Young Foliage Research Articles

Larval gregariousness and neonate establishment of the eucalypt‐feeding beetle Chrysophtharta agricola (Coleoptera: Chrysomelidae: Paropsini)

The selective advantage offered to individuals living within groups may relate to natural enemy defence, but in leaf feeding insects may also relate to overcoming plant defences, especially with respect to feeding establishment. We conducted a series of experiments focusing on neonate larval survival, examining the effect of group size and leaf age on the survival of a eucalypt‐feeding beetle, Chrysophtharta agricola, which formed groups of up to 43 larvae on the foliage of Eucalyptus nitens in the field. In the laboratory, in the absence of natural enemies, we found that initial density, leaf age and damage to the leaf margin significantly affected larval survival. Survival of solitary first‐instar larvae on young foliage was around 80% whereas on older foliage it was around 11%. Prior damage to the leaf margin significantly increased survival on older leaves to around 61%. Initial larval density also affected survival, although mortality was always significantly higher on older leaves. On older leaves the larval group size above which mortality increased no further was over two‐fold that on young leaves. Observations of group feeding behaviour at each instar showed that the majority of larvae (75.7%) were aligned facing away from the feeding site and that only around 7.5%, or just 1–2 larvae per group, fed at any one time. Feeding larvae chewed the leaf edge by straddling the leaf margin. Measurements of leaf margins showed that older leaves had significantly thicker leaf margins and ‘thickness’ ratios (leaf margin to leaf lamina proper). In the field, approximately 85% of all larvae occurred on the first two expanded leaf pairs, and larval mortality was highest between eclosion and establishment of the first instar. However, beetles apparently did not adjust clutch size according to leaf age.

Effects of elevated atmospheric carbon dioxide on insect–plant interactions

Effects of elevated atmospheric carbon dioxide on insect–plant interactions

Factors contributing to the superior growth and N nutrition of 11-year-old lodgepole pine compared with Sitka spruce on a N-poor cedar-hemlock cutover

We tested several hypotheses to explain the superior growth and nitrogen (N) status of lodgepole pine (Pinus contorta Dougl. ex Laws. var. contorta) compared with Sitka spruce (Picea sitchensis (Bong.) Carrière) on a N-poor site by comparing N distribution, N retranslocation, rooting distribution, and mycorrhizal fungi in plots of 11-year-old trees on a cedar–hemlock cutover. Aboveground N content was nine times greater in pine than in spruce of the same age, and thus, we conclude that pine acquired more N during the 11 years than spruce. Greater N acquisition by pine was not related to rooting depth, as both species rooted primarily in the residual forest floor. There were differences in mycorrhizal fungal associates: a high proportion of pine roots were infected with Suillus-like fungi. Pine produced more aboveground biomass per unit N (388 compared with 292 g·g–1 in spruce) and distributed more N to young foliage. Nitrogen retranslocation efficiency (based on foliar N contents in July and October) was higher in pine (50–52%) than in spruce (24–36%). These characteristics all appear to contribute to pine's abilities to both acquire more N and use it more efficiently and, thus, outperform spruce on this N-poor site.

Delayed greening of mountain birch leaves:Ecological and chemical correlates

Flushing leaves of deciduous trees can be exposed to high herbivore pressure. Young foliage provides high quality food for herbivores, and therefore herbivore pressure is much higher in young than mature foliage. Plants may escape the effects of herbivory in time by delaying leaf greening. We measured delayed greening as an intensity of redness in leaves in mountain birch at bud burst. Furthermore, we analyzed covariation of leaf redness with leaf growth and leaf consumption by the autumnal moth, Epirrita autumnata (Bkh.), a major defoliator of mountain birch. We also analyzed concentrations of amino acids, sugars and phenolic compounds of leaves. Leaf redness was positively associated with leaf growth, and consumption by E. autumnata indicated reduced leaf resistance against herbivores. Concentrations of protein-bound amino acids and gallotannins in young leaves were closely and positively correlated with leaf redness. Concentrations of glucose exhibited close positive correlations with leaf redness at the beginning of the season, whereas the correlation was negligible in mature leaves. Concentrations of other sugars increased with increasing degree of leaf redness towards the end of leaf development. This may be one reason for high leaf biomass losses in trees with delayed greening.

