Preventive measures to limit the spread of Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) in mainland Europe

Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) vectors the most important citrus disease, namely huanglongbing (HLB) or citrus greening. This vector has been recently found on the European mainland in the north-western region of the Iberian Peninsula (Spain and Portugal), although HLB has not yet been detected in Europe. Thus, preventing the spread of the vector is currently an urgent priority. Here, we show two prevention methods to avoid the spread of this psyllid from areas where it is present to psyllid-free areas. Our results showed that two types of anti-insect mesh with a pore size of 0.4 × 0.77 mm² and 0.27 × 0.77 mm² were effective in excluding T. erytreae in two field experiments. These results have direct implications in the nursery plant production system, which should adopt meshes with pore sizes small enough to guarantee the exclusion of T. erytreae. Additionally, we evaluated the longevity of T. erytreae on fruit to understand the risk of dispersion of the psyllid with unprocessed fruit movement between infested and non-infested areas. The longevity of T. erytreae on mandarin and lemon fruit under winter conditions (13.8°C and 85.4% of relative humidity) was 11 days for both fruits. We anticipate that our results could help enhance the preventive measures in citrus fruit areas without a presence of T. erytreae.     

Sampling and distribution pattern of Trioza erytreae Del Guercio, 1918 (Hemiptera: Triozidae) in citrus orchard

Developing efficient sampling protocols is essential to monitor crop pests. One vector of the citrus disease HLB, the African citrus psyllid Trioza erytreae Del Guercio, 1918 (Hemiptera: Triozidae), currently threatens the lemon industry throughout the Mediterranean region. In this work, a pool of sampling methods devoted to monitoring the population of T. erytreae was compared, its spatial distribution in the orchard was assessed, and the minimum sampling effort for the best sampling method was estimated. Three lemon orchards in North-western Portugal were sampled for one year using two types of yellow sticky traps (standard yellow and fluorescent Saturn yellow), B-vac sampling and sweep net sampling. The method that best performed, in terms of cost-efficiency, was the yellow sticky traps. The two colours of the sticky traps tested did not yield a significantly different number of catches. The spatial distribution throughout the orchards was found to be aggregated towards the borders. A minimum of three sticky traps per hectare was found to be enough to estimate the population at 90% accuracy for the mean during the outbreak. These results should help to monitor and anticipate outbreaks that may even colonize neighbour orchards. Studies on the local dispersion patterns of T. erytreae throughout the orchard are mandatory to further refine and optimize efficient monitoring protocols.     

Host suitability and feeding preference of the African citrus triozid Trioza erytreae Del Guercio (Hemiptera: Triozidae), natural vector of “Candidatus Liberibacter africanus”

African citrus greening (ACGD) and huanglongbing (HLB) diseases are the most damaging diseases of citrus worldwide. Currently, the disease has no cure and has been attributed to the collapse of the citrus industry in several countries. In Africa, the causative agent “Candidatus” Liberibacter africanus is vectored by African citrus triozid (ACT) Trioza erytreae Del Guercio (Hemiptera: Triozidae). African citrus triozid is native to Africa but has been recently reported in Asia and Europe. Apart from citrus, Murraya koenigii (L.) and Clausena anisata (Willd) Hook. F. ex Benth. are also considered as preferred host plants. At present, there is scant information on host plant suitability and preference of T. erytreae. Also, there are contradictory reports on its reproduction and survival on rutaceous and non‐rutaceous host plants. In the present study, we tested the suitability and preference of rutaceous and non‐rutaceous trees and shrubs as potential ACT host plants in choice and no‐choice bioassays. The development from egg to the adult stage was longest on Calodendrum capense (Wright & Arn.) Engl. Host plants of superior quality accordingly to several ACT's biological parameters measured also revealed significantly higher morphometric characteristics. Our findings on the host status of the five rutaceous plants imply that these plants can greatly influence the population dynamics of ACT as well as the epidemiology of ACGD, and these can be a useful guide in the area‐wide management of the pest in Kenya.     

