Multivoltine Species Research Articles

Internal Reproductive System and Diapausing Morphology of the Brassica Leaf Beetle PhaedonbrassicaeBaly (Coleoptera: Chrysomelidae: Chrysomelinae)

The brassica leaf beetle Phaedon brassicae Baly, one of the pests of cruciferous vegetables in China and Japan, is a multivoltine species that over-winters and over-summers mainly as diapausing adults. In this paper, the internal reproductive system is described and illustrated for this species. Its morphology associated with diapause is also described. The accessory glands, lateral ejaculatory duct, common ejaculatory duct and ejaculatory sac are poorly developed in diapausing male, in contrast, these are obvious and swollen in the reproductive male. In the diapausing female, no obvious previtellogenic oocytes can be found in the ovariole. The ovarioles contain numerous previtellogenic oocytes, and the basal oocytes have visible yolk uptake in the reproductive female. In addition, the fat bodies are numerous and dark yellow in color for diapausing adults, but few and light yellow in color for reproductive adults.

Effects of anthropogenic disturbances on the butterfly assemblage in an urban green area: the changes from 1990 to 2005 in Kanazawa Castle Park, Japan

AbstractKanazawa Castle Park (KCP) is an isolated urban green area in Kanazawa, Japan. A mature forest had developed there since 1949, but it was partially deforested from 1996 to 1999. Moreover, most of the grasslands in KCP were removed from 2000 to 2002. In this study, we report the damage to the butterfly assemblage by these anthropogenic disturbances and subsequent recovery after the disturbances, using previous literature on the butterfly assemblage in KCP from 1990 to 1994 and our monitoring data from 1999 to 2005. In addition, to understand urbanization effects, we also compared the butterfly assemblage of KCP with that of Tawara, a satoyama area 6 km away from KCP. Before the urbanization around KCP, KCP might have had a butterfly assemblage similar to Tawara. The previous articles indicate that 33 species lived in KCP before the partial deforestation. The number of generalist species (multivoltine and polyphagous species) was similar in KCP and Tawara (22 vs. 19), but that of specialist species (uni‐bivoltine and oligophagous species) was lower in KCP than in Tawara (5 vs. 15). Six species, composed of a bamboo grass feeder, mantle feeders, herb/grass feeders, and a multi‐feeder, disappeared from KCP after the deforestation and have not yet recolonized. The grassland removal also affected herb/grass feeders negatively, but they have been recovering quickly following the partial grassland recovery. Some species that disappeared after the deforestation were sporadically found from 2000 to 2005 probably due to immigration from the surrounding rural areas (the nearest one is 2 km away). For recolonization of the lost species, recovery of the interior and edge of the forest, which are the habitats for these species, is necessary.

The role of temperature and photoperiod in diapause induction in the brassica leaf beetle, Phaedon brassicae (Coleoptera: Chrysomelidae)

The brassica leaf beetle, Phaedon brassicae Baly (Coleoptera: Chrysomelidae), one of the pests infesting cruciferous vegetables in China and Japan, is a multivoltine species that oversummers and overwinters as an adult. The effects of both temperature and photoperiod on reproductive diapause induction were systematically investigated in this beetle. Under 16L : 8D, most of the beetles entered reproductive diapause at 12-30°C, indicating that photoperiod played a crucial role in estivation diapause induction. Under 12L : 12D, all adults developed without diapause at 28 and 30°C; less than 25% of the individuals entered reproductive diapause at 16-24°C; however, 46.1% of the individuals entered diapause at 12°C, suggesting that low temperature also had a relatively important influence on the determination of diapause. The photoperiodic response curves indicate that this species is a typical short-day species. The critical day-lengths at 20, 24 and 28°C were 13.2, 13.6 and 13.8 h, respectively. Transferring them from 16L : 8D to 12L : 12D or vice versa at different ages and/or stages during their development revealed that the photoperiod experienced by adults during the first 11 days might be important for diapause determination, even though an effect of photoperiod on the larval and pupal stages can not be excluded. Transferring individuals kept at a photoperiod of 12L : 12D from 25°C to 12°C or vice versa at different ages and/or stages during their development revealed that the temperature cue for diapause is mainly perceived by the late instar larvae and pupae.

