Evaluation of green lacewings, Chrysoperla plorabunda (Fitch) (Neurop., Chrysopidae), for augmentative release against Toxoptera citricida (Hom., Aphididae) in citrus

Larvae of the lacewing Chrysoperla plorabunda (Fitch) were evaluated in laboratory and field tests for potential to control the brown citrus aphid, Toxoptera citricida (Kirkaldy) in inundative releases. Larvae surviving to pupation consumed an average of 1676, 1297, 392, 165 and 130 1st–4th instar T. citricida nymphs and apterous adults, respectively, and the mean developmental time was 27.0, 23.0, 16.5, 13.8 and 18.3 days, respectively. The average pupation rate was 37.5%, but only 6.3% of pupae yielded adults. Developmental time and survival to pupation varied with the life stage of aphids fed to larvae, 4th instars yielding the highest survival and shortest developmental time. Development of C. plorabunda was compared on diets of T. citricida and Aphis spiraecola . Only 6.3% of larvae completed development on T. citricida , whereas 37.5% yielded adults on A. spiraecola . Larvae consumed more of the brown T. citricida than the green A. spiraecola in a choice test on a white background, but no preference was evident when aphids were offered on a black background. Two separate field trials were performed in citrus groves with T. citricida infestations in which an average of 275 and 116 C. plorabunda larvae/tree were released, respectively. The rate of T. citricida colony maturation (= survival to alate production) was very low in the first trial, and relatively high in the second trial, but did not differ between control and release trees in either trial. The most apparent cause of aphid colony mortality was predation by the coccinellids Cycloneda sanguinea L. and Harmonia axyridis Pallas. Despite acceptance of T. citricida in the laboratory, very few C. plorabunda larvae were observed feeding on aphid colonies on release trees.     

Three homopteran pests of citrus as prey for the convergent lady beetle: suitability and preference

The convergent lady beetle, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), is an important predator of soft-bodied insect pests in many regions of the United States, but generally uncommon in Florida citrus. Certain citrus producers in Florida recently initiated releases of commercially available H. convergens from California against the Asian citrus psyllid Diaphorina citri Kuwayama, vector of Huanglongbing or citrus greening disease. However, there is little information on potential efficacy of this predator against the psyllid or other pests of citrus. Preference, development, and reproduction by H. convergens was evaluated on freshly collected nymphs of D. citri, brown citrus aphid Toxoptera citricida Kirkaldy, green citrus aphid Aphis spiraecola Patch, and frozen eggs of the flour moth Ephestia kuehniella Zeller. Larvae preferred D. citri over T. citricida in two-way choice tests and consumed more D. citri or A. spiraecola than T. citricida in no-choice tests. Adults consumed equal numbers of all three species in both tests. Development times of larvae at 25.5±0.05°C on A. spiraecola were longer than on the other three diets. Larval survival and pupation times did not differ among diets. Females lived longer than males irrespective of diet, and longevity of both genders was greatly increased on E. kuehniella compared with D. citri and A. spiraecola. Life table analysis indicated that H. convergens should increase on all three species, with a greater potential on psyllids than aphids. Further studies are warranted to assess establishment and persistence of this potential biological control agent in the Florida citrus environment.     

Intra- and interspecific interactions between Lysiphlebus testaceipes and Lipolexis scutellaris (Hymenoptera: Aphidiidae) reared on Toxoptera citricida (Homoptera: Aphididae)

Classical biological control of the brown citrus aphid Toxoptera citricida Kirkaldy in Florida has involved the release of Lipolexis scutellaris Mackauer. Lysiphlebus testaceipes Cresson is already present in Florida and also parasitizes T. citricida. Because parasitoid-parasitoid interactions may affect the establishment of a newly introduced parasitoid species, intra- and interspecific larval interactions of both parasitoids were studied in the laboratory using T. citricida reared on citrus. Five time intervals were allowed between successive oviposition opportunities. Early developmental times were determined for both parasitoids: eggs of L. testaceipes and L. scutellaris hatched after 54.3 and 61.7 h, while molt to second instar occurred after 73.3 and 87.1 h, respectively, after oviposition at 22 degrees C. At intervals <12 h, both parasitoids had a greater tendency to multiparasitize than to superparasitize, and the tendency to superparasitize or multiparasitize decreased with an increase in time between successive oviposition opportunities. Of the 10 interspecific interactions studied, 5 produced a winning wasp species, 3 of which could be explained by the hypothesis of physical conflict. A combination of development time, age of competing larvae, and oviposition sequence were responsible for the outcomes observed. Neither parasitoid proved to be intrinsically superior when interspecific competition occurs in second- and third-instar T. citricida, indicating there is no reason to suggest that they cannot coexist in Florida citrus groves.     

