Invasion and Displacement of Experimental Populations of a Conventional Parasitoid by a Heteronomous Hyperparasitoid

Aphelinid parasitoids have an outstanding record of success in programmes of classical biocontrol against whiteflies and scale insects. Heteronomous hyperparasitoids are aphelinids in which the sexes develop on or in different hosts. The female always develops as a primary endoparasitoid of Homoptera. The male develops as a secondary parasitoid hyperparasitoid of his own or another species of homopteran endoparasitoid. Caged experiments were performed with the cabbage whitefly, Aleyrodes proletella, to examine the invasion of a population of a conventional parasitoid, Encarsia inaron both sexes primary endoparasitoids by a heteronomous hyperparasitoid, E. tricolor. In all cages the heteronomous hyperparasitoid successfully invaded an established population of the conventional parasitoid and the conventional species population declined to very low levels within 8 weeks of the introduction of the heteronomous hyperparasitoid. The patterns of invasion were different in each cage. In two cages, high levels of male production by E. tricolor were observed, indicating that hyperparasitism of the conventional species was probably an important factor in causing the decline in the E. inaron population. In a reciprocal experiment in which E. inaron was introduced to an established population of E. tricolor the conventional species failed to invade or persist. A survey of published references to complexes of parasitoids containing a heteronomous hyperparasitoid and one or more conventional species indicated that, in the majority of cases, the heteronomous hyperparasitoid was the most important species in the complex. There are clear implications for the use of these parasitoids in programmes of classical biocontrol. This is because high competitive ability against other parasitoids is not necessarily a good indicator of the ability of a species to maintain high levels of pest control, especially when hyperparasitic behaviour is involved.     

Population dynamics of Siphoninus philyreae in California in the presence and absence of a parasitoid, Encarsia partenopea

Abstract. 1. Densities of the whitefly, Siphoninus phillyreae Haliday, remained at low levels at two sites where a parasitoid, Encarsia parknopea (Walker), was released on whitefly-infested ash, Fraxinus sp., and pomegranate, Punica granatum. Populations of S.phillyreae at control sites, where parasitoids were absent, were increasing in density at the beginning of the summer.
2. By mid-summer, E.partenopea had appeared at all four control sites, and densities of S.phillyreae declined to levels similar to those at the release sites.
3. In the absence of the parasitoid, the age structure of S.phillyreae populations was dominated by the egg stage, indicating a population increasing in density. After E.partenopea became abundant at a site, the age structure of the population had a decreasing proportion of young stages.
4. The changes in S.phillyreae age structures were explained by examining the percentage of fourth instar S.phillyreae from which E.partenopea , as opposed to adult whiteflies, emerged. After the parasitoid became abundant at a site, the majority of fourth instars produced parasitoids rather than whitefly adults. The result was that the adult S.phillyreae population declined, and few eggs were laid.
5. The dynamics of the interaction between E.partenopea and S.phillyreae were similar on ash and pomegranate.     

Bemisia tabaci (Hemiptera: Aleyrodidae) biotype B colonisation and leaf morphology relationships in upland cotton cultivars

Cultivars of upland cotton, Gossypium hirsutum L., are widely grown throughout the world for fibre production. They are also good reproductive hosts for Bemisia tabaci (Gennadius) biotype B. We studied the relationships between cotton leaf morphology and whitefly population densities in eight United States Deltapine and six Australian cotton cultivars and breeding lines at Holtville, California, in 1996. Results showed that okra-leaf cultivars and lines were colonised with fewer whitefly adults, eggs and nymphs compared to normal-leaf cultivars. The distance from underleaf surfaces of cotton leaves to the centres of nearest minor vascular bundles was negatively correlated with whitefly adult, egg and nymphal densities on leaves for all genotypes with the exception of the Australian breeding line 89013–114. Our results suggest that okra-leaf and distance from underleaf surfaces to the centre of nearest minor vascular bundles of cotton leaves are genetic traits that have potential for breeding whitefly-resistant upland cotton cultivars.     

