William A. Overholt

Chloroplast and microsatellite DNA diversities reveal the introduction history of Brazilian peppertree (Schinus terebinthifolius) in Florida.

Brazilian peppertree (Schinus terebinthifolius) is a woody perennial that has invaded much of Florida. This native of northeastern Argentina, Paraguay, and Brazil was brought as an ornamental to both the west and east coasts of Florida at the end of the 19th century. It was recorded as an invader of natural areas in the 1950s, and has since extended its range to cover over 280 000 ha. Our goals were to understand the history of this invasion, as one step toward understanding why this exotic was so successful, and ultimately to improve development of biological control agents. We sampled plants from the native and exotic ranges, particularly Florida, and genotyped these individuals at nuclear and chloroplast loci. Nuclear microsatellite and cpDNA loci reveal strong genetic population structure consistent with limited dispersal in the introduced and native ranges. Bayesian clustering of microsatellite data separates the east and west coast plants in Florida into distinct populations. The two chloroplast haplotypes found in Florida are also concordant with this separation: one predominates on the east coast, the other on the west coast. Analysis of samples collected in South America shows that haplotypes as distinct as the two in Florida are unlikely to have come from a single source population. We conclude that the genetic evidence supports two introductions of Brazilian peppertree into Florida and extensive hybridization between them. The west coast genotype likely came from coastal Brazil at about 27° south, whereas the east coast genotype probably originated from another, as yet unidentified site. As a result of hybridization, the Florida population does not exhibit low genetic variation compared to populations in the native range, possibly increasing its ability to adapt to novel environments. Hybridization also has important consequences for the selection of biocontrol agents since it will not be possible to identify closely co‐adapted natural enemies in the native range, necessitating more extensive host testing.

Colonization patterns of the invasive Brazilian peppertree, Schinus terebinthifolius, in Florida.

Invasive species are believed to spread through a process of stratified dispersal consisting of short-distance diffusive spread around established foci and human mediated long-distance jumps. Brazilian peppertree (Schinus terebinthifolius), native to South America, was introduced twice as an ornamental plant into Florida, USA, just over 100 years ago. A previous study indicated that these two introductions were from genetically differentiated source populations in the native range. In this study, we took advantage of these contrasting genetic signatures to study the spatial spread of Brazilian peppertree across its entire range in Florida. A combination of spatial genetic and geostatistical analyses using chloroplast and nuclear microsatellite markers revealed evidence for both diffusive dispersal and long-distance jumps. Chloroplast DNA haplotype distributions and extensive bands of intra-specific hybridization revealed extensive dispersal by both introduced populations across the state. The strong genetic signature around the original introduction points, the presence of a general southeast to northwest genetic cline, and evidence for short-distance genetic spatial autocorrelation provided evidence of diffusive dispersal from an advancing front, probably by birds and small mammals. In the northernmost part of the range, there were patches having a high degree of ancestry from each introduction, suggesting long-distance jump dispersal, probably by the movement of humans. The evidence for extensive movement throughout the state suggests that Brazilian peppertree will be capable of rapidly recolonizing areas from which it has been eradicated. Concerted eradication efforts over large areas or the successful establishment of effective biocontrol agents over a wide area will be needed to suppress this species.

Foraging behavior and life history of the stemborer parasitoid Cotesia flavipes (Hymenoptera : Braconidae)

The gregarious parasitoidCotesia flavipes (Hymenoptera: Braconidae) attacks larvae of pyralid and noctuid stemborers by entering the stemborer tunnel. The short-range foraging behavior of femaleC. flavipes was studied on stemborerinfested plants, in patches with host-related products and in artificial transparent tunnels. In addition, the longevity under specific conditions and the potential and realized fecundity of femaleC. flavipes were determined. Larval frass, caterpillar regurgitate, and holes in the stem are used in host location byC. flavipes. The response to host products byC. flavipes seems not to be host species specific. FemaleC. flavipes respond to frass from four stemborer species and one leaf feeder. No differences are found in the behavior ofC. flavipes on maize plants infested with the suitable host,Chilo partellus (Lepidoptera: Pyralidae), or the unsuitable host,Busseola fusca (Lepidoptera: Noctuidae). Attacking a stemborer larva inside the stem is risky for the parasitoid. The mortality rate of the parasitoids inside the stem is high: 30–40% of the parasitoids are killed by the spitting and biting stemborer larva.C. flavipes is relatively shortlived: without food the parasitoids die within 2 days; with food and under high-humidity conditions they die within 5–6 days.C. flavipes is proovigenic and has about 150 eggs available for oviposition. A relatively large proportion of the available egg load (20–25%) is allocated to each host, so femaleC. flavipes are egg depleted after parasitizing only five or six hosts.

