RFID tracking of sublethal effects of two neonicotinoid insecticides on the foraging behavior of Apis mellifera

The development of insecticides requires valid risk assessment procedures to avoid causing harm to beneficial insects and especially to pollinators such as the honeybee Apis mellifera. In addition to testing according to current guidelines designed to detect bee mortality, tests are needed to determine possible sublethal effects interfering with the animal's vitality and behavioral performance. Several methods have been used to detect sublethal effects of different insecticides under laboratory conditions using olfactory conditioning. Furthermore, studies have been conducted on the influence insecticides have on foraging activity and homing ability which require time-consuming visual observation. We tested an experimental design using the radiofrequency identification (RFID) method to monitor the influence of sublethal doses of insecticides on individual honeybee foragers on an automated basis. With electronic readers positioned at the hive entrance and at an artificial food source, we obtained quantifiable data on honeybee foraging behavior. This enabled us to efficiently retrieve detailed information on flight parameters. We compared several groups of bees, fed simultaneously with different dosages of a tested substance. With this experimental approach we monitored the acute effects of sublethal doses of the neonicotinoids imidacloprid (0.15-6 ng/bee) and clothianidin (0.05-2 ng/bee) under field-like circumstances. At field-relevant doses for nectar and pollen no adverse effects were observed for either substance. Both substances led to a significant reduction of foraging activity and to longer foraging flights at doses of ≥0.5 ng/bee (clothianidin) and ≥1.5 ng/bee (imidacloprid) during the first three hours after treatment. This study demonstrates that the RFID-method is an effective way to record short-term alterations in foraging activity after insecticides have been administered once, orally, to individual bees. We contribute further information on the understanding of how honeybees are affected by sublethal doses of insecticides.     

吡虫啉对成年意大利蜜蜂脑神经细胞致凋亡作用

【目的】蜜蜂是重要的授粉昆虫, 但一直受到新烟碱类杀虫剂（如吡虫啉）的危害, 该类杀虫剂主要作用于蜜蜂脑神经细胞。本研究旨在明确吡虫啉对意大利蜜蜂Apis mellifera ligustica脑神经细胞致凋亡作用。【方法】利用亚致死剂量吡虫啉饲喂成年意大利蜜蜂, 通过原位末端标记法（TUNEL）检测脑神经细胞的凋亡情况, 利用免疫荧光法检测Caspase-1激活情况, 通过透射电镜观察脑神经细胞的超微结构。【结果】在对选取的脑部7个部位进行总体观测后, 摄入亚致死剂量的吡虫啉（9.90 ng/蜜蜂）诱导成年意蜂工蜂脑神经细胞凋亡率随时间递增而增加, 在处理9 d和12 d时, 处理组与空白对照组差异极显著（P<0.01）; Caspase-1阳性细胞率也随时间递增而增加, 在处理3, 6, 9和12 d时, 处理组与空白对照组差异极显著（P<0.01）。凋亡率和Caspase-1阳性细胞率均表现出时间效应, 且两者成正相关性。超微结构表明凋亡的神经细胞呈现凋亡和自噬双重特征, 包括： 细胞固缩、 染色质浓缩、 凋亡小体和自噬体出现; 线粒体肿胀, 有的被自噬泡包裹后进行线粒体自噬。【结论】本研究从细胞水平证实了亚致死剂量吡虫啉对成年意蜂工蜂脑神经细胞具有致凋亡作用, 并且其凋亡途径与Caspase-1和细胞自噬有关, 这为利用细胞凋亡法评价杀虫剂对非靶标生物的神经毒性提供一定的理论基础。     

亚致死剂量杀虫剂对意蜂工蜂嗅觉敏感性的影响

喙伸反应(PER)试验适用于评价杀虫剂对蜜蜂行为的影响。本实验利用喙伸反应研究了亚致死剂量(LD50/100～LD50/10)溴氰菊酯和吡虫啉对意蜂Apis mellifera ligustica L.工蜂嗅觉敏感性的影响。结果发现,经口饲喂溴氰菊酯5ng和10ng后,工蜂对0.1%的蔗糖溶液的敏感性显著下降(P<0.05),水应激指数降低,但对0.3%,1%,3%,10%和30%的蔗糖溶液的敏感性没有显著变化;而经口饲喂吡虫啉0.3ng和0.6ng后,工蜂对上述各浓度蔗糖溶液的敏感性变化不明显,但其水应激指数升高。     

