Implications of guppy (Poecilia reticulata) life‐history phenotype for mosquito control

Guppies (Poecilia reticulata) are frequently introduced to both natural and artificial water bodies as a mosquito control. Laboratory studies have demonstrated that guppies can consume large numbers of larval mosquitoes. Our study investigates how intraspecific variability in guppy phenotype affects their importance as a mosquito biocontrol and how habitat conditions (natural ponds vs. water storage containers) may influence insect biomass and guppy feeding. Using a blocked experimental design, we established stream‐side mesocosm ponds with half receiving gravel substrate to simulate pond‐bottom habitat. To provide realistic diet choices and insect abundances, we allowed the mesocosms to colonize naturally with aquatic insect larvae for 1 month before introducing guppies. We tested two distinct guppy phenotypes (from high‐ and low‐predation streams) alongside fish‐free controls. After 1 month, we measured insect biomass in the mesocosms and examined guppy gut contents to document direct predation. While overall insect biomass was not significantly different across the three fish treatments, we observed a significant reduction in mosquito biomass in fish treatments compared to fish‐free controls, as well as intraspecific differences in feeding. Overall insect biomass was significantly higher in mesocosms without gravel, while habitat condition had no effect on mosquito biomass. As guppy phenotype responds to changes in their environments, it is an important consideration for biocontrol policy to anticipate potential ecosystem effects. We close by relating our findings to other studies and by discussing the implications and potential risks of using guppies to control mosquitoes.     

Biology and host preference of the planthopper Taosa longula (Hemiptera: Dictyopharidae), a candidate for biocontrol of water hyacinth

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae) is a planthopper from the South American tropics that feeds on water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae). The biology of T. longula was studied in the laboratory and field to evaluate it as a potential biological control agent for this widespread aquatic weed. The developmental time of nymphs was recorded at different temperatures (15, 19, 23, 25, 27 and 30 °C), and developmental threshold temperatures were obtained for the different instars. The host range was evaluated in terms of development and feeding preference. Development from instar I to adult was recorded in two no-choice trials, one with cut leaves of Pontederiaceae, and a second with growing whole plants. In the cut-leaf tests, adults were obtained from Pontederia cordata var. cordata, P. rotundifolia and water hyacinth. In the whole plant test, T. longula adults were obtained only from water hyacinth. Feeding preference was evaluated by means of a paired-choice test with 10 T. longula first instars on whole plants of P. c. cordata, P. rotundifolia and water hyacinth. The number of insects that fed on water hyacinth was significantly higher than on P. c. cordata and P. rotundifolia. Taosa longula showed a clear preference for water hyacinth and exhibited warm climate requirements, making it an attractive candidate for water hyacinth biological control in tropical and subtropical areas.     

Prey preference of predatory mite Amblyseius swirskii (Acari: Phytoseiidae) on Tetranychus urticae (Acari: Tetranychidae) and Bemisia tabaci (Hemiptera: Aleyrodidae)

Tetranychus urticae Koch (Acari: Tetranychidae) and Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) are major pests in greenhouse crops. Recently, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) was shown to be an effective biological control agent of both pests. Therefore, the prey preference of A. swirskii was determined using immature stages of T. urticae and B. tabaci in three various treatments based on Manly's β preference index (β). These treatments consisted of immature stages of two prey species (egg, first and second instar nymphs) with densities 12:12, 6:6 and 3:3, respectively, and with 13 replicates. After 24?h starvation, same-aged females of A. swirskii were added to the leaf discs. All experiments were done on bean leaf discs in Petri dishes (8?cm in diameter) in laboratory conditions with 25?±?2°C, 70?±?5% relative humidity and the photoperiod of 16L:8D hours. Comparing the preference indices using t-tests indicates a significant preference of the predator on eggs (t?=?10.80, df?=?24, P?t?=?8.17, df?=?24, P?T. urticae than B. tabaci. Our findings suggest that developmental stages of prey have effect on the prey selection by A. swirskii.     

