Life history of Axinoscymnus cardilobus (Col., Coccinellidae), a predator of Bemisia tabaci (Hom., Aleyrodidae)

Abstract:  Axinoscymnus cardilobus is an indigenous coccinellid predator in South China, which feeds on many whitefly species. Its development, consumption rate, survivorship, longevity and fecundity on a diet of eggs and nymphs of Bemisia tabaci were evaluated. Larval consumption decreased sharply as instars of B. tabaci become bigger, and development time of beetle larvae was significantly different when fed on different stages of B. tabaci . The sex ratio was 0.44. The performances were better after feeding on whitefly eggs than nymphs. Axinoscymnus cardilobus showed good potential for biological control of B. tabaci , especially in greenhouse situations.     

Effects of temperature on development,survival, longevity,and fecundity of Serangium japonicum (Coleoptera: Coccinellidae), a predator of Bemisia tabaci Gennadius (Homoptera: Aleyrodidae)

In this study, we evaluated the effect of temperature on the development and reproductive biology of Serangium japonicum (Coleoptera: Coccinellidae) at seven constant temperature regimes (17, 20, 23, 26, 29, 32 and 35°C) for its effect as a predator of Bemisia tabaci (Homoptera: Aleyrodidae). Results indicated that the duration of the egg, larval and pupal stages were significantly affected by temperature. The developmental time gradually declined with the increase of temperature from 17 to 29°C, however an extension in the developmental periods was observed in the temperature range of 32 to 35°C. The survival rates of different insect stages were stable at temperatures between 20 and 32°C; however at extreme temperatures of 35°C, a sharp decrease was evident. The highest fecundity of the female (387.2 eggs per female) was recorded at 20°C. Based on these results, life tables of S. japonicum were constructed for temperatures in the range 20–35°C. The maximum reproductive rate (R ₀=279.9) occurred at 26°C. The maximum values for innate capacity for increase (r _m=0.1131) and the finite rate of increase (λ=1.1197) occurred at 29°C. The mean generation time (T) decreased with increased temperature, the longest of which was 76.0 days (at 20°C) and the shortest was 36.6 days (at 32°C). These results offer valuable insight on the importation and establishment of S. japonicum into new environments with diverse temperature regimes.     

Effects of bio-pesticides on Eretmocerus warrae (Hym., Aphelinidae), a parasitoid of Bemisia tabaci (Hom., Aleyrodidae)

The sweet potato whitefly Bemisia tabaci (WF) can be controlled by two commercial neem products, NeemAzal-T/S^® (1% azadirachtin) for foliar application, and NeemAzal-U (17% azadirachtin) for soil application, alongwith two biorational products of microbial origin, Abamectin (avermectin) and Success^® (spinosad). Side effects of these products were tested in a laboratory bioassay against a native aphelinid, Eretmocerus warrae (EW). Eggs and early larval instars of the parasitoid, commonly found outside the host body, were highly susceptible to foliar spray of neem with only 8%, 18% and 55% emergences of adults from treated eggs. larval and pupal stages respectively at recommended dose-rates of 5 ml/l and 1%, 8% and 40% at twice recommend dose-rate (10 ml/l). Soil application with NeemAzal-U marginally affected EW. At highest tested dose-rate of 3.0 g/l, 46%, 64% and 81% emergence was recorded after treatement of plants harbouring WF parasitized by egg, larval and pupal stages of EW respectively. In contrast to neem application, Success^® and Abamectin caused high mortality in development stages of the parasitoids. In particular, abamectin was highly toxic to the parasitoids with less than 1% emergence from either of the three development stages if treated with 1–2 ml/l.     

A new host plant species for the cassava biotype of Bemisia tabaci (Gennadius) (Hom., Aleyrodidae)

Abstract:  The cassava biotype of Bemisia tabaci (Gennadius) is known to colonize cassava ( Manihot esculenta Crantz) whereas the sweet potato biotype colonizes various plant and weed species but not cassava. Both biotypes have Solanum melongena L. and Solanum aethiopicum L. as common host plant species. This study shows for the first time that both biotypes can successfully feed, survive and reproduce on a new host plant species, Nicotiana debneyi Domin. These findings have important implications for better understanding the disease epidemics, related to whitefly transmissible geminiviruses.     

