Responses to \u3ci\u3eVarroa destructor\u3c/i\u3e and \u3ci\u3eNosema ceranae\u3c/i\u3e by several commercial strains of Australian and North American honeybees (Hymenoptera: Apidae)

The potential impact of varroa (Varroa destructor, Anderson & Trueman) on Australian beekeeping and agriculture depends in part on the levels of resistance to this parasite expressed by Australian commercial honeybees (Apis mellifera). The responses of seven lines of Australian honeybees to V. destructor were compared with the responses of a stock of Italian honeybees from the United States known for its susceptibility to V. destructor and two stocks known for their resistance to V. destructor, Russian honeybees (RHB) and a stock expressing the varroa sensitive hygiene trait (VSH). The experiment began in May with uniform colonies having uniform infestation of V. destructor. V. destructor infestations measured as the percentage of adult bees infested in the Australian lines and the Italian stock rose from less than 10% in August to over 25% in October. From August to November, 44% of both the Australian and Italian colonies died while strongly exhibiting symptoms of parasitic mite syndrome. In contrast, RHB and VSH colonies displayed comparative resistance to V. destructor. Their infestation rates rose from about 5% in August to 10% (RHB) and 14% (VSH) in October. Likely, some of this increase resulted from invasion pressure by mites from the dying Australian and Italian colonies. During the August to November period, 4.4% of the RHB and 14.3% of the VSH colonies died. In comparisons of the seven Australian lines, only non-significant and trivial differences were found for infestation and mortality rates. All Australian lines were highly susceptible to V. destructor. Additionally, evaluations of rates of Nosema ceranae infections were made throughout the course of the experiment. Although high levels of infection were found across all stocks and lines, no stock or line exhibited an adverse effect from N. ceranae infection

Prevalence and reproduction of Tropilaelaps mercedesae and Varroa destructor in concurrently infested Apis mellifera colonies

The prevalence of Tropilaelaps mercedesae and Varroa destructor in concurrently infested A. mellifera colonies in Thailand was monitored. We also assessed the fecundity of T. mercedesae and V. destructor in naturally infested brood and in brood cells deliberately infested with both mite genera. Results showed that the natural co-infestation of an individual brood cell by both mite genera was rare (<0.1 %). Overall, T. mercedesae was the more dominant brood parasite of A. mellifera than V. destructor. In naturally infested brood, the proportion of nonreproductive Tropilaelaps (29.8 ± 3.9 %) was lower than that of Varroa (49.6 ± 5.9 %). Both mites produced similar numbers of progeny (T. mercedesae = 1.48 ± 0.05; V. destructor = 1.69 ± 0.14). The two mite genera also reproduced normally when they were deliberately introduced into the same brood cells. In two separate assessments, the average worker brood infestations of T. mercedesae (19.9 %) were significantly higher than that of V. destructor (0.7 %). Our results on the higher prevalence and reproductive ability of T. mercedesae in concurrently infested colonies reaffirm Tropilaelaps’ competitive advantage over V. destructor and their reported negative impact to A. mellifera colonies.Keywords: concurrent infestation, Tropilaelapsmercedesae, Varroa destructor, Apis mellifera, seasonal abundanc

Comparative Flight Activities and Pathogen Load of Two Stocks of Honey Bees Reared in Gamma-Irradiated Combs

Gamma irradiation is known to inactivate various pathogens that negatively affect honey bee health. Bee pathogens, such as Deformed wing virus (DWV) and Nosema spp., have a deleterious impact on foraging activities and bee survival, and have been detected in combs. In this study, we assessed the effects of gamma irradiation on the flight activities, pathogen load, and survival of two honey bee stocks that were reared in irradiated and non-irradiated combs. Overall, bee genotype influenced the average number of daily flights, the total number of foraging flights, and total flight duration, in which the Russian honey bees outperformed the Italian honey bees. Exposing combs to gamma irradiation only affected the age at first flight, with worker bees that were reared in non-irradiated combs foraging prematurely compared to those reared in irradiated combs. Precocious foraging may be associated with the higher levels of DWV in bees reared in non-irradiated combs and also with the lower amount of pollen stores in colonies that used non-irradiated combs. These data suggest that gamma irradiation of combs can help minimize the negative impact of DWV in honey bees. Since colonies with irradiated combs stored more pollen than those with non-irradiated combs, crop pollination efficiency may be further improved when mite-resistant stocks are used, since they performed more flights and had longer flight durations

