Resistance of the honey bee, Apis mellifera to the acarian parasite Varroa destructor: behavioural and electroantennographic data

Abstract. One way in which Apis mellifera honey bees resist Varroa destructor is by detection and elimination of nestmates. This study uses behavioural tests and electroanntennography to assess the role of chemostimuli in recognition by honey bees of this acarian ectoparasite. Behavioural tests using living or dead parasites involved observation of honey bee grooming activity (antennation) under controlled conditions in Petri dishes, and removal behaviour (uncapping and elimination of parasitized and unparasitized control brood cells) under natural conditions. Some bees from colonies with both small and large parasite populations showed aggressive behaviour (biting). No difference was observed according to whether the mite was dead or alive. Under natural conditions, bees uncapped more parasitized cells than control cells. Electroantennographic tests were performed to measure sensitivity to various Varroa extracts at three concentrations (10, 20 and 30 Varroa Equivalents). Only 30 Varroa Equivalent methanol extracts made from Varroa collected from brood cells elicited significantly greater antennal response than controls (pure solvent). All three methanol extracts elicited significantly greater antennal response than controls. No response was observed using Varroa extracts made with acetone or hexane. These findings suggest that polar products may act as chemostimuli for recognition of V. destructor by honey bees. Further study will be necessary to determine which polar products are involved in this recognition and assess grooming and removal behaviour using these products.     

Natural selection of Varroa jacobsoni explains the different reproductive strategies in colonies of Apis cerana and Apis mellifera

In colonies of European Apis mellifera, Varroa jacobsoni reproduces both in drone and in worker cells. In colonies of its original Asian host, Apis cerana, the mites invade both drone and worker brood cells, but reproduce only in drone cells. Absence of reproduction in worker cells is probably crucial for the tolerance of A. cerana towards V. jacobsoni because it implies that the mite population can only grow during periods in which drones are reared. To test if non-reproduction of V. jacobsoni in worker brood cells of A. cerana is due to a trait of the mites or of the honey-bee species, mites from bees in A. mellifera colonies were artificially introduced into A. cerana worker brood cells and vice versa. Approximately 80% of the mites from A. mellifera colonies reproduced in naturally infested worker cells as well as when introduced into worker cells of A. mellifera and A. cerana. Conversely, only 10% of the mites from A. cerana colonies reproduced, both in naturally infested worker cells of A. cerana and when introduced into worker cells of A. mellifera. Hence, absence of reproduction in worker cells is due to a trait of the mites. Additional experiments showed that A. cerana bees removed 84% of the worker brood that was artificially infested with mites from A. mellifera colonies. Brood removal started 2 days after artificial infestation, which suggests that the bees responded to behaviour of the mites. Since removal behaviour of the bees will have a large impact on fitness of the mites, it probably plays an important role in selection for differential reproductive strategies. Our findings have large implications for selection programmes to breed less-susceptible bee strains. If differences in non-reproduction are mite specific, we should not only look for non-reproduction as such, but for colonies in which non-reproduction in worker cells is selected. Hence, in selection programmes fitness of mites that reproduce in both drone and worker cells should be compared to fitness of mites that reproduce only in drone cells. © Rapid Science Ltd. 1998     

Perizin, an acaricide to combat the mite Varroa jacobsoni: its distribution in and influence on the honeybee Apis mellifera

Abstract. The distribution of coumaphos (the active component of perizin), fed to individual honeybees, in the honey stomach, haemolymph, midgut and rectum was studied over time. Concurrently, we investigated changes occurring in the haemolymph volume due to the ingestion of perizin, and we examined the influence of a Nosema apis infection on the survival of bees that had been fed perizin. The maximum amount of coumaphos in the haemolymph was found 4h after ingestion, but it was only 2–3% of the total amount recovered. After 15 min 55% of the total amount of the coumaphos recovered was in the honey stomach and available for distribution within the colony by trophallaxis, while 45% had already passed the proventriculus. Ultimately the coumaphos accumulated in the rectum. The volume of the haemolymph significantly increased in bees which were fed perizin compared with bees which were fed syrup and with non-fed bees. The lethal dose of coumaphos to 3-day-old bees was three times higher than the lethal dose for 18- and 1-day-old bees. The number of Nosema apis spores in the alimentary canal was not correlated with the survival of the bees that were fed perizin. It is concluded that coumaphos can act as a systemic agent and can be distributed to other individuals in a colony through trophallaxis, but these effects are limited to a maximum period of 12h after ingestion.     