Status of biological control by egg parasitoids of Diaprepes abbreviatus (Coleoptera: Curculionidae) in citrus in Florida and Puerto Rico

Eggs of Diaprepes abbreviatus (L.) were routinely monitored in citrus groves at ten locations in Florida during 1997 and 1998 to study egg parasitism. One citrus location was studied in Puerto Rico. No native parasitoids were recovered from 1,337 D. abbreviatus egg masses studied in Florida citrus. In contrast, an average of 35.5% (range 12.5 to 68.8%) parasitism of egg masses was reported in Puerto Rico. The parasitoids Aprostocetus gala, Horismenus spp, and Quadrastichus haitiensis were recovered from the eggs of D. abbreviatusfstudied in Puerto Rico. The Horismenus parasitoids were suspected hyperparasitoids. Releases of the parasitoid Ceratogramma etiennei from Guadeloupe were initiated during 1998 at each of the Florida research sites. By the end of 1998, C. etiennei had been recovered from D. abbreviatus eggs at two of nine locations in Florida citrus. The parasitoid was recovered from 1 of 34 egg masses at one of these locations during the month of September and from 3 of 34 egg masses at the other location during the month of November. Whether or not C. etiennei establishes itself at one or more locations in Florida remains to be seen.     

Genome Similarity Implies that Citrus-Parasitic Burrowing Nematodes do not Represent a Unique Species

Burrowing nematodes from Central America, Dominican Republic, Florida, Guadeloupe, Hawaii, and Puerto Rico were characterized for their ability to parasitize citrus, but citrus parasites were found only in Florida. Sequence tag sites originally amplified from a citrus-parasitic burrowing nematode were polymorphic among 37 burrowing nematode isolates and were not correlated with citrus parasitism, nematode isolate collection site, or amplification of a 2.4-kb sequence tag site (DK#1). Results of a RAPD analysis and characterization of the isozymes phosphoglucose isomerase, lactate dehydrogenase, and malate dehydrogenase indicated that the burrowing nematode isolates were highly similar. Citrus parasitism in Florida appears to be associated with limited changes in the burrowing nematode genome. Findings did not substantiate a previous report that R. citrophilus was present in Hawaii. Overall, these data do not support assignment of sibling species status to burrowing nematodes that differ with respect to citrus parasitism.     

Effects of prey aphid species on the abundance of a parasitoid and two predator species in aphid colonies attended by ants on citrus

This study focused on three species of enemies, the parasitoid wasp Lysiphlebus japonicus Ashmead (Hymenoptera: Aphidiidae), the ladybird Scymnus posticalis Sicard (Coleoptera: Coccinellidae) and the predatory gall midge Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), all of which are able to exploit aphids attended by ants. I experimentally evaluated the effects of prey aphid species on the abundance of each of the three enemy species in ant‐attended aphid colonies on citrus. The aphids compared were Aphis gossypii Glover versus Aphis spiraecola Patch in late spring, and Toxoptera citricidus (Kirkaldy) versus A. spiraecola in late summer (all, Hemiptera: Aphididae). Colonies of the three aphid species were attended by the ant Pristomyrmex punctatus Smith (Hymenoptera: Formicidae). The initial number of attending ants per individual aphid did not differ significantly between the colonies of the two aphid species compared in each season. Between A. gossypii and A. spiraecola, there was no significant difference in the number of mummies formed by the parasitoid or foraging larvae of each of the two predators per aphid colony. A significant difference was detected between T. citricidus and A. spiraecola for each of the three enemy species, with a far greater number of L. japonicus mummies in T. citricidus colonies and distinctly more larvae of each of the two predators in A. spiraecola colonies. Thus, the abundance of each of the three enemy species in ant‐attended aphid colonies was significantly influenced by the species of the prey aphids, with the three enemies showing different responses to the three aphid species.     