Field Colonization of the Melaleuca Snout Beetle (Oxyops vitiosa) in South Florida

Abstract The Australian melaleuca snout beetle, Oxyops vitiosa Pascoe, a biological control agent of Melaleuca quinquenervia (Cav.) S. T. Blake, was first released in south Florida during spring 1997. Field-emerged adults appeared 3 months later, which affirmed survival of pupae despite occasional flooding. Releases at 12 other locations totaled more than 1500 adults and 6700 larvae by June 1998. Populations established at nine sites in Dade, Broward, Lee, Collier, Palm Beach, and Glades Counties. Habitats with short hydroperiods, intermediate stages of melaleuca invasion, and dry winter conditions engendered field colony development, whereas releases failed at aquatic sites. Even small releases (60 adults) produced populations at favorable sites. Abundant young foliage facilitated establishment, whereas soil type seemed unimportant: colonies developed at typical “glades” sites characterized by organic soils and at pineland sites with sandy soils. Larvae predominated during October to May, coincident with flushes of plant growth. In contrast, only adults remained during summer, except at a site that was periodically mowed. The new growth induced by mowing supported a persistent year-round larval population. This demonstrated that population trends are influenced more by plant phenology than by climatic conditions, possibly reflecting adaptation to the nonseasonal climatic oscillations (El Nino) of Australia. Transect sampling estimated the population at more than 2000 adults and 22,000 larvae, 1 year after release of 3300 larvae. Numbers swelled to almost 80,000 adults and over 15,000 larvae by June 1999 and to nearly 83,000 adults and 137,000 larvae by January 2000. Weevils dispersed throughout the 8.1-ha site but remained concentrated near release plots during the first 18 months. Ease of establishment and slow dispersal suggests an optimal strategy of many small releases at carefully selected but widely dispersed sites. Adults and larvae were subsequently relocated to other areas, and O. vitiosa is now widely established in southern Florida.

Insect herbivores foraging on seedlings in an unlogged rain forest in Guyana: spatial and temporal considerations

About 9,000 individuals of sap-sucking and leaf-chewing insects, representing 345 species, were collected from 10,000 seedlings belonging to 5 rainforest tree species in an unlogged forest in Guyana. For the 40 most common species, it was possible to estimate their host specificity, diurnal activity, seasonal distribution, spatial aggregation, abundance and body weight. Most species were generalists but more specialised species tended to show a higher spatial aggregation, a more restricted diurnal activity and a higher seasonality. Although insect abundance was highest at the onset of the long wet season in May, seasonal amplitude was not pronounced. The combined effects of host and rainfall explained 14.5% of the total variance in insect seasonality, which was poorly explained by the leaf production of seedlings. The spatial distribution of insects was often aggregated and, overall, explained by host effect, production of young foliage, number of conspecific trees within a radius of 50m, and number of dead seedlings at each collecting station. However, these variables explained only 7% of the variance in spatial distribution. The lack of notable influence of leaf production and other important variables recorded at the collecting stations suggests that the seedlings represent a marginal food resource for most of the insect species collected.

First Report of Tomato spotted wilt virus in Common Agapanthus.

Common agapanthus (Agapanthus praecox subsp. orientalis), native to South Africa, is a popular ornamental flowering bulb species belonging to the Amaryllidaceae and is commonly found in residential gardens. Roots from some Agapanthus sp. also are used in traditional medicine in Africa. Common agapanthus collected from a residential property in Hobart, Tasmania, Australia, showed leaf symptoms of concentric ring and line patterns, irregular chlorotic blotches, and streaks. Symptomatic plants were severely stunted and failed to flower. Symptomatic leaves prematurely senesced, but young foliage subsequently produced was symptomless. Similar symptoms have been reported in other members of the Amaryllidaceae and are associated with infection by Tomato spotted wilt virus (TSWV; e.g., Nerine and Hippeastrum spp.) or Cucumber mosaic virus (CMV; e.g., Hippeastrum sp.) (2). The presence of TSWV and absence of CMV in symptomatic plants of common agapanthus was determined by enzyme-linked immunosorbent assay. Confirmation of TSWV infection was provided by reverse-transcription polymerase chain reaction assay with primers specific to the nucleocapsid protein gene of TSWV, with nucleic extracts from symptomatic plants producing an expected ≈800-bp amplicon (1). This is the first report of TSWV infection of any species within the Amaryllidaceae in Australia and the first report of the occurrence of TSWV in common agapanthus.

Chemical and morphological variation of Mediterranean woody evergreen species: Do plants respond to ungulate browsing?