Behavioural responses of Varroa destructor (Acari: Varroidae) to extracts of larvae, cocoons and brood food of worker and drone honey bees, Apis mellifera (Hymenoptera: Apidae)

Abstract. Varroa destructor is a parasitic mite of the honey bee species Apis cerana Fabr . and A. mellifera L. Mature females reproduce on the immature stages of their hosts, producing more viable female offspring on drone hosts than on worker hosts. Thus, immature drones are more likely to be infested with mites than immature workers. To investigate the hypothesis that differences in host chemistries underlie the biased distribution of mites between worker and drone brood, the arrestment responses of mites to solvent extracts of a number of stimuli normally encountered by a mite during its life cycle were measured. Mites were arrested by cuticular extracts of worker and drone larvae obtained at 0, 24 and 48 h prior to the time when cell capping is completed. Mites were also arrested by extracts of worker and drone, brood food and cocoons, and by a blend of synthetic fatty acid esters previously shown to be active in the host acquisition process. In a wind tunnel bioassay, mites were attracted to odours from living fifth-instar worker and drone larvae, but not to volatiles from cocoons, brood food or a blend of fatty acid esters. The sex of the host was not an important factor affecting the behavioural responses of the mites in any assay. We conclude that host kairomones play a role in the host acquisition process, but we found no evidence to support the hypothesis that mites use these substances to differentiate between worker and drone brood.     

狄斯瓦螨和蜜蜂残翅病毒对蜜蜂健康的协同影响

世界各地大范围的西方蜜蜂Apis mellifera蜂群损失现象已引起科学界和公众的持续关注。狄斯瓦螨Varroa destructor和蜜蜂残翅病毒(Deformed wing virus,DWV)是西方蜜蜂群中最主要的两大生物威胁。尽管二者侵害蜜蜂均已有较长历史,但直至近十年来的研究才发现两者间的协同效应对蜂群健康的影响远超过其单独作用时所造成的危害:(1)蜜蜂残翅病毒可在狄斯瓦螨体内大量复制,继而进一步传播;(2)狄斯瓦螨的刺吸行为使病毒粒子跨越寄主的生理屏障而直接进入蜜蜂血淋巴;(3)狄斯瓦螨的寄生促使蜜蜂残翅病毒的高毒力毒株在蜂群中优势扩增和盛行;(4)狄斯瓦螨影响蜜蜂个体发育与免疫系统等生理机能,以致降低了蜂群对病毒的抵抗力;(5)蜜蜂残翅病毒对宿主造成的免疫抑制有利于狄斯瓦螨的寄生与繁殖。狄斯瓦螨、蜜蜂残翅病毒和西方蜜蜂间的关系已经成为昆虫外寄生物、病原体与寄主相互作用研究的一个典型模型。本文对近十年该领域的相关研究进行综述,以期为蜂群损失的原因调查以及昆虫寄生虫、病原微生物与寄主间关系的研究提供参考和借鉴。     

Dose-related upwind anemotaxis and movement up odour gradients in still air in the presence of methyl eugenol by the wild tobacco fly, Bactrocera cacuminata

The behaviour of Bactrocera cacuminata (Hering) in wind varied according to the concentration of methyl eugenol (0, 95, 327 and 500 μg m^?3, respectively). General locomotor activity (as measured by mean distance moved in 5 min, regardless of direction) was not significantly different in the first two treatments but was significantly lower in the others. Most flies in the fourth treatment did not move more than one body length. In the first two treatments, the rate and pattern of movement of most flies was basically similar, with walking in tortuous paths interspersed with short flights and usually no obvious bias in direction. However, 32% of flies in the second treatment did move in a biased direction, achieving upwind anemotaxis of at least 400 mm, but only 2–8% did so in the other conditions. Flies moved up a concentration gradient to a source of methyl eugenol in still air when released at a distance of 100, 150 or 200 mm. With one exception, no more than 40% did this within 3 min of release (whether or not the olfactory stimulus was augmented by a visual one). However, 77% responded when released 100 mm from a combined olfactory and visual stimulus. Visual augmentation of an olfactory stimulus may also be responsible for far fewer flies flying out of the vicinity at distances up to 150 mm, but not 200 mm.     

Number of adult female mites Varroa jacobsoni Oud. on hive debris from honey bee colonies artificially infested to monitor mite population increase (Mesostigmata: Varroidae)

Six honey bee colonies hived in Langstroth nuclei were each artificially infested with 100 phoretic Varroa mites. Hive debris on bottom inserts was inspected every 3–4 days. The adult Varroa mites were compared with mounted specimens and catalogued into lightly pigmented and darkly pigmented females. After 4 months, an acaricide treatment was used to estimate the final mite population. Based on light and dark adult counts, we propose a balancing equation that follows the Varroa population increase at 7 day intervals and allows the calculation of experimental population growth rates. The calculated Varroa finite rate of increase is =1.021. Exponential and logistic growth models fitted to the balancing equation data gave R ²=0.986 and R ²=0.991, respectively. To develop a more precise model it would be necessary to follow the population growth beyond our experimental data.     