The effects of diet, mating duration, female to male ratios, and temperature on ovary activation, mating success, and fecundity of Aethina tumida

International audienceThe effects of natural diet (brood, pollen, honey, and their various combinations), mating duration (1 day versus 2 days), female (F) to male (M) ratio (1F/1M, 2F/1M, and 1F/2M), and temperature (34 versus 27–29 °C) on ovary activation, mating success, and fecundity of small hive beetles (SHBs) were studied. Our results indicated that regardless of mating duration, (1) a diet of brood, pollen, and honey presented together supported the highest fecundity; (2) intake of protein-rich diets encouraged ovary activation and egg-laying; and (3) diet of honey alone did not encourage ovary activation, mating success, and egg-laying at room temperature. Regardless of the number of males available for mating, egg-laying varied through time. Overall, females that were presented with two males for a 5-day mating period had higher fecundity than females provided with one male or three male partners. High temperature accelerated ovary activation and egg-laying regardless of female to male ratio during a 15-h mating period. Knowledge of these factors that influence fecundity helps elucidate why SHBs are very successful pests of honey bees

Phenotypic and genetic analyses of the varroa sensitive hygienic trait in Russian honey bee (hymenoptera: apidae) colonies.

Varroa destructor continues to threaten colonies of European honey bees. General hygiene, and more specific Varroa Sensitive Hygiene (VSH), provide resistance towards the Varroa mite in a number of stocks. In this study, 32 Russian (RHB) and 14 Italian honey bee colonies were assessed for the VSH trait using two different assays. Firstly, colonies were assessed using the standard VSH behavioural assay of the change in infestation of a highly infested donor comb after a one-week exposure. Secondly, the same colonies were assessed using an "actual brood removal assay" that measured the removal of brood in a section created within the donor combs as a potential alternative measure of hygiene towards Varroa-infested brood. All colonies were then analysed for the recently discovered VSH quantitative trait locus (QTL) to determine whether the genetic mechanisms were similar across different stocks. Based on the two assays, RHB colonies were consistently more hygienic toward Varroa-infested brood than Italian honey bee colonies. The actual number of brood cells removed in the defined section was negatively correlated with the Varroa infestations of the colonies (r2 = 0.25). Only two (percentages of brood removed and reproductive foundress Varroa) out of nine phenotypic parameters showed significant associations with genotype distributions. However, the allele associated with each parameter was the opposite of that determined by VSH mapping. In this study, RHB colonies showed high levels of hygienic behaviour towards Varroa -infested brood. The genetic mechanisms are similar to those of the VSH stock, though the opposite allele associates in RHB, indicating a stable recombination event before the selection of the VSH stock. The measurement of brood removal is a simple, reliable alternative method of measuring hygienic behaviour towards Varroa mites, at least in RHB stock

<i>P</i>- value of associations between allele homozygosity and colony phenotypes.

<p>Percentage of <i>Varroa</i>-infested brood removed was calculated as the % change in <i>Varroa</i> infestation of donor combs. Manipulated brood = brood removed + opened brood;</p><p>*reproductive foundress mites = produced one or more progeny; viable progeny = with adult male and young daughter.</p><p>**significant at <i>P</i> < 0.05.</p><p><i>P</i>- value of associations between allele homozygosity and colony phenotypes.</p

Sample sizes, means (± SE) of different infestation parameters in resident brood of Italian and Russian honey bee colonies, and results of the student’s t-tests.

<p>NR = no progeny. Rows with different letters are significantly different at <i>P</i> < 0.05.</p><p>ns = not significant.</p><p>Sample sizes, means (± SE) of different infestation parameters in resident brood of Italian and Russian honey bee colonies, and results of the student’s t-tests.</p

Results of the regression analyses relating percentages of <i>Varroa</i>-infested brood removed for whole comb and brood section of donor frames, and brood removal of brood section to different measurements related to hygiene.

<p>Percentage of <i>Varroa</i>-infested brood removed was calculated as the % change in <i>Varroa</i> infestation of donor combs.</p><p>*NR = no progeny produced.</p><p>Results of the regression analyses relating percentages of <i>Varroa</i>-infested brood removed for whole comb and brood section of donor frames, and brood removal of brood section to different measurements related to hygiene.</p