Evaluation of the local population of Eretmocerus mundus (Hymenoptera: Aphelinidae) for biological control of Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) in greenhouse peppers in Argentina

Bemisia tabaci biotype B is a key pest in pepper crops in Argentina. The parasitoid Eretmocerus mundus is frequently found parasitizing this whitefly in greenhouses without pesticide applications. The present studies were carried out with the objective of evaluating control obtained with different rate and number of parasitoid releases under experimental conditions. Release rate: cages with pepper pots were positioned in an experimental greenhouse and randomly assigned to the release rate treatments (0, 1 and 3 pairs of E. mundus/plant/week with a total of three introductions). Number of releases: similar cages were assigned to the number of parasitoid introduction treatments (0, 1, 2 and 3) with the best release rate obtained in the previous trial. In both assays whitefly (adults and nymphs) and parasitoid (parasitized nymphs) population sizes in each cage were monitored weekly for a period of 10 weeks. Results suggested that the introduction of 2 E. mundus/plant/week was enough to suppress host population compared to control treatment (peaks of 7.75 adults and 58.75 nymphs/cage and 643.75 adults and 1598 nymphs/cage, respectively) (p < 0.05), with 85% of parasitism. E. mundus had to be introduced three times to achieve the best pest control (peaks of 1.17 adults and 20.33 nymphs/cage vs. 55.67 adults and 75 nymphs/cage in control treatment) with 84% of parasitism (p < 0.05). These results were then validated in a pepper crop under experimental greenhouse conditions. Whitefly population was lower in those greenhouses where E. mundus was released compared to control greenhouses (0.15 adults and 0.71 nymphs/4 leaves and 0.73 adults and 1.64 nymphs/4 leaves, respectively), with a peak of 54% of parasitism (p < 0.05). We concluded that good suppression of B. tabaci could be achieved using E. mundus under spring conditions in Argentina.     

Effects of UV-blocking films on the dispersal behavior of Encarsia formosa (Hymenoptera: Aphelinidae)

The parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae) has been used successfully for the control of Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae). The development of UV-blocking plastic films has added a new component to future integrated pest management systems by disrupting insect pest infestation when UV light is excluded. Because both T. vaporariorum and E. formosa are reported to have similar spectral efficiency, there was a need to identify the impact of UV-blocking films on the dispersal behavior of both the pest and the natural enemy. In field studies, using choice-chamber experiments, E. formosa showed some preference to disperse into compartments where less UV light was blocked. However, further studies indicated that the effect was primarily attributable to the different light diffusion properties of the films tested. Thus, unlike its whitefly host, when the UV-absorbing properties of the films were similar, but the light diffusion properties differed, E. formosa adults preferred to disperse into compartments clad with films that had high light diffusion properties. When the plastic films differed most in their UV-absorbing capacity and had no light-diffusion capability, the initial dispersal of E. formosa between treatments was similar, although a small preference toward the environment with UV light was observed over time. When parasitoid dispersal was measured 3 h after release, more parasitoids were found on plants, suggesting that the parasitoids would search plants for whitefly hosts, even in a UV-blocked light environment. The potential for the integration of UV-blocking films with E. formosa in an advanced whitefly management system is discussed.     

Rates of population increase, abundance, and life stage distribution of Rhynchites cribripennis (Coleoptera: Attelabidae) on trees and in the soil in an olive grove

The seasonal population abundance of Rhynchites cribripennis (Desbrochers) adults on olive trees was studied by collecting samples from an olive grove on the island of Zakynthos, Greece, from April 1994 to the end of July 1995. Moreover, the population abundance of larvae, pupae, and adults of R. cribripennis was recorded in soil samples from two soil depths (0-4 and 4-8 cm) from October 1994 to October 1995. Results showed that adult populations increased considerably on trees during May and June and peaked on 16 June (19.9 adults per twig) and 8 July (7.7 adults per twig) in 1994 and 1995, respectively. In 1994, no significant differences were found in the number of adults sampled from the different tree quadrants (northwest [NW], northeast [NE], southwest [SW], and southeast [SE]). However, in 1995, adult numbers in the NW quadrant of trees were significantly higher than those in the SE or SW quadrants. In soil samples, larvae were recorded throughout the sampling period with the highest numbers occurring in December, 2.4 larvae per soil sample, whereas pupae were found in lowest numbers in October and November. Adults were present in the soil samples from December to May, but the highest numbers were recorded in December, with a peak of one adult per sample. The number of adults was significantly higher, and that of larvae numerically higher, in the upper compared with lower soil layer, whereas pupae were found with similar numbers in both soil layers. Results of these studies suggest that this weevil exhibits a prolonged larval diapause and a 2-yr life cycle. The ecological implications of this behavior are discussed. Moreover, a prediction of the highest adult population on trees was estimated by taking into account the rate of increase of adult numbers in the early period of adult occurrence on trees.     