Abstract. Plant defense theories suggest that chemical or structural defences should be maximized when and where browsing is most likely to occur. We tested this hypothesis on four evergreen woody species growing in a Mediterranean area with a high density of ungulates. In this system, levels of browsing are more intense in the winter (due to the lack of annual plants) and young foliage is often preferred. Therefore we predicted that the chemical defences of these species, namely their phenolic content, would vary with leaf age, season and damage intensity. In addition, we tested whether ungulates preferentially selected species containing lower phenolic levels, and also whether browsing induced either chemical or morphological changes in damaged plants. Phenolic levels varied greatly between plant species; ungulates browsed preferentially on the species with the lowest phenolic levels. No difference in phenolic content was found between browsed and unbrowsed trees. Morphological changes in heavily browsed trees included an increase in shoot and leaf density and a net decrease in leaf size. We suggest that for Mediterranean plants, which have evolved under high browsing pressure from large mammals, the production of small leaves and dense shoots in response to browsing might decrease ungulate foraging efficiency and hence reduce the rate of further damage as effectively as high levels of chemical defence.

PHYSIOLOGICAL ADAPTATION TO TEMPORAL VARIATION IN CONIFER FOLIAGE BY A CATERPILLAR

AbstractLarvae of the hemlock looper, Lambdina fiscellaria fiscellaria (Guenée) (Lepidoptere: Geometridae), consume both new and old foliage within the crowns of their host, balsam fir, Abies balsamea (L.) Miller (Pinaceae), despite the poor nutritional quality generally ascribed to old tissues. Laboratory studies evaluated whether the consumption of old foliage by hemlock looper larvae could be an adaptation to the relative paucity of new versus old foliage, and to the limited temporal window during which young foliage remains high in nutritional quality. Access to new foliage was critical to hemlock looper survival; 55% of larvae fed an exclusive diet of new foliage survived, whereas only 5% and 0% of larvae fed exclusively 1-or 2-year-old foliage survived, respectively. Moreover, larvae reared on branches in synchrony with bud flush were more than twice as likely to survive than those whose emergence was delayed by 2 weeks. Despite the reliance by the hemlock looper upon new foliage for survival, larvae given access to both new and old foliage survived better and were heavier than those restricted to new foliage. By incorporating older foliage into their diet, the hemlock looper can circumvent the limited availability of new foliage, thereby gaining access to more abundant tissues.

Dry mass production in seedlings of Norway spruce infected by the needle rust Chrysomyxa rhododendri

Summary The aim of this study was to assess the losses in productivity of Norway spruce (Picea abies) due to the attack by Chrysomyxa rhododendri, a rust that only penetrates new developing flushes. Three-year-old seedlings were artificially infected once or twice in two consecutive years and the dry mass was determined at the end of the growing season. Dry mass accumulation of all parts including roots was significantly reduced if more than about one-third of the young foliage was infected. Shoot and root dry mass of once severely infected seedlings were 32 and 48% less than that of controls. This deficit could not be compensated during a following rust-free year. When seedlings were infected in two consecutive years, dry mass accumulation was reduced by 58% compared with controls. Results indicate that rejuvenation of and afforestation with Norway spruce can seriously be impaired by Chrysomyxa at the alpine timberline where Rhododendron sp. (the telial host of the parasite) is widespread.

Observations on the Oviposition Process of Diaprepes abbreviatus (Coleoptera: Curculionidae)