Development and Reproduction of Ladybeetles (Coleoptera: Coccinellidae) on the Citrus Aphids Aphis spiraecola Patch and Toxoptera citricida (Kirkaldy) (Homoptera: Aphididae)

Seven species of Coccinellidae inhabiting citrus groves in Florida were evaluated for ability to develop and reproduce on the citrus aphids Toxoptera citricida (Kirkaldy) and Aphis spiraecola Patch. Choice tests performed with adults and larvae indicated that both aphid species were generally acceptable prey. Coccinella septempunctata L., Coleomegilla maculata fuscilabris (Mulsant), Coelophora inaequalis F., and Olla v-nigrum Mulsant were unable to complete development on either aphid. Hippodamia convergens Guerin larvae completed development on A. spiraecola with 68% survival; none survived on T. citricida. Only Cycloneda sanguinea (L.) and Harmonia axyridis Pallas completed development on both A. spiraecola (60 and 70% survival, respectively) and T. citricida (100 and 95% survival, respectively). Larval developmental time was shorter on T. citricida than on A. spiraecola, and resulting adults were heavier, differences being more pronounced in H. axyridis. Females of C. septempunctata, C. inaequalis, and O. v-nigrum produced viable eggs on T. citricida. O. v-nigrum did not produce eggs on A. spiraecola. Females of C. m. fuscilabris and H. axyridis produced no eggs on A. spiraecola and mostly infertile eggs on T. citricida. Female H. convergens laid twice as many eggs feeding on T. citricida as on A. spiraecola and egg viability was similar. C. sanguinea females laid similar numbers of eggs on both aphids, but eggs produced on A. spiraecola had higher fertility. Pollen added to the T. citricida diet temporarily improved the fertility of H. axyridis females, but not that of C. sanguinea females. C. sanguinea was judged the best candidate for augmentative biocontrol of T. citricida, the primary vector of citrus tristeza virus.     

Evaluation of aboveground and belowground biomass recovery in physically disturbed seagrass beds

Several studies addressed aboveground biomass recovery in tropical and subtropical seagrass systems following physical disturbance. However, there are few studies documenting belowground biomass recovery despite the important functional and ecological role of roots and rhizomes for seagrass ecosystems. In this study, we compared the recovery of biomass (g dry weight m(-2)) as well as the biomass recovery rates in ten severely disturbed multi-species seagrass meadows, after the sediments were excavated and the seagrasses removed. Three sites were located in the tropics (Puerto Rico) and seven in the subtropics (Florida Keys), and all were originally dominated by Thalassia testudinum. Total aboveground biomass reached reference values at four out of ten sites studied, two in the Florida Keys and two in Puerto Rico. Total belowground biomass was lower at the disturbed locations compared to the references at all sites, apart from two sites in the Florida Keys where the compensatory effect of opportunistic species (Syringodium filiforme and Halodule wrightii) was observed. The results revealed large variation among sites in aboveground and belowground biomass for all species, with higher aboveground recovery than belowground for T. testudinum. Recovery rates for T. testudinum were highly variable across sites, but a general trend of faster aboveground than belowground recovery was observed. Equal rates between aboveground and belowground biomass were found for opportunistic species at several sites in the Florida Keys. These results indicate the importance of belowground biomass when assessing seagrass recovery and suggest that the appropriate metric to assess seagrass recovery should address belowground biomass as well as aboveground biomass in order to evaluate the full recovery of ecological services and functions performed by seagrasses. We point out regional differences in species composition and species shifts following severe disturbance events and discuss ecological implications of gap dynamics in multi-species seagrass meadows.     