亚致死剂量吡虫啉胁迫对意大利蜜蜂内勤蜂与外勤蜂免疫解毒相关基因表达及免疫解毒酶系活力的影响

摘要: 【目的】吡虫啉(imidaclorprid)是广泛使用的新烟碱类杀虫剂之一。大量研究表明亚致死剂量吡虫啉影响意大利蜜蜂Apis mellifera ligustica(简称“意蜂”)幼虫的发育和成年蜜蜂的采集、学习等行为。本实验旨在探究亚致死剂量吡虫啉对意大利蜜蜂内勤蜂(1日龄成年工蜂)与外勤蜂(21日龄成年工蜂)免疫解毒相关基因表达及免疫解毒酶系活力的影响,进而为蜜蜂健康的维护提供科学依据。【方法】测定饲喂含0.1 ng/μL吡虫啉的50%蔗糖溶液不同时间后意蜂成年工蜂的存活率;利用荧光定量PCR检测饲喂含0.1 ng/μL吡虫啉的50%蔗糖溶液6 d后其体内免疫基因多酚氧化酶基因(PPOA3, GenBank登录号： GB43738), Abaecin类抗菌肽基因(ABA, GenBank登录号： GB18323),葡萄糖脱氢酶基因(GLD, GenBank登录号： GB43007)和解毒基因细胞色素P450基因(CYP450 6a2, GenBank登录号： GB49876)的表达,并采用双抗体一步夹心法酶联免疫吸附试验测定其体内细胞色素P450酶(cytochrome P450, CYP450)含量和多酚氧化酶(polyphenol oxidase,PPO)活力。【结果】1日龄和21日龄意蜂成年工蜂连续饲喂6 d含0.1 ng/μL吡虫啉的50%蔗糖溶液后,其存活率与对照组(饲喂含0.1 ng/μL丙酮的50%蔗糖溶液)无显著差异;连续饲喂9 d含0.1 ng/μL吡虫啉的50%蔗糖溶液后,1日龄意蜂成年工蜂存活率与对照组无显著差异,而21日龄意蜂成年工蜂存活率与对照组有显著差异。1日龄意蜂成年工蜂自由取食含0.1 ng/μL吡虫啉的蔗糖溶液6 d后, PPOA3, CYP450 6a2, ABA和GLD表达水平,细胞色素P450含量以及多酚氧化酶活力与对照组相比均有显著下调趋势;而21日龄意蜂成年工蜂取食该药液6 d后,CYP450 6a2, ABA和GLD表达水平及多酚氧化酶活力与对照组相比均有显著下调趋势,PPOA3表达水平和细胞色素P450含量有显著上调趋势。【结论】亚致死剂量吡虫啉影响意大利蜜蜂内勤蜂与外勤蜂免疫解毒相关基因的表达及免疫解毒酶系活力;吡虫啉短期胁迫对意大利蜜蜂内勤蜂与外勤蜂的存活无显著影响,长期胁迫则会影响意大利蜜蜂内勤蜂与外勤蜂的存活。     

Adult honeybee's resistance against Paenibacillus larvae larvae, the causative agent of the American foulbrood.

American foulbrood is a widespread disease of honeybee larvae caused by the spore-forming bacterium Paenibacillus larvae subsp. larvae. Spores represent the infectious stage; when ingested by a larva they germinate in the midgut. The rod-shaped vegetative forms penetrate the larva's intestinal tissue and start multiplying rapidly, which finally kills the larva. Spores fed to adult honeybees, however, do not harm the bees. We investigated this phenomenon. Specifically, we studied the influence of the adult honeybee midgut on the vegetative growth and on the germination of spores of P. larvae larvae. We focused on two groups of adult workers that are likely to have large numbers of spores in their gastrointestinal tracts in infected colonies: middle-aged bees, which are known to remove or cannibalize dead larvae and clean brood cells, and winterbees, which do not have frequent chances to defecate. We found that midgut extract from winterbees and worker-aged bees of different colonies almost completely inhibited the growth of the vegetative stage of P. larvae larvae and suppressed the germination of spores. The inhibiting substance or substances from the adult midgut are very temperature stable: they still show about 60% of their growth-inhibiting capacity against this bacterium after 15 min at 125 degrees C. We established a method to test growth-inhibiting factors against P. larvae larvae in vitro.     