Whitefly control in cut gerbera: is it possible to control Trialeurodes vaporariorum with Encarsia formosa?

We investigated the impact of inundative releases of the parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), on cut gerbera (Gerbera jamesonii L.) under controlled greenhouse conditions. Experimental units consisted of ten plants covered and separated from other units by gauze tents. We assessed three release rates of the aphelinid parasitoid: a 7-week experiment with a standard release rate (10 m⁻²/14 days), and a subsequent 3-month trial with high (100 m⁻²/week) and very high (1,000 m⁻²/week) release rates. Experimental units without release of parasitoids served as control treatment. Gerbera plants were infested initially with 50–100 juvenile and 50–70 adult whiteflies in the first experiment, and in the second experiment with less than 50 juveniles per plant and 50–70 adults. Whitefly and parasitoid population density were assessed in weekly intervals using infestation and activity categories. Results show that parasitized whiteflies were present in all treatments within 2 weeks after initial release. Unfortunately, it was not possible to control whiteflies with standard release rates of E. formosa. Although parasitism rates slightly increased, the effect on whitefly populations was negligible. Large amounts of honeydew and growth of sooty mold fungi caused the termination of the first experiment. In a second experiment, E. formosa was tested at 10–100 times higher release densities. In contrast to the first experiment, whitefly densities increased steadily during the first 8 weeks, but remained constant until the end of the experiment in both treatments. Parasitism by E. formosa reached its maximum after 8 weeks. We discuss possible reasons for the low efficiency of E. formosa as a whitefly antagonist in greenhouse production of gerbera.     

Factors influencing the dispersal of a native parasitoid, <Emphasis Type="Italic">Phasgonophora sulcata</Emphasis>, attacking the emerald ash borer: implications for biological control

High parasitism by a native parasitoid, Phasgonophora sulcata Westwood (Hymenoptera: Chalcididae), has been reported on emerald ash borer (hereafter EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in North America. Use of this parasitoid in an augmentative biological control program has been proposed to slow the spread of EAB, yet information is lacking on key aspects of this parasitoid’s dispersal. We document the flight capacity and walking activity of P. sulcata, its potential fecundity, and describe how age, body size, temperature, and time of day affect these parameters. Wasp flight capacity, measured using flight mills, increased with temperature and decreased with age. Unexpectedly, age and body size did not affect wasp walking activity, and we saw no relationship between walking activity and flight capacity. Older wasps had lower potential fecundity than younger wasps. These results suggest that P. sulcata should be released as pupae near EAB-infested ash trees to improve efficacy and potential biological control success.     

Yellow sticky trap catches of parasitoids of Bemisia tabaci (Hemiptera: Aleyrodidae) in vegetable crops and their relationship to in-field populations