Nesting biology of the trap-nesting Neotropical wasp Trypoxylo n(Trypargilum) aurifrons Shuckard (Hymenoptera, Crabronidae)

The present study was carried out in three localities of the state of São Paulo, Brazil: Araras (Dec/03-Dec/06), São Carlos (Nov/04-Nov/06) and Rifaina (Jul/04-Dec/06). Trap-nests were distributed among sites in the sampling areas and were collected every 35 days. Data from 295 nests indicate that T. aurifrons is a multivoltine species, with higher rates of nest building and cell production in the warm, rainy season. The trap-nests used by the females ranged from 117 to 467 mm in length and 3.1 to 16.6 mm in diameter. All nests showed deep plugs and a vestibular cell was found in 37% of the complete nests. The number of cells per nest ranged from one to 12. Females were larger than males, emerged from longer cells and their cocoons were significantly larger. A secondary 1:1 sex ratio was found in Araras and Rifaina. No correlation was observed between the diameter of the trap-nest and sex ratio. Males were usually oviposited in the first brood cells. Male and female developmental time from egg to adult was longer in the cold, dry season. Trypoxylon aurifrons provisioned their nests mainly with orb-spiders from the family Araneidae. The most important mortality factor was the death of immature forms, probably due to development failure. The most important parasitoid was Melittobia sp.

Morphology and biology of Porphyrosela minuta Clarke 1953 (Lepidoptera: Gracillariidae, Lithocolletinae) in Uruguay

Porphyrosela minuta Clarke is a gracillariid that causes damage on white clover (Trifolium repens) in Uruguay. In this article, the eggs, all the larval instars, the pupa and the external morphological characteristics of the adult are described. Information about the insect's biology under laboratory and field conditions is presented. The eggs are laid singly on the upper surface of the leaflets. The larvae make extensive mines that appear as white blotches. The larvae develop through five instars and do not remain exposed during their development. At 25 degrees C the life cycle lasted 16.2 days, made up of 3.0 for eggs, 8.8 for larvae and 4.4 for pupae. Females began laying on the first night, and during an oviposition period that varied between five and 12 days deposited an average of 71.8 eggs. It is a multivoltine species and seven to nine generations occur between November and the end of March.

Life-history and sex allocation in Trypoxylon (syn. Trypargilum) lactitarse (Hymenoptera; Crabronidae)

Hymenopterans have become a model for the study of factors that govern sex allocation. In 1983, Seger proposed a model to study Sphecidae wasps with a strong prediction that sex ratio for univoltine wasps should be 1 : 1 (female : male), and for partially bivoltine species it should be male-biased. The present study investigates if Trypoxylon lactitarse (Saussure, 1867) is a univoltine or a bivoltine species and if Seger's model prediction fits the pattern of sex ratio found in this species. The study was carried out at Parque Municipal das Araucarias, in the municipality of Guarapuava, state of Parana, southern Brazil, from December 2001 to December 2004. Nests of T. lactitarse were obtained using trap-nests drilled longitudinally to a depth to 80 mm with 7.0, 10.0 and 13.0 mm opening diameter. They were placed in a very heterogeneous site filled with araucaria forests, swamps and grasslands. Trypoxylon lactitarse showed two alternative life histories: either they pupated immediately and emerged as adults later in the same season (direct development), or they entered diapause, overwintering and pupating the following spring (delayed development). Its annual sex ratios were not significantly different from 1 : 1, and both sex ratio of overwintering and sex ratio of direct-developing wasps were also not significantly different from 1 : 1, in all years of this study. By examining these results, it was possible to conclude that although T. lactitarse is a multivoltine species, with four generations per year and two alternative life histories, its sex ratio did not support Seger's model.

