Orley R. Taylor

Stable isotopes (δD and δ13C) are geographic indicators of natal origins of monarch butterflies in eastern North America

Abstract Wing membranes of laboratory and field-reared monarch butterflies (Danaus plexippus) were analyzed for their stable-hydrogen (δD) and carbon (δ13C) isotope ratios to determine whether this technique could be used to identify their natal origins. We hypothesized that the hydrogen isotopic composition of monarch butterfly wing keratin would reflect the hydrogen isotope patterns of rainfall in areas of natal origin where wings were formed. Monarchs were reared in the laboratory on milkweed plants (Asclepias sp.) grown with water of known deuterium content, and, with the assistance of volunteers, on native milkweeds throughout eastern North America. The results show that the stable hydrogen isotopic composition of monarch butterflies is highly correlated with the isotopic composition of the milkweed host plants, which in turn corresponds closely with the long-term geographic patterns of deuterium in rainfall. Stable-carbon isotope values in milkweed host plants were similarly correlated with those values in monarch butterflies and showed a general pattern of enrichment along a southwest to northeast gradient bisecting the Great Lakes. These findings indicate that natal origins of migratory and wintering monarchs in Mexico can be inferred from the combined δD and δ13C isotopic signatures in their wings. This relationship establishes that analysis of hydrogen and carbon isotopes can be used to answer questions concerning the biology of migratory monarch butterflies and provides a new approach to tracking similar migratory movements of other organisms.

Decline of monarch butterflies overwintering in Mexico: is the migratory phenomenon at risk?

Abstract.  1. During the 2009–2010 overwintering season and following a 15‐year downward trend, the total area in Mexico occupied by the eastern North American population of overwintering monarch butterflies reached an all‐time low. Despite an increase, it remained low in 2010–2011.

Demography and life history characteristics of two honey bee races (Apis mellifera).

SummaryIntra-colony demography and life history characteristics of neotropical Africanized and temperate European honey bearaces were compared under simulated feral conditions. Major differences in colony demography were found which nevertheless resulted in some similar reproductive characteristics. European colonies were larger than Africanized colonies, had more rapid initral growth rates of worker populations, showed better survivorship of brood and adult workers, and differed in patterns of worker age distribution. However, both races were similar in the brood and adult populations when colonies swarmed, the frequency and timing of swarming, and the number of workers in prime swarms. The factors most important in determining these colony growth and reproductive patterns were likely worker mortality rates, climate, and resource availability.

Aphrodisiac pheromones of the sulfur butterflies Colias eurytheme and C. philodice (Lepidoptera : Pieridae)

Male wing compounds involved in maintaining reproductive isolation between the sulfur butterfliesColias eurytheme andC. philodice have been identified. MaleC. philodice produce threen-hexyl esters; myristate, palmitate, and stearate, which are absent inC. eurytheme. A branched hydrocarbon, 13-methylheptacosane, is found on the wings of maleC. eurytheme, but notC. philodice. Several straight-chain hydrocarbons are on the wings of both species. The esters and 13-methylheptacosane have significant electrophysiological activity. Preliminary behavioral experiments indicate that the esters (especiallyn-hexyl myristate) function as species-recognition signals. The esters and 13-methylheptacosane also have low-to-moderate aphrodisiac activity.

Absconding Behaviour of the Africanized Honeybee in South America

SummaryAbsconding behaviour of the Africanized honeybee in French Guiana, South America, is described. Two types of absconding were recognized: disturbance-induced (i.e., predation, manipulation, etc.) and resource-related or seasonal absconding, probably induced by a dearth of resources during the wet season or by overheating during the dry season. In pre-absconding colonies where disturbance was not involved, brood rearing decreased dramatically, with few or no larvae present in colonies about ten days before absconding. Egg-laying continued at a low level until nearly all of the sealed worker brood emerged; colonies absconded within a day of the end of the sealed brood emergence. Patterns of nectar and pollen storage prior to absconding were highly variable. Inspection of colonies immediately after absconding showed that there was little (< 100 cm2) or no eggs, larvae, sealed brood or stored pollen, nectar or honey. Comparison of pre-absconding and persisting colonies prior to the absconding season rev...

The inheritance of pheromone production in the sulphur butterflies Colias eurytheme and C. Philodice

SummaryThe inheritance of male pheromone production in the sulphur butterflies Colias eurytheme and C. philodice was determined by gas chromatographic analyses of wing extracts from various genotypes derived from interspecific crosses. A wing ultraviolet-reflectance pattern (found only in C eurytheme males) which is controlled by an X-linked gene served as a marker for determining the relative influence of this chromosome v. the autosomes on pheromone production. The data indicate that production of the most important C. philodice wing compounds, three different n-hexyl esters, is controlled by one or more autosomal genes that are at least codominant. The X-chromosome carries most of the genes or the gene controlling production of the most important C. eurytheme compound, 13-methyl heptacosane. Expression of this compound in hybrids displays a codominant pattern. Because the wing ultraviolet-reflectance pattern of male C. eurytheme is an important courtship signal, it appears that all of the genes controlling the male courtship signals of this species are inherited as a co-adapted gene complex on the X-chromosome. The evolution of X-chromosomal control of both the visual (wing UV-reflectance pattern) and olfactory (13-methyl heptacosane) components of the courtship communication system of C. eurytheme is discussed and compared to the mode of inheritance of other communication systems.

Engorgement and Dispersal of Africanized Honeybee Swarms

SummaryThe contribution of pre-swarming engorgement by workers to the energetics of long-distance dispersal by swarms of Africanized honeybees was examined, by measuring the volumes and concentrations of nectar from honey sacs of bees from different types of swarms. The extent of worker engorgement varied with the type of swarm; in order of decreasing volumes of honey sac contents, these were: (1) absconding swarms, (2) prime swarms, (3) afterswarms, (4) in-transit swarms, (5) colonizing swarms. Relative to body weight. Africanized honeybees carried greater weights of nectar than have been reported for European honeybees. Calculations based on our measurements of engorgement, and estimates of metabolic rates, indicate that the maximum flight range for reproductive and absconding swarms was 64 km and 131 km, respectively. Colonizing reproductive swarms were moderately engorged, which suggests that these swarms had moved relatively short distances.These observations are insufficient to account for the obser...

Quasi-extinction risk and population targets for the Eastern, migratory population of monarch butterflies ( Danaus plexippus )

The Eastern, migratory population of monarch butterflies (Danaus plexippus), an iconic North American insect, has declined by ~80% over the last decade. The monarch’s multi-generational migration between overwintering grounds in central Mexico and the summer breeding grounds in the northern U.S. and southern Canada is celebrated in all three countries and creates shared management responsibilities across North America. Here we present a novel Bayesian multivariate auto-regressive state-space model to assess quasi-extinction risk and aid in the establishment of a target population size for monarch conservation planning. We find that, given a range of plausible quasi-extinction thresholds, the population has a substantial probability of quasi-extinction, from 11–57% over 20 years, although uncertainty in these estimates is large. Exceptionally high population stochasticity, declining numbers, and a small current population size act in concert to drive this risk. An approximately 5-fold increase of the monarch population size (relative to the winter of 2014–15) is necessary to halve the current risk of quasi-extinction across all thresholds considered. Conserving the monarch migration thus requires active management to reverse population declines, and the establishment of an ambitious target population size goal to buffer against future environmentally driven variability.

SOME CHARACTERISTICS OF HYBRIDS DERIVED FROM THE SULFUR BUTTERFLIES, COLIAS EURYTHEME AND C. PHILODICE: PHENOTYPIC EFFECTS OF THE X-CHROMOSOME

Species which exhibit premating reproductive isolation in nature but can interbreed to produce F1, F2, and backcross progeny offer a rare opportunity to study the genetic basis of the species-specific traits which maintain their isolation and make them recognizable as separate forms. The ubiquitous and abundant sulfur butterflies, Colias eurytheme and C. philodice, are morphologically and ecologically similar and were long thought to hybridize at random throughout their large range of sympatry (Hovanitz, 1944). However, Taylor (1972) demonstrated that these species display strong ethological isolation under most natural conditions. Despite this isolation, several investigations (Gerould, 1943; Hovanitz, 1944; and Ae, 195 9) have shown that C. eurytheme and C. philodice retain a large degree of genetic compatibility. This characteristic has been exploited to determine the mode of inheritance of the traits which constitute the species-specific courtship communication systems (Silberglied and Taylor, 1973; Grula, 1978). In the course of this genetic analysis a large number of F1, F2, and backcross progeny were reared in the laboratory and some of their characteristics are described here. In addition, evidence is provided for the existence of X-chromosomal supergenes which exert a very large influence on most of the traits which distinguish the two species.

THE EFFECT OF A STRONG MAGNETIC FIELD ON MONARCH BUTTERFLY (DANAUS PLEXIPPUS) MIGRATORY BEHAVIOR

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