We examined the relationship of yellow sticky trap captures of Bemisia tabaci (Gennadius) biotype B parasitoids to the local population of parasitoids as measured by leaf samples of parasitized whiteflies and mass release of parasitoids. Traps were placed in experimental collard and cowpea field plots in Charleston, SC, and in commercial organic fields of spring cantaloupe and watermelon in the Imperial Valley, CA. The exotic parasitoid Eretmocerus emiratus Zolnerowich and Rose was released in Imperial Valley fields to ensure parasitoid populations would be present. Bemisia adults were trapped in the greatest numbers on the upper surface of horizontally oriented sticky traps in melon fields. In contrast, the lower trap surfaces consistently captured more Eretmocerus than upper surfaces. Female parasitoids were trapped in greater numbers than males, especially on the lower trap surfaces. Progeny of released exotic Eretmocerus greatly outnumbered native E. eremicus Rose and Zolnerowich and Encarsia spp. on traps. Throughout the season, the trend of increasing numbers of Eretmocerus on traps parallelled the increase in numbers of whiteflies. Over the season, 23-84% of all B. tabaci fourth instars were visibly parasitized by Eretmocerus. The numbers of Eretmocerus caught by traps in cantaloupe were similar in trend to numbers on leaf samples in melons, but not with those in watermelon, where whitefly populations were lower. Parasitoid numbers were low in collard and cowpea samples, and no trend was observed in numbers of parasitoids captured on traps and numbers on leaves for these two crops. Overall, there were no significant correlations between sticky trap catches of parasitoids and numbers of parasitized whiteflies on leaf samples in any test fields. Nevertheless, sticky traps placed within crops may be useful for observing trends in whitefly parasitoid populations at a particular site and for detecting parasitoids at specific locations.     

北京地区杨潜叶跳象生物学特性及药物防治效果

杨潜叶跳象Rhynchaenu sempopulifolis Chen是杨树的重要食叶害虫之一。该虫在北京密云1年发生1代,以成虫越冬。翌年3月下旬越冬成虫开始出蛰上树危害。4月上旬成虫交尾,4月中旬开始产卵,卵产于叶片背面,孵化后即开始潜入叶肉内为害,4月下旬化蛹。5月上旬成虫羽化,然后继续上树取食叶片,直到10月下旬进入枯枝落叶内、石缝、表土中进行越冬。发现2种重要的寄生性天敌:杨跳象金小蜂Pteromalus miyunensis和三盾茧蜂Triaspissp.。它们对害虫种群起着较大的控制作用。用5%高效氯氰菊酯1000倍液进行土壤处理,杨潜叶跳象成虫和蛹的平均校正死亡率分别达到94.05%和66.5%。     

The dispersal rate of a beetle, Osmoderma eremita, living in tree hollows

The dispersal of an endangered beetle, Osmoderma eremita, that lives in tree hollows, was studied by mark-release-recapture with pitfall traps. As only a small proportion of all dispersals is observed by this method, a simulation model was constructed to estimate the dispersal rate per individual. The model results suggest that 15% of the adults leave the original tree for another hollow tree, and consequently most individuals remain in the same tree throughout their entire life. This suggests that each hollow tree sustains a local population with limited connection with the populations in surrounding trees. It supports the view that O. eremita has a metapopulation structure, with each tree possibly sustaining a local population, and with the population in an assemblage of trees forming a metapopulation. Low dispersal rate and range make the species vulnerable to habitat fragmentation, probably at a scale of only a few hundred meters.     

Compatibility of Insect Growth Regulators with Eretmocerus eremicus (Hymenoptera: Aphelinidae) for Whitefly (Homoptera: Alyerodidae) Control on Poinsettias: II. Trials in Commercial Poinsettia Crops

