Dorsalis Populations Research Articles

Molecular and Biochemical Mechanisms of Scutellum Color Variation in Bactrocera dorsalis Adults (Diptera: Tephritidae)

Bactrocera dorsalis (Hendel) is an invasive fruit and vegetable pest, infesting citrus, mango, carambola, etc. We observed that the posterior thoracic scutella of some B. dorsalis adults are yellow, some light yellow, and some white in China. Compared with the B. dorsalis races with a yellow scutellum (YS) and white scutellum (WS), the race with a light-yellow scutellum (LYS) is dominant in citrus and carambola orchards. To reveal genetic correlates among the three races, the genomes of 22 samples (8 with YS, 7 with LYS, and 7 with WS) were sequenced by high-throughput sequencing technology. Single-nucleotide polymorphism (SNP) annotation showed that there were 17,580 non-synonymous mutation sites located in the exonic region. Principal component analysis based on independent SNP data revealed that the SNPs with LYS were more similar to that with YS when compared with WS. Most genes associated with scutellum color variation were involved in three pathways: oxidative phosphorylation, porphyrin and chlorophyll metabolism, and terpenoid backbone biosynthesis. By comparing the sequences among the three races, we screened out 276 differential genes (DGs) in YS vs. WS, 185 DGs in LYS vs. WS, and 104 DGs in YS vs. LYS. Most genes determining color variation in B. dorsalis scutella were located on chromosomes 2–5. Biochemical analysis showed that β-carotene content in YS and LYS was significantly higher than that in WS at any stage of adult days 1, 10, and 20. No significant differences were observed in cytochrome P450 or melanin content in YS, LYS, or WS. Our study provides results on aspects of scutellum color variation in B. dorsalis adults, providing molecular and physiological information for revealing the adaptation and evolution of the B. dorsalis population.

The effects of diet and semiochemical exposure on male Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) metabolic rate at a range of temperatures

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is an invasive species that has rapidly spread across the African continent, endangering the security of agricultural industries. The sterile insect technique (SIT) is being investigated as a viable additional pest management tool to suppress B. dorsalis populations after its successful implementation in other parts of the world. There is evidence to suggest that pre-release nutritional and semiochemical treatments for sterilised males can enhance their competitive performance against wild type males in SIT programs. This study examined how sterilisation, a diet rich in protein (addition of yeast hydrolysate) or containing semiochemicals (methyl eugenol or eugenol) affected the resting metabolic (RMR) of male B. dorsalis at different temperatures (15 – 30 °C), measured using flow-through respirometry. Our results indicated that the negative effect of sterilisation on RMR decreased as temperature increased and that duration of exposure to semiochemicals for 1 to 4 days was not a significant influencing factor on male B. dorsalis RMR. Protein-rich diet increased average RMR, but the difference in RMR between dietary groups decreased as temperature increased. Semiochemical feeding reduced the average RMR in male B. dorsalis. The difference in RMR between males that consumed semiochemical and those that did not increased with as temperature increased.

Whole-Genome Sequencing of the Entomopathogenic Fungus Fusarium solani KMZW-1 and Its Efficacy Against Bactrocera dorsalis.

Fusarium solani KMZW-1 is recognized for its potential as a biocontrol agent against agricultural and forestry pests, particularly due to its compatibility with integrated pest management (IPM) strategies. This study aimed to investigate the complete genome of F. solani KMZW-1 and assess its pathogenicity against Bactrocera dorsalis. Whole-genome sequencing revealed a genome size of 47,239,278 bp, comprising 27 contigs, with a GC content of 51.16% and fungus identified as F. solani KMZW-1. The genome completeness was assessed as 97.93% using BUSCO analysis, the DFVF sequence identifier was Fusarium 0G092560.1, and AntiSMASH analysis identified 35 gene clusters associated with secondary metabolite biosynthesis, providing insights into the genetic basis of its pathogenic mechanisms and biocontrol potential. Comparative genomic analysis found 269 unique genes for F. solani KMZW-1, and collinearity analysis exhibited a high degree of synteny with Fusarium solani-melongenae. The pathogenicity of F. solani KMZW-1 was assessed using concentrations ranging from 1 × 104 to 1 × 1011 conidia/mL. Higher concentrations (1 × 1010 to 1 × 1011 conidia/mL) resulted in significantly increased cumulative mortality rates of B. dorsalis adults compared to the control group. Notably, the pathogenicity was higher in male adults than in females. Probit analysis yielded LC50 (50% lethal concentration) values of 5.662 for female and 4.486 for male B. dorsalis adults. In summary, F. solani, KMZW-1 exhibits strong insecticidal activity against B. dorsalis and shows potential as a biocontrol agent with IPM strategies. These findings provide robust genomic evidence supporting the use of F. solani KMZW-1 in managing against B. dorsalis populations.