Generation-dependent female choice: behavioral polyphenism in a bivoltine butterfly

Climatic and biotic circumstances vary as seasons shift, and different cohorts of multivoltine species are likely subjected to different selection regimes. The bivoltine butterfly Leptidea reali (Réal's wood white; Lepidoptera: Pieridae) appears during May and June in central Sweden and has a partial second generation in late July. We manipulated both generations to appear simultaneously and performed laboratory mating experiments that showed the presence of a behavioral polyphenism in mating propensity, which is induced during the developmental stages. Females of the summer generation expressed higher mating propensities than spring generation females. Spring females showed an increase in mating propensity with increasing age, whereas summer females accepted most matings already when they were only 1 or 2 days old. It is likely that larval time constraints, a lower abundance of males and a lower risk of accepting a male of their univoltine sister species Leptidea sinapis (wood white), have relaxed selection on mate discrimination among summer generation females. A major challenge for future research is to further investigate the developmental pathways causing the polyphenism and the adaptive implications of cohort-dependent behaviors.

Intraspecific Variability in Number of Larval Instars in Insects

The number of larval instars varies widely across insect species. Although instar number is frequently considered to be invariable within species, intraspecific variability in the number of instars is not an exceptional phenomenon. However, the knowledge has remained fragmentary, and there are no recent attempts to synthesize the results of relevant studies. Based on published case studies, we show that intraspecific variability in the number of larval instars is widespread across insect taxa, occurring in most major orders, in both hemimetabolous and holometabolous insects. We give an overview of various factors that have been observed to affect the number of instars. Temperature, photoperiod, food quality and quantity, humidity, rearing density, physical condition, inheritance, and sex are the most common factors influencing the number of instars. We discuss adaptive scenarios that may provide ultimate explanations for the plasticity in instar number. The data available largely support the compensation scenario, according to which instar number increases in adverse conditions when larvae fail to reach a species-specific threshold size for metamorphosis. However, in Orthoptera and Coleoptera, there are some exceptional species in which instar number is higher in favorable conditions. In more specific cases, the adaptive value of the variability in instar number may be in reaching or maintaining the developmental stage adapted to hibernation, producing additional generations in multivoltine species, or increasing the probability of surviving in long-lasting adverse conditions.

Intraspecific Variability in Number of Larval Instars in Insects

The number of larval instars varies widely across insect species. Although instar number is frequently considered to be invariable within species, intraspecific variability in the number of instars is not an exceptional phenomenon. However, the knowledge has remained fragmentary, and there are no recent attempts to synthesize the results of relevant studies. Based on published case studies, we show that intraspecific variability in the number of larval instars is widespread across insect taxa, occurring in most major orders, in both hemimetabolous and holometabolous insects. We give an overview of various factors that have been observed to affect the number of instars. Temperature, photoperiod, food quality and quantity, humidity, rearing density, physical condition, inheritance, and sex are the most common factors influencing the number of instars. We discuss adaptive scenarios that may provide ultimate explanations for the plasticity in instar number. The data available largely support the compensation scenario, according to which instar number increases in adverse conditions when larvae fail to reach a species-specific threshold size for metamorphosis. However, in Orthoptera and Coleoptera, there are some exceptional species in which instar number is higher in favorable conditions. In more specific cases, the adaptive value of the variability in instar number may be in reaching or maintaining the developmental stage adapted to hibernation, producing additional generations in multivoltine species, or increasing the probability of surviving in long-lasting adverse conditions.

