Christine Y.S. Peng

Aging and development in social insects with emphasis on the honey bee, Apis mellifera L.

Honey bee colonies typically consist of about 20-40 thousand workers, zero to few thousand males (drones), depending on the time of year, and a single queen, the mother of the colony. Workers typically live 3-6 weeks during the spring and summer and can live about 4months during the winter. Queens are longer lived. Anecdotes of queens living 2-3years are not unusual, though they normally live less than a year in commercial hives. Little is known about the life span of drones. Queens develop from fertilized eggs that are not different from the eggs that develop into workers. Queens are, however, twice as large, have specialized anatomy, live much longer, and develop faster from egg to adult. All of these differences are derived from differences in larval rearing environment, primarily nutrition. The developmental trajectory of a female larva from worker into a queen can be determined as late as the third day of larval development, after this time the developmental pathway is fixed for a worker phenotype. The total time of larval development is only 5-6 days, therefore, just 2-3 days of differential feeding can lead to profound differences in development, and longevity. Workers undergo age development after they become adults. Workers usually initiate foraging behavior when they are 2-3 weeks old. The age at which a worker initiates foraging is a strong determinant of her length of life. This is presumed to be a result of the hazards of foraging, but natural senescence also occurs. Some bees remain in the nest and are never observed to forage, thereby outliving their forager sisters. Corresponding to this behavioral development are changes in the sizes of glands and the production of glandular products, increases in biogenic amine titers within the brain, an increase in the volume of specific regions of the brain, and changes in the neural system that affect perception of stimuli, and learning and memory. These age-related changes in behavior are regulated by intrinsic and extrinsic factors. Genetic variation has been demonstrated for many of these life history and behavioral traits. Selection and genome mapping studies have demonstrated relationships between the neural system, behavior, and life history traits.

Ultrastructure of honey bee, Apis mellifera, sperm with special emphasis on the acrosomal complex following high‐pressure freezing fixation

Abstract. The ultrastructure of ejaculated sperm of the honey bee, Apis mellifera L., was studied after sperm were processed by using a high‐pressure freezing fixation and freezing substitution method. The electron micrographs of samples processed by this method clearly revealed previously unobserved or unresolved fine details, particularly those in the acrosomal complex. The present study demonstrates that the acrosomal complex of honey bee sperm consists of an anterior tubular acicular apex, an enlarged spherical region, and the elongated acrosomal proper. Internally, the structures of acrosomal complex confirm the general description of the tri‐layer model; having an extra‐acrosomal layer, an acrosome vesicle, and a central acrosomal rod located in a subacrosomal cavity. The acrosomal rod terminates anteriorly with an electron dense corpuscle in an ensheathing cap at the spherical region. The electron micrographs also show the presence of a centriolar adjunct and a structure possibly of a centriolar or basal body origin. The chemical and functional aspects of these ultrastructures remain unknown.

Virulence and site of infection of the fungus, Hirsutella thompsonii, to the honey bee ectoparasitic mite, Varroa destructor

The Varroa mite, Varroa destructor, is recognized as the most serious pest of both managed and feral Western honey bee (Apis mellifera) in the world. The mite has developed resistance to fluvalinate, an acaricide used to control it in beehives, and fluvalinate residues have been found in the beeswax, necessitating an urgent need to find alternative control measures to suppress this pest. Accordingly, we investigated the possibility of using the fungus, Hirsutella thompsonii, as a biocontrol agent of the Varroa mite. Among the 9 isolates of H. thompsonii obtained from the University of Florida and the USDA, only the 3 USDA isolates (ARSEF 257, 1947 and 3323) were infectious to the Varroa mite in laboratory tests. The mite became infected when it was allowed to walk on a sporulating H. thompsonii culture for 5 min. Scanning electron micrographs revealed that the membranous arolium of the mite leg sucker is the focus of infection where the fungal conidia adhered and germinated. The infected mites died from mycosis, with the lethal times to kill 50% (LT(50)s) dependent on the fungal isolates. Thus, the LT(50)s were 52.7, 77.2, and 96.7h for isolates 3323, 257, and 1947, respectively. Passage of H. thompsonii through Varroa mite three times significantly reduced the LT(50)s of isolates 257 and 1947 (P<0.05) but not the LT(50) of isolate 3323. The fungus did not infect the honey bee in larval, prepupal, pupal, and adult stages under our laboratory rearing conditions. Our encouraging results suggest that some isolates of H. thompsonii have the potential to be developed as a biocontrol agent for V. destructor. However, fungal infectivity against the mites under beehive conditions needs to be studied before any conclusion can be made.

Seasonal Patterns of Female Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) Reproductive Physiology in Riverside, California

Abstract Female Homalodisca coagulata (Say) were collected from October 2001 to February 2005 from citrus at the University of California, Riverside. Between 5 and 20 females per sampling date were dissected, and each was assigned an ovarian rank: previtellogenic, vitellogenic, or postvitellogenic. Ovarian ranking was used to characterize H. coagulata reproductive activity. Results of these dissections revealed consistent annual patterns in the proportion of previtellogenic females present in this field population. These patterns indicate that there are two distinct generations annually, with an occasional third generation. A time-dependent model of H. coagulata vitellogenesis cycles in Riverside, CA, was developed, which makes it possible to predict the appearance of the subsequent generation based on previous observed peaks in the proportion of vitellogenic females.