Food preference of the rove beetle, Atheta coriaria Kraatz （Coleoptera： Staphylinidae） under laboratory conditions

A study, involving laboratory choice tests, was conducted to determine the feeding behavior, based on food preference, of the adult and larval stage of the rove beetle, Atheta coriaria Kraatz when presented with both fresh moistened oatmeal and second instar fungus gnat, Bradysia sp. nr. coprophila （Lintner） larvae in Petri dishes. Rove beetles used in this study came from a laboratory-reared colony. A rating scale from 1 to 5, based on percent missing （1 = 0 to 10%, 2 = 11 to 30%, 3 = 31 to 50%, 4 = 51 to 75%, and 5 = 76 to 100%）, was used to objectively assess the amount of oatmeal and number of fungus gnat larvae consumed by each rove beetle adult and larva. In all the choice tests, A. coriaria adults and larvae preferred to feed on fungus gnat larvae （78% and 69%, respectively） significantly more so than oatmeal （9% and 5%, respectively） based on the amount of oatmeal and number of fungus gnat larvae consumed after 4 and 6 hours. There were relatively minimal differences in the amount of food consumed for both adults and larvae after 4 and 6 hours. The results of this study indicate that oatmeal may be an inexpensive supplemental food source, during the rearing process, which will not inhibit the effectiveness of rove beetles to control fungus gnat larvae when released into greenhouses.     

水稻矮缩病毒对黑尾叶蝉取食及产卵偏好性的影响

水稻矮缩病毒（Rice dwarf virus, RDV）是水稻普通矮缩病（Rice dwarf disease）的病原,主要依赖黑尾叶蝉Nephotettix cincticeps经卵以持久增殖方式传播。本研究采用室内试验观测了带毒与无毒的黑尾叶蝉在健康及感病水稻间的取食、产卵选择趋性。取食偏好性试验发现,无毒叶蝉对感病水稻趋性更强,从观测的第8小时开始达显著差异水平;带毒叶蝉则对健康水稻趋性更强,在观测的第24小时开始达到显著差异水平,表明RDV侵染水稻会引起黑尾叶蝉取食偏好性的改变。产卵偏好性试验发现无毒及带毒黑尾叶蝉在健康及感病水稻间3个观测指标（每植株卵块数、每卵块的卵量及每植株上的总卵量）均无显著差异,表明RDV侵染水稻对黑尾叶蝉产卵选择偏好性无显著影响。本文初步明确RDV对黑尾叶蝉取食和产卵偏好性的影响,为揭示介体昆虫-病毒-寄主植物三者之间的互作机制提供佐证。     

柑橘大实蝇对不同柑橘品种的产卵偏好和幼虫取食选择

【目的】掌握柑橘大实蝇Bactrocera minax对不同品种柑橘的产卵偏好,以及与幼虫取食喜嗜性的关系。【方法】我们用五点取样法分别调查了自然条件下不同品种柑橘果园的虫果率,统计了各品种柑橘虫果基半部和端半部产卵痕量和卵量,并在实验室内采用培养皿桔瓣选择法研究了其幼虫对不同柑橘品种果实的取食选择。【结果】在未采取防控措施的情况下,果树面朝杂树林的方位虫果率显著高于其他方位;同一片受害柑橘园内,不同柑橘品种的虫果率为脐橙Citrus sinensis cv. Navel、酸橙C. aurantium＞冰糖橙C. sinensis cv. Bingtang、天草(Amakusa)、蜜橘C. reticulata cv. Satsuma＞沙田柚C. maxima cv. Shatian＞椪柑C. reticulata cv. Ponkan;柑橘大实蝇产卵痕数和卵量均为橙类（脐橙、酸橙和冰糖橙）大于橘类（天草、蜜橘和椪柑）和沙田柚（P＜0.05）;除蜜橘外,所调查的其他柑橘品种端半部的产卵痕数显著多于基半部（P＜0.05）;幼虫对不同品种柑橘橘瓣肉的取食选择顺序依次为：脐橙、酸橙＞冰糖橙＞天草、南橘C. reticulata cv. Nanju＞蜜橘＞椪柑＞沙田柚。【结论】结果提示,柑橘大实蝇成虫偏向于选择幼虫所喜嗜的橙类品种产卵,且产卵量更多。     

Reproductive biology of Galaxias maculatus (Jenyns 1842) in the Río Ovando,a high‐latitude environment in southernmost Patagonia,Argentina

