B型烟粉虱对23种寄主植物适应度的评估和聚类分析

本文利用前期开发的两个寄主植物适应度评估模型对B型烟粉虱能够完成发育的23种寄主进行了寄主适应度评估,并对评估结果进行了聚类分析,分析结果显示供试烟粉虱种群存在明显的寄主偏好性,黄瓜与甘蓝为嗜好寄主,繁殖力大,若虫成活率高,非常有利于烟粉虱的种群发育;而其它寄主在营养状况、物理性状及次生化合物的综合作用下,烟粉虱的寄主植物适应度变化较大且整体低于嗜好寄主,结果暗示烟粉虱的寄主生态位可能存在从核心到周缘的分层现象。比较了两个评估模型的分析结果,虽然在低层聚类中存在差异,但高层聚类的结果趋于一致。     

Olfactory Cues Used in Host Selection by Frankliniella occidentalis (Thysanoptera: Thripidae) in Relation to Host Suitability

Olfactory responses of Frankliniella occidentalis (Pergande) to odors from six vegetable host plants-cabbage (Brassica oleracea), lettuce (Lactuca sativa), cucumber (Cucumis sativus), eggplant (Solanum melongena), celery (Apium graveolens) and garlic (Allium sativum) - were measured in choice tests in a Y-tube olfactometer, while host suitability of these same plants was assessed based on life table parameters-development time, survival rates, fertility, offspring sex ratio, female longevity, and an index of population change (I) - measured on leaf disks. Olfactory response was measured on both undamaged and mechanically-damaged plants. Regardless of plant damaged, female F. occidentalis responded positively to the odors of cabbage, lettuce, cucumber, and eggplant, but showed negative responses to celery and garlic, when offered a choice of plant odor or clean air. When female thrips were offered choices between each possible pairing of undamaged plants, or pairings of mechanically-damaged plants, the order of preference was cabbage = lettuce = cucumber > eggplant > celery = garlic. Male thrips responded differently, males responded positively only to undamaged lettuce and eggplant compared to clean air, while among mechanically-damaged plants only cucumber elicited a positive response. Given a choice between all possible pairings of undamaged plants, male thrips preferred lettuce to celery, and eggplant to garlic, whereas among pairings of mechanically-damaged plants male thrips preferred lettuce to celery, and cucumber to eggplant. The order of suitability of the six host plants based on life table parameters for F. occidentalis was essentially the same as the order of preference by female thrips. These results indicate that host plant odor is an important cue for female F. occidentalis in recognizing hosts suitable for oviposition. Information on plant attraction and repellency may be useful in thrips pest management. In addition, the correspondence of preference and performance that we found suggests that evolution of local host adaptation and, perhaps, host specialization, is possible.     

Effects of Tomato chlorosis virus on the performance of its key vector,Bemisia tabaci,in China

Tomato chlorosis virus (ToCV), which is a newly emerged and rapidly spreading plant virus in China, has seriously reduced tomato production and quality over the past several years. In this study, the effect of ToCV on the demography of the whitefly, Bemisia tabaci biotype Q (Hemiptera: Aleyrodidae), fed on infected and healthy tomato plants was evaluated using the age‐stage, two‐sex life table. When reared on ToCV‐infected tomato plants, the fecundity, length of oviposition period and female adult longevity of B. tabaci biotype Q decreased significantly, while the pre‐adult duration significantly increased compared to controls reared on healthy tomatoes. Consequently, the intrinsic rate of increase (r) and finite of increase (λ) of B. tabaci biotype Q on ToCV‐infected tomato plants significantly decreased compared to those on healthy tomatoes. Population projection predicted that a population of B. tabaci biotype Q fed on ToCV‐infected tomatoes increases slower than on healthy plants. These findings demonstrated that ToCV infection decreased the performance of B. tabaci biotype Q on tomato plants.     