Butterfly community composition and oak woodland vegetation response to rural residential development

Conservation of biodiversity on private lands has become increasingly important, particularly in regions where most of the land is privately owned. This study examined the effects of rural residential development on the oak woodland butterfly community in central California, U.S.A. We sampled butterflies on 26 8-ha sites that spanned a range in development intensity from sites containing small 0.4 ha (1 acre) parcels and highly modified vegetation, to sites contained within parcels greater than 81 ha (200 acres) that were characterized by substantial amounts of undeveloped oak woodland. The percent area of oak woodland vegetation was positively related to parcel size across the range of parcel sizes observed. The numbers of hostplant-specialist butterfly species and univoltine butterfly species were positively correlated with the percent area of oak woodland at a site, while the numbers of multivoltine and hostplant generalist species were higher at sites with smaller parcel sizes and lower percent area of oak woodland vegetation. These trends represent a shift in butterfly species composition from specialist to generalist with loss of historic vegetation and support the notion that zoning for larger parcel sizes may be useful for conserving oak woodland vegetation and its associated biotic diversity.

Native braconid parasitism of the Tarnished plant bug (Hemiptera: Miridae) in Southern Ontario

Three agricultural regions in southern Ontario (London, Niagara and Guelph) were sampled weekly from May to September for Lygus spp. and their parasitoids in 1998, 1999 and only one region in 2000. Alfalfa was the primary crop sampled, including both “clean” and weedy alfalfa fields. Lygus lineolaris (Palisot de Beauvois) accounted for 99% of all Lygus spp. collected by sweepnet. Lygus lineolaris had two generations (mid-June and late July) on alfalfa with a partial third generation in early September which contributes to the over-wintering adults. In 1998 and 2000, an early first generation peak of Lygus nymphs was observed in mid-May on the weeds, chickweed and shepherd's purse. Overall rates of parasitism (from dissections) for native parasitoids were consistent from year to year and the means of the three regions in each growing season were below 11%. Both nymphs and adult Lygus were parasitized, with the highly mobile adults being a potential means of dispersing the parasitoids. In general weedy fields were more highly parasitized than fields of weed-free alfalfa. Six species of native braconid parasitoids were collected from L. lineolaris in southern Ontario (in decreasing order of occurrence): Peristenus pallipes (Curtis), Peristenus pseudopallipes (Loan), Leiophron lygivorus (Loan), L. solidaginis Loan, L. uniformis (Gahan), and Leiophron sp. near brevipetiolatus Loan. The large populations of Lygus and the low percent baseline parasitism in southern Ontario, particularly of second generation Lygus, support the need for introduction of a multivoltine parasitoid species in this region.

Butterfly assemblages in a traditional agricultural landscape: importance of secondary forests for conserving diversity, life history specialists and endemics

Satoyama, the traditional agricultural landscape in Japan, has drawn much attention from the viewpoint of biodiversity conservation. It is composed of diverse vegetation types, including secondary forests, paddy fields and cultivated fields in a narrow area (ca. 1 km2). To clarify the characteristics of butterfly assemblage and the relative contribution of each vegetation type to butterfly diversity and endemism in satoyama, we conducted a line-transect survey along a 1.1-km route with five sections (two forest interior, one interior-edge, one edge-openland and one openland). Life history features (voltinism, host plant range and host plant type) and endemism of butterflies were discussed in relation to their abundance and vegetation association. Fifty-one species and 856 individuals were recorded. Species richness was highest in the two sections with edges, 32 and 36 species, respectively. Analysis of vegetation association of each butterfly species showed that 16 species were forest interior species, 24 forest edge species and 11 openland species, indicating that vegetation diversity enhanced butterfly diversity. However, the point is that forest interior and edge species contained many specialists sensitive to human impact (univoltine and/or oligophagous species) and many species within temperate East Asia including all endemic species. In contrast, most openland species were generalists (multivoltine and/or polyphagous species) feeding on herbs/grasses with the widest geographic range. Since secondary forests kept more butterfly diversity and specialists than openlands, and had all endemic species, they must be maintained without over fragmentation in order to avoid loss of specialists and endemics in satoyama.