The efficacy and cost of reduced release rates of the parasitoid Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae) when combined with application of the insect growth regulator buprofezin were compared to those of a higher parasitoid release rate used alone for whitefly control (Homoptera: Aleyrodidae) on poinsettia (Euphorbia pulcherrima Willd. ex Koltz.). The trial was conducted in seven greenhouses in Methuen, Massachusetts from August through December 1997 and employed commercial poinsettia production practices. Two whiteflies species, Trialeurodes vaporariorum (Westwood) and Bemisia argentifolii Bellows and Perring (= Bemisia tabaci [Gennadius] strain B), were present. Three treatments were examined: (1) E. eremicus used alone at a release rate of three females per plant per week (two greenhouses); (2) E. eremicus at an intermediate release rate of two females per plant per week, combined with mid-season use of buprofezin (two applications, spaced 1 week apart, applied in weeks 9 and 10) (two greenhouses); and (3) E. eremicus at a low release rate of one female per plant per week, combined with mid-season use of buprofezin, applied as in treatment 2 (two greenhouses). In addition, observations were made in one additional greenhouse at the site, in which the grower used pesticides for whitefly control. Prior to the start of the trial, cuttings used for all treatments experienced some pesticide use, first abamectinduring rooting and later buprofezin at potting to reduce whitefly numbers, which were initially very high. At harvest, densities of live whitefly nymphs were not statistically different among the biological control treatments, indicating that a low parasitoid release rate combined with buprofezin was as effective as a higher release rate of the parasitoid used alone. Nymphal densities in separate market samples (based on smaller sample sizes) showed differences among treatments, but all treatments, including the low parasitoid release rate + buprofezin maintained densities of live nymphs + pupae at or below approximately two per leaf, a level commercially acceptable in local markets. Control costs per single-stemmed poinsettia plant were $1.18 for the high parasitoid release treatment, $0.75 for the treatment of weekly releases of two female parasitoids per plant per week + buprofezin, $0.38 for the treatment of releases of one female parasitoid per plant per week + buprofezin, and $0.14 for the chemical control greenhouse.     

Responses of the sweetpotato whitefly, Bemisia tabaci, to the chinaberry tree (Melia azedarach L.) and its extracts

Host preference bioassays for adults of the sweetpotato whitefly were performed with leaves of the chinaberry tree Melia azedarach L., tomato, cucumber and bean. Fruit and leaf extracts of the chinaberry tree were tested against adults of the sweetpotato whitefly. Fruit extracts were tested against eggs, first and second instar nymphs, and pupae of the insect. Treatments included aqueous, methanol, and acetone fruit extracts of 200 mg ml^?1 and serial dilutions of 20.0 and 2.00 mg ml^?1, ether extract, the botanical insecticides Azatin® and Margosan® ‐O and the control, water or water with Triton®. Mortality data was collected at 6, 7, and 8 days after treatment of the eggs, nymphs and pupae, respectively. Results of the host preference bioassays indicated a significantly lower number of live insects on leaves of the chinaberry tree vs leaves of bean, cucumber, and tomato after 24 h. This indicates that M. azedarach is not a good host for the sweetpotato whitefly. Adults of the insect were significantly more repelled from tomato plants treated with the undiluted extracts when compared to the control after 72 h. There were significant differences in percent mortality of nymphal instars when exposed to the undiluted extracts compared to other extracts and the control. However, there was no significant effect of the fruit extracts on the egg and pupa instars. Thus M. azedarach extracts were found to be repellent to the whitefly adults, while the fruit extracts have shown a significant detrimental effect against early nymphal instars. In general, the methanol extracts were more active against B. tabaci than extracts with other solvents.     

Intraguild predation by the generalist predator Dicyphus hesperus on the parasitoid Encarsia formosa

Predation was measured in the laboratory by Dicyphus hesperus females on patches of greenhouse whitefly (Trialeurodes vaporariorum) pupae. The patches contained different proportions of unparasitized pupae and those parastisized as nymphs by Encarsia formosa. Dicyphus hesperus fed readily on parasitized pupae and the number of parasitized pupae consumed increased with the proportion available indicating a capacity for intraguild predation. However, D. hesperus females did not display a preference for feeding on parasitized pupae versus unparasitized pupae. Dicyphus hesperus adults were released at three densities into greenhouse enclosures containing tomato plants harbouring greenhouse whitefly and immature E. formosa. Numbers of killed and parasitized whitefly nymphs and pupae and the total number of healthy whitefly were compared among Dicyphus density treatments. On upper leaves, the amount of predation on whitefly nymphs was higher at the highest predator density than at the lower density or in enclosures where D. hesperus was not released. On lower leaves, the number of parasitized pupae was lowest with the highest predator density indicating a negative effect of intraguild predation by D. hesperus on E. formosa. Despite this, Dicyphus density did not affect the density of whitefly in the presence of E. formosa. The results are discussed as they relate to concurrent use of D. hesperus and E. formosa for regulation of greenhouse whitefly populations.     