Host finding byCryptolaemus montrouzieri (Col., Coccinellidae) a predator of mealybusgs (Hom., Pseudococcidae)

AdultC. montrouzieri were able to detect their prey by visual and chemical stimuli. Presence of mealybug caused a significant increase in the number of turns and a sharp decrease in flight attempts suggesting detection by olfaction. In the light, adult predators found polystyrene dummies significantly faster than under dark (red light) conditions, but light had no effect on the time taken for adults to pass across an invisible test point. Fourth instar larvae could only perceive the prey by physical contact.      

Effect of foliar tomentosity on phenotypic plasticity in Bemisia tabaci (Hom., Aleyrodidae)

Some whitefly species, as well as members of other insect families, are known to develop different phenotypes under different environmental conditions. In this study, the identification of an environmental trigger and its sensitive stage for the development of the setose phenotype of Bemisia tabaci nymphs are reported. Quantification tests revealed phenotypic plasticity manifested by positive correlation between trichome density on tomentose leaves and the percentage of setose nymphs found upon them. Artificial simulation of leaf tomentosity provided sufficient stimulation to induce the setose nymph phenotype. The crawler was found to be the only sensitive stage for this induction. Polymorphism of the nymphal phenotypes correlated with additional biological features of both nymph and adult, which could be treated as proxies of fitness. Setose nymphs were smaller and developed (from eggs to adult) faster. Adults emerging from such nymphs were smaller and had shorter lives. Adaptivity of the detected phenotypic plasticity and of the correlating nymphal and adult features are discussed.     

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.     

Intraguild predation of Serangium parcesetosum (Coleoptera: Coccinellidae), on whitefly Bemisia tabaci (Homoptera: Aleyrodidae) parasitized by Eretmocerus mundus (Hymenoptera: Aphelinidae)

We studied intraguild predation of Serangium parcesetosum on Eretmocerus mundus, both natural enemies of Bemisia tabaci, on eggplant under laboratory conditions. Fourth instar and adult predators attacked parasitized and unparasitized hosts equally if immature parasitoids were larvae, but avoided predating on parasitized hosts containing pupae.     

Predation of Clitostethus arcuatus (Col.: Coccinellidae) on Trialeurodes vaporariorum (Hem.: Aleyrodidae)

Greenhouse whitefly, Trialeurodes vaporariorum, is a serious pest of glasshouse crops. It shows resistance to different insecticides and growers are interested in finding other useful control methods. This research was carried out to study the predation potential and biology of Clitostethus arcuatus (Rossi) as one of the most important predators of this pest. Adult C. arcuatus were reared on tobacco leaves bearing colonies of greenhouse whitefly eggs under controlled conditions (25±2°C, 65±5% RH and 16 h L:8 h D). Results showed that the average developmental time of the egg, first through fourth instar larva and pupa were 2.82±0.12, 4.47±0.14, 4.54±0.1, 6.3±0.2, 7±0.22 and 3.8±0.13 days, respectively; and longevity of female and male were 66.4±2.6 and 54.9±2.5 days, respectively. The average feeding rates of female, male and larvae (first through fourth) were 61.4±0.7, 27.6±0.9 eggs/day and 12±1.03, 30.3±2.4, 41.3±2, 68.04±2 eggs/day, respectively. The larvae consumed an average of 992.2±36 eggs during the total larval developmental period with a daily mean of 45.8±0.5. A significant difference was shown between the feeding rate of fourth instar larval stages and between sexes. Females, males and one pair of C. arcuatus (♀,♂) consumed an average of 17.2±0.4, 10.6±0.8, 23.1±0.5 nymph/day; 28.5±0.9, 20.3±0.6, 47.2±0.6 pupa/day and 8±0.3, 6.5±0.54, 13.6±0.4 adult/day, respectively. The feeding rate was significantly different among whitefly life stages. Females laid an average of 3±0.23 eggs/day.     