Life-cycle nitrogen budget for the gypsy moth, Lymantria dispar, reared on artificial diet

Lymantria dispar larvae were reared on a wheat germ-based artificial diet from egg eclosion until pupation. Utilization efficiency of dietary nitrogen underwent an age-specific decrease from 75% in the first instar to 54 and 43% for last-instar female and male larvae, respectively. Relative rates (mg/day/mg biomass) of nitrogen consumption and assimilation also decreased during larval development, but the excretion rate of nitrogen was constant for all instars and both sexes. Larval % nitrogen decreased as the larvae matured, while the percentage in the frass increased. These data suggest that need for nitrogen decreases as the larva matures. While L. dispar is comparatively inefficient at assimilating dietary nitrogen, over one-half of that assimilated by the female larva is transferred to egg production by the adult.     

八种杀虫剂对韭菜迟眼蕈蚊发育和繁殖的亚致死效应

用胃毒触杀法确定8种常用杀虫剂对韭菜迟眼蕈蚊Bradysiaodoriphaga 3龄幼虫的LC₂₀和LC₅₀剂量后,以其LC₂₀分别处理3龄幼虫,将存活幼虫正常饲养,测定该剂量药剂对韭菜迟眼蕈蚊化蛹率、蛹重、羽化率,成虫存活率、雌雄比、单雌产卵量及卵孵化率等指标的影响。结果表明:毒死蜱等4种药剂的影响较显著,其影响程度由高到低依次为毒死蜱＞辛硫磷＞阿维菌素溴虫腈;而另4种药剂丙硫克百威、灭多威、丁硫克百威和吡虫啉则影响不显著。此外也测定了用后4种药剂LC₅₀剂量处理的存活试虫的上述生物学指标,结果表明：除化蛹率和羽化率较对照降低且差异显著外,其他生物学指标与对照处理无明显变化。     

锈翅蚁蛉(脉翅目:蚁蛉科)的发育生物学研究

锈翅蚁蛉为全变态类昆虫,在贵州省一年发生1代,11月下旬开始越冬,各龄幼虫均可越冬,次年3月苏醒.在室内饲养条件下,卵期13 d±0.56 d,幼虫期63.58 d±1.81d,蛹期26.35 d±1.14 d,成虫期20 d± 1.06 d.结合野外调查和室内饲养,详细描述了锈翅蚁蛉各虫态的形态特征,幼虫的筑穴、捕食、蜕皮、化蛹、羽化以及成虫的捕食、交配等行为习性.     

饥饿程度对美国白蛾生长发育和繁殖的影响

不同龄期幼虫饥饿对美国白蛾Hyphantria cunea(Drury)生长发育和繁殖影响的研究结果表明:美国白蛾低龄(2龄)幼虫短时间的饥饿对其生长发育和繁殖的影响不明显;美国白蛾中龄(4龄)幼虫饥饿2,4,6d使美国白蛾的历期相应增长,存活率、化蛹率、羽化率、产卵量都相应降低,交配率与对照之间没有差异;老熟(6龄)幼虫短时间饥饿(4d)的存活率、羽化率、交配率、产卵量都稍有下降;长时间饥饿(12d)的老熟幼虫有70%左右因饥饿而提前化蛹,提前化蛹的蛹体外没有薄茧的包裹。提前化蛹的美国白蛾的羽化率、交配率均非常低,产卵量很少。     