Effects of rearing conditions on reproduction of Spathius agrili (Hymenoptera: Braconidae), a parasitoid of the emerald ash borer (Coleoptera: Buprestidae)

Spathius agrili Yang (Hymenoptera: Braconidae) can be successfully reared on emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), larvae feeding in chambers drilled in small ash twigs that are wrapped with floral tape. Females maintained in groups with males for one week can receive enough sperm for production of female progeny throughout their lives. Volatiles released by emerald ash borer adults feeding on ash foliage increased parasitoid fecundity over ash foliage alone or no stimulus. The temperature at which the parasitoids were reared ranged from 20 to 25 degrees C in a daily cycle; however, raising the daily maximum temperature to 28 degrees C did not affect parasitoid longevity or fecundity. Adult females lived between 12 and 127 d, with an average of 60.8 +/- 4.5 d. Males lived slightly longer, with an average of 66 +/- 4.5 d. The first clutch of eggs was laid when the female was between 2 and 42 d old, with the average preoviposition period lasting 11.4 +/- 1.4 or 19.5 +/- 2.0 d in 2007 and 2009 trials, respectively. A higher proportion of the emerald ash borer larvae were feeding and thus attractive to parasitoids in the 2009 trial, and female S. agrili laid an average of 9.5 +/- 1.0 clutches containing 5.4 +/- 0.2 eggs, for an average of 51.2 eggs per female. Approximately three quarters of the progeny were female. The number of eggs per clutch was significantly greater when deposited on larger emerald ash borer larvae, further highlighting the need for quality larvae in rearing. Chilling S. agrili pupae at 10 degrees C to stockpile them for summer release was not successful; chilling resulted in lower survival and lower fecundity of emerging progeny. Female S. agrili proved capable of attacking emerald ash borer larvae through even the thickest bark of an ash tree that was 30-cm diameter at breast height. Even emerald ash borer larvae that were creating overwintering chambers in the outer sapwood of the tree were successfully attacked, suggesting that S. agrili could be reared on field collected logs infested with emerald ash borer.     

Estimating the influence of population density and dispersal behavior on the ability to detect and monitor Agrilus planipennis (Coleoptera: Buprestidae) populations

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), a phloem-feeding pest of ash (Fraxinus spp.) trees native to Asia, was first discovered in North America in 2002. Since then, A. planipennis has been found in 15 states and two Canadian provinces and has killed tens of millions of ash trees. Understanding the probability of detecting and accurately delineating low density populations of A. planipennis is a key component of effective management strategies. Here we approach this issue by 1) quantifying the efficiency of sampling nongirdled ash trees to detect new infestations of A. planipennis under varying population densities and 2) evaluating the likelihood of accurately determining the localized spread of discrete A. planipennis infestations. To estimate the probability a sampled tree would be detected as infested across a gradient of A. planipennis densities, we used A. planipennis larval density estimates collected during intensive surveys conducted in three recently infested sites with known origins. Results indicated the probability of detecting low density populations by sampling nongirdled trees was very low, even when detection tools were assumed to have three-fold higher detection probabilities than nongirdled trees. Using these results and an A. planipennis spread model, we explored the expected accuracy with which the spatial extent of an A. planipennis population could be determined. Model simulations indicated a poor ability to delineate the extent of the distribution of localized A. planipennis populations, particularly when a small proportion of the population was assumed to have a higher propensity for dispersal.     

Comparing four methods of augmentative release of Eretmocerus nr. emiratus against Bemisia argentifolii