Satiation time and appetite revival of Coccinella septempunctata L. (Col., Coccinellidae), a predator of Lipaphis erysimi Kalt. (Hom., Aphididae)

After a 24 h period of starvation the Coccinella septempunctata grub satiated in 85 min after eating 31.57 ± 7.12 prey (aphids). After 6, 12, 18, 24, 30 and 36 h of prey deprivation, the grub consumed 14.31 ± 5.67, 22.05 ± 5.39, 27.10 ± 6.49, 31.57 + 7.12, 33.76 + 6.52, and 36.98 ± 8.56 prey, respectively. The voluntary intake (appetite) shows a sigmoid relationship with the time since the last meal, with an upper limit of 44.30 prey irrespective of the prey deprivation period. As maximum appetite was attained after 24–36 h of deprivation, it is recommended that C. septempunctata grubs should be starved for 24 h prior to release in the biological control programme of Lipaphis erysimi.     

两种蚜小蜂对烟粉虱寄主的产卵选择性(英文)

双斑恩蚜小蜂和桨角蚜小蜂是华南地区烟粉虱的两种优势种寄生蜂。本文研究了两种寄生蜂对不同龄期烟粉虱寄主的产卵选择特性。结果表明:两种寄生蜂均可寄生烟粉虱的1~4龄若虫。当只有1个龄期的烟粉虱若虫存在时,双斑恩蚜小蜂更多地寄生3龄和4龄若虫,较少寄生1龄和2龄若虫;而桨角蚜小蜂则更多地寄生3龄和2龄若虫,较少寄生1龄和4龄若虫。在4个龄期若虫同时存在时,双斑恩蚜小蜂会明显增加对3龄和4龄若虫的产卵寄生,降低对1龄和2龄若虫的寄生;而桨角蚜小蜂则增加对2龄和3龄若虫的寄生,减少对1龄和4龄若虫的寄生。寄主植物的差异不影响这二种蚜小蜂对各龄期烟粉虱若虫的产卵选择倾向。结果提示,烟粉虱若虫3龄和4龄是双斑恩蚜小蜂最适宜的寄主,而桨角蚜小蜂最适宜的寄主是烟粉虱2龄和3龄若虫。     

Suitability of Aphis craccivora (Hemiptera: Aphididae) and Bemisia tabaci (Hemiptera: Aleyrodidae) biotype-B as prey for Chrysopa pallens (Neuroptera: Chrysopidae)

The suitability of Aphis craccivora Koch (Hemiptera: Aphididae) and Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) biotype-B eggs and nymphs as prey for pre-imaginal development and survival, adult longevity, and fecundity of the lacewing, Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae) was evaluated under laboratory conditions at 25±1°C, 50±10% RH and a photoperiod of 16 h L:8 h D. Survival of C. pallens from first instar to adult eclosion was significantly different between the larvae that fed on the two prey species. C. pallens fed on A. craccivora completed development from egg to adult emergence, but those fed on eggs and nymphs of B. tabaci could not complete development, resulting in abnormal pupae and no normal adults emerged. The net reproductive rate (R ₀), intrinsic rate of natural population increase (r _m ), finite rate of increase (λ), mean generation time (T), index of population trend (I), doubling time (DT), and gross reproductive of rate (GRR) of C. pallens that fed on A. craccivora were 201.9 eggs per female, 0.13/d, 1.1/d, 40.1 d, 68.5, 5.2 d, 203.1 eggs per female, respectively. These results could be useful for mass-rearing of C. pallens and for understanding its population dynamics in the field in relation to the availability of different prey species.     