Summer diapause and winter quiescence of Hippodamia (Semiadalia) undecimnotata (Coleoptera: Coccinellidae) in central Greece

The aestivo-hibernation in central Greece of the aphidophagous ladybeetle Hippodamia (Semiadalia) undecimnotata (Schneider) (Coleoptera: Coccinellidae) was studied. H. undecimnotata is a multivoltine species in Greece. In the lowlands, all instars are abundant in spring, becoming scarce from July until the end of October and they are absent in winter. In June, most H. undecimnotata adults migrate to mountainous aestivo-hibernation sites. The duration of pre-oviposition period in females sampled monthly from the summits of the mountains Chlomo and Kitheron in central Greece and transferred to laboratory conditions of high temperature (25°C), long day (16L : 8D), and abundance of aphids (Aphis fabae), indicated that the H. undecimnotata females were in diapause during July and August. The diapause gradually terminated from late August to late October and was followed by a period of quiescence extending from November to March of the following year. During the summer diapause, arrested ovarian devel- opment was indicated by the undifferentiated state of the ovaries in all females. Males and females had enlarged fat bodies, and the median preoviposition period after the transfer to the laboratory was 92 days in early July and 64 days in early August. During the winter quiescence, arrested ovarian development was characterized by immature ovaries in females and, in some samples, by vitello- genic resorption in a few females. In winter, adults contained varying amounts of fat body reserves, and the median preoviposition period of females transferred to breeding conditions was 30 days in early November and 16 days in mid January.

Sex ratio in relation to season and host plant quality in a monogenous stem‐galling midge (Diptera: Cecidomyiidae)

Abstract. 1. The sex determination mechanism in gall midges is little understood, although it is known that the females of several species primarily or exclusively produce unisexual broods throughout their lifetime.2. The gall midge Izeniola obesula Dorchin is a multivoltine species, inducing multi‐chambered stem galls on the salt‐marsh plant Suaeda monoica. Each gall contains 5–70 individuals, all being the progeny of a single female. Sampling of more than 450 galls, from which adult midges were reared, suggested that I. obesula exhibits strict monogeny, resulting in galls that contain either all female or all male progeny.3. Characterisation of the growth pattern of young S. monoica shoots revealed that shoots in apical positions grew more rapidly than shoots in more basal positions. Galls that were induced on such shoots were larger and yielded more adult midges.4. No difference in the site of gall induction was found between male and female galls, with galls of either sex being mainly induced on more rapidly growing shoots. It is concluded that I. obesula females cannot control the sex of their progeny, and that both female‐producers and male‐producers strive to maximise their reproductive success by choosing the faster‐growing shoots for gall induction.5. Female galls were larger and more abundant than male galls at almost all times. The sex ratio among galls fluctuated throughout the year, ranging from 4:1 in spring to 1:1 in winter. The skewed sex ratio among galls possibly results from greater mortality rates among male galls than among female galls, due to either primary or secondary factors. Alternatively, it is possible that the number or fitness of male‐producers in the population is reduced relative to female‐producers.

Biological diversity versus risk for mosquito nuisance and disease transmission in constructed wetlands in southern Sweden.

In southern Sweden, many wetlands have been constructed, and maintaining or increasing biological diversity is often included in the aims. Some wetlands are constructed near human settlements, thus raising the problem of wetlands being associated with mosquitoes (Diptera: Culicidae). Increased biodiversity (including mosquito diversity) is considered desirable, whereas mosquito nuisance from a human point of view is not. Adult mosquito abundance, diversity and species assemblages of constructed wetlands were compared to natural wetlands. The potential of constructed wetlands for mosquito nuisance and transmission of mosquito-borne viruses was evaluated. The study areas included five constructed and four natural wetlands. Mosquito abundance and species richness were higher in the natural than in the constructed wetlands, and showed a positive correlation with wetland size. Mosquito species assemblages formed three clusters, which were not explained by origin, size and water permanence of wetlands. In a redundancy analysis, however, mosquito faunas showed significant relationships with these variables, and size and origin of wetlands were most important. Major nuisance species (multivoltine species feeding on mammals and laying eggs on soil) were found in all wetlands, although in relatively low numbers. Risk assessment for Sindbis virus transmission showed moderate risk for two constructed wetlands near human settlements. It is concluded that small size of constructed wetlands has the advantage of low mosquito numbers from a human point of view. The use of functional groups is recommended as a tool for presenting mosquito data to the public, and for helping communication between scientists and administrative decision makers.