石蒜总生物碱对家蝇的生物活性

在室内测定了石蒜总生物碱对家蝇的生物活性,表明石蒜总生物碱对家蝇具有一定的触杀作用和生长发育抑制作用.石蒜总生物碱不同浓度(15、12、9、6、3 mg/mL)、不同作用时间(24 h、36 h、48 h、60 h、72 h)以及它们的交互作用分别对家蝇幼虫和成虫的触杀作用有显著影响.当石蒜总生物碱的浓度为15 mg/mL时,家蝇幼虫(3龄早期)和成虫(羽化3d)平均校正死亡率最高,分别为40.96％和38.25％,随着浓度的降低,触杀作用逐渐降低,随着作用时间的延长,触杀作用逐渐增强,72 h的平均校正死亡率分别达39.35％和37.55％,但总生物碱对家蝇幼虫和成虫的触杀作用间无显著差异.处理24、36、48、60、72 h后,石蒜总生物碱对家蝇幼虫的LC50值分别为57.42、36.48、21.92、13.13和10.95 mg/mL,对成虫的LC50值分别为86.66、37.86、23.91、14.15和11.51 mg/mL.老熟幼虫的平均重量除了在3 mg/mL时与对照差异不显著,其他各浓度下都显著低于对照,而在各浓度下的化蛹率、蛹的平均重量和羽化率均显著低于对照.     

吡虫啉对意大利蜜蜂脑乙酰胆碱受体分布的影响

蜜蜂是自然界主要的授粉昆虫; 新烟碱类杀虫剂(neonicotinoid insecticide)通过结合害虫体内乙酰胆碱受体（nAChR）使害虫致死, 是目前广泛用于田间害虫防控的杀虫剂。本研究以意大利蜜蜂Apis mellifera ligustica和新烟碱类杀虫剂的代表品种吡虫啉为材料, 应用免疫组织化学的方法, 研究了正常成年蜜蜂脑内蘑菇体及视叶nAChR-α7的表达和分布; 分析了亚致死剂量新烟碱类杀虫剂吡虫啉对nAChR-α7表达和分布的影响。结果表明, nAChR-α7在正常蜜蜂脑蘑菇体和视叶中均可检测到, 在蘑菇体中分布相对较少, 但在视叶分布丰富。吡虫啉对nAChR-α7在视叶的表达和分布有显著抑制作用, 但对蘑菇体nAChR-α7的表达没有显著影响。结果提示, 新烟碱类杀虫剂吡虫啉除了文献报道的抑制nAChR的表达外, 还能抑制nAChR-α7的表达量, 这是新烟碱类杀虫剂作用机制的新发现。     

亚致死剂量吡虫啉对意大利蜜蜂中肠细菌群落的影响（英文）

【目的】在实验室条件下,研究亚致死剂量吡虫啉对意大利蜜蜂 Apis mellifera ligustica 中肠细菌群落的影响,以期为杀虫剂的生物安全性评价体系提供理论依据。【方法】分别用3种不同浓度（0.005, 0.015 和0.045 mg/L）的吡虫啉蔗糖溶液以及含丙酮（0.03%）的糖水(空白对照)在实验室内饲喂刚出房的意大利蜜蜂,在饲喂3, 6, 9, 12和15 d时分别取样。提取中肠细菌基因组DNA,采用下一代高通量测序技术对4个处理组蜜蜂中肠细菌群落进行检测分析。【结果】细菌序列分析表明,意大利蜜蜂中肠细菌主要属于变形菌门（Proteobacteria）和厚壁菌门（Firmicutes）,同一时间内各处理组间主要细菌数量差异不显著（P>0.05）,同时细菌群落多样性指数差异也不显著（P>0.05）。【结论】在实验室条件下亚致死剂量吡虫啉对意大利蜜蜂中肠细菌群落结构影响不显著。     

Effect of gamma-irradiation on some biological activities of the larval stage of the khapra beetle, Trogoderma granarium Everts (Col., Dermestidae)