Four methods were tested for release of Eretmocerus nr. emiratus (Hymenoptera:Aphelinidae) against the silverleaf whitefly,Bemisia argentifolii Bellows & Perring(Hemiptera: Aleyrodidae), in cotton and melons. Ten thousand parasitoids were released in 0.1ha plots as follows: (1) as adults in each ofthe four quadrants of the plot, (2) as pupae ingel-caps affixed to the undersides of leaves inthe center of each of four quadrants, (3) at thecenter of the plot in shaded paper cups, and (4)to simulate release from a drop-box. Survivalafter 3 d, dispersal, mating success,sex-ratio, cost, and delivery speed werecompared among the four methods. Significantlymore parasitoids were recovered after 3 d whenparasitoids were released using the paper cupmethod, however, few parasitoids were capturedoutside the area directly adjacent to therelease point. More parasitoids wererecaptured near the release points with thegel-cap and adult release methods, but becausethere were four release points per plot, thedistribution was more uniform. Few parasitoidswere recovered when parasitoids were releasedusing a simulated drop-box method. Althoughthe sex-ratio of released parasitoids was±70% males, more than 30% of the recoveredparasitoids were female. In melons, where thedensity of whiteflies was more than 20 times asgreat as in cotton, the sex-ratio of recapturedparasitoids was greater than 70% females forall treatments. The most expensive releasemethod was the drop-box at $38.79 per ha,followed by $13.02 for adults, $7.62 forgel-caps, and $3.31 for the paper cups. Thegel-cap method was superior in providing a muchmore even distribution of individualsthroughout the field, especially in melons, butconsiderable time was necessary to prepare thegel-caps for release. Of the four releasemethods tested, releasing parasitoids in papercups resulted in higher numbers recaptured, alow cost, and rapid delivery speed. BecauseE. nr. emiratus does not dispersefar from the release point, however, a greaternumber of release points with fewer parasitoidsper point should provide a more evendistribution of parasitoids throughout therelease field.     

First report of airborne begomovirus infection in Melia azedarach (Pride of India), an ornamental tree in India

The begomovirus infection in plants has been widely reported throughout the world. The chief carrier of this virus is the whitefly. All of the reports, however, concern plants that grow at a stumpy height from the ground; moreover, the whitefly transmits the begomovirus infection to plants at this low height only by residing under their leaves. To date, there has been no record of the begomovirus infection in trees as the prevalence of the whitefly at tree level is unlikely. For this reason, this study focuses on and presents the first report of airborne begomovirus infection in an ornamental tree—the Melia azedarach (or Pride of India) found on the Indian subcontinent.     

不同林分白蜡树云斑白条天牛种群空间格局地统计学分析

云斑白条天牛是我国重要林业害虫,在黄河三角洲地区对白蜡树造成严重危害。利用地统计学方法,通过调查城市行道绿化林、庭院绿化林、公路林和片林4种不同林分类型的白蜡树林地,以产卵刻槽、排粪孔和羽化孔为调查指标,对危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)的空间格局进行了研究。结果表明:除片林样点成虫(蛹)的半变异函数模型为指数模型外,危害白蜡云斑白条天牛种群卵、幼虫、成虫(蛹)在不同林分类型下的半变异函数模型均为球形模型,其指明空间分布均为聚集分布,种群的聚集分布习性与林分类型相关性不强。但不同林分类型云斑白条天牛种群的空间相关性地统计学参数存在差异,片林调查样点的卵、幼虫和成虫(蛹)的变程a、块金值C0和基台值C0+C均小于其他3种林分类型的统计值,片林样点成虫(蛹)的半变异函数模型不同于其他林分类型为指数模型。     

不同作物田烟粉虱发生的时空动态

2008～2009年连续2年系统调查了番茄、茄子、棉花、大豆、玉米等寄主植物上烟粉虱种群发生的时间与空间动态。结果表明：不同寄主植物上的烟粉虱成虫及其伪蛹数量有显著性差异,其密度大小依次为：茄子>棉花>番茄>大豆>玉米。其中,在玉米上除了发现极少量的成虫逗留外,没有发现烟粉虱的卵及若虫。在发生的时间序列上,烟粉虱成虫及伪蛹的数量呈现为先逐渐上升后又下降的变化过程,发生高峰期集中在8月5日到8月31日,9月初以后烟粉虱数量慢慢减少。在空间分布上,表现为烟粉虱成虫喜食寄主的上部叶片。统计分析显示,寄主对烟粉虱成虫和伪蛹的数量的影响极显著,而年份对其数量的影响没有显著差异。由此得出的烟粉虱发生和达到高峰的时间,可为烟粉虱预测预报和区域性综合治理提供重要理论依据。