A single adult Diaprepes abbreviatus L. was discovered in a citrus nursery in Orange County Florida (Woodruff 1964). D. abbreviatus was not collected again until 1968, when larvae were collected at the same nursery and several hundred adults and larvae were subsequently collected in and around Apopka, FL (Woodruff 1968). Since its introduction in 1964, D. abbreviatus has spread to 20 counties in Florida, where it currently infests approximately 164,000 acres (66,420 ha) (Anonymous 1997). This area contains approximately 30,000 acres (12,150 ha) of infested commercial citrus and has a limited and localized geographical distribution. D. abbreviatus is an insidious pest; tree symptoms may not appear until the larvae are well established on the tree roots (Wolcott, 1936). Adults feed on young foliage, females lay egg clusters between leaves, and the larvae feed on the roots of a host (Fennah 1942, Jones 1915, Wolcott 1936, Woodruff 1968). Oviposition by D. abbreviatus appears to be restricted to nighttime hours (Jones 1915, Schroeder 1981, Wolcott 1936). Females oviposit approximately 60 egg masses during their lifetime which may contain from 30 to 260 eggs each and an average of about 5,000 eggs over their life span (Wolcott 1936). Wolcott (1933) observed that female D. abbreviatus preferred to oviposit between paper strips compared to leaves. Neonate larvae failed to emerge from these strips (Wolcott 1933). Fennah (1942) found that D. abbreviatus preferred paper strips over tin foil strips and mature leaves which were both favored over immature leaves for oviposition. Immature leaves are preferred feeding sites (Jones 1915, Wolcott 1936). Adair et al. (1998) reported that freezer paper strips might serve as a potential oviposition trap in citrus. Adult D. abbreviatus were field collected in Vero Beach, Florida and maintained as previously described (Adair et al. 1998). Thirty females and 30 males per cage were held in 30 x 30 x 60 cm aluminum rearing cages (Bioquip Products, Gardena, CA 90248-3602) at 27 ? 2?C, 30% RH and photoperiod of 11:13 (L:D). Five 2.54 cm x 15.24 cm doubled strips of transparency film (polyester, Labelon, Canadaigua, NY 14424) were provided for oviposition sites. At 10:00 PM, transparency film strips containing an ovipositing female were removed to a microscope stage for observation and photographing. Microscopic observations were conducted with an Olympus S2-6045 zoom stereo microscope with a 100AL 0.5x objective lens, lOx eyepiece and a NFK 2.5 x LD 125 lens and Olympus S2-PT (with L-adapter) adapter for a SLR camera. An Olympus OM 2S camera with automatic shutter speed and f-stop was used with Kodak Kodacolor 400 Gold? film. The transparency film strip with an ovipositing female was placed across an open Petri dish and illuminated above and below with a tungsten halogen lamp (Olympus Highlight 3000) equipped with bifurcating cold fiber optic goose neck

Effects of rainfall acidity and ozone on foliar leaching in red spruce (Picea rubens)

The effects of acid rain and ozone on the leaching of chemicals from the canopy of red spruce (Picea rubens Sarg.) saplings was measured over a 4-year treatment period. The saplings were exposed to various levels of ozone and to acid rain (pH 3.1, 4.1, and 5.1) using open-top chambers. No effects of ozone treatments on canopy leaching were observed. Significant effects of rainfall pH on canopy leaching of Ca2+ and Mg2+ were observed, and post-hoc analysis indicated that these effects were associated only with the most acidic treatment (pH 3.1). In the low pH treatment (high NO3- and SO42-) significant canopy retention of both NO3- and SO42- were observed. The observed increase in base cation leaching flux from the red spruce canopy in the low pH treatment was particularly prominent early in the growing season (June) probably reflecting incomplete cuticle formation in the young foliage. Although the annual magnitude of extra Ca2+ leaching from the canopy of red spruce trees in the low pH treatment was small relative to the foliar calcium pool (about 10%), if this leaching preferentially depletes a physiologically important pool, it may influence tree health.

Viruses in Salix grown for bioenergy

SummaryA study was completed to determine if willows propagated vegetatively for bioenergy in New York State were infected by viruses. Unrooted, dormant cuttings from 10 willow clones were planted in a greenhouse. Four months later the young foliage and roots were tested for tomato mosaic tobamovirus, tobacco necrosis necrovirus (TNV), and brome mosaic bromovirus by double‐antibody sandwich enzyme‐linked immunosorbent assay. All three viruses were detected in the roots of some plants, but rarely in foliage. Every clone was infected with at least one virus. Tobacco mosaic virus and TNV were also transmitted to Chenopodium quinoa from extracts of roots collected from field‐grown willows. Imported willow material may be virus‐infected.

Oviposition preference of a Eucalyptus herbivore and the importance of leaf age on interspecific host choice

1. Paropsine chrysomelids are eucalypt folivores for which it has been hypothesized that the availability of suitable age class foliage (i.e. young foliage) is a more important determinant of host use than the physical and/or chemical characteristics of foliage from different hosts. This prediction was tested by assessing the oviposition preference of Chrysophtharta bimaculata (Olivier) on excised branches of Eucalyptus regnans F. Mueller and E. nitens (Deane & Maiden) Maiden.2. In cage trials, and as observed in the wild, beetles oviposited preferentially on E. regnans when the branches of both eucalypt species displayed the full range of foliar developmental classes, from immature to fully expanded. However, when the branches were pruned so that both species displayed only immature and expanding leaves, no difference in oviposition between the species occurred. Further, when the branches were pruned so that E. regnans displayed only fully expanded leaves and E. nitens displayed only immature and expanding leaves, females oviposited entirely on the latter species.3. These results support and extend the hypothesis that C. bimaculata's ovipositional preference is dictated more by leaf age class than by the tree species from which the leaves derive. In the discussion it is proposed that a eucalypt that initiates and expands leaves rapidly will be less preferred for oviposition than one that develops and expands leaves slowly, because of the smaller area of its canopy with less sclerophyllous foliage.