Biology of Lilioceris spp. (Coleoptera: Chrysomelidae) and their parasitoids in Europe

The biology and parasitoid complex of the lily leaf beetle (LLB), Lilioceris lilii Scopoli, and two congeneric species were investigated in Europe, as part of a biological control program against the LLB in North America. Eggs, larvae, and adults of L. lilii were collected in several countries in Europe, on both cultivated and wild Lilium spp., and reared in the laboratory and under natural conditions. Parasitoids were obtained and their biologies were studied. Similar investigations were made in Switzerland on two closely related species Lilioceris tibialis (Villa) found on wild Lilium spp., and Lilioceris merdigera (L.) on several other Liliaceae. The three species are strictly univoltine. Adults overwinter and lay eggs on leaves in early spring. The three beetle species have four instars, which were characterized by their head capsule width. Pupation occurs in a cocoon in the soil. Adults emerge in late summer and start feeding before reaching overwintering sites. Egg and larval parasitoids were obtained. Eggs of L. lilii and L. merdigera were parasitized by the mymarid Anaphes sp., a multivoltine species that needs alternate hosts for overwintering. Larvae were heavily attacked by several parasitoids, among which the most abundant were three ichneumonids, Lemophagus pulcher (Szepligeti), L. errabundus (Gravenhorst), and Diaparsis jucunda (Holmgren), and the eulophid Tetrastichus setifer Thomson. All four parasitoid species were found in the three beetles and in most European regions, but strong variations were observed in their relative abundance among hosts and geographic regions. Three of the four main larval parasitoids are strictly univoltine, whereas L. pulcher has a partial second generation. Lemophagus spp. are frequently parasitized by the ichneumonid hyperparasitoid Mesochorus lilioceriphilus Schwenke. Further details of the biology of the parasitoids are described, and their potential as biological control agents is discussed.

Effects of climatic change on the phenology of butterflies in the northwest Mediterranean Basin

AbstractPhenological changes in response to climatic warming have been detected across a wide range of organisms. Butterflies stand out as one of the most popular groups of indicators of climatic change, given that, firstly, they are poikilothermic and, secondly, have been the subject of thorough monitoring programmes in several countries for a number of decades. Here we provide for the first time strong evidence of phenological change as a consequence of recent climatic warming in butterflies at a Spanish site in the northwest Mediterranean Basin. By means of the widely used Butterfly Monitoring Scheme methodology, three different phenological parameters were analysed for the most common species to test for trends over time and relationships with temperature and precipitation. Between 1988 and 2002, there was a tendency for earlier first appearance dates in all 17 butterfly species tested, and significant advances in mean flight dates in 8 out of 19 species. On the other hand, the shape of the curve of adult emergence did not show any regular pattern. These changes paralleled an increase of 1–1.5°C in mean February, March and June temperatures. Likewise, a correlation analysis indicated the strong negative effect of spring temperature on phenological parameters (i.e. higher temperatures tended to produce phenological advances), and the opposite effect of precipitation in certain months. In addition, there was some evidence to indicate that phenological responses may differ between taxonomic lineages or species with similar diets. We discuss the consequences that these changes may have on species' population abundances, especially given the expected increase in aridity in the Mediterranean Basin caused by current climatic warming. We predict that varying degrees of phenological flexibility may account for differences in species' responses and, for multivoltine species, predict strong selection favouring local seasonal adaptations such as diapause phenomena or migratory behaviour.