Diversity and phylogenetic analysis of endosymbionts from Trioza erytreae (Del Guercio) and its parasitoids in Kenya

The African citrus triozid (ACT), Trioza erytreae (Del Guercio), is the primary vector of Candidatus Liberibacter africanus (CLaf), the causative agent of Africa citrus greening disease (ACGD). This study evaluates the diversity of ACT parasitoids and further characterizes endosymbionts associated with both T. erytreae and its parasitoids that could be used as biological control agents of T. erytreae and management of ACGD. Mitochondrial cytochrome oxidase I gene was used to reconstruct T. erytreae and its parasitoids phylogeny, while 16S rRNA gene was used for the bacterial phylogeny. One well-supported clade of ACT was detected within the Triozidae phylogeny, while the parasitoid species clustered into four groups within eulophid and encyrtid phylogeny. The phylogenetic result of parasitoids was supported by morphological identification where five different parasitoid species could be identified, that is Tamarixia dryi, Psyllaephagus pulvinatus, Tetrastichus sp., Aphidencyrtus cassatus and Charipine species. Moreover, four eubacterial symbionts (Wolbachia,Rickettsia,Arsenophonus and Candidatus Liberibacter sp.) were detected in T. erytreae and three symbionts (Wolbachia,Rickettsia and Cardinuim) in the parasitoid specimens. Maximum likelihood phylogenetic inferences clustered the identified eubacterial symbionts within α and γ proteobacteria subdivisions. Phylogenetic inferences of 16S rRNA gene sequences indicated that Wolbachia strains from ACT and the parasitoids did not form a single monophyletic clade; however, both clustered within Supergroup B. The impacts of these parasitoid species and endosymbionts on ACT are still unknown, but their occurrence and broad distribution indicate the possibility of future use for control of T. erytreae.     

Interactions between citrus psylla,Trioza erytreae (Hem. Triozidae), and spiders in an unsprayed citrus orchard in the transvaal lowveld

During a two year survey, a total of 3,054 spiders represented by 21 families were sampled in an unsprayed citrus orchard in the Transvaal Lowveld. Numerically the Salticidae was the dominant family (34.4%) followed by the Theridiidae (21.9%), Thomisidae (11.9%), Araneidae (7.9%), Clubionidae (7.0%) and the Tetragnathidae (3.7%). Eighteen species of spiders were observed to prey on citrus psylla,Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), while six species trap nymphs and adults under their retreats and webs. There were significant positive correlations between the weekly psylla populations and the weekly populations of web-building spiders and wandering spiders present one to four weeks later but no significant correlation between the weekly spider populations and the weekly psylla populations present one to five weeks later. This seems to indicate that while spiders are unable to keep citrus psylla populations at acceptable low levels, they may contribute in reducing their numbers.      

Detection and Inoculation of Peanut Witches' Broom Phytoplasma (16SrII‐A) and Periwinkle Leaf Yellowing Phytoplasma (16SrI‐B) in Citrus Cultivars in Taiwan

To clarify the phytoplasma associated with Huanglongbing (HLB), a detection survey of phytoplasma in field citrus trees was performed using the standardized nested PCR assay with primer set P1/16S‐Sr and R16F2n/R16R2. The HLB‐diseased citrus trees with typical HLB symptoms showed a high detection of 89.7% (322/359) of HLB‐Las, while a low detection of phytoplasma at 1.1% (4/359) was examined in an HLB‐affected Wentan pummelo (Citrus grandis) tree (1/63) and Tahiti lime (C. latifolia) trees (3/53) that were co‐infected with HLB‐Las. The phytoplasma alone was also detected in a healthy Wentan pummelo tree (1/60) at a low incidence total of 0.3% (1/347). Healthy citrus plants were inoculated with the citrus phytoplasma (WP‐DL) by graft inoculation with phytoplasma‐infected pummelo scions. Positive detections of phytoplasma were monitored only in the Wentan pummelo plant 4 months and 3.5 years after inoculation, and no symptoms developed. The citrus phytoplasma infected and persistently survived in a low titre and at a very uneven distribution in citrus plants. Peanut witches' broom (PnWB) phytoplasma (16SrII‐A) and periwinkle leaf yellowing (PLY) phytoplasma belonging to the aster yellows group (16SrI‐B) maintained in periwinkle plants were inoculated into healthy citrus plants by dodder transmission. The PnWB phytoplasma showed infection through positive detection of the nested PCR assay in citrus plants and persistently survived without symptom expression up to 4 years after inoculation. Positive detections of the phytoplasma were found in a low titre and several incidences in the other inoculated citrus plants including Ponkan mandarin, Liucheng sweet orange, Eureka lemon and Hirami lemon. None of the phytoplasma‐infected citrus plants developed symptoms. Furthermore, artificial inoculation of PLY phytoplasma (16SrI‐B) into the healthy citrus plants demonstrated no infection. The citrus symptomless phytoplasma was identified to belong to the PnWB phytoplasma group (16SrII‐A).     

Biology and epidemics of Candidatus Liberibacter species,psyllid‐transmitted plant‐pathogenic bacteria

Candidatus Liberibacter species are Gram‐negative bacteria that live as phloem‐limited obligate parasites in plants, and are associated with several plant diseases. These bacteria are transmitted by insects called psyllids, or jumping plant lice, which feed on plant phloem sap. Citrus huanglongbing (yellow shoot) or citrus greening disease is associated with three different species of Ca. Liberibacter – Ca. L. asiaticus, Ca. L. africanus and Ca. L. americanus – all originally found on different continents. Ca. L. asiaticus is the most severe pathogen, spread by Asian citrus psyllid Diaphorina citri and causing devastating epidemics in several countries. Ca. L. africanus occurs in Africa where it is spread by the African citrus psyllid Trioza erytreae. Ca. Liberibacter solanacearum is associated with diseases in several solanaceous plants, and transmitted by potato psyllid Bactericera cockerelli. Zebra chip disease is causing large damage in potato crops in North America. In Europe Ca. Liberibacter solanacearum is associated with diseases of the Apiaceae family of plants, carrot and celery, and transmitted by psyllids Trioza apicalis and Bactericera trigonica. When Ca. Liberibacter is suspected as the disease agent, the diagnosis is confirmed by DNA‐based detection methods. Ca. Liberibacter‐associated plant diseases can be controlled by using healthy plant propagation material, eradicating symptomatic plants, and by controlling the psyllid populations spreading the disease.     

Distribution,degree of damage and risk of spread of Trioza erytreae (Hemiptera: Triozidae) in Kenya

The African citrus triozid (ACT), Trioza erytreae Del Guercio, is a destructive pest particularly on citrus, and vectors, “Candidatus” Liberibacter africanus (CLaf), which is the causal agent of the African citrus greening disease. Our study seeks to establish the distribution and host‐plant relationship of ACT across citrus production areas in Kenya. We also modelled the risk of spread using the maximum entropy modelling algorithm with known occurrence data. Our results infer that ACT is widely distributed and causes severe damage to four alternative host plants belonging to the family Rutaceae. The adults, immature stages (eggs and nymphs), galls and the percentage of infested leaves were significantly higher in shaded than unshaded trees. However, adult ACTs preferred Kenyan highlands to Victoria Lake and coastal regions. The average area under the curve of the model predictions was 0.97, indicating an optimal model performance. The environmental variables that most influenced the prediction were the precipitation of wettest quarter, precipitation of wettest month, mean diurnal range, temperature seasonality and mean temperature of the coldest quarter. The current prediction of ACT exceeded its existing range, especially in the Western, Nyanza, Central, Rift valley and Eastern regions of Kenya. The model predicted a contraction of suitable habitats for a potential spread in 2040 with an inland shift to higher altitudes in the cooler regions. The potential for further expansion to climatically suitable areas was more pronounced for the 2080 forecast. These findings provide relevant information to improve monitoring/surveillance and designing IPM strategies to limit its spread and damage.     

Essential oils of citrus fruit stimulate oviposition in the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae)

Female Mediterranean fruit flies (medfly) Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) perceive both qualitative and quantitative aspects of citrus fruit chemistry. However, the behavioural and biological adjustments of this response remain largely unknown. In the present study, the ovipositional responses of gravid female medflies to essential oils (i.e. the most critical resistance factor to medfly infestation) of various citrus fruits are investigated. In dual‐choice (treatment versus distilled water control) experiments, females lay significantly more eggs into pre‐punctured hollow oviposition hemispheres (domes) provided with 1 µL of citrus peel oil from sweet orange, satsuma mandarin, bitter orange, grapefruit and lemon compared with odourless domes. No‐choice tests show a weak effect of lemon essential oils in stimulating oviposition. The female ovipositional response to sweet orange oil (the most active in eliciting oviposition) is dose‐dependent. Additionally, limonene, the most abundant chemical in all citrus oils, stimulates oviposition, whereas linalool, a representative compound of immature citrus fruit associated with high toxicity against immature stages of fruit flies, has a significant deterrent effect. In further no‐choice tests, females lay approximately 23% fewer eggs in limonene (93%) (amount found in orange oil) and 60% fewer eggs in limonene 93% plus linalool 3% (approximately 10‐fold the amount found in orange oil) mixtures, relative to sweet orange oil. The results suggest that the limonene content accounts largely (but not completely) for the ovipositional responses observed in sweet orange oil, whereas high linalool proportions are capable of significantly masking and/or disrupting its stimulatory effects in citrus oils. The importance and practical implications of these findings with respect to understanding how citrus fruit chemistry influences the ovipositional responses of medfly is discussed.     

The parasitoid complex of the citrus psyllaTrioza erytreae (Del Guercio) [Homoptera: Psyllidae]

Associated with the citrus psylla,Trioza erytreae (Del Guercio), in Salisbury, Rhodesia, are two primary parasitoids and 13 secondary and tertiary hyperparasitoids. One of the primary parasitoidsTetrastichus? radiatus remains external to the psyllid host whereas the other primary,Psyllaephagus pulvinatus, is an internal parasitoid. The major secondary hyperparasitoidAphidencyrtus cassatus, which was recorded in large numbers, attacks both primary parasitoids. Accounts are given of the biology of the two primary parasitoids and ofA. cassatus. The other hyperparasites in the complex are numerically unimportant and summaries of their biology are contained in a table. A diagram is given to illustrate the interrelationships of the parasitoids in the citrus psylla complex. It is concluded that, apart from phenological effects on the insects and host plant, the two primary parasitoids have considerable impact in controlling numbers of their host,T. erytreae, and that the secondary parasitoidA. cassatus through its attacks on the primary parasitoids is also of major importance in determining population levels achieved by the citrus psylla. Some characteristics of the parasitoids in the complex are discussed which might explain the high population levels of citrus psylla achieved in the Salisbury area. Several research avenues exist which would clarify the feasibility of biological control procedures againstT. erytreae.     

Distribution ofGeotrichum candidum citrus race in citrus groves and non-citrus fields in Japan

The presence ofGeotrichum candidum citrus race, the citrus sour rot pathogen, was examined in soils of citrus groves and non-citrus fields of Japan. Soil samples were collected from 223 sites (118 sites in citrus groves, and 105 sites in fields cultivated with 33 species of non-citrus plants and in evergreen broad-leaved forest) in 11 main citrus-growing prefectures, and Hokkaido, a non-citrus-growing area. Of 236 soil samples from citrus groves, 95.76% containedG. candidum citrus race and 0.42% contained the non-citrus race; while of 210 samples from non-citrus fields, 62.85% and 4.76% contained the citrus race and the non-citrus race respectively. All of the citrus race isolates obtained either from citrus groves or non-citrus fields were pathogenic on lemon (Citrus limon) and satsuma mandarin (Citrus unshiu), but some of these isolates failed to infect orange (Citrus sinensis). The non-citrus races were pathogenic on ripe tomato fruit (Lycopersicon esculentum) and ripe muskmelon fruit (Cucumis melo var.reticulatus). Results indicated that citrus sour rot pathogen is widely distributed in citrus groves and non-citrus fields of diverse plant species in Japan.     

In vitro micrografting for production of Indian citrus ringspot virus (ICRSV)-free plants of kinnow mandarin (Citrus nobilis Lour × C. deliciosa Tenora)

Production of Indian citrus ringspot virus (ICRSV)-free plants from an infected plant of kinnow mandarin (Citrus nobilis Lour × C. deliciosa Tenora) is reported. The shoot apices of different sizes (0.2–1.0 mm) excised from the ICRSV-infected plant were micrografted onto decapitated rootstock seedlings of rough lemon (C. jambhiri). Micrograft survival depended on the size of shoot apex and the sucrose concentration of the culture medium. Increase in scion size from 0.2 to 0.7 mm resulted in an increase in micrografting success rate from 30.55 to 51.88%. Further, micrograft survival obtained with 0.2 mm was improved from 30.55 to 38.88% by increasing sucrose concentration in the culture media from 5 to 7.5%. The micrografted plants were tested for ICRSV using ELISA and RT-PCR. All plants raised from 0.2-mm scion were found negative with both ELISA and RT-PCR whereas only 20% of the ELISA negative plants raised from 0.3-mm scion were found negative for ICRSV with RT-PCR. The outcome of this research is the successful establishment, acclimatization and virus testing of micrografted plants.     