Dynamics of Bactrocera dorsalis Resistance to Seven Insecticides in South China.

Bactrocera dorsalis is a highly invasive and destructive pest distributed worldwide. Chemical insecticides remain the primary measure for their control; however, this species has already developed resistance to several insecticides. In recent years, there have been several reports of monitoring B. dorsalis resistance in China, but continuous monitoring results are lacking and do not even span a decade. In this study, we monitored the dynamics of resistance to seven insecticides among 11 geographically distinct Chinese populations of B. dorsalis (2010-2013; follow-up in 2023). The 11 populations were found to adapt rapidly to antibiotic insecticides (spinosad, emamectin benzoate, and avermectin), reaching high levels of insecticide resistance in several areas. Overall, a decreasing trend in resistance to organophosphorus insecticides (chlorpyrifos and trichlorfon) was observed, whereas pyrethroid (beta-cypermethrin and cyhalothrin) resistance trends were observed to both increase and decrease. The monitoring of field resistance among different B. dorsalis populations over the duration of this study is important for improving the efficiency and sustainability of agricultural pest management, and the results provide a scientific basis for the development of more effective resistance management strategies.

Hierarchizing multi-scale environmental effects on agricultural pest population dynamics: a case study on the annual onset of Bactrocera dorsalis population growth in Senegalese orchards

Hierarchizing multi-scale environmental effects on agricultural pest population dynamics: a case study on the annual onset of Bactrocera dorsalis population growth in Senegalese orchards

Persistence of widespread moderate Spinosad resistance among wild melon fly (Zeugodacus cucurbitae) and oriental fruit fly (Bactrocera dorsalis) populations on the major Hawaiian islands.

Insecticide resistance among invasive tephritid fruit flies poses a great risk to national food security and has the potential to disrupt quarantine and eradication programs, which rely on the efficacy of Spinosad to prevent widespread establishment in North America. During 2022 to 2023 we surveyed the extent of Spinosad resistance of two key species, oriental fruit fly Bactrocera dorsalis, and melon fly Zeugodacus cucurbitae, from 20 sites across five Hawaiian Islands including Kaua'i, O'ahu, Maui, Molokai and the "Big Island" (Hawai'i). We used topical thoracic applications of eight concentrations of Spinosad ranging from 0.028 to 3.6 mg/mL to evaluate the lethal concentration (LC50 and LC99) required to kill wild-caught males. Resistance ratios (RR) were calculated by comparing the LC50 of wild flies to laboratory susceptible lines maintained in colony. Our results identified at least two new sites of concern for melon fly resistance on the Big Island, and at least four sites of concern for oriental fruit fly, all of which were located on the Big Island. At these locations RRs were >5. On O'ahu, melon fly RRs were >10. The persistence of Spinosad resistance is concerning, yet it is a reduction compared to the values reported previously and before changes to Spinosad use recommendations by local extension agents beginning in 2017. For oriental fruit fly, these RR values are the highest levels that have been detected in wild Hawai'i populations. These data suggest that expanded Spinosad reduction and replacement programs are warranted given the ongoing issues with Spinosad resistance in Hawai'i and expansion in the number of species affected. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Developing an Effective Push–Pull System for Managing Outbreaks of the Invasive Pest Bactrocera dorsalis (Diptera: Tephritidae) in Nephelium lappaceum Orchards