The status ofBemisia tabaci (Hom.: Aleyrodidae),Trialeurodes vaporariorum (Hom.: Aleyrodidae) and their natural enemies in Crete

The non «B» biotype ofBemisia tabaci (Gennadius) is recorded for the first time in Crete in 1992, in the north east and south east of the island.Trialeurodes vaporariorum (Westwood) is the predominant whitefly on plants in the north and west of the island. Three surveys of Crete were made in 1992 and 1993 for natural enemies ofB. tabaci andT. vaporariorum and resulted in the collection of 4 species ofEncarsia, (plus a number of species that are unidentifiable at this time), anEretmocerus sp. (unidentifiable at this time) and a fungal pathogen,Paecilomyces farinosus (Dickson Ex Fries) Brown &; Smith.Encarsia adrianae was identified fromT. vaporariorum; which constitutes its most westerly distribution point and a new host record respectively.B. tabaci andT. vaporariorum were found on horticultural crops, ornamentals and weeds. Populations of both whitefly species were severely depleted on field hosts throughout the island during the winter of 1992/93. Climatic constraints, competition withT. vaporariorum in otherwise suitable niches, effective natural enemies and an observed low level of polyphagy may explain the present limited distribution of the non «B» biotype ofB. tabaci in Crete.     

Effects of different application methods of azadirachtin against sweetpotato whitefly Bemisia tabaci Gennadius (Hom., Aleyrodidae) on tomato plants

Abstract:  Studies on three different neem treatment methods (seed, soil and foliar) and two different commercial neem products (NeemAzal T/S 1% azadirachtin and NeemAzalU 17% azadirachtin) against sweetpotato whitefly (WF) Bemisia tabaci Gennadius (Hom., Aleyrodidae) on tomato plants were conducted in cages in air-conditioned cultivation rooms. All three methods of neem treatments resulted in reduced colonization and oviposition. Overall oviposition intensity was significantly reduced (44%) by the treatment of tomato seeds but an even higher reduction (74%) was achieved through soil drenching both with 3.0 g/l NeemAzalU and foliar spraying (82%) with 10 ml/l of NeemAzal TS compared with control treatments. In contrast, soil and foliar treatment increased fecundity per female up to 33% and 32%, respectively, at the highest tested concentrations. Reduced egg hatch could be observed only at high neem concentrations; 62% and 51% of deposited eggs hatched at the highest dose rates of NeemAzalU in case of seed and foliar treatments, respectively; whereas only 43% of deposited eggs hatched in case of foliar treatments at highest dose rates of NeemAzal T/S. Seed (35%), foliar (93%) and soil treatments (91%) caused high mortality rates of immatures and reduced number of hatching adults compared with control plants treated with a blank formulation or water. The mortality among immatures increased in relation to azadirachtin concentrations. Concerning susceptibility of different developmental stages, young larvae were the most sensitive. Foliar treatment was the most efficient, with 100% mortality for all three larval stages at high concentrations (10 ml/l of NeemAzal T/S) compared with 78–87% mortality with soil treatment (at 3.0 g/l NeemAzalU). The findings are discussed in the context of integrated control of WF in protected cultivation environments in the humid tropics.     

Identification and Localization of a Rickettsia sp. in Bemisia tabaci (Homoptera: Aleyrodidae)

Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor “Candidatus Portiera aleyrodidarum,” an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the sweet potato whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbiont-housing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.     

Identification and localization of a Rickettsia sp. in Bemisia tabaci (Homoptera: Aleyrodidae)

Whiteflies (Homoptera: Aleyrodidae) are sap-sucking insects that harbor "Candidatus Portiera aleyrodidarum," an obligatory symbiotic bacterium which is housed in a special organ called the bacteriome. These insects are also home for a diverse facultative microbial community which may include Hamiltonella, Arsenophonus, Fritchea, Wolbachia, and Cardinium spp. In this study, the bacteria associated with a B biotype of the sweet potato whitefly Bemisia tabaci were characterized using molecular fingerprinting techniques, and a Rickettsia sp. was detected for the first time in this insect family. Rickettsia sp. distribution, transmission and localization were studied using PCR and fluorescence in situ hybridizations (FISH). Rickettsia was found in all 20 Israeli B. tabaci populations screened but not in all individuals within each population. A FISH analysis of B. tabaci eggs, nymphs, and adults revealed a unique concentration of Rickettsia around the gut and follicle cells, as well as a random distribution in the hemolymph. We postulate that the Rickettsia enters the oocyte together with the bacteriocytes, leaves these symbiont-housing cells when the egg is laid, multiplies and spreads throughout the egg during embryogenesis and, subsequently, disperses throughout the body of the hatching nymph, excluding the bacteriomes. Although the role Rickettsia plays in the biology of the whitefly is currently unknown, the vertical transmission on the one hand and the partial within-population infection on the other suggest a phenotype that is advantageous under certain conditions but may be deleterious enough to prevent fixation under others.     