Effects of Selected Fungicides on Growth and Development of Larval Honey Bees, Apis mellifera L. (Hymenoptera: Apidae)

Abstract Laboratory studies were conducted to determine the effects of incorporating selected almond fungicides into the diet of larval honey bees, Apis mellifera Linnaeus. One-day-old larvae, from mixed Italian stocks, were grafted to basic larval diet or basic diet containing various fungicides. Experimental concentrations were calculated from field dose application rates of formulated product per hectare. Larvae were transferred to fresh diet daily and incubated in the dark at 35°C and 95% RH. After defecation, prepupae were moved into a dark incubator at 35°C and 75% RH. Mortalities of larvae, prepupae, and pupae were recorded daily. No larvae fed Captan, Rovral, or Ziram completed development to adults. In the case of Rovral, a novel amorphogenic effect was observed. There were no significant differences in total mortality between the controls and larvae fed Abound, Elevate, Flint, Rally, and Vangard.

The effects of azadirachtin on the parasitic mite, Varroa jacobsoni and its host honey bee (Apis mellifera)

SUMMARY We conducted a series of experiments under laboratory conditions to evaluate the feasibility of using a neem-based (Azadirachta indica) insecticide to control varroa (Varroa jacobsoni). The experiments included studies of anti-feeding effects of azadirachtin, the active ingredient of neem-based insecticides, on adult worker honey bees (Apis mellifera); toxicity of azadirachtin to adult workers, worker larvae and associated mites; and the effects of azadirachtin on female V. jacobsoni reproduction. Both commercially formulated and purified azadirachtin were used in the experiments. The results of adult feeding experiments showed that azadirachtin significantly reduced syrup consumption by worker bees (P < 0.05) and exhibited a dose response in mortality: with an oral LC50 of 10.87 μg/ml in mite-free bees, 13.69 μg/ml in mite-infested bees, and 41.87 μg/ml for associated mites. The topical LC50 of azadirachtin was 12.53 μg/ml in mite-free bees, 12.31 μg/ml in mite-infested bees, and 35.43 μg/ml in the associated mites. The results of larval feeding experiments showed that worker larvae were more sensitive to azadirachtin than adult worker bees: exhibiting an LC50 of 180.92 μg/ml to purified azadirachtin and 100.13 μg/ml to formulated azadirachtin. More than 90% of treated, normal-appearing, white prepupae and pupae showed precocious and abnormal pigmentation on their mouthparts and other appendages. LC50‘s of topical applications of formulated azadirachtin were 104.91, 99.12 and 171.37 μg/ml for mite-free worker larvae, mite-inoculated larvae and associated mites, respectively. In addition, feeding host larvae with azadirachtin significantly reduced the fecundity of mother mites (P < 0.001) as well as egg hatching rate (P < 0.001). However, more research is needed to evaluate the reproductive effects of azadirachtin on drones, queens, and varroa under hive conditions.

Anatomy and Histology of Reproductive Organs of Female Homalodisca coagulata (Hemiptera: Cicadellidae: Proconiini), with Special Emphasis on Categorization of Vitellogenic Oocytes

Abstract The anatomy and histology of female Homalodisca coagulata (Say) (Hemiptera: Cicadellida: Proconiini) reproductive organs is described using light microscopy. The reproductive organs of H. coagulata consist of one pair of ovaries, each with 10 telotrophic ovarioles, a pair of lateral oviducts, a common oviduct, a spermatheca, an enlarged genital duct, a complex bursa copulatrix, a vagina, two types of accessory glands, and a genital chamber. The reproductive organs follow the general pattern seen in cicadellids. The complex bursa copulatrix, important in copulation and sperm transfer, is described. A set of morphological criteria were selected, based on the stage of oocyte development, and used to evaluate and assign the rank of ovarian development for field-collected individuals and to assess the overall reproductive status of female insect populations. A principal component analysis of morphological and physiological characteristics suggests that the ovarian ranks reflect the reproductive status of the females. Understanding reproductive status and patterns is critical for determining the optimal time to implement control methods to suppress H. coagulata populations in southern California.

Ultrastructure of the freeze-etched spore of Ascosphaera apis, an entomopathogenic fungus of the honeybee Apis mellifera.

Abstract The freeze-fractured outer surface of the spore wall of Ascophaera apis is covered with granules which are 21.5 nm in diameter. The cross-fractured spore wall consists of subunits which are 9 nm in diameter. The inner surface of the spore wall is granular and has many stud-like projections measuring approximately 120 nm long × 26 nm wide. The convex face of the spore membrane carries many particles as well as many depressions which are complementary to the projections on the inner surface of the spore wall. The nucleus possesses double nuclear membranes which contain numerous well-defined nuclear pores. In the cytoplasm of the spore there are many mitochondria which have well-defined cristae and many particles on the internal membranes. The sporoplasm contains many lipid droplets which possess concentric smooth-surfaced lamellae.

In vitro activity of 15-azasterol (A25822B) against chalkbrood pathogen Ascosphaera apis in the honey bee

The antifungal agent 15-azasterol A25822B was examined for effects on the growth and development of Ascosphaera apis. The minimum inhibition concentration (MIC) of azasterol against A. apis was 1 μm. Growth and development of A. apis was completely controlled at this concentration. At a concentration of 0.01 μm growth of A. apis was retarded and although sporocysts were formed developing spores were not be able to reach maturation. A major effect of azasterol at this low concentration was the accumulation of lipid in the hyphae, sporocysts and immature spores. In addition it caused a conformational change in mitochondria and damage to the spore membrane structure. On the basis of these results, further investigations of azasterol for the treatment of chalkbrood disease in the honey bee are warranted.