Catherine A. Tauber

Sympatric Speciation Based on Allelic Changes at Three Loci: Evidence from Natural Populations in Two Habitats

Allelic changes at three loci largely explain Chrysopa downesis sympatric speciation from a Chrysopa carnea-like ancestor. Disruptive selection first produced a stable polymorphism based on a single pair of alleles that adapted individuals to two habitats, and second, it established seasonal asynchrony in reproduction through allelic substitutions at two loci.

Thermal Requirements for Development in Chrysopa Oculata: A Geographically Stable Trait

Chrysopa oculata from five widespread localities (southern Canada to montane Mexico), exhibited remarkable similarities in their thermal requirements for nondiapause development. Lower thermal thresholds (t) varied by only 1.2°C., and the degree—days required for total preimaginal development (K) differed among the populations by °85°d. Despite the similarities among populations, the results suggest that the thermal requirements for development are genetically variable. However, two factors may limit the geographical expression of this variation: (1) the multivoltine life cycle could result in seasonal oscillations in the magnitude and projection of directional selection on the nondiapause thermal responses, and/or (2) the thermal thresholds for development and the rates of development above the thresholds may be functionally correlated and constrained in their evolution. Males from all populations emerged slightly but consistently earlier than females. Temperature did not affect sex or survival, other than at 15.6.° where mortality was significantly increased. Among the five populations, only one large difference occurred in the thermal responses; under low temperatures, a relatively high proportion of the two northern populations entered diapause. The differences in diapause induction resulted from the differential effect of temperature on the critical photoperiod for diapause induction, rather than on the developmental rates.

Two Genes Control Seasonal Isolation in Sibling Species

Interspecific hybridization tests between Chrysopa carnea and Chrysopa downesi show that single allele differences at two unlinked autosomal loci cause large differences in photoperiodic responses. These differences produce asynchronous seasonal reproductive cycles, thus forming an effective temporal reproductive barrier between the two sympatric species. The results subserve the development of a genetic model for allochronic speciation.

Food specificity in predacious insects: a comparative ecophysiological and genetic study

SummaryComparative ecological, physiological and genetic data from two hybridizable predacious species (Chrysopa quadripunctata andC. slossonae) illustrate that host (prey) specificity is based on a broad variety of genetically controlled traits. The array of traits parallels that found in host specific herbivores, and it includes: (i) female choice of oviposition site, (ii) adult dietary requirements for mating, (iii) large egg size, (iv) specialized larval behavior, (v) enhanced larval development, and (vi) univoltinism.Considerable genetic variation, in both quantitative, polygenically controlled characters, as well as qualitative traits, underlies the differences between the general predator,C. quadripunctata, and the monophagousC. slossonae. The interaction between the predators and their prey is more consistent with the sympatric than the allopatric model of speciation, and theC. quadripunctata/C. slossonae case provides an excellent opportunity for testing various assumptions underlying the sympatric model of speciation.

The Genus Ceraeochrysa (Neuroptera: Chrysopidae) of America North of Mexico: Larvae, Adults, and Comparative Biology

Abstract Ceraeochrysa, with 46 described species, is the largest New World genus in the green lacewing tribe Chrysopini. It encompasses numerous species that have major potential for efficient mass rearing and use in biological control. Here we record Ceraeochrysa claveri (Navás) from the United States for the first time, and we describe or redescribe the trash-carrying larvae and adults of all seven Ceraeochrysa species that are known from America, north of Mexico. In addition to C. claveri, these include C. cincta (Schneider), C. cubana (Hagen), C. lineaticornis (Fitch), C. placita (Banks), C. smithi (Navás), and C. valida (Banks). Furthermore, the literature on the biology of each species is summarized, and keys are presented for identifying larvae and adults. Larvae of six of the species share numerous traits that indicate a close phylogenetic relationship; whereas those of C. placita have a number of unique character states, particularly in the first instar. The pattern of variation indicates that Ceraeochrysa, as it currently stands, is a diverse genus that may need subdivision.

Prolonged Dormancy in Leptinotarsa decemlineata (Coleoptera: Chrysomelidae): A Ten-Year Field Study with Implications for Crop Rotation

Abstract This 10-yr field study examined prolonged dormancy (dormancy of more than 1 yr) in Colorado potato beetles, Leptinotarsa decemlineata (Say), from Upstate New York. The research focused on whether the life cycle of the Colorado potato beetle could reduce the effectiveness of crop rotation as a pest management tactic. One set of experiments quantified variation in the occurrence and duration of prolonged dormancy in a natural population. A second set of experiments tested the effect of artificial selection for increased incidence of prolonged dormancy. Of the ≈12,600 unselected beetles in the field cages overall survival (= % emergence) averaged 56.5 ± 18.4% (mean ± SD, range = 23.5–84.3%, n = 19 cages). Most (97.7%) of the emerging beetles surfaced after one winter; the remainder (2.3%) emerged after more than one winter in dormancy. The range of variation in the incidence of prolonged dormancy among the experimental cages during the 10-yr period was 0–7.2%. The incidence of emergence from prolonged dormancy was higher among beetles from the first summer-generation [mean ± SD = 3.0 ± 2.0% (10 cages)] than from the second [1.0 ± 1.5 (7 cages)], and significantly more females than males emerged from prolonged dormancy (female:male = 97:64). Most (≈70%) of the beetles that underwent prolonged dormancy emerged after two winters in diapause; the majority of the remainder (≈29%) emerged after 3–7 yr in diapause; and, one beetle (≈1%) emerged after 9 yr. Artificial selection for prolonged dormancy over three generations did not result in a significant increase in the incidence of delayed emergence, nor did it result in incidences of prolonged dormancy greater than those in the controls (unselected field-reared beetles and lines selected for 1-yr dormancy). From our results, we conclude that the Colorado potato beetle has considerable variation in both the incidence and duration of prolonged dormancy, and that this variation has strong environmental and genetic determinants. Viewed in the context of the beetle’s life history, these findings lead us to suggest that the evolution of resistance to crop rotation would require strong and sustained selection over large areas.