Functional response of Orius albidipennis (Hemiptera: Anthocoridae) to Megalurothrips sjostedti (Thysanoptera: Thripidae)

Abstract A locally available anthocorid predator, Orius albidipennis Reuter, was evaluated as a candidate biocontrol agent for Megalurothrips sjostedti Trybom, a major pest of French beans, Phaseolus vulgaris (L), in Kenya. The functional response of adult O. albidipennis to larval and adult M. sjostedti was studied at 15, 25, and 28 °C and densities of 5, 10, 20, and 30 larval and adult M. sjostedti per cage, over 24 h. More larvae and adult M. sjostedti were killed at the higher densities and with an increase in temperature. The data provided good fit to both type I and II functional response models. Attack rates increased with temperature for both the second instar larva and adult M. sjostedti. Handling times for the larvae decreased with an increase in temperature while those for the adults increased with increase in temperature. The implications of these results are discussed.

Brazilian peppertree (Schinus terebinthifolius) in Florida and South America: evidence of a possible niche shift driven by hybridization

Brazilian peppertree (Schinus terebinthifolius Raddi, Anacardiaceae) was introduced into Florida from South America in the 1800s and commercialized as an ornamental plant. Based on herbaria records and available literature, it began to escape cultivation and invade ruderal and natural habitats in the 1950s, and is now considered to be one of Florida’s most widespread and damaging invasive plants. Historical records and molecular evidence indicate that two genetic lineages of Brazilian peppertree were established in Florida, one in Miami on the east coast and a second near Punta Gorda on the west coast. Since arriving, the distributions of these two types have greatly expanded, and they have extensively hybridized. Principal component analysis and reciprocal niche fitting were used to test the equivalency of climatic niches of the Florida populations with the climatic niches of the two South American chloroplast haplotype groups which established in Florida. Both approaches indicated a significant shift in niches between the parental populations in the native range and the invasive populations in Florida. The models, however, closely predicted the areas of initial establishment. We hypothesize that (1) Brazilian peppertree was able to gain an initial foothold in Florida due to niche similarity and (2) the current dissimilarity in native and exotic niches is due to hybridization followed by rapid selection of genotypes adapted to Florida’s climate. In addition, to examine the potential consequence of the introduction of additional genetic diversity from the native range on invasion success, a niche model constructed with occurrences of all native genotypes was projected onto the continental United States. The result of this test indicated that under such an event, the potential invasive range would greatly expand to cover most of the southeastern USA. Our study suggests that multiple introductions from disjunct regions in the native range can facilitate invasion success.

Host specificity of Psyttalia cosyrae (Hymenoptera: Braconidae) and the effect of different host species on parasitoid fitness

Abstract Psyttalia cosyrae (Wilkinson) (Hymenoptera: Braconidae) is a synovigenic, koinobiont larval-pupal parasitoid of Ceratitis cosyra (Walker) (Diptera: Tephritidae), and possibly other tephritid fruit flies. Host acceptance and suitability of medfly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), mango fruit fly, Ceratitis cosyra , Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), Ceratitis anonae Graham, and melon fruit fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae), for oviposition and development of this parasitoid were investigated. The effect of different host species on traits widely used to assess parasitoid fitness was also evaluated. Psyttalia cosyrae accepted all host species tested, but acceptance varied. In no choice tests, C. cosyra and C. capitata were accepted at a significantly higher rate than the other four species. The parasitoid successfully developed only in C. cosyra and C. capitata . Eggs oviposited in C. rosa , C. fasciventris , C. anonae , and B. cucurbitae were encapsulated. Developmental time was shorter in C. capitata than in C. cosyra , but parasitoid progeny emerging from the latter host were more fit, as measured by percent female progeny, adult size, egg load, and adult survival.

CHANGES IN THE DISTRIBUTION OF LEPIDOPTERAN MAIZE STEMBORERS IN KENYA FROM THE 1950S TO 1990S

Three hundred and ninety-two maize fields in the southern arable zone of Kenya were sampled for lepidopteran cereal stemborers from 1996–2000. Chilo partellus (Swinhoe) was the most abundant stemborer, and was found at all locations with elevations below 1500 m, and at some locations between 1500 and 2300 m. The highest density of C. partellus was in the semi-arid ecological zone of eastern Kenya. Chilo orichalcociliellus (Strand) was found in the lowland southern coastal area, and a few inland sites on the border of Tanzania in southeastern Kenya. Busseola fusca Fuller was dominant in highland areas. In the Lake Victoria Basin, which has an elevation of about 1100 m, B. fusca was dominant at some sites, but overall, C. partellus was more abundant. Sesamia calamistis Hampson was present at all elevations and all locations, but typically at low densities. Eldana saccharina (Walker) was found in two-thirds of the fields sampled in the Lake Victoria Basin. These results are compared with the distributions of the various stemborers in the 1950s to 1960s, as reported in the literature.RésuméTrois cent quatre vingt douze champs de maïs ont été échantillonnés dans la zone arable du sud Kenya pour les lépidoptères foreurs de tiges entre 1996 et 2000. Chilo partellus (Swinhoe) est le foreur le plus abondant, il a été trouvé dans toutes les localités situées à une altitude inférieure à 1500 m, et dans certaines localités entre 1500 et 2300 m. La plus forte densité de C. partellus a été trouvée dans les zones écologiques semi-arides de l’Est du Kenya. On trouve Chilo orichalcociliellus dans les basses terres de la zone côtière sud et dans plusieurs localités de l’intérieur des terres près de la frontière tanzanienne au sud-est du Kenya. Busseola fusca Fuller est dominant dans les hautes terres. Près du bassin du lac Victoria, qui a une altitude d’environ 1100 m, B. fusca est dominant dans certaines localités, mais d’une manière générale, C. partellus est l’espèce la plus abondante. Sesamia calamistis Hampson est présent à toutes les altitudes et toutes les localités, mais à faibles densités. On trouve Eldana saccharina (Walker) dans deux tiers des champs échantillonnés sur le bassin du lac Victoria. Ces résultats sont comparés avec la distribution des foreurs de tiges des années 1960 et 1960, rapportée dans la litérature.

Identification of behaviourally active components from maize volatiles for the stemborer parasitoid Cotesia flavipes cameron (hymenoptera: braconidae)

In the present study, Y-tube olfactometric assays confirmed that volatiles from maize seedlings infested with Chilo partellus larvae were more attractive to the borer’s larval endoparasitoid Cotesia flavipes, than volatiles from uninfested maize. Coupled gas chromatography-electroantennographic detector (GC-EAD) analysis of the volatiles from larvae-infested maize revealed six electrophysiologically active compounds on the antennae of the female parasitoid. These compounds were identified by GC-MS as (Z)-3-hexenyl acetate, linalool, (E)-4, 8-dimethyl-1, 3, 7-nonatriene, heptanal, (E)-ß-ocimene and a C-5 aliphatic compound. (E)-4, 8-Dimethyl-1, 3, 7-nonatriene was present in EAG-detectable amounts in the volatiles of uninfested seedlings. In bioassays, a blend comprised of (Z)-3-hexenyl acetate, linalool, (E)-4, 8-dimethyl-1,3,7-nonatriene, (E)-ß-ocimene and heptanal was significantly attractive to the parasitoid. Of the individual compounds, (Z)-3-hexenyl acetate was attractive at the doses tested while (E)-4,8-dimethyl-1,3,7-nonatriene and heptanal showed varying degree of attractiveness to the parasitoid at different doses. Linalool and (E)-ß-ocimene were unattractive at the same doses. The significance of these results is discussed.RésuméDans cette étude, des essais olfactométriques en tubes Y ont confirmé que les matières volatiles de jeunes plants de maïs infestés par des larves du foreur de tige, Chilo partellus attiraient plus de larves de Cotesia flavipes un endoparasitoïde de ce foreur, en comparaison des matières volatiles du maïs non infesté. L’analyse par chromatographie à phase gazeuse couplée avec un détecteur électro-antennographique des matières volatiles du maïs infesté de larves a révélé six composés avec des activités éléctro-physiologiques sur les antennes de la femelle du parasitoïde. Ces composés ont été identifiés par méthodes GC-MS comme (Z)-3-hexényle acétate, linalol, (E)-4, 8-diméthyle-1,3,7-nonatriène, heptanal, (E)-ß-ocimène et un autre composé, le C-5 aliphatique. (E)-4, 8-diméthyle-1,3,7-nonatriène était présent en quantités détectables par méthode EAG, dans les matières volatiles de jeunes plants non infestés. Au cours des essais biologiques, un cocktail fait de (Z)-3-hexényle acétate, de linalool, de (E)-4,8-diméthyle-1,3,7-nonatriène, de (E)-ß-ocimène et d’heptanal, attirait fortement le parasitoïde. Quant aux différents composés pris isolément, (Z)-3-hexényle acétate était attrayant aux doses testées tandis que (E)-4, 8-diméthyle-l, 3, 7-nonatriène et heptanal montraient des degrés variables d’attractivité à différentes doses. Le linalol et (E)-ß-ocimène ne montraient pas d’attrait aux mêmes doses. L’article discute de la signification des résultats obtenus.

The temporal correlation and spatial synchrony in the stemborer and parasitoid system of Coast Kenya with climate effects

Abstract The spatial synchrony and the temporal auto-correlationship of the exotic stemborer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) and the indigenous Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Chilo orichalcociliellus (Strand) (Lepidoptera: Crambidae), and crosscorrelationship with their indigenous and introduced larval parasitoids Cotesia sesamiae (Cameron) and Cotesia flavipes Cameron (Hymenoptera: Braconidae) was studied using 3-year data collected in coastal Kenya. An autoregressive model was used to study the effect of climatic stochasticity or population density-dependent factors on stemborer populations. It appeared that rainfall did have a direct impact on stemborers in the south coast and an indirect one in the north coast. Spatial nonparametric correlation functions (SNCF) and cross-correlation functions (SNCCF) were applied for spatial synchrony analysis. The regional synchrony of Ch. partellus and S. calamistis decreased and that of Ch. orichalcociliellus increased after the introduction of Co. flavipes. The positive crosscorrelation coefficient between stemborers and parasitoids suggests a synchrony between the pest and its natural enemy.

Temperature-dependent development, cold tolerance, and potential distribution of Gratiana boliviana (Coleoptera: Chrysomelidae), a biological control agent of tropical soda apple, Solanum viarum (Solanaceae)

Abstract The leaf beetle Gratiana boliviana Spaeth (Coleoptera: Chrysomelidae) was introduced from South America into the southeastern United States in 2003 as a classical biological control agent of tropical soda apple, Solanum viarum Dunal (Solanaceae). Temperature-dependent development and survival studies revealed that development was completed at temperatures >16°C and ≤34°C. The number of degree-days required to complete one generation was 341 and the estimated lower developmental threshold was 13.37°C. Using nonlinear regression, the upper lethal threshold was estimated to be 34–35°C. Cold tolerance studies revealed that the lethal time for 90% of adults (LT90) was 12.6 days at 5°C and 8.68 days at 0°C. Based on the developmental and cold tolerance data, a map predicting the areas of establishment and number of generations per year was generated, which suggests that the northern extent of the G. boliviana range in the USA will be near 32–33° north latitude. Fewer generations per year in more northern areas of the southeastern USA may decrease the effectiveness of this biological control agent.