Production of milk and nutrition of the dependent young of free-ranging koalas (Phascolarctos cinereus).

The production of milk by lactating females, and energy expenditure and foliage intake of their dependent young, were investigated in free-ranging koalas. Koalas had the lowest mass-specific daily milk-energy production at peak lactation so far recorded in a mammal, but the duration of reproduction was 58% longer than the combined marsupial and eutherian average. As a consequence, the total energy input to reproduction in koalas was similar to that in other mammals. We propose that the prolonged lactation and low daily rate of energy transfer to the young by female koalas is an adaptation to the low energy availability from their diet of Eucalyptus foliage. Energy requirements (field metabolic rates) of young koalas were lower than those expected for typical marsupials (only 60% at permanent pouch exit), which may be a necessary preadaptation that allows the low rate of maternal energy transfer. However, the energy requirements of the adult females were no lower than expected for marsupials. This pattern of energy requirements and age resulted in a linear relationship between field metabolic rate and mass for the koalas in this population. Differences in milk production between the years of the study coincided with fluctuations in the availability of preferred young foliage, which suggests that lactational output by koalas may be flexible and affected by diet quality. Despite the interannual differences in milk production, growth of the young was similar in the two years.

Systemic Induction of Terpenoid Aldehydes in Cotton Pigment Glands by Feeding of Larval Spodoptera exigua

Pigment glands in cotton contain terpenoid aldehydes that are toxic and deterrent to feeding of several generalist lepidopteran insects. We hypothesized that previously observed systemically induced feeding deterrence may be associated with pigment glands. We conducted experiments to determine the dynamics and chemical nature of inducible feeding deterrents in leaves of cotton, Gossypium hirsutum L, to larvae of the beet armyworm, Spodoptera exigua. Production and/or filling of pigment glands was influenced by physiological age of Deltapine 90 cotton plants. In undamaged plants, successively formed leaves contained more pigment glands, up to the seventh or eighth true-leaf developmental stage. Feeding choice tests conducted one or seven days after initial feeding damage revealed that third instars of S. exigua consumed more of the two youngest leaves from control cotton plants than from plants whose two oldest leaves had been fed on previously for 24 hr by S. exigua. The preference for leaves from control plants was significant one day after initial damage and highly significant seven days after damage. Consumption of mature foliage (leaf immediately above initially damaged leaves) from control plants and damaged plants did not differ. More pigment glands were counted on the youngest leaf of damaged plants than on the youngest leaf of control plants one day after initial damage. HPLC analysis revealed greater amounts of hemigossypolone, heliocides 1 and 2 (H1 and H2), and total terpenoid aldehydes per gland in young foliage of damaged plants than control plants one day after initial injury. By seven days after initial injury, greater quantities of hemigossypolone and all heliocides except H4 were detected in young foliage from damaged plants compared to control plants. Concentrations of H1 per gland in young leaves from damaged plants increased the most of all terpenoid aldehydes measured (3.4× the amount found in leaves from control plants). Mature leaves from damaged plants did not contain more terpenoid aldehydes than mature leaves from control plants. We suggest that systemically induced feeding deterrence to S. exigua in young leaves of glanded cotton was due to increased amounts of terpenoid aldehydes in pigment glands.

Local Dispersion of the Eucalyptus Leaf-Beetle Chrysophtharta bimaculata (Coleoptera: Chrysomelidae), and Implications for Forest Protection