Abstract: The present study was carried out on the larval stage of the khapra beetle, Trogoderma granarium Everts to determine some biological effects of gamma irradiation at levels between 20 to 100 Gy on various aspects of larval behaviour such as number of moults, developmental time, larval growth, starvation and mortality, pupal promptness in addition to larval density. Larval mortality of 92.5% was obtained by treating with 80 Gy and no larva lived after an exposure of 100 Gy or more. With increasing doses from 40 Gy or more, half of the male and female larvae had six moults as compared with three to five moults in the control. The larval duration increased gradually and reached 40.2 days for male larvae and 44.2 days for female ones at a dose of 80 Gy as compared to 25.2 and 28.3 days, respectively, for the control. Larvae irradiated with 60 and 80 Gy did not feed as much as those irradiated at 20 and 40 Gy or the control group. A negative correlation was observed between increasing dosage levels and reduction in the fresh body weight of larvae. The highest larval starvation of 79.8% occurred at 80 Gy and the least (23.8%) at 20 Gy. Pupal promptness seems to be lower at the higher radiation doses. With 40, 60 and 80 Gy, approximately 69.5, 19.6 and 7.5%, respectively, of the larvae succeeded in pupation compared with 94.6% in the control. High doses of radiation seem to enhance the production of males. An increase of larval density enhances the effects of radiation doses to retard the developmental time, to increase larval and pupal mortality and to reduce adult eclosion.     

Imidacloprid-induced impairment of mushroom bodies and behavior of the native stingless bee Melipona quadrifasciata anthidioides

Declines in pollinator colonies represent a worldwide concern. The widespread use of agricultural pesticides is recognized as a potential cause of these declines. Previous studies have examined the effects of neonicotinoid insecticides such as imidacloprid on pollinator colonies, but these investigations have mainly focused on adult honey bees. Native stingless bees (Hymenoptera: Apidae: Meliponinae) are key pollinators in neotropical areas and are threatened with extinction due to deforestation and pesticide use. Few studies have directly investigated the effects of pesticides on these pollinators. Furthermore, the existing impact studies did not address the issue of larval ingestion of contaminated pollen and nectar, which could potentially have dire consequences for the colony. Here, we assessed the effects of imidacloprid ingestion by stingless bee larvae on their survival, development, neuromorphology and adult walking behavior. Increasing doses of imidacloprid were added to the diet provided to individual worker larvae of the stingless bee Melipona quadrifasciata anthidioides throughout their development. Survival rates above 50% were only observed at insecticide doses lower than 0.0056 μg active ingredient (a.i.)/bee. No sublethal effect on body mass or developmental time was observed in the surviving insects, but the pesticide treatment negatively affected the development of mushroom bodies in the brain and impaired the walking behavior of newly emerged adult workers. Therefore, stingless bee larvae are particularly susceptible to imidacloprid, as it caused both high mortality and sublethal effects that impaired brain development and compromised mobility at the young adult stage. These findings demonstrate the lethal effects of imidacloprid on native stingless bees and provide evidence of novel serious sublethal effects that may compromise colony survival. The ecological and economic importance of neotropical stingless bees as pollinators, their susceptibility to insecticides and the vulnerability of their larvae to insecticide exposure emphasize the importance of studying these species.     

柑桔爆皮虫幼期各虫态的形态学观察

采用田间观察和室内观察相结合的方法,使用Leica MZ 16A研究型体视解剖镜,对柑桔爆皮虫Agrilus auriventris Saunders幼期各虫态的形态进行了系统的观察。结果发现：卵初产时为乳白色,后变为浅褐色并开始皱缩,末期变为黄褐色,孵化前部分卵壳分离为白色蜡质外层和黄褐色内层两层;幼虫孵化的同时直接从卵壳贴近树皮的一侧蛀入韧皮部,同时将大量虫粪排入卵壳;幼虫随着虫龄的增加钳状突的阶数和口上片的宽度发生有规律的变化,末龄幼虫在木质部作一椭圆形蛹室化蛹,身体的头部和尾部以3∶7的比例对折; 化蛹前的幼虫经历一个身体缩短的预蛹状态;刚化的蛹为乳白色,复眼颜色与身体相似,化蛹后蛹的颜色逐渐变为淡黄色,复眼颜色变为浅红褐色,后期复眼变为红褐色,口器变黑,羽化前蛹的复眼、口器和体表全部变黑;羽化过程中,成虫体表的膨胀导致蛹表皮脱裂,前翅变黑和腹部背面变成碧蓝色后羽化成完整的成虫。本结果进一步支持将柑桔爆皮虫幼虫期分为5龄。     

Studies on the impact of two Nosema isolates from Bulgaria on the gypsy moth (Lymantria dispar L.)

