyses using an electrical penetration graph showed that sublethal concentrations of flonicamid and imidacloprid had significant effects on the duration of phloem ingestion. Higher doses of flonicamid induced starvation by inhibiting phloem ingestion, whereas imidacloprid acted as a contact toxin rather than an inhibitor of feeding behavior.