1. Chrysophtharta bimaculata is a native chrysomelid species that can cause chronic defoliation of plantation and regrowth Eucalyptus forests in Tasmania, Australia. Knowledge of the dispersion pattern of C. bimaculata was needed in order to assess the efficiency of an integrated pest management (IPM) programme currently used for its control. 2. Using data from yellow flight traps, local populations of C. bimaculata adults were monitored over a season at spatial scales relevant to commercial forestry: within a 50-ha operational management unit (a forestry 'coupe') and between coupes. In addition, oviposition was monitored over a season at a subset of the between-coupe sites. 3. Dispersion indices (Taylor's Power Law and Iwao's Mean Crowding regression method) demonstrated that C. bimaculata adults were spatially aggregated within and between coupes, although the number of egg-batches laid at the between-coupe scale was uniform. Spatial autocorrelation analysis showed that trap-catches at the within-coupe level were similar (positively autocorrelated) to a radius distance of approximately 110 m, and then dissimilar (negatively autocorrelated) at approximately 250 m. At the between-coupe scale, no repeatable spatial autocorrelation patterns were observed. 4. For any individual site, rapid changes in beetle density were observed to the associated with loosely aggregated flights of beetles into and out of that site. Peak adult catches (>the weekly mean plus standard deviation trap-catch) for a site occurred for a period of 2.0 ± 0.22 weeks at a time (n = 37), with normally only one or two peaks per site per season. Peak oviposition events for a site occurred on average 1.4 ± 0.11 times per season and lasted 1.5 ± 0.12 weeks. 5. Analysis of an extensive data set (n = 417) demonstrated that adult abundance at a site was positively correlated with egg density, but negatively correlated with tree damage (caused by conspecifics) and the presence of conspecific larvae. There was no relationship between adult abundance and a visual estimate of the amount of young foliage on trees. 6. Adults of C. bimaculata are shown to occur in relatively small, mobile aggregations. This means that pest surveys must be both regular (less than 2 weeks apart) and intensive (with sampling points no more than 150 m apart) if beetle populations are to be monitored with confidence. Further refinement of the current IPM strategy must recognize the problems posed by this temporal and spatial patchiness, particularly with regard to the use of biological insecticides, such as Bacillus thuringiensis, for which only a very short operational window exists.

Plate 309. Rosa cymosa ‘Rebecca Rushforth’

Rosa cymosa (Rosaceae) is a vigorous climbing rose from China, belonging to sect. Banksianae; its history, taxonomy, distribution, and cultivation requirements are discussed and there is a full description of the species. The clone depicted has striking, brightly coloured young foliage and has been provided with a cultivar name, ‘Rebecca Rushforth’.

Variation in budbreak phenology affects the distribution of a leafmining beetle (Brachys tessellatus) on turkey oak (Quercus laevis)

:Variation in plant phenology may be a major determinant of the distribution of herbivores on their host plants. We describe a field study in which we examined the consequences of budbreak phenology for densities of a leafmining beetle, Brachys tessellatus, on turkey oak, Quercus laevis. Budbreak phenology varies both within and among populations of Q. laevis in South Carolina. This variation appears to reflect mostly environmental variation within and among populations of trees, mediated in part by topography; larger trees and higher elevation trees broke bud earlier than smaller and lower elevation trees. Q. laevis that broke bud earlier suffered more leaf area loss to adult herbivory by B. tessellatus than trees that broke bud later; early-breaking trees lost as much as 15–20% leaf area to adult B. tessellatus feeding, while later-breaking trees generally lost < 5%. The effect of phenology on larval densities was more complicated; early-breaking trees accumulated more eggs than later-breaking trees early in the season. However, this relationship disappeared by mid-summer and there was no relationship between tree phenology and final numbers of mines or miners on trees at the end of the season. Thus, the consequences of variation in tree phenology for B. tessellatus abundance and herbivory on Q. laevis depend on the life history stage of the insect examined. This variable response to phenology by B. tessellatus reflects the patterns reported in other studies; insects primarily attacking young foliage and active early in the season are sensitive to phenological variation among plants, while herbivores primarily attacking mature foliage later in the season are not.

Seasonal Occurrence of the Herbivore Trirhabda geminata (Coleoptera: Chrysomelidae) on Encelia farinosa in Southern California

The seasonal distribution of Trirhabda geminata Horn, the dominant herbivore of brittle brush, Encelia farinosa Gray, was monitored in California coastal sage scrub. Larval emergence coincided with the 1st precipitation of the growing season and the development of young host-plant foliage. Larvae were present from December through April; 3 instars were detected. Pupation occurs in the upper 5 cm of the soil immediately underneath host plants. Adults were present from early March through mid-June. The number of adults exhibiting mating behaviors (mate selection, copulation, mate guarding) was at a maximum in April. Larval T. geminata are parasitized by the tachinid fly Chaetonodexodes vanderwulpi (Town-send) with parasitism rates ranging from 3.4 to 34.9% for the 2 yr of study. The presence of a summer quiescence period and the apparent lack of a diapause period is discussed for this species.