Responses of Lipolexis oregmae (Hymenoptera: Aphidiidae) to different instars of Toxoptera citricida (Homoptera: Aphididae)

The effects of host instar of Toxoptera citricida Kirkaldy (Homoptera: Aphididae) on the performance of the parasitoid Lipolexis oregmae (Gahan) (Hymenoptera: Aphidiidae), originally Lipolexis scutellaris Mackauer, were evaluated in an effort to increase basic knowledge of this host-parasitoid association, improve field sampling methods, and potentially predict the success of parasitism in the field. L. oregmae was able to oviposit and develop in all four instars of T. citricida; however, there are differences in the quality of different host instars. Although second-instar hosts produce more L. oregmae progeny and a higher female-biased sex ratio, fourth-instar hosts produce L. oregmae progeny that are larger and have a higher realized fecundity. However, fourth-instar hosts require a longer handling time and expose the parasitoid female to more aphid behavioral defenses than do second-instar hosts. Additionally, results suggest that fourth-instar hosts may elicit a physiological immune response to parasitism; when aphids were observed being stung once, the number of L. oregmae larvae present on dissection after 4 d and the number of eclosed adults was lower in fourth- than in second-instar hosts. Pupal mortality of L. oregmae was also higher in fourth-instar hosts compared with second-instar hosts. The results of this study confirm that L. oregmae has a high reproductive rate and low incidence of incomplete parasitization on this host and is one of only a few natural enemies able to complete development in all instars of the brown citrus aphid in Florida.     

Population patterns of

In the first quantitative study of an endemic New Zealand aphid, the only known field populations of the rare Paradoxaphis plagianthiwere monitored for two years from 1999 to 2001. The species appears to be anholocyclic, persisting viviparously throughout the year on its deciduous host tree, the lowland ribbonwood (Plagianthus regius). Local aphid abundance increased rapidly in spring as new leaves appeared, but collapsed abruptly in November, probably due to dispersal and a decline in resource quality. Numbers then remained low until leaf senescence in late autumn, when they increased again to a smaller Peak. Aphids persisted on plump terminal buds for the short time in winter when host trees were completely leafless. Though several colonization events were observed in late spring, these were generally unsuccessful in establishing new populations, and local colony extinction was common. The apparent rarity of P. plagianthi suggests it could be threatened by introduced predators and competitors, or climate change.     

Assessment of current rates of Diadema antillarum larval settlement

The generally slow and incomplete recovery of the long-spined sea urchin, Diadema antillarum, from the 1983–84 Caribbean-wide die-off, particularly in the Florida Keys, USA, raises the question of factors limiting population recovery. This study sought to quantify larval settlement rates as an indicator of larval supply at two sites in the Florida Keys, utilizing methods comparable to an historic study. Settlement at two sites in southwest Puerto Rico was also examined as a comparison of present-day settlement rates at a site where D. antillarum recovery has been moderate. Monthly settlement rates were low (max < 2 m⁻²) and did not differ between the two sites examined in the Florida Keys. Settlement was significantly higher at only one of the Puerto Rico sites (max 16 m⁻²), but still an order of magnitude lower than that reported for historic populations in Cura?ao (1982–83). Results are consistent with the hypothesis of low larval supply limiting D. antillarum recovery in the Florida Keys.     

Relative importance of fertiliser addition to plants and exclusion of predators for aphid growth in the field

Herbivore dynamics and community structure are influenced both by plant quality and the actions of natural enemies. A factorial experiment manipulating both higher and lower trophic levels was designed to explore the determinants of colony growth of the aphid Aphis jacobaeae, a specialist herbivore on ragwort Senecio jacobaea. Potential plant quality was manipulated by regular addition of NPK-fertiliser and predator pressure was reduced by interception traps; the experiment was carried out at two sites. The size and persistence of aphid colonies were measured. Fertiliser addition affected plant growth in only one site, but never had a measurable effect on aphid colony growth. In both habitats the action of insect predators dominated, imposing strong and negative effects on aphid colony performance. Ants were left unmanipulated in both sites and their performance on the aphid colonies did not significantly differ between sites or between treatments. Our results suggest that, at least for aphid herbivores on S. jacobaea, the action of generalist insect predators appears to be the dominant factor affecting colony performance and can under certain conditions even improve plant productivity.     