Newly isolated bacterial strains belonging to Bacillaceae (Bacillus sp.) and Micrococcaceae accelerate death of the honey bee mite, Varroa destructor (V. jacobsoni), in laboratory assays

Newly isolated bacterial strains belonging to Bacillaceae (Bacillus sp.), Micrococcaceae and three unidentified strains were tested for their pathogenicity against the mite, Varroa destructor. The Bacillus sp. strain and two of the strains belonging to the Micrococcaceae family significantly decreased the time for 50% mortality of the mite population (up to 57%) and hence may be potential control agents. In in vitro bioassay whole cells, extracellular broth and cellular extract of the Bacillus sp. strain effectively killed the mites, suggesting that both endotoxins and exotoxins contributed to the killing.     

Zigzagging and casting as a programmed response to wind-borne odour: a review

ABSTRACT. 'Counterturning' (meaning here the execution of a succession of alternating left and right turns) is the common feature in upwind zigzagging and cross-wind casting by flying insects manoeuvring towards a small source of wind-borne odour. Recent progress in understanding its control and function is discussed. Counterturning is internally controlled ('self-steered') in the limited sense that, once initiated by a chemical stimulus, it continues without further changes in the chemical input both in clean air and in a homogeneous cloud of odour. As a reaction it appears to be the kind of chemotaxis distinguished as longitudinal klinotaxis, for which the stimulus is a difference of chemical concentration detected over time along the insect's path, not across it. The new directions taken in response to the stimulus, being self-steered in the above sense, have no necessary relation to the direction of the chemical gradient that provided the stimulus but are influenced by the visual cues generated by wind drift. In wind, the counterturning programme is modulated by changes in the chemical input and simultaneously integrated with anemotaxis, but it can then continue in similar form after the wind has ceased. Unambiguous evidence for these conclusions is so far available only for certain flying male moths responding to sex pheromone. The primary function of counterturning, of all amplitudes and in both zigzagging and casting, appears to be the regaining of contact with an elusive scent.     

The effect of host odour on the landing responses of tsetse flies (Glossina morsitans morsitans) in a wind tunnel with and without visual targets

Abstract The effect of artificial host odour on the landing responses of males of Glossina m.morsitans West, and on their reaction to visual targets has been investigated in a wind tunnel. Landing was induced in flies that traversed steep odour gradients as they flew upwind and downwind across the edge of an odour plume, irrespective of whether visual targets were present or not; the landing response could be elicited over a wide range of odourconcentrations. When targets were present such odour gradients also tended to increase the proportion of landing flies which alighted on or near the targets; and the bigger the target, or the hungrier the flies, the greater was the propensity for target landing. In air which was more uniformly permeated with odour, the propensity to land on targets was increased only at high odour concentration.     

EAG and behavioural responses of the larger grain borer, Prostephanus truncatus, and its predator, Teretriosoma nigrescens, to the borer‐produced aggregation pheromone

Abstract.Electroantennogram (EAG) and behavioural studies were conducted with Prostephanus truncatus (Horn) (Col.: Bostrichidae) and the predatory beetle, Teretriosoma nigrescens Lewis (Col: Histeridae) in regard to their responses to the components of the prey‐produced aggregation pheromone. There were hardly any differences between species or sexes regarding perception thresholds. In field and olfactometer experiments, female P. truncatus were more responsive to the pheromone than males, and both sexes reacted more strongly to the minor pheromone component, T2, than to T1. Sex ratios among trap catches of T. nigrescens were slightly male‐biased. The predator did not differentiate behaviourally between the pheromone components.     