This study establishes the reproductive cycle, batch fecundity and oocyte diameter of a diadromic population of the puyen, Galaxias maculatus, in the Río Ovando, Tierra del Fuego, (54°S), at the southernmost limit of its distribution. Given the short ‘favourable season’ in relation to other populations of the species (in terms of temperature, photoperiod and food availability), the study also explores the trade‐offs between feeding and oocyte production and between phases of growth and reproduction. The reproductive cycle was analyzed by the monthly evolution of the proportion of gonadal maturity stages (determined from microscopic examination of the gonads). Oocytes were measured using a micrometric ocular scale and classified by diameter and morphological characteristics; absolute fecundity was established as the total number of hydrated oocytes per ovary. The studied population exhibits a repetitive spawning strategy, given the coexistence of post‐ovullatory follicles and hydrated oocytes in histological sections and the presence in ripe ovaries of an intermediate cohort of yolked oocytes ready for hydration. Individual fecundity is lower (1422 ± 422 oocytes/ovary) than in other puyen populations, but the egg production increases through individual repetitive spawnings during the protracted spawning period (from October to February). Females attain larger sizes than those of other South American populations (the largest female reaching 115 mm total length), maximizing its potential fecundity. The present paper contributes to the knowledge of the variability of reproductive traits of G. maculatus in relation to diadromic populations, given that the bulk of information in South America refers to landlocked populations.     

Increased drag, and thus lower speed: a cost for morphological defence in Bosmina (Eubosmina) (Crustacea: Cladocera)

1. The swimming speed of two forms, an extreme and a typical, within the cladoceran subgenus Eubosmina were examined using a three-dimensional video-technique. The extreme form has a very high carapax and extremely long antennule, features probably involved in predator defence.
2. It was found that the extreme form swam almost 40% slower than the typical form.
3. Calculations show that the extreme form had to work at least 12% harder to swim at the same speed, or if it used the same amount of energy to swim, the extreme form would swim 6% slower. Increased drag, because of its distinguishing carapax and antennule, is thus the most likely explanation for the slower swimming speed of the extreme form, assuming it selects the same power output.
4. Swimming speed can be correlated to food intake either by the frequency of hits to edible food particles or by the time to swim from a poor food patch to a good one. So the reduced speed is probably a great cost for the extreme form.     

Evaluation of an indigenous parasitoid Habrobracon gelechiae (Hymenoptera: Braconidae) for biological control of light brown apple moth Epiphyas postvittana (Lepidoptera: Tortricidae) in California

Light brown apple moth, Epiphyas postvittana (Walker), is a newly invasive pest in California. Habrobracon gelechiae Ashmead is an indigenous North American ectoparasitoid of lepidopterans. Using E. postvittana as the host, we determined H. gelechiae host stage preference for oviposition and suitability for larval growth: the parasitoid attacked second to fifth instars, but preferred older (third to fifth) host larvae for oviposition, laying more eggs per clutch on the largest (fifth instar). Offspring survival was better on larger (third to fifth instars) hosts. Adult survival and fecundity and immature temperature development were studied at three key temperatures. At 12°C, H. gelechiae failed to oviposit. At 22 and 30°C, H. gelechiae had, respectively, egg to adult developmental times of 15.4 and 8.7 days, adult female survival of 54.8 and 27.2 days, lifetime parasitism of 39.9 and 21.8 hosts and 181 and 151 eggs per female, an intrinsic rate of increase of 0.107 and 0.165, and mean generation time 30.7 and 18.9 days. We studied intraguild interactions with the endoparasitoid Meteorus ictericus Nees, and found that H. gelechiae did not discriminate against hosts that were parasitised by M. ictericus. Neither the paralysing venom injected by H. gelechiae or the presence of the ectoparasitoid's eggs or larvae arrested M. ictericus development. We also conducted a field release of H. gelechiae on two plant species commonly infested by E. postvittana and showed that H. gelechiae was able to locate and attack moth larvae on both hosts.     

Induction of host‐plant preference in Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae)

The coconut hispine beetle, Brontispa longissima, is a serious invasive pest of coconut palm (Cocos nucifera) in Southeast Asia and the Pacific region. Recently, however, it has been reported that on Ishigaki Island, Japan, where C. nucifera is rare, the endemic palm Satakentia liukiuensis serves as a regular host. To explore this phenomenon, we examined the preferences of the beetle for the two palm hosts by choice tests and measurements of feeding amount using four different groups: naïve adults obtained from a colony reared on C. nucifera (NC); naïve adults from a colony reared on S. liukiuensis (NS); wild adults collected on C. nucifera on Ishigaki Island (WC); and wild adults collected on S. liukiuensis on Ishigaki Island (WS). Both NC and NS consumed significantly more C. nucifera leaves than S. liukiuensis leaves and were observed more often on the leaves of C. nucifera. These results suggest that B. longissima has an innate preference for C. nucifera. In contrast, field‐collected adults (WC, WS) initially showed preferences for the species on which they were collected, but after exposure to the other host plant for 2 weeks, their preferences for that host increased. These results suggest that the feeding experience of B. longissima adults affected their subsequent host preferences. This flexible host preference may have facilitated the beetle’s successful establishment in novel Japanese habitats where the original host plant was rare.     