Evaluation of the lady beetle,Serangium parcesetosum for control of Bemisia tabaci on greenhouse eggplant in the Mediterranean region

Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is one of the most serious pests of greenhouse crops. It is mainly controlled by chemical means, requiring some 10–12 sprays during the average growing season in Turkey. There is growing interest in finding alternatives to pesticides for control of B. tabaci in greenhouse crops because this heavy pesticide usage disrupts biocontrol and leads to rapid build-up of insecticide resistance in the pest. In our study, the control of B. tabaci on greenhouse eggplants was evaluated following releases of the lady beetle Serangium parcesetosum Sicard (Coleoptera: Coccinellidae). In cage experiments, four adults per plant were introduced and, within 3–4 weeks, resulted in 97 and 98% reductions in whitefly populations in 2004 and 2005, respectively. In a large plot experiment, two adults per plant were released only one time. Beetle larvae were observed through 2–9 weeks after release. The density of whitefly in large plot receiving beetle adults showed fluctuations to a level lower than in control plot receiving no beetle in 2004 and 2006. Further study is needed to develop new managing strategies in biological control of B. tabaci with S. parcesetosum in protected culture.     

Functional and numerical responses of Propylea dissecta (Col., Coccinellidae)

The functional response of a ladybeetle, Propylea dissecta, to increasing density of aphid, Aphis gossypii, was of the curvilinear shape depicting Holling's type II response with fourth instar larva being the most voracious stage when compared with adult male and female. Prey handling time by different predatory stages decreased from 65.45 to 8.72 min with increase in prey density from 25 to 800. The predator aggregation and high prey density reduces the searching efficiency of the predator. Area of discovery was highest (1.4437) when a single predator was searching at minimum aphid density (25) and lowest (0.0366) when eight predators were searching at a constant aphid density (200). Mutual interference and quest constants were 0.75 and 0.40, respectively. The reproductive numerical response, in terms of eggs laid, increased curvilinearly with prey density and female laid 70.5 ± 5.55 eggs when exposed to highest prey density (400) and 12.3 ± 0.79 eggs at lowest prey density (10). The similar shapes of both functional and reproductive responses indicate that both responses are interlinked and function simultaneously.     

Electrophoretic analysis of the prey spectrum of Teretrius nigrescens (Lewis) (Col., Histeridae), a predator of Prostephanus truncatus (Horn) (Col., Bostrichidae), in Mexico, Honduras, and Benin

Abstract: Extensive collections of Teretrius nigrescens in Mexico, Honduras, and Benin, were electrophoretically analysed to elucidate the prey spectrum of the predator. Both polyacrylamide gel electrophoresis and cellulose acetate electrophoresis were used. Beetles were sampled with pheromone traps, using the synthetic aggregation pheromone of Prostephanus truncatus , and directly from farmers' maize stores. The proportion of electrophoretically detected prey protein from adult T. nigrescens in pheromone traps was low: of the 1108 specimens analysed, only in 34 cases, prey protein could be clearly identified. More frequently, prey protein was detected in adult T. nigrescens sampled in maize stores in Mexico, Honduras, and Benin, with 87 samples showing distinct prey bands of the total 1214 predators analysed. Of the 241 T. nigrescens larvae sampled in maize stores in Benin, 136 showed distinct bands of prey protein. In all samples, P. truncatus was the most frequently detected prey species. The second most often identified prey species was Sitophilus zeamais . The results are discussed with regard to various methods for prey spectrum analysis and specifically the biology of T. nigrescens .