Food consumption and utilization responses to dietary dilution with cellulose and water by velvetbean caterpillars, Anticarsia gemmatalis

Abstract Dilution of an artificial diet with water or cellulose to nutrient levels of 32% (undiluted), 19% and 10% fresh weight (fw) resulted in increased fw and dry weight (dw) food consumption (both absolute amounts and weight-relative rates) by velvetbean caterpillars, Anticarsia gemmatalis Hübner. Despite these increases, the absolute amount and relative rate of nutrient intake by the caterpillars declined with dilution, as did their dw gain and dw (% fw) and lipid (% dw) contents. The proportion of consumed food (dw, including cellulose) that was digested and absorbed declined with increased dietary cellulose; however, the proportion of consumed nutrients (dw, excluding cellulose) that was digested and absorbed was not affected by the presence of cellulose, although it increased slightly (but significantly) with dietary water. The efficiency with which the absorbed nutrients were converted to biomass energy showed a negative relationship with the various measures of food consumption and thus a positive relationship with dietary nutrient level.
The compensatory increases in feeding mitigated the deleterious impact of dietary dilution on growth, which would have declined further without the increased feeding. These data suggest that food consumption is regulated primarily through an evaluation of food nutrient level, and that the metabolic costs associated with the increased consumption and processing of food may be substantial, especially on the most diluted diets. Another hypothesized cost of increased feeding, reduced efficiency of digestion and absorption as food presumably passes more rapidly through the gut, was not detected.     

Nursery pollination by a moth in Silene latifolia: the role of odours in eliciting antennal and behavioural responses

Since the 1970s it has been known that the nursery pollinator Hadena bicruris is attracted to the flowers of its most important host plant, Silene latifolia, by their scent. Here we identified important compounds for attraction of this noctuid moth. Gas chromatographic and electroantennographic methods were used to detect compounds eliciting signals in the antennae of the moth. Electrophysiologically active compounds were tested in wind-tunnel bioassays to foraging na?ve moths, and the attractivity of these compounds was compared with that to the natural scent of whole S. latifolia flowers. The antennae of moths detected substances of several classes. Phenylacetaldehyde elicited the strongest signals in the antennae, but lilac aldehydes were the most attractive compounds in wind-tunnel bioassays and attracted 90% of the moths tested, as did the scent of single flowers. Our results show that the most common and abundant floral scent compounds in S. latifolia, lilac aldehydes, attracted most of the moths tested, indicating a specific adaptation of H. bicruris to its host plant.     

Adaptive responses in Cypridopsis vidua (Crustacea: Ostracoda) to food and shelter offered by a macrophyte (Chara fragilis)

The ostracod Cypridopsis vidua prefers periphyton growing on Chara fragilis to other feeding substrates. This species actively searches for periphyton, scrapes it off from Chara stems and handles it with a well organized feeding technique. When exposed to different quantities of periphyton on Chara stems, C. vidua selects foraging sites according to their nutritional value. When exposed to low quantities of water from tanks containing fish, C. vidua responds to these weak chemical cues moving from uncovered areas into Chara plants. Experiments with juvenile cyprinids (Abramis brama) as predators and C. vidua as prey clearly showed that the presence of Chara reduces fish foraging success and that C. vidua survival rate increases with increasing density of Chara.     

Reticulocyte and micronucleated reticulocyte responses to gamma irradiation: dose–response and time-course profiles measured by flow cytometry

A flow cytometric, anti-CD71-based method was used to measure peripheral blood reticulocyte and micronucleated reticulocyte frequencies in response to ¹³⁷Cs total body irradiation (TBI). In three independent experiments, groups of five female C57BL/6N mice were irradiated at graded doses up to 3 Gy, and peripheral blood specimens were collected at 43 h post-irradiation. Whereas the frequency of reticulocytes declined over the range of doses studied, micronucleated reticulocyte incidence was observed to increase in a dose-dependent manner up to 1 Gy. At doses greater than approximately 1 Gy, micronucleated reticulocyte frequencies declined with increasing exposure. These responses were highly reproducible, with significant effects on reticulocyte and micronucleated reticulocyte frequencies observed for the lowest dose studied (0.125 Gy). A time-course experiment was performed to test whether radiation-induced cell cycle delay may explain saturation of the micronucleated reticulocyte endpoint at doses >1 Gy. For this experiment, groups of four female C57BL/6N mice were exposed to 1, 1.5, or 2 Gy TBI, and blood collection occurred at 12 h intervals from 43 to 115 h post-exposure. Reduced reticulocyte frequencies were observed for each dose studied, and the recovery of reticulocytes was increasingly delayed with higher radiation doses. Maximal micronucleated reticulocyte frequencies were observed at 43 or 55 h, with progressively lower values at later time points. At no time did micronucleated reticulocyte frequencies induced by 1.5 or 2 Gy significantly exceed that observed for 1 Gy at 43 h. These time-course data suggest that radiation-induced cell cycle delay cannot account for the micronucleated reticulocyte downturn phenomenon observed at doses greater than 1 Gy. An alternate hypothesis is discussed whereby apoptotic elimination of severely damaged bone marrow erythroid precursors plays a dominant role in saturating the radiation-induced micronucleated reticulocyte response observed for C57BL/6N mice.