Molecular and field analyses of the fortuitous establishment of Lipolexis oregmae (Hymenoptera: Aphidiidae) in Jamaica as a natural enemy of the brown citrus aphid

The brown citrus aphid, Toxoptera citricida (Kirkaldy), is a serious pest of citrus because it efficiently transmits citrus tristeza closterovirus (CTV). The invasion of Jamaica's citrus by T. citricida resulted in serious economic losses and the importation and consideration was given to the establishment of Lipolexis oregmae Gahan (Hymenoptera: Aphidiidae) in a classical biological control program. Prior to introducing L. oregmae, we conducted a survey to determine the abundance of Lysiphlebus testaceipes Cresson (Hymenoptera: Aphidiidae) in T. citricida. A high-fidelity PCR analysis was conducted using Lysiphlebus- and Lipolexis-specific ITS2 rRNA primers on alcohol-preserved brown citrus aphids and the results were positive for both parasitoids. The fortuitous establishment of L. oregmae in Jamaica was surprising, and was confirmed by rearing adults from parasitized aphids and obtaining taxonomic confirmation based on morphology. In addition, its identity was confirmed molecularly by cloning and sequencing 16S, 12S, and COI sequences from the Florida colony of L. oregmae and from Jamaican specimens. The three DNA sequences were 100% identical for specimens from both sources. The phylogenetic analysis using 16S sequences indicated a close relationship of the Florida and Jamaica populations of L. oregmae with L. gracilis. During 2005, an island-wide survey of citrus in six parishes confirmed that both L. testaceipes and L. oregmae commonly parasitize T. citricida, but that L. oregmae was the more widely distributed and abundant parasitoid. The pathway by which L. oregmae might have entered Jamaica is discussed.     

Role of aphid predator guild in controlling spirea aphid populations on apple in West Virginia,USA

Spirea aphid populations and their predators were studied on apple to identify predators of importance in controlling aphid populations. Methods included random and non-random sampling from apple orchards in West Virginia, USA, sentinel aphid colonies, laboratory feeding studies, and predator exclusion studies. Aphidoletes aphidimyza (Diptera: Cecidomyiidae), chrysopids (Neuroptera: Chrysopidae), Harmonia axyridis (Coleoptera: Coccinellidae), and Orius insidiosus (Hemiptera: Anthocoridae) were the most abundant predators associated with spirea aphid colonies on apple. Parasitoids were all but absent in the study. Abundance of all predators was density dependent with greater responses to aphid populations at the orchard scale than to tree or individual colony scales. A. aphidimyza, O. insidiosus, chrysopids, and syrphids (Diptera) had the greatest degree of density dependence on aphid populations, and spiders showed inverse density dependence. Exclusion of predators with both cages and insecticides produced significantly higher aphid populations. Because of high abundance, good synchrony with aphid populations, and high impact per individual, H. axyridis adults were the most important spirea aphid predator on apple.     

Seed predation,disease and germination on landslides in Neotropical lower montane wet forest

Abstract. Seed mortality (caused by predators and pathogens) and germination were compared between Puerto Rico and Costa Rica on landslides in lower montane wet forest. Seeds of six common species on five Puerto Rican landslides and four common species on two Costa Rican landslides were used with a Cecropia species and a Gonzalagunia species included at both sites. In the Puerto Rican experiments Cecropia schreberiana was the only species to show significant seed predation (which was due to insects), pathogens grew from all species and fewer seeds were lost to predators than pathogens. Also in Puerto Rico mean germination across all species was 57 % before dispersal (filled seeds collected while still on the tree) and 71 % after, with Phytolacca rivinoides seeds germinating most abundantly, followed in descending order by Ocotea leucoxylon, Cecropia spec, Miconia racemosa, Palicourea riparia and Gonzalagunia spicata. In the Costa Rican experiments three species had significant predation: Cecropia polyphlebia and Urera caracasana (both due to insects) and Witheringia coccoloboides (due to mammals); pathogenic disease caused more seed loss than predation, and germination was high (61 % pre-dispersal, 69 % post-dispersal). Similarities between these island and mainland sites included (1) percentage of seeds lost to predation and percentage lost to pathogens (all in the 5–15 % range), (2) generalist pathogens which claimed more seeds than predators and (3) majority germination with a general increase after dispersal. Finally sites were dissimilar only in the number of species with significant predation loss and whether it was by insects or mammals, casting doubt on the traditional island/mainland dichotomy.     