Prevalence of the Trichomycete Fungus Harpella melusinae (Harpellales: Harpellaceae) in Larval Black Flies (Diptera: Simuliidae) across a Heterogeneous Environment

A total of 2063 mid- to late-instar larval black flies were collected from 64 stream sites in South Carolina and screened for the presence of the trichomycete fungus Harpella melusinae. Sixteen of 18 host species were colonized by H. melusinae on at least one occasion. Prevalence of H. melusinae in larvae of Simulium tuberosum cytospecies “A” was highest in acidic streams with low conductivity, whereas H. melusinae colonized larvae of Simulium verecundum most frequently in slower-moving streams. Ecological conditions, therefore, can serve as predictors of the prevalence of H. melusinae. Prevalence in host larvae was significantly lower in the Piedmont ecoregion than in the Mountain ecoregion. Prevalence did not differ in the host species S. verecundum across ecoregions, suggesting that different prevalences among host species might indicate some host preference. The prevalence of H. melusinae differed significantly between two univoltine host species (Simulium venustum and Prosimulium magnum) at the same site but not between two multivoltine host species (S. tuberosum cytospecies “FG” and S. tuberosum cytospecies “CDE”), suggesting that host life history could be important in determining fungal prevalence.

Prevalence of the trichomycete fungus Harpella melusinae (Harpellales: Harpellaceae) in larval black flies (Diptera: Simuliidae) across a heterogeneous environment

A total of 2063 mid- to late-instar larval black flies were collected from 64 stream sites in South Carolina and screened for the presence of the trichomycete fungus Harpella melusinae. Sixteen of 18 host species were colonized by H. melusinae on at least one occasion. Prevalence of H. melusinae in larvae of Simulium tuberosum cytospecies “A” was highest in acidic streams with low conductivity, whereas H. melusinae colonized larvae of Simulium verecundum most frequently in slower-moving streams. Ecological conditions, therefore, can serve as predictors of the prevalence of H. melusinae. Prevalence in host larvae was significantly lower in the Piedmont ecoregion than in the Mountain ecoregion. Prevalence did not differ in the host species S. verecundum across ecoregions, suggesting that different prevalences among host species might indicate some host preference. The prevalence of H. melusinae differed significantly between two univoltine host species (Simulium venustum and Prosimulium magnum) at the same site but not between two multivoltine host species (S. tuberosum cytospecies “FG” and S. tuberosum cytospecies “CDE”), suggesting that host life history could be important in determining fungal prevalence.

Can Host Susceptibility to Baculovirus Infection be Predicted from Host Taxonomy or Life History?

Host range is a fundamental aspect of host-pathogen population dynamics and is a vital determinant of the risks associated with the use of a pathogen for biological control. Yet even for widely studied baculoviruses we often do not know which hosts they infect under natural conditions. Baculoviruses are primarily pathogens of Lepidoptera and Hymenoptera and exhibit great variation in host range. Some are apparently monospecific, whereas others are able to infect numerous hosts from diverse families. In this report, I review host range data, concentrating on two generalist viruses, Autographa californica (Speyer) multicapsid nucleopolyhedrovirus (AcMNPV) and Mamestra brassicae L. multicapsid NPV (MbMNPV). To my knowledge, 145 and 78 host species have been assayed with AcMNPV and MbMNPV, respectively. I examined susceptibility of these species according to various life history parameters using a phylogenetic analysis. Host susceptibility was poorly predicted by taxonomic relationships. Host susceptibility was correlated with some life history traits; of the species tested, a significantly higher proportion of polyphagous species and pest species were susceptible to AcMNPV compared with mono- or oligophagous species or nonpest species, respectively. A higher proportion of multivoltine species were susceptible to MbMNPV compared with univoltine species, although the opposite trend was shown for AcMNPV. Providing convincing explanations for these patterns is problematic and highlights the inadequacies in our understanding of the ecology of baculoviruses. Some possible explanations are discussed. I suggest that current patterns of host susceptibility may, in part, reflect an ongoing evolutionary arms race between numerous host species and each baculovirus, in which the virus repeatedly colonizes new host populations and new species while others evolve resistance.