Development of an Optimized Method to Obtain a Limonene-Rich Concentrate from the Discarded Lemon Peels

In this study, lemon peels were used as volatile component source. Automatic solvent extraction has been used for the recovery of limonene rich citrus volatile extract for the first time. The process parameters (amount of raw material, immersion time and washing time) were analyzed to optimize the process by means of Box-Behnken design via response surface methodology. The optimum conditions were achieved by ~10 g fresh lemon peel, and ~15 min immersion time and ~13 min washing time. The difference between the actual (89.37 mg/g limonene) and predicted (90.85 mg/g limonene) results was satisfactory (<2 %). α-Terpinene, β-pinene, citral, ɣ-terpinene and linalool were determined as other major volatiles in the peel extract. FT-IR and ¹H- and ¹³C-NMR spectroscopies were applied to verify the identified volatile compounds.     

Guava leaf volatiles and dimethyl disulphide inhibit response of Diaphorina citri Kuwayama to host plant volatiles

The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors the causal pathogen of huanglongbing (HLB), which is likely the most important disease affecting worldwide citrus production. Interplanting citrus with guava, Psidium guajava L., was reported to reduce D. citri populations and incidence of HLB. We describe a series of investigations on the response of D. citri to citrus volatiles with and without guava leaf volatiles and to synthetic dimethyl disulphide (DMDS), in laboratory olfactometers and in the field. Volatiles from guava leaves significantly inhibited attraction of D. citri to normally attractive host‐plant (citrus) volatiles. A similar level of inhibition was recorded when synthetic DMDS was co‐released with volatiles from citrus leaves. In addition, the volatile mixture emanating from a combination of intact citrus and intact guava leaves induced a knock‐down effect on adult D. citri. Compounds similar to DMDS including dipropyl disulphide, ethyl‐1‐propyl disulphide, and diethyl disulphide did not affect the behavioural response of D. citri to attractive citrus host plant volatiles. Head‐space volatile analyses were conducted to compare sulphur volatile profiles of citrus and guava, used in our behavioural assays, with a gas chromatography‐pulsed flame photometric detector. DMDS, produced by wounded guava in our olfactometer assays, was not produced by similarly wounded citrus. The airborne concentration of DMDS that induced the behavioural effect in the 4‐choice olfactometer was 107 pg/ml. In a small plot field experiment, populations of D. citri were significantly reduced by deployment of synthetic DMDS from polyethylene vials compared with untreated control plots. Our results verify that guava leaf volatiles inhibit the response of D. citri to citrus host plant volatiles and suggest that the induced compound, DMDS, may be partially responsible for this effect. Also, we show that field deployment of DMDS reduces densities of D. citri and thus may have potential as a novel control strategy.     

The resistance of sour orange to Citrus tristeza virus is mediated by both the salicylic acid and RNA silencing defence pathways

Citrus tristeza virus (CTV) induces in the field the decline and death of citrus varieties grafted on sour orange (SO) rootstock, which has forced the use of alternative decline‐tolerant rootstocks in affected countries, despite the highly desirable agronomic features of the SO rootstock. Declining citrus plants display phloem necrosis below the bud union. In addition, SO is minimally susceptible to CTV compared with other citrus varieties, suggesting partial resistance of SO to CTV. Here, by silencing different citrus genes with a Citrus leaf blotch virus‐based vector, we have examined the implication of the RNA silencing and salicylic acid (SA) defence pathways in the resistance of SO to CTV. Silencing of the genes RDR1, NPR1 and DCL2/DCL4, associated with these defence pathways, enhanced virus spread and accumulation in SO plants in comparison with non‐silenced controls, whereas silencing of the genes NPR3/NPR4, associated with the hypersensitive response, produced a slight decrease in CTV accumulation and reduced stunting of SO grafted on CTV‐infected rough lemon plants. We also found that the CTV RNA silencing suppressors p20 and p23 also suppress the SA signalling defence, with the suppressor activity being higher in the most virulent isolates.     

Detection of <Emphasis Type="Italic">Diaphorina citri</Emphasis> Kuwayama (Hemiptera: Liviidae) in Kenya and potential implication for the spread of Huanglongbing disease in East Africa

The Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a damaging pest of citrus globally and has recently been detected in Tanzania. Although direct damage by the pest is seldom of economic importance, the insect is more notorious for its ability to vector the fastidious phloem-limited bacterium Candidatus Liberibacter asiaticus (CLas), the putative causal bacterium of Huanglongbing or Asian citrus greening disease. For many years, Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) was known to be the main vector of the African citrus greening disease caused by Candidatus Liberibacter africanus (CLaf), but the recent arrival of D. citri on the continent adds to the dynamics of infection and spread of both diseases on mainland Africa. Following the recent report of the presence of D. citri in Tanzania, an additional delimiting survey was carried out in the region, focusing on Kenya, mainland Tanzania and Zanzibar to detect the presence and ascertain the extent of spread of D. citri. We employed molecular tools based on the use of DNA barcoding to confirm the identity of D. citri. In addition to D. citri, the occurrence of T. erytreae in the same sampling locations is also reported. Adults and nymphs of either D. citri or T. erytreae were collected from citrus at many of the surveyed sites ranging from 19 to 668 m above sea level (masl) in Tanzania, 20–1666 masl in Kenya, and 42–48 masl in Zanzibar. Diaphorina citri was sympatric with T. erytreae at the mid to higher elevations of 1375–1666 masl and no T. erytreae or its open-gall symptoms were detected below 523 masl. Sequences obtained were queried via BLAST and all linked to D. citri of different accession numbers already available on GenBank. This is the first report of the presence of D. citri in Kenya and Zanzibar. The potential implication of the detection and spread of the two pathogens, CLaf and CLas to the citrus industry in East Africa and movement of suitable host plants is discussed.     

Behavioral analysis of learning and memory in Anastrepha fraterculus

We evaluate the influence of prior exposure to artificial substrate for oviposition on learning and memory in the fruit fly Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae). Some females were previously exposed to artificial fruits made of water, agar, and blackberry [Rubus spec. (Rosaceae)] or guava [Psidium guajava L. (Myrtaceae)] pulp for 48 and 72 h. We also studied adult flies exposed for 72 h to essential oil of lemongrass [Cymbopogon citratus (DC) Stapf, Poaceae] and adult flies from larvae exposed to the oil. Control females were naive with respect to these experimental substrates. Prior experience with blackberry‐based artificial fruits resulted in an increase in the number of punctures and deposited eggs by A. fraterculus, and memory lasted for up to 72 h. On the other hand, fly behavior was independent of exposure to guava‐based substrate. Prior exposure of 1‐ or 15‐day‐old females to artificial substrate with lemongrass oil modified innate substrate selection behavior. The scent of lemongrass oil during the larval stage modified innate oviposition responses of adult A. fraterculus. The study shows that A. fraterculus females are able to learn and retain information through chemical stimuli released by both host (blackberry and guava) and non‐host (lemongrass) species, and they can use olfactory memory obtained during the larval stage to select oviposition sites.     

Repellent activity of Cymbopogon citratus and Tagetes minuta and their specific volatiles against Megalurothrips sjostedti

Cowpea is an important source of protein for people in Africa. However, the crop suffers major damage and yield losses due to bean flower thrips, Megalurothrips sjostedti Trybom (Thysanoptera: Thripidae). Although companion plants are known to reduce the damage caused by insect pests, the role of their volatiles in repelling pests from target plants has been the subject of few investigations. Here, we used the Y‐tube olfactometer experiments and chemical analyses to investigate the effect of volatiles from cowpea flowers and two companion plants; lemongrass, Cymbopogon citratus and Mexican marigold, Tagetes minuta on the olfactory responses of M. sjostedti. The results revealed that M. sjostedti males and females were repelled by the volatiles from freshly cut leaves of C. citratus. The combination of freshly cut leaves of C. citratus and cowpea flower was repellent to females but not to males. The female thrips, but not males, were repelled by the volatiles from the vegetative stage of T. minuta. Fifty‐four compounds were identified in the volatiles from two herbal plants. Among the major compounds, citral and a 4‐component blend comprised of dihydrotagetone, (Z)‐3‐hexenyl acetate, limonene and (Z)‐β‐ocimene repelled females but dihydrotagetone alone attracted females. While myrcene combined with cowpea flower volatiles enhanced the attraction of females M. sjostedti, when tested alone was not attractive. These results highlight the potential of volatiles from C. citratus and T. minuta to repel M. sjostedti females. The use of these plants as companion plants in a cowpea cropping system could reduce M. sjostedti infestation.     

Performance of Cryptolaemus montrouzieri feeding on Pulvinaria aurantii ovisacs on citrus plants

We studied the performance of the coccinellid Cryptolaemus montrouzieri on citrus plant species infested with orange pulvinaria scale, Pulvinaria aurantii, under controlled conditions in the laboratory. The experimental host plants were blood orange, grapefruit, lemon, pummelo and kumquat. All life history parameters indicated best performance of C. montrouzieri, when reared on P. aurantii ovisacs on the leaves of grapefruit. Pummelo, blood orange, lemon or kumquat were less suitable.