We investigated host-parasite interactions of two Nosema-type microsporidian isolates recovered from populations of Lymantria dispar L. in northwestern Bulgaria, one near Veslec and one near Levishte. Bioassay studies produced information on development, stage specific mortality, pupation, and adult eclosion of infected individuals. Horizontal transmission of the two isolates was investigated in a second set of experiments. At dosages ranging from 2 x 10(2) to 5 x 10(4) spores/microl, the infection rates varied between 77 and 100% for the isolate from Veslec and between 92 and 99% for the Levishte isolate. The Veslec isolate caused a slightly higher mortality rate and the median time to death was shorter compared to the isolate from Levishte. The total mortality for both isolates varied between 79 and 99%, independent of spore dosages. A lower relative growth rate was recorded for male and female L. dispar larvae infected with either isolate during the third larval instar and a higher relative growth rate during the fourth instar compared to the control groups. Pupal weight did not differ significantly among females, but male infected pupae were heavier than the controls. Nosema sp. [Veslec] was as efficiently transmitted as Nosema sp. [Levishte]; 42% of the susceptible larvae became infected with the Veslec isolate when uninfected larvae were exposed to infected larvae; 43% of larvae became infected with the Nosema sp. [Levishte]. The latency period varied between 7 and 8 days for both isolates.     

取食重金属铜对棕尾别麻蝇亲代及子代生长发育与繁殖的影响

为了评估取食含重金属铜饲料对棕尾别麻蝇Boettcherisca peregrine亲代及子代的生长发育与繁殖的影响,在室内给棕尾别麻蝇初产幼虫饲喂含不同浓度（200, 400,800和1 600 µg/g）Cu²⁺的饲料直至化蛹,并对亲代和子代的生长发育和繁殖有关指标进行了观察和分析。结果表明：低浓度的Cu²⁺（200 µg/g）对其体重和体长起促进作用,但对幼虫历期、化蛹率、蛹历期、羽化率、性比、交配率和产仔量无显著作用;较高浓度的Cu²⁺ 则有抑制作用,且Cu²⁺处理浓度越高,亲代幼虫、蛹和雌雄成虫的体重越轻,幼虫和蛹的体长越短,化蛹率、羽化率、交配率和产仔量越低,幼虫历期和蛹期越长,成虫寿命越短。但Cu²⁺处理对成虫性比则无显著的影响。相比之下,经Cu²⁺处理后雌虫所产的子代若不再经Cu²⁺处理,其子代生存、生长发育与繁殖则基本不受影响,说明Cu²⁺对亲代的影响不能遗传至子代。此外,还探讨了该蝇亲代与子代体内Cu²⁺含量在其变态过程中的变化。     