Feeding and oviposition preference of the Sakhalin pine sawyer Monochamus saltuarius (Coleoptera: Cerambycidae) for various tree species

Monochamus saltuarius was recently identified as an important vector of Bursaphelenchus xylophilus, the cause of pine wilt disease. In this study, M. saltuarius adults preferred different species of tree based on the longevity, ingested amount and wounded area that were determined for 90 d. Among eight tree species, the longevity of feeding by M. saltuarius was not significantly different except when feeding in Sciadopitys verticillata. However, the highest ingested amounts with the largest wounded areas were associated with Pinus koraiensis. The highest oviposition preference was in P. densiflora for the first 20 d. However, after 40 d, the oviposition highest preference was noted in P. koraiensis. For oviposition activities, M. saltuarius preferred the tree species in the following order: P. densiflora > P. koraiensis > P. rigida > Larix leptolepis. Although many oviposition scars were observed, M. saltuarius laid fewer eggs in P. rigida than other species of pine, which was related to the bark thickness. The oviposition frequencies were highest with bark 2.0–2.5 mm thick and with tree diameters of 110–130 mm. The current study increased understanding of the ecology of M. saltuarius by identifying specific tree preferences.     

Prey‐mediated changes in the selectivity of the predator Macrolophus pygmaeus (Heteroptera: Miridae)

When foraging in communities with mixed prey, generalist predators may be confronted with prey species that differ in quality, size and mobility and interact with one another. To examine prey selection, predation by Macrolophus pygmaeus (Heteroptera: Miridae) was recorded by providing a diet of either one or two prey species of Myzus persicae (third‐instar nymphs), Aphis gossypii (fourth‐instar nymphs), Trialeurodes vaporariorum (third‐instar nymphs) and Ephestia kuehniella (eggs). In the experiments, prey mobility, prey quality and prey biomass were considered. The biomass consumed by the predator was dependent on the combination of prey species and the quantity of biomass offered. In choice experiments with diets mixed of two prey species at equal densities, the predation to A. gossypii was significantly reduced in the presence of E. kuehniella but the rate of consumption of M. persicae, T. vaporariorum and E.kuehniella was not significantly affected by the coexistence of any other species in the mixed prey diet. When equal amounts of biomass from two prey species were provided in combination, the total consumed biomass was significantly reduced in the mixed prey diets composed of E. kuehniella eggs and aphid nymphs. Thus, under the mixed‐prey situation, prey selection by predators may be affected by interactions among prey species differing in traits such as quality, mobility and size.     

Plant water deficits and insect responses: the preference of Corythucha arcuata (Heteroptera: Tingidae) for the foliage of white oak, Quercus alba

ABSTRACT.

• 1 The preference of Corythucha arcuata (Say) (Heteroptera: Tingidae) for the foliage of Quercus alba L. (Fagaceae) grown under water deficit was examined. Potted Q.alba saplings were grown under controlled levels of water deficit in a glasshouse. Adult C.arcuata were exposed to excised Q.alba foliage under controlled conditions in a growth chamber, and feeding preference assessed by recording the percentage of individuals feeding on leaves from each level of water deficit.
• 2 Two experiments were performed. In the first, all foliage was supplemented with water (via the petiole) to alleviate physical changes in the leaves that accompany plant water deficits. In the second experiment, leaves were not supplemented with water.
• 3 C.arcuata had no preference when presented water supplemented leaves, but preferred leaves that were fully hydrated when presented leaves that were not supplemented with water.
• 4 These results suggest that plant water deficits are important in determining the feeding preference of C.arcuata because they lead to avoidance of drought grown foliage. This avoidance may be caused by an increase in the metabolic cost to the herbivore of maintaining water balance when ingesting drought grown foliage or to an increase in foliage toughness.