Adult male height in an American colony: Puerto Rico and the USA mainland compared, 1886–1955

The links between adult height and socioeconomic-political marginality are controversial. We test hypotheses by comparing secular trends between two groups of USA adult male citizens born during 1886-1930: (a) 9805 men surveyed in Puerto Rico during 1965 and (b) 3064 non-Hispanic Whites surveyed on the mainland during 1971-1975. Puerto Rico provides an apt case study because it is the oldest colony in the world and was the poorest region of the USA during the 20th century. During the period considered the average adult man in Puerto Rico was 164.8 cm tall, 8.3 cm shorter than the average adult man on the mainland (173.1cm). Both groups experienced secular improvements in height, with men on the mainland having higher rates than men in Puerto Rico. In neither case were results statistically significant. The modest changes in Puerto Rico likely reflect the offsetting role of improved health and a stagnant rural economy during the first half of the 20th century.     

Sucrose octanoate toxicity to brown citrus aphid (Homoptera: Aphididae) and the parasitoid Lysiphlebus testaceipes (Hymenoptera: Aphidiidae)

We report the toxicological effects of a new biorational, synthetic sucrose octanoate (AVA Chemical Ventures L.L.C., Portsmouth, NH), on brown citrus aphid, Toxoptera citricida (Kirkaldy), nymphs and adults and to its native parasitoid Lysiphlebus testaceipes (Cresson). Sucrose octanoate topically applied was equally toxic to brown citrus aphid adults and nymphs with LC50 and LC90 values ranging from 356 to 514 and 1029 to 1420 ppm, respectively. Mortalities of both stages did not differ significantly over time during the 3-24-h sampling period. Dry residues of sucrose octanoate exhibited similar levels of toxicity to both nymphs and adults. Mortality ranged from 60 to 70% at 6,000 ppm 4 h after exposure. L. testaceipes was not harmed by treatments as high as 4,000 ppm of sucrose octanoate as long as the parasitoid had mummified before treatment. Based on these results, sucrose octanoate would be a useful biorational in citrus integrated pest management programs.     

Establishment of the exotic parasiteTetrastichus haitiensis [Hym.: Eulophidae] and recovery of a newTrichogramma [Hym.: Trichogrammatidae] from root weevil egg masses in Florida

The exotic root weevil egg parasite,Tetrastichus haitiensis Gahan, imported from Puerto Rico and released in Florida between 1969 and 1971, was found established on citrus root weevil egg masses in 1978 near Oakhill, Florida. It was also recovered there from field-collected weevil egg masses from June to August 1978 and from citrus bouquets containing egg masses placed in the grove during July and August 1978. In addition, a new species ofTrichogramma was discovered. In the laboratory, this species parasitized egg masses of 4 species of weevils that attack citrus in Florida. These areDiaprepes abbreviatus (L.),Pachnaeus litus (Germar),P. opalus (Olivier) andArtipus floridanus Horn.     

3种抑制剂对褐色橘蚜乙酰胆碱酯酶活性的影响

乙酰胆碱酯酶(Acetylcholinesterase,ACh E;EC3.1.1.7)作为有机磷和氨基甲酸酯类杀虫剂的作用靶标,一直是昆虫毒理学领域研究的热点。本研究采用微量滴度酶标板法研究了褐色橘蚜Toxoptera citricida不同发育阶段ACh E的生化特性及个体活性频率,离体条件下分析了3种药剂对ACh E的影响。结果表明,无翅成蚜对底物碘化硫代乙酰胆碱亲和力显著高于若蚜;就个体活性分布频率而言,25%-30%的无翅成蚜分布在9.5-10.5 nmol/(min·insect)区间,而50%-55%的若蚜分布在2-3 nmol/(min·insect)区间;离体条件下,毒扁豆碱、残杀威、异丙威等3种杀虫剂对褐色橘蚜ACh E有显著的抑制作用,与成蚜相比,若蚜ACh E对3种药剂更敏感,而毒扁豆碱对褐色橘蚜无翅成蚜与若蚜ACh E的抑制作用最好。本研究表明褐色橘蚜成蚜与若蚜生化特性及对药剂的敏感性存在显著差异。