Outbreaks of the oriental fruit fly, Bactrocera dorsalis (Hendel), present significant challenges to global fruit production, necessitating effective control measures that minimize environmental risks and pesticide resistance. This study aimed to develop and evaluate the effectiveness of four distinct push–pull control strategies for managing B. dorsalis outbreaks in a Nephelium lappaceum orchard. These strategies involved the inclusion of low-concentration abamectin, spraying repellent with a drone or manually, using methyl eugenol (ME) or food bait and employing either two types of attractants and repellents or a single type. The findings indicated that incorporating the low-concentration abamectin into the push–pull system, utilizing ME as an attractant instead of food lures and manually applying abamectin and attractants were all effective in reducing the B. dorsalis population size and minimizing fruit damage. While increasing the diversity of repellents and attractants enhanced the long-term effectiveness of the system, it did not result in a significant decrease in B. dorsalis population size or fruit damage rate compared to using a single repellent or attractant. In conclusion, the push–pull strategy emerged as a viable method for managing B. dorsalis outbreaks, offering potential benefits in reducing environmental risks and pesticide resistance. However, the study underscored the importance of the context-specific construction of push–pull strategies to optimize their effectiveness in orchard settings.

Attractancy of a Sesquiterpene, β-caryophyllene to Males of the Oriental Fruit Fly, Bactrocera dorsalis (Diptera: Tephritidae).

The recent discovery of a sesquiterpene, β-caryophyllene (CP) as a male attractant of the guava fruit fly, Bactrocera correcta (Bezzi) (Diptera: Tephritidae) prompted investigations into the attractancy of CP to the Oriental fruit fly, B. dorsalis (Hendel). This is because males of both species of fruit flies are attracted to, and feed on a phenylpropanoid compound, methyl eugenol (ME). Although CP was a more potent attractant than ME for B. correcta, it is not known if males of B. dorsalis are also attracted to CP. The possible attraction of B. dorsalis to CP as a sesquiterpene may indicate its wide host range through its attraction to different groups of plant volatiles i.e., phenylpropanoids and sesquiterpenes. In this paper, we report that males of B. dorsalis were also attracted to, and feed on CP. Subsequently, we conducted a probit regression analysis to determine the quantal response of sexually mature male flies that were attracted to CP in cage bioassays. Therefore, as a measure of male B. dorsalis' sensitivity of CP, the median dose of CP required to elicit a positive response in 50% of the tested B. dorsalis population (ED50) was calculated as 3.7mg. This value was over 10,000x higher than known ED50 of B. dorsalis' male attraction ME (between 171 and 268 ng). We propose that the attraction of male B. dorsalis flies to CP was much weaker than to ME. Further, we suggest that in any fruit fly surveillance and monitoring programme, application of lures must consider the specificity and potency of each compound to target fruit fly species. The probit regression analysis of male fly quantal response to lure offers such information.

Rapid cold hardening and cold acclimation promote cold tolerance of oriental fruit fly, Bactrocera dorsalis (Hendel) by physiological substances transformation and cryoprotectants accumulation.

Insect response to cold stress is often associated with adaptive strategies and chemical variation. However, low-temperature domestication to promote the cold tolerance potential of Bactrocera dorsalis and transformation of main internal substances are not clear. Here, we use a series of low-temperature exposure experiments, supercooling point (SCP) measurement, physiological substances and cryoprotectants detection to reveal that pre-cooling with milder low temperatures (5 and 10°C) for several hours (rapid cold hardening) and days (cold acclimation) can dramatically improve the survival rate of adults and pupae under an extremely low temperature (-6.5°C). Besides, the effect of rapid cold hardening for adults could be maintained even 4 h later with 25°C exposures, and SCP was significantly declined after cold acclimation. Furthermore, content of water, fat, protein, glycogen, sorbitol, glycerol and trehalose in bodies were measured. Results showed that water content was reduced and increased content of proteins, glycogen, glycerol and trehalose after two cold domestications. Our findings suggest that rapid cold hardening and cold acclimation could enhance cold tolerance of B. dorsalis by increasing proteins, glycerol, trehalose and decreasing water content. Conclusively, identifying a physiological variation will be useful for predicting the occurrence and migration trend of B. dorsalis populations.