     

Host-size preference of the parasitoidAnisopteromalus calandrae [Hym: Pteromalidae] onSitophilus zeamais (Col.: Curculionidae) larvae with a uniform age distribution

First generationAnisopteromalus calandrae (Howard) collected from commercial stored maize in South Carolina were exposed to a mixture of all sizes of immatureSitophilus zeamais Motschulsky, representative of a uniform age distribution, in shelled maize. Eighty-seven percent of parasitism is expected on larvae with tunnel diameters of 0.9 to 1.8 mm and 6% on prepupae and pupae, given this host-size distribution. Preference was greatest for large host larvae (1.6 mm diameter), intermediate for other larvae in the range 0.9 to 1.8 mm, and least for pupae and small larvae. Host-stage preference is discussed with respect to Chesson's (1983) parameters for preference, α_i, probability of parasitism, P_i, and electivity index, ?_i.     

Prey preference and consumption capacity of Nephus arcuatus (Coleoptera: Coccinellidae): the influence of prey stage,prey size and feeding experience

This study examined the feeding habits of Nephus arcuatus Kapur (Coleoptera: Coccinellidae), an important predator of mealybugs in south-western Iran. The consumption capacity of male and female N. arcuatus adults was determined by their feeding on eggs, first-instar nymphs, and adult females of two destructive mealybugs, Nipaecoccus viridis (Newstead) and Planococcus citri Risso, over a 24-h period. N arcuatus consumed significantly more first-instar nymphs than eggs, and more eggs than female adults of both prey species. In addition, we also studied the developmental stage prey preference of adults reared on either N. viridis or P. citri and found that the prey preference of females did not change with the developmental stage of the mealybug. Meanwhile, the males reared on either N. viridis or P. citri showed a significant preference for the first-instar nymphs of P. citri over first-instar nymphs of N. viridis, while a preference for the eggs or adult females of these two mealybugs was not observed. This selection of first-instar nymphs by males was not tied to its previous feeding experience. Our findings suggest that prey stage, prey size and previous feeding experience had no effect on the prey selection of N. arcuatus, making it a good candidate for the biological control of mealybugs.     

Host finding, feeding patterns and evidence for a memorized home range of the mosquito Aedes cantans

Abstract. ELISA tests of Aedes cantans bloodmeals in woodland near Liverpool during 1989 and 1990, revealed preferences for sheep and cows, these hosts representing more than 60% of the total. Dispersal studies carried out on newly-emerged adults and those caught at human bait, indicated that individuals move freely between the two woods studied, mixing as a single population. Mean recapture rates for mosquitoes marked with paint were 2.28% in 1989 and 6.3% in 1990. Recapture rates for mosquitoes marked with powder were 3.66% in 1989 and 6.25% in 1990. The patterns of dispersal of adult females suggest that Aedes cantans has a learned and memorized familiar area map and possesses a sense of location.     

The contribution of silver carp (Hypophthalmichthys molitrix) to the biological control of Netofa reservoirs

When silver carp were introduced into the Netofa reservoirs at an initial density of 300–4500 fish per hectare in order to control phytoplankton and zooplankton, there was a significant reduction of algae, zooplankton, and suspended organic matter; the silver carp prevents the growth of blue-green algae.Annual yield ranged from 600 to 1500 kg per hectare. The growth of individual fish after 6 to 8 years was 6 to 15 kg per fish.Introducing silver carp to reservoirs as a means of biological control creates a balanced ecological system in which the interspecific competition is minimal and the environmental improvements are considerable.Silver carp and bottom-feeding fish create a positive synergism in the water-body by filtering phytoplankton and zooplankton from the water, excreting a major part of it to the bottom and enriching it with organic matter suitable for zoobenthos.     

Haematological parameters in a neotropical fish, Corydoras paleatus (Jenyns, 1842) (Pisces, Callichthyidae), captured from pristine and polluted water

We report normal ranges of haematological indices in healthy Corydoras paleatus from an unpolluted area. Haematological parameters studied include: erythrocyte counts (Er), haematocrit (Ht), haemoglobin concentration (Hb), mean cell volume (MCV), mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC). Normal red blood parameters did not change according to maturation stages, sex or seasons. Then, we compared them with those coming from fish captured in a site polluted by sewage. Fish exposed to pollution presented significantly higher values of Er, Ht, Hb, MCH and MCHC than those captured in an unpolluted area. Discriminant analysis showed that Hb is a key parameter to point out differences between populations exposed to different environmental conditions. We suggest that haematological values of C. paleatus, registered during this study, could be used as biomarkers in future works evaluating the incidence of environmental stress on fish as well as pointing out changes in the water quality.     

Amino acids as determinants of host preference for the xylem feeding leafhopper,Homalodisca coagulata (Homoptera: Cicadellidae)

Summary Homalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in it's selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.Florida Agricultural Experiment Station Journal Series No. 9672