Feeding behaviour and performance of different populations of the black currant‐lettuce aphid,Nasonovia ribisnigri,on resistant and susceptible lettuce

When crops are bred for resistance to herbivores, these herbivores are under strong selection pressure to overcome this resistance, which may result in the emergence of virulent biotypes. This is a growing problem for crop species attacked by aphids. The Nr‐gene in lettuce confers near‐complete resistance against the black currant‐lettuce aphid, Nasonovia ribisnigri (Mosely) (Hemiptera: Aphididae). Since 2007, populations of N. ribisnigri have been reported in several locations in Europe to infest resistant lettuce varieties that possess the Nr‐gene. The objective of this study was to analyse the behaviour and level of virulence of several N. ribisnigri populations observed to have colonized Nr‐locus‐containing lettuce lines. We analysed the stylet penetration and feeding behaviour, and the performance of these N. ribisnigri populations on resistant and susceptible lettuce lines. Large variation in the degree of virulence to the Nr‐locus‐containing lettuce lines was found among populations of the Nr:1 biotype. The German population was highly virulent on the Nr‐containing resistant lettuce lines, and showed similar feeding behaviour and performance on both the susceptible and resistant lettuces. The French population from Paris was the second most virulent, though reproduction on the resistant lines was reduced. The French population from Perpignan and a population from Belgium, however, showed reduced performance and feeding rate on the resistant compared to the susceptible lettuces. The lettuce background in which the Nr‐gene is expressed influences the level of resistance to the various Nr:1 aphid populations, because the performance and feeding behaviour differed between the aphids on the cultivars (romaine lettuce) compared to the near‐isogenic lines (butterhead/iceberg lettuce). This study also shows that being able to feed on a plant not automatically implies that a population can successfully develop on that plant, because aphids showed phloem ingestion during the 8‐h recording period on resistant lettuce, but were not able to survive and reproduce on the same lettuce line.     

Host preference and suitability of some selected crops for two biotypes of Bemisia tabaci in Ghana

The economic importance of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is mainly due to its wide host range, variable kinds of damage, and great intraspecific variation. The delineation of two African biotypes of this pest has been carried by molecular, ecological, and host‐affiliation approaches, with largely consistent results. However, an understanding of its intricate host–pest interaction is necessary as a basis of its sustainable integrated control. This study investigated the host preference and suitability of cassava and okra biotypes of B. tabaci, based on multiple‐choice landing and oviposition preference assays and stage‐specific survival on eight common whitefly hosts. The cassava biotype significantly preferred cassava, Manihot esculenta, for landing and oviposition, but did not oviposit on okra, Abelmoschus esculentus. The okra biotype preferred okra, oviposited on eggplant, Solanum melongena, tomato, Lycopersicon esculentum, garden egg, Solanum integrifolium, and cowpea, Vigna unguiculata, but did not oviposit on cassava. The okra biotype developed on all hosts except cassava, but only survived marginally on cabbage, Brassica oleracea, and pepper, Capsicum annum var. grosum, while the cassava biotype did not develop on okra, cabbage, or pepper. Thus the observed host acceptance of the two biotypes is wider than earlier reported by host transfer experiments and molecular genetic surveys. Mortality was highest in the first instar nymphal stage, during which total mortality occurred on non‐hosts. Development time was slightly longer on marginal hosts than on the preferred hosts. Cowpea, garden egg, and tomato are additional common hosts of the two biotypes, whose role as reservoir hosts and biotype interbreeding grounds should be investigated further.     

Morphological variation inBemisia endosymbionts

Summary The ultrastructure of the endosymbionts of several populations of whitefly (Homoptera: Aleyrodidae) was examined using transmission electron microscopy. Consistent differences in morphology and relative number of endosymbionts were observed between species and biotypes of whitefly within the Bemisia taxon.Bemisia argentifolii (=B. tabaci B biotype) individuals from Hawaii, Florida, and Arizona contained two morphological types of microorganisms housed within the mycetocyte cells of immature whiteflies. In contrast, individuals from populations ofB. tabaci A biotype from Arizona and Mexico, andB. tabaci Jatropha biotype from Puerto Rico, consistently contained three distinct morphological types of microorganisms within their mycetocytes. Organisms fromB. tabaci A and Jatropha biotypes differed from each other in the relative frequency of each type of microorganism. These observations suggest that different whitefly biotypes may have variable combinations of micro-fauna, with some possibly unique to each group, and furthers the hypothesis that variation in whitefly endosymbionts may be associated with the development of biotypes.     

Functional divergence of three glutathione transferases in two biotypes of the English grain aphid,Sitobion avenae

The English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is a significant pest of cereal crops, but molecular factors and mechanisms that underpin its ability to develop differential biotypes on variable host plants are still not well understood. In this study, we investigated the interactions between two plant secondary metabolites (i.e., gramine and gallic acid) and three glutathione S-transferases (GSTs) of S. avenae. Using artificial diets complemented or not with one of these two plant compounds, we found that gramine had relatively stronger negative effects on fitness of S. avenae biotype 3 (adapted to barley), and gallic acid on that of biotype 4 (adapted to wheat). Gramine significantly induced overexpression of SaveGST1 and SaveGST2 in biotype 4, but not in biotype 3. Gramine also reduced SaveGST3 expression in biotype 4, but not in biotype 3, suggesting biotype-specific effect of GSTs’ regulation. In the treatments with gallic acid, the overexpression of SaveGST1, but not SaveGST2 or SaveGST3, was significantly induced in both biotypes, suggesting a critical role of SaveGST1 in detoxification of phenolic compounds such as gallic acid. The total constitutive GST activity was much higher in biotype 4 than in biotype 3. Significant increase in GST activity was obtained by the addition of both secondary metabolites in biotype 4, but not in biotype 3, showing significantly higher expression plasticity of GSTs in biotype 4. Thus, both constitutive and induced expression of GSTs could affect the adaptability of S. avenae on plants with variable secondary compounds, and thus contribute to the divergence of biotypes in this aphid species.     

How does the host‐specialized aphid deal with food deficiency?

Aphis gossypii Glover shows obvious host specialization, with cucurbit‐ and cotton‐specialized biotypes or host races in many regions. Because its annual natal host crops senesce earlier the cucurbit‐specialized biotype may suffer food deficiency. The method this biotype uses to overcome this challenge is still poorly understood. In order to understand the potential of the cucurbit‐specialized biotype aphids in host shift and usage, the performance of this biotype on cotton (Gossypium hirsutum), a common but poor quality host plant, was explored in this study. The cucurbit‐specialized aphids could establish populations on cotton only when these plants had at least nine leaves, and subsequent populations developed rather slowly. The presence of whitefly populations on cotton improved the success rate of cucurbit‐specialized aphids. The cucurbit‐specialized aphids were mainly distributed on the older leaves of cotton, with only a few settling on the upper leaves. The cucurbit‐specialized aphids reared on cotton for 40, 54 and 61 days still maintained strong preference for their natal host plant, cucumber (Cucumis sativus), rather than cotton, and their net reproductive rates and intrinsic rates of natural increase were dramatically lower when they were transferred onto new six‐leaf cotton plants or detached leaves. Therefore, we concluded that the cucurbit‐specialized aphids have the potential to utilize mature or whitefly‐stressed cotton plants, but that this feeding experience on cotton did not alter their specialization for cucurbits. Some cotton plants could act as a temporary host for the cucurbit‐specialized aphids to overcome food deficiency arising from senescing cucurbits.     

Comparison of performance on different host plants between the B biotype and a non-B biotype of Bemisia tabaci from Zhejiang, China

The capacity of the B biotype of the whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), to invade has often been linked to its presumably wider host range than the non‐B indigenous biotypes. However, there are few experimental studies of the relative performance of the B biotype and non‐B biotypes on different host‐plant species. Here, we compared the performance of the B biotype and an indigenous non‐B biotype (China‐ZHJ‐1) of B. tabaci from Zhejiang, China on five commonly cultivated host plants, each from a different family: cotton, tobacco, cabbage, squash, and kidney bean. We also examined the effect of rearing host plants on the performance of the B biotype. Overall, the performance of the B biotype on the five species of plants was much better than that of the indigenous non‐B population. On tobacco, cabbage, and kidney bean, no individuals of ZHJ‐1 completed development to adulthood, whereas the B biotype developed successfully from egg to adult on all three plants. On squash, the B biotype survived better, developed to adulthood earlier and had a higher fecundity than ZHJ‐1. The two biotypes performed more equally on cotton, but even on this plant the B biotype female adults lived nearly twice as long as that of ZHJ‐1 and may have realized a higher life‐time fecundity. The B biotype also showed a substantial capacity to acclimatize to alternative host plants for improved survival and reproduction, on both highly suitable and marginally suitable host plants. We conclude that the host range of the B biotype of B. tabaci may be much wider than those of some indigenous biotypes, and this advantage of the B biotype over the non‐B biotypes may assist in its invasion and displacement of some indigenous biotypes in the field.     

Tomato yellow leaf curl virus infection of tomato does not affect the performance of the Q and ZHJ2 biotypes of the viral vector Bemisia tabaci

Abstract To better understand the etiology of begomovirus epidemics in regions under invasion we need to know how indigenous and invasive whitefly vectors respond to virus infection. We investigated both direct and indirect effects of infection with Tomato yellow leaf curl virus (TYLCV) on the performance of the invasive Q biotype and the indigenous Asian ZHJ2 biotype of whitefly Bemisia tabaci. The Q biotype performed better than the ZHJ2 biotype on either uninfected or virus‐infected tomato plants. However, virus‐infection of host plants did not, or only marginally affected, the performance of either biotype of whiteflies in terms of fecundity, longevity, survival, development and population increase. Likewise, association of the vectors with TYLCV did not affect fecundity and longevity of the Q or ZHJ2 biotypes on cotton, a non‐host of TYLCV. These results indicate that the alien Q biotype whitefly, but not the indigenous ZHJ2 biotype, is likely to become the major vector of TYLCV in the field and facilitate virus epidemics.     

Different effects of exogenous jasmonic acid on preference and performance of viruliferous Bemisia tabaci B and Q

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), B and Q biotypes have caused severe losses to crops and vegetables through virus transmission. Our previous studies showed that Q is more efficient than B in acquisition and transmission of tomato yellow leaf curl virus (TYLCV) and viruliferous Q is better equipped than B in counterattacking jasmonic acid (JA)‐related plant defense. To understand how plant‐mediated defensive responses involving JA affect insect vectors within a tritrophic framework of plants, insects, and viruses, we examined the effects of exogenous JA on preference and performance of non‐viruliferous and viruliferous B and Q on tomato plants (Solanum lycopersicum L., Solanaceae). Our results demonstrated a significantly lower fecundity, shorter longevity, shorter developmental time, and lower survival rate of whiteflies on JA‐treated than on control plants. In addition, viruliferous Q performed significantly better than B in fecundity, longevity, developmental time, and survival rate. When given a choice between JA‐treated and control tomato plants, viruliferous Q was not repelled to JA‐treated plants when the JA concentration was 0.01 and 0.1 mm , whereas others all preferred the untreated control plants. Exogenous JA increased the concentration and the composition of plant volatiles, such as α‐terpinene and β‐ocimene, which deterred whiteflies in a Y‐tube bioassay. It is worth noting that Q has a mutualistic relationship with TYLCV to counteract the host defenses. A better understanding of tritrophic interactions between plants, insects, and viruses will facilitate the development of sustainable management of this invasive global pest.     

Ingestion, transmission, and persistence of Chino del tomate virus (CdTV), a New World begomovirus, by Old and New World biotypes of the whitefly vector Bemisia tabaci

Two whitefly biotypes of Bemisia tabaci, from either the Eastern or Western Hemisphere, respectively, were compared with respect to their competency to ingest and their efficiency to transmit the New World begomovirus, Chino del tomate virus (CdTV). The AZ A biotype of B.tabaci originates from the arid southwestern USA and northwestern Mexico, while the B biotype has an origin in the Middle East or Northern Africa. The ability of these two vector biotypes to ingest and subsequently to transmit CdTV were evaluated for an acquisition‐access period (AAP) that ranged from 0 to 72 h, followed by a 48 h inoculation‐access period (IAP). Individual adult whiteflies were monitored for CdTV ingestion using polymerase chain reaction (PCR) to detect the viral coat protein gene (AV1 ORF), and transmission efficiency (frequency) was determined by allowing potentially viruliferous whiteflies access to tomato seedlings following each experimental AAP. PCR results for individual adult whiteflies indicated that CdTV was ingested from infected tomato plants by both biotypes 93% of the time. Transmission frequencies by both vector biotypes increased with longer AAPs. However, the AZ A biotype transmitted CdTV 50% of the time, compared to only 27% for the B biotype. Evidence that virus was ingested with equal competency by the A and B biotypes confirmed that both vectors were capable of ingesting CdTV from tomato at the same frequency, even when the AAP was 0.5 h. Consequently, either the acquisition and/or transmission stages of the pathway, rather than ingestion competency, were responsible for differences in vector‐mediated transmissibility. Detection frequency of CdTV, after 48 h AAP, by PCR in single females of AZ B biotype was significantly higher than males.     

烟粉虱对四种蔬菜寄主的选择性

为探讨利用趋避作用防治烟粉虱的可能性,进行了3方面试验：1）烟粉虱Bemisia tabaci (Gennadius) 对黄瓜、花椰菜、油菜和莴苣等4种蔬菜的寄主选择性; 2）互喷烟粉虱不同嗜好的寄主植物汁液对其寄主选择性的影响; 3）不同间作方式对黄瓜叶上烟粉虱成虫密度的影响。结果表明,烟粉虱对供试植物有明显的选择性,其嗜好程度为花椰菜>黄瓜>油菜>莴苣。喷施莴苣和花椰菜汁液对烟粉虱的寄主选择性均有显著影响,喷施莴苣原液后,花椰菜和黄瓜上的成虫数分别减少79.6%和87.4%,花椰菜上的着卵量减少84.3%;喷施花椰菜原液后,莴苣上的成虫数和着卵量分别增加82.4%和79.2%,表明不同蔬菜中的内含物是引起烟粉虱对寄主选择性的重要原因。在黄瓜中间作莴苣可使黄瓜叶上烟粉虱成虫数平均减少76.5%;间作花椰菜时,通过诱集作用,也可使黄瓜叶上的成虫数平均降低69.7%。这些结果为利用喷施蔬菜汁液和间作方式控制烟粉虱危害提供了理论依据。     

Abundance of Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) and its parasitoids on vegetables and cassava plants in Burkina Faso (West Africa)

The whitefly Bemisia tabaci is a pest of many agricultural and ornamental crops worldwide and particularly in Africa. It is a complex of cryptic species, which is extremely polyphagous with hundreds of host plants identified around the world. Previous surveys in western Africa indicated the presence of two biotypes of the invasive MED species (MED‐Q1 and MED‐Q3) living in sympatry with the African species SSA and ASL. This situation constitutes one of the rare cases of local coexistence of various genetic entities within the B. tabaci complex. In order to study the dynamics of the distribution and abundance of genetic entities within this community and to identify potential factors that could contribute to coexistence, we sampled B. tabaci populations in Burkina Faso in 2015 and 2016 on various plants, and also their parasitoids. All four genetic entities were still recorded, indicating no exclusion of local species by the MED species. While B. tabaci individuals were found on 55 plant species belonging to eighteen (18) families showing the high polyphagy of this pest, some species/biotypes exhibited higher specificity. Two parasitoid species (Eretmocerus mundus and Encarsia vandrieschei) were also recorded with E. mundus being predominant in most localities and on most plants. Our data indicated that whitefly abundance, diversity, and rate of parasitism varied according to areas, plants, and years, but that parasitism rate was globally highly correlated with whitefly abundance suggesting density dependence. Our results also suggest dynamic variation in the local diversity of B. tabaci species/biotypes from 1 year to the other, specifically with MED‐Q1 and ASL species. This work provides relevant information on the nature of plant–B. tabaci‐parasitoid interactions in West Africa and identifies that coexistence might be stabilized by niche differentiation for some genetic entities. However, MED‐Q1 and ASL show extensive niche overlap, which could ultimately lead to competitive exclusion.     

Identification of Aphis gossypii Glover (Hemiptera: Aphididae) Biotypes from Different Host Plants in North China

Background

The cotton-melon aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a polyphagous species with a worldwide distribution and a variety of biotypes. North China is a traditional agricultural area with abundant winter and summer hosts of A. gossypii. While the life cycles of A. gossypii on different plants have been well studied, those of the biotypes of North China are still unclear.

Results

Host transfer experiments showed that A. gossypii from North China has two host-specialized biotypes: cotton and cucumber. Based on complete mitochondrial sequences, we identified a molecular marker with five single-nucleotide polymorphisms to distinguish the biotypes. Using this marker, a large-scale study of biotypes on primary winter and summer hosts was conducted. All A. gossypii collected from three primary hosts—hibiscus, pomegranate, and Chinese prickly ash—were cotton biotypes, with more cotton-melon aphids found on hibiscus than the other two species. In May, alate cotton and cucumber biotypes coexisted on cotton and cucumber seedlings, but each preferred its natal host. Both biotypes existed on zucchini, although the cucumber biotype was more numerous. Aphids on muskmelon were all cucumber biotypes, whereas most aphids on kidney bean were cotton biotypes. Aphids on seedlings of potato and cowpea belong to other species. In August, aphids on cotton and cucumber were the respective biotypes, with zucchini still hosting both biotypes as before. Thus, the biotypes had different fitnesses on different host plants.

Conclusions

Two host-specialized biotypes (cotton and cucumber) are present in North China. Hibiscus, pomegranate, and Chinese prickly ash can serve as winter hosts for the cotton biotype but not the cucumber biotype in North China. The fitnesses of the two host-specialized biotypes differ on various summer hosts. When alate aphids migrate to summer hosts, they cannot accurately land on the corresponding plant.     

No evidence for early fitness penalty in glyphosate‐resistant biotypes of Conyza canadensis: Common garden experiments in the absence of glyphosate

Strong selection from herbicides has led to the rapid evolution of herbicide‐resistant weeds, greatly complicating weed management efforts worldwide. In particular, overreliance on glyphosate, the active ingredient in RoundUp^®, has spurred the evolution of resistance to this herbicide in ≥40 species. Previously, we reported that Conyza canadensis (horseweed) has evolved extreme resistance to glyphosate, surviving at 40× the original 1× effective dosage. Here, we tested for underlying fitness effects of glyphosate resistance to better understand whether resistance could persist indefinitely in this self‐pollinating, annual weed. We sampled seeds from a single maternal plant (“biotype”) at each of 26 horseweed populations in Iowa, representing nine susceptible biotypes (S), eight with low‐level resistance (LR), and nine with extreme resistance (ER). In 2016 and 2017, we compared early growth rates and bolting dates of these biotypes in common garden experiments at two sites near Ames, Iowa. Nested ANOVAs showed that, as a group, ER biotypes attained similar or larger rosette size after 6 weeks compared to S or LR biotypes, which were similar to each other in size. Also, ER biotypes bolted 1–2 weeks earlier than S or LR biotypes. These fitness‐related traits also varied among biotypes within the same resistance category, and time to bolting was inversely correlated with rosette size across all biotypes. Disease symptoms affected 40% of all plants in 2016 and 78% in 2017, so we did not attempt to measure lifetime fecundity. In both years, the frequency of disease symptoms was greatest in S biotypes and similar in LR versus ER biotypes. Overall, our findings indicate there are no early growth penalty and possibly no lifetime fitness penalty associated with glyphosate resistance, including extremely strong resistance. We conclude that glyphosate resistance is likely to persist in horseweed populations, with or without continued selection pressure from exposure to glyphosate.     

Volatiles released from foliar extract of host plant enhance landing rates of gravid Polygonia c‐album females,but do not stimulate oviposition

The role of olfactory cues for host search is much less investigated in day‐active butterflies than in their relatives, the nocturnal moths. The goal of this study was to investigate whether host‐plant volatiles from foliar extracts of hop, Humulus lupulus L. (Cannabaceae), evoke electroantennographic (EAG) responses, increase landing rates, and stimulate egg‐laying behavior of gravid Polygonia c‐album L. (Lepidoptera: Nymphalidae) females. Eighty‐nine volatile compounds were detected in a non‐concentrated methanol extract of hop by gas chromatography–mass spectrometry, 11 of which elicited an EAG response. Concentration of the crude extract significantly reduced landing rates on artificial leaves treated with the sample due to loss of volatile compounds, but after landing the oviposition response of gravid females was not affected. A mixture of eight commercially available EAG‐active volatiles increased the landing rate of gravid females to their source but did not act as oviposition stimulants. Dividing the volatile compounds into two groups – consisting of (1) hexanal, (E)‐2‐hexenal, octanal, nonanal, and decanal, and (2) sulcatone, humulene, and benzyl alcohol – obliterated effectiveness, revealing synergism between compounds. Although volatiles did not stimulate oviposition, they significantly contributed to the distribution of eggs by increasing the landing rates on treated artificial leaves.     

Characterization of a fungal strain capable of degrading chlorpyrifos and its use in detoxification of the insecticide on vegetables

A fungal strain capable of utilizing chlorpyrifos as sole carbon and energy sources was isolated from soil by enrichment cultivation approach. The half-lives of degradation (DT₅₀) for chlorpyrifos at concentrations of 1, 10, and 100 mg l⁻¹ by the fungal strain DSP in mineral salt medium were measured to be 2.03, 2.93, and 3.49 days, respectively. Two cell-free extracts [E (1:10) and E (1:20)] from the fungal strain DSP in bran–glucose medium were prepared and used to enhance chlorpyrifos degradation on vegetables. Compared with the controls, the DT₅₀ of chlorpyrifos were reduced by 70.3%, 65.6%, 80.6%, 80.6%, and 86.1%, and by 53.8%, 43.2%, 66.0%, 54.3%, and 67.7% on E (1:20) and E (1:10) treated pakchoi, water spinach, Malabar spinach, haricot beans, and pepper, respectively. The 7-day residual values (R ₇) of chlorpyrifos on E (1:10) treated vegetables were all lower than the corresponding maximum residue levels of European Union (EU MRLs), except that the R ₇ value on haricot beans was slightly higher than the corresponding EU MRLs. The results indicate that cell-free extracts could rapidly degrade chlorpyrifos residues on vegetables.     

Identification,comparison, and functional analysis of salivary phenol‐oxidizing enzymes in Bemisia tabaci B and Trialeurodes vaporariorum

The differences in the ability of the invading whitefly, Bemisia tabaci (Gennadius) (commonly known as biotype B and hereafter as B) and Trialeurodes vaporariorum (Westwood) (both Hemiptera: Aleyrodidae) to utilize salivary phenol‐oxidizing enzymes – polyphenol oxidase (PPO) and peroxidase (POD) to detoxify plant defensive phenolic compounds were explored. Polyphenol oxidase and POD were found in the saliva of both B and T. vaporariorum. For tomato colonies, the PPO and POD activities in the watery saliva of B were 2.27‐ and 1.34‐fold higher than those of T. vaporariorum. The PPO activities against specific phenolic compounds commonly found in plants were compared. The activities of those from B were significantly greater than those from T. vaporariorum. We also measured PPO activity in both species after they had fed on plants that were undamaged or had been previously damaged with either a plant pathogen [Phytophthora infestans (Mont.) de Bary (Peronosporales)] infection, mechanical damage, B infestation, or exogenous salicylic acid. For B, PPO activities in watery saliva increased 229, 184, 152, and 139% in response to the four treatments, whereas those of T. vaporariorum only increased 133, 119, 113, and 103%, respectively. Biotype B infestation significantly increased the total phenolic content of tomato leaves. Meanwhile, feeding on tomato infestation with B had no significant effect on the survival rate of B, but decreased the survival rate of T. vaporariorum significantly. These results suggest that B has stronger ability utilizing PPO to detoxify high concentrations of phenolics than T. vaporariorum, and this contributes to a significant advantage for B to hold high fitness on plants with induced resistance. Possible roles of salivary PPO in the competition between B and T. vaporariorum are discussed.