Reduced insecticide susceptibility among populations of Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) in strawberry production

AbstractChilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is a major, economically important, and recent invasive pest of strawberries and other horticultural crops in United States. Several conventional insecticides are used for S. dorsalis management, and resistance development threatens loss of few available tools. Hence, our objectives were to: (1) determine the susceptibility of S. dorsalis to commonly used conventional insecticides: spinetoram, acetamiprid, cyantraniliprole and bifenthrin, and (2) establish LC50 and LC90 dosages for spinetoram against S. dorsalis. Sampling of S. dorsalis populations was conducted twice in seven strawberry fields in Florida during the strawberry field season between 2019 and 2020. Leaf‐disc bioassays were performed with field collected populations along with a susceptible 2‐year‐old laboratory culture of S. dorsalis. Overall, at highest recommended rate the percent mortality of late season S. dorsalis populations from five out of seven collection sites was lower (~41%) than average mortality observed with early season populations (~72%). Populations from at least four out of seven sampling sites exhibited significantly lower mortality than the laboratory susceptible culture in late season. The LC50 and LC90 values for spinetoram for the susceptible laboratory population were 0.026 and 8.64 ppm, respectively. On the other hand, LC50 values of field collected populations to spinetoram varied with resistance ratios ranging from 6 to 269 fold as compared against the laboratory strain. Our results suggest that susceptibility of S. dorsalis to commonly used insecticides in strawberries varies significantly between early and late season populations within the same crop season. The efficacy of bifenthrin against S. dorsalis was particularly low (~ reduced to half in late season), especially among field collected populations. Our results indicate an urgent need to incorporate other pest management strategies, as well as effective rotation programs to reduce selection for resistance among populations of S. dorsalis in strawberry production.

Monitoring of the Fruit Flies (Bactrocera spp.) Infesting Jujube Orchard using Static Spinosad Traps

Fruit flies (Bactrocera spp.) are regarded as serious insect pests of fruits and vegetables in the world. The goal of this study was to examine the effect of spinosad traps on Bactrocera spp. at different heights 0, 1, 2, and 3 m on jujube tree during 2020-2021. Flies’ populations were counted weekly. The results revealed that the highest population of B. zonata (225.6 flies) were recorded at 2 m height on (22 October, 2020) and the lowest ones (21.6 flies) were recorded at the ground level (0 m height) during (4 February, 2021). However, the overall maximum catches were 158.95 at 2 m height and minimum was 68.72 at the ground level. Similarly, the maximum population of B. dorsalis was (50.5 flies) at 2 m height during (9 October, 2020), but the minimum (2.5 flies) was in the ground level during (4 February, 2021). The overall highest B. dorsalis catches were (43.50 flies) at 2 m height and the lowest was (3.55 flies) at ground level. The population of B. zonata correlated positively (r= 0.2939**) with temperature, but negatively (r= -0.0223NS) with relative humidity. However, B. dorsalis populations was positive correlated with both of the temperature and relative humidity (r= 0.0261** and r= 0.0091NS, respectively). Ultimately, pheromone traps (Spinosad+Methyl eugenol) at 2 m height are highly recommended to catches both fruit flies (B. zonata and B. dorsalis) in Jujube Orchards.

Monitoring the Methyl Eugenol Response and Non-Responsiveness Mechanisms in Oriental Fruit Fly Bactrocera dorsalis in China.

Bactrocera dorsalis is a notorious polyphagous pest in China, and its management strategies largely depend on methyl eugenol (ME), which has been widely used as an attractant to monitor and eradicate B. dorsalis populations for seven decades. However, the non-responsiveness levels in field B. dorsalis populations to ME is unknown. In this study, we monitored the response to ME in field populations from the four most heavily infested provinces in China, and the results showed that the populations had lower sensitivity to ME relative to GZS susceptible strain. The percent responsiveness of the lowest sensitivity population was 5.88-, 3.47-, and 1.47-fold lower relative to the susceptible strain at doses of 1, 10, and 100 µL of ME, respectively. Gene expression analysis and inhibitor assays further revealed that odorant binding protein (BdorOBP2, BdorOBP83b) and the P450 enzyme system may be associated with the lower response to ME. To our knowledge, this work is the first to report that the P450 enzyme system confers a lower responsiveness to lure insects. These findings provided valuable insights for exploiting ME non-responsiveness to protect sterile males from ME-based control strategies and the use of lures combined with insecticides.