Gypsy moth (Lepidoptera: Lymantriidae) egg development: a simulation analysis of laboratory and field data

A simulation model was used to examine the idea thea diapause development in the egg of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), is a dynamic process in which the response to temperature gradually changes over the course of development. No clear demarcation of diapause and post-diapause development was presumed. Rather, an initial developmental response having low thresholds and optimal temperatures was assumed to give way gradually to a response having higher thresholds and optima. With one set of parameter values, the model produced results comparable to those from experiments conducted with Russian and Japanese Populations of the gypsy moth, and consistent with one set of data from North America. However, these results were inconsistent with data from other, more detailed experiments conducted with North American eggs. Changes to the model that improved the fit to the North American data were then determined. The model served to identify areas of disagreement among the published data, and to suggest experiments that will help resolve unanswered questions about diapause development in the gypsy moth.

Reproduction and quality of F1 offspring in Chrysoperla carnea: Differential influence of quiescence, artificially-induced diapause, and natural diapause

Abstract We asked how physiological status during cold storage might influence the subsequent reproduction of mass-produced Chrysoperla carnea adults and the quality of their F 1 offspring. To achieve an answer, we examined the performance of adults and their offspring after adults experienced three treatments: cold-induced quiescence under constant low temperature, artificially induced diapause followed by constant low temperature, and natural diapause out-of-doors. Physiological state did not affect survival during and after storage under constant low temperature, but during extremely cold winter conditions, the naturally overwintering adults suffered significant mortality. Cold-induced quiescence resulted in a slight loss of post-storage reproduction (lower incidences of fertile oviposition and decreased fecundity and lifetime fertility), as well as reduced rates of survival and development in F 1 offspring. In contrast, adults that were either stored in an artificially induced diapause or overwintered naturally out-of-doors, exhibited sustained high levels of post-diapause reproduction and they produced high-quality F 1 offspring. Overall, storage of diapausing adults under constant low temperature resulted in both high survival and high levels of post-storage reproduction. Unstored, nondiapause pairs had significantly poorer reproductive performance and lower quality F 1 offspring than cohorts that underwent storage in a state of diapause. These data and other data from C. carnea adults collected early and late in the season indicate that the occasional intervention of diapause may help prevent deterioration of stock during continuous rearing of this predator.

Nutritional and photoperiodic control of the seasonal reproductive cycle in Chrysopa mohave (Neuroptera)

Abstract Chrysopa mohave adults, which are predaceous, undergo a facultative reproductive diapause which can be induced, averted, and terminated in the laboratory by manipulating either photoperiod or diet. Photoperiods of LD 14:10 or shorter evoke a photoperiodically controlled diapause which breaks in long day (LD 16:8) conditions. Withholding prey induces the diapause syndrome in animals experiencing long day lengths, whereas supplying prey terminates this diapause; thus food constitutes a major factor in diapause induction and termination. Under short day regimens, with prey continuously present, diapause persists for approximately 60 days at 24±1°C; however, protein-fed, short day animals retain the diapause characteristics until they receive prey. Our experimental results in combination with field observations and examination of collected specimens, indicate four periods in the annual reproductive cycle as follows. The animals reproduce during April, May, and June when photoperiods are long and prey abundant. When prey become scarce during the dry months of the California summer, part of the population enters a food mediated diapause. During October, November, and December a short day diapause occurs in the population. Although the photoperiodic maintenance of diapause probably ends during early winter, the insects retain the diapause symptoms until prey becomes abundant at the end of March.

Developmental requirements of the univoltine species Chrysopa downesi: Photoperiodic stimuli and sensitive stages

Abstract Chrysopa downesi reproduces only in the spring and the resulting adults enter an aestival-autumnal-hibernal diapause which is primarily controlled by photoperiod. In the laboratory, constant photoperiods result in diapause induction and maintenance, whereas a series of short days followed by long days prevents or terminates diapause and promotes reproduction. The stages most sensitive to the diapause-averting stimulus are the free-living third instar, the third instar within the cocoon, and the pupa. C. downesi responds in different ways to three aspects of photoperiod: (a) an all-or-none response (diapause prevention or induction) to a sequence of two critical photoperiods, (b) an all-or-none response (diapause prevention or induction) to the difference between the long and short daylengths (a 4 hr difference is sufficient to avert diapause but a 2 hr difference is not), and (c) a quantitative response to the absolute duration of day (or night) length (after the short day requirement is fulfilled the rate of diapause termination is related to daylength). Differences and similarities in phenological adaptations and in photoperiodic responses of C. downesi, C. carnea , and C. harrisii reflect the degree of phylogenetic relationship between these closely related species.