影响蜜蜂球囊菌侵染蜜蜂幼虫的因素及侵染过程观察

为探究蜜蜂球囊菌Ascosphaera apis只侵染封盖前后蜜蜂幼虫的原因及相关侵染机制, 本研究利用实验室饲养的意大利蜜蜂Apis mellifera ligustica幼虫, 给其接种球囊菌孢子, 探究不同接种量（0, 1.0×10², 1.0×10³, 1.0×10⁴, 1.0×10⁵ 和1.0×10⁶ 孢子/mL）、 接种时期（3, 4, 5和6龄幼虫）以及28℃低温处理6 h对蜜蜂球囊菌侵染的影响。同时对处于不同侵染阶段的蜜蜂幼虫做病理学切片, 探究球囊菌侵染的过程。结果显示： 球囊菌孢子接种量与蜜蜂的发病率密切相关（r=0.9883）, 蜜蜂幼虫对低于1.0×10³孢子/mL的侵染有抗性, 与不接孢子的对照组差异不显著（P>0.05）。蜜蜂不同龄期接种发病率的差异是因不同龄幼虫食量不同导致的摄入孢子剂量的不同引起的, 28℃低温处理能够显著提高处于幼虫到蛹转化期蜜蜂的发病率（P<0.05）, 而对取食阶段的蜜蜂幼虫没有影响。病理学研究表明, 在整个幼虫期, 摄入的孢子因中肠没有氧气不生长, 对幼虫没有致病性, 幼虫的取食和发育过程正常, 至幼虫期结束进入蛹期后, 蜜蜂的中后肠接通, 摄入的孢子伴随蜜蜂的蛹便进入后肠并在此迅速萌发生长, 在1~2 d内菌丝即突破体表, 导致蜜蜂死亡。蜜蜂球囊菌选择营养物质储存最多而防御能力较低的幼虫到蛹转化期侵染, 降低了侵染成本, 提高成功率。该研究阐明了蜜蜂球囊菌侵染蜜蜂的机制, 丰富了昆虫与病原菌之间相互作用的内容。     

A Locomotor Deficit Induced by Sublethal Doses of Pyrethroid and Neonicotinoid Insecticides in the Honeybee Apis mellifera

The toxicity of pesticides used in agriculture towards non-targeted organisms and especially pollinators has recently drawn the attention from a broad scientific community. Increased honeybee mortality observed worldwide certainly contributes to this interest. The potential role of several neurotoxic insecticides in triggering or potentiating honeybee mortality was considered, in particular phenylpyrazoles and neonicotinoids, given that they are widely used and highly toxic for insects. Along with their ability to kill insects at lethal doses, they can compromise survival at sublethal doses by producing subtle deleterious effects. In this study, we compared the bee’s locomotor ability, which is crucial for many tasks within the hive (e.g. cleaning brood cells, feeding larvae…), before and after an acute sublethal exposure to one insecticide belonging to the two insecticide classes, fipronil and thiamethoxam. Additionally, we examined the locomotor ability after exposure to pyrethroids, an older chemical insecticide class still widely used and known to be highly toxic to bees as well. Our study focused on young bees (day 1 after emergence) since (i) few studies are available on locomotion at this stage and (ii) in recent years, pesticides have been reported to accumulate in different hive matrices, where young bees undergo their early development. At sublethal doses (SLD_48h, i.e. causing no mortality at 48h), three pyrethroids, namely cypermethrin (2.5 ng/bee), tetramethrin (70 ng/bee), tau-fluvalinate (33 ng/bee) and the neonicotinoid thiamethoxam (3.8 ng/bee) caused a locomotor deficit in honeybees. While the SLD_48h of fipronil (a phenylpyrazole, 0.5 ng/bee) had no measurable effect on locomotion, we observed high mortality several days after exposure, an effect that was not observed with the other insecticides. Although locomotor deficits observed in the sublethal range of pyrethroids and thiamethoxam would suggest deleterious effects in the field, the case of fipronil demonstrates that toxicity evaluation requires information on multiple endpoints (e.g. long term survival) to fully address pesticides risks for honeybees. Pyrethroid-induced locomotor deficits are discussed in light of recent advances regarding their mode of action on honeybee ion channels and current structure-function studies.     

Sublethal effects of indoxacarb on the diamondback moth, <Emphasis Type="Italic">Plutella xylostella</Emphasis> (L.) (Lepidoptera: Yponomeutidae)

The effects of sublethal concentrations of indoxacarb on Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) were examined. In comparison with the control, sublethal concentrations led to a significant decrease in adult emergence, the percentage of pupation and pupal weight of the parent generation, fecundity, and adult longevity. They also significantly decreased the net reproductive rate (R ₀), intrinsic rate of increase (r _m), finite rate of increase (λ), and gross reproduction rate (GRR), and had significantly increased egg developmental time and doubling time (Dt) of P. xylostella. However, sublethal concentrations of indoxacarb had no significant affect on adult emergence, percentage of pupation, larva, prepupa and pupa developmental periods, hatchability, and sex ratio of offspring. The results of this study indicated that sublethal concentrations can decrease the biological parameters of P. xylostella.