Field efficacy of insecticides against chilli thrips (Scirtothrips dorsalis) and their effect on coccinellids

Considering the economic significance of S. dorsalis in chilli crop, a study was carried out at the ICAR-Research Complex for Eastern Region, Farming System Research Centre for Hill and Plateau Region, Ranchi, Jharkhand during the spring season of 2019 and 2020 to find out the effective chemical molecules for managing this pest. Effectiveness of 8 modern insecticides against S. dorsalis and their effect on coccinellid predators was evaluated. Efficacy of insecticides was determined by comparing number of thrips, immature stages and adults of natural enemies, marketable yield in insecticide treated versus untreated control plots. Application of spinosad @70 g a.i./ha, Emamectin benzoate 5 sg @11 g a.i./ha, Imidacloprid 200 sl @40 g a.i./ha and Fipronil 5 sc @30 g a.i./ha were found to be effective against S. dorsalis in chilli. Other insecticides were inconsistent in effectiveness against S. dorsalis population. Fenpropathrin followed by Imidacloprid were found to cause maximum reduction and Spinosad and Emamectin benzoate caused lowest reduction of coccinellid population. Thus, based on the present study, Spinosad, Emamectin benzoate, Fipronil and Imidacloprid are recommended to manage S. dorsalis on rotational basis in chilli ecosystem.

The Fallacy of Year-Round Breeding in Polyphagous Tropical Fruit Flies (Diptera: Tephritidae): Evidence for a Seasonal Reproductive Arrestment in Bactrocera Species.

The genus Bactrocera (Diptera: Tephritidae) is endemic to the monsoonal rainforests of South-east Asia and the western Pacific where the larvae breed in ripe, fleshy fruits. While most Bactrocera remain rainforest restricted, species such as Bactrocera dorsalis, Bactrocera zonata and Bactrocera tryoni are internationally significant pests of horticulture, being both highly invasive and highly polyphagous. Almost universally in the literature it is assumed that Bactrocera breed continuously if temperature and hosts are not limiting. However, despite that, these flies show distinct seasonality. If discussed, seasonality is generally attributed to the fruiting of a particular breeding host (almost invariably mango or guava), but the question appears not to have been asked why flies do not breed at other times of the year despite other hosts being available. Focusing initially on B. tryoni, for which more literature is available, we demonstrate that the seasonality exhibited by that species is closely correlated with the seasons of its endemic rainforest environment as recognised by traditional Aboriginal owners. Evidence suggests the presence of a seasonal reproductive arrest which helps the fly survive the first two-thirds of the dry season, when ripe fruits are scarce, followed by a rapid increase in breeding at the end of the dry season as humidity and the availability of ripe fruit increases. This seasonal phenology continues to be expressed in human-modified landscapes and, while suppressed, it also partially expresses in long-term cultures. We subsequently demonstrate that B. dorsalis, across both its endemic and invasive ranges, shows a very similar seasonality although reversed in the northern hemisphere. While high variability in the timing of B. dorsalis population peaks is exhibited across sites, a four-month period when flies are rare in traps (Dec-Mar) is highly consistent, as is the fact that nearly all sites only have one, generally very sharp, population peak per year. While literature to support or deny a reproductive arrest in B. dorsalis is not available, available data is clear that continuous breeding does not occur in this species and that there are seasonal differences in reproductive investment. Throughout the paper we reinforce the point that our argument for a complex reproductive physiology in Bactrocera is based on inductive reasoning and requires specific, hypothesis-testing experiments to confirm or deny, but we do believe there is ample evidence to prioritise such research. If it is found that species in the genus undergo a true reproductive diapause then there are very significant implications for within-field management, market access, and biosecurity risk planning which are discussed. Arguably the most important of these is that insects in diapause have greater stress resistance and cold tolerance, which could explain how tropical Bactrocera species have managed to successfully invade cool temperate regions.

Chilli thrips rose management using an Amblyseius swirskii or Amblydromalus limonicus (Acari: Phytoseiidae) pepper banker plant

AbstractBanker plant systems can enhance biological control of arthropod pests in protected agriculture if they facilitate the persistence of beneficial organisms by providing them with persistent habitats or supplemental food such as pollen or nectar. Ornamental pepper banker plants infested with either the predatory phytoseiid mites Amblyseius swirskii (Athias‐Henriot) or Amblydromalus limonicus (Garman and McGregor) were tested under greenhouse conditions in Florida, USA, for management of the chilli thrips, Scirtothrips dorsalis Hood on Double Knock Out® roses. After two 6‐week studies, performed from October to December 2019 and 2020, both mite species reduced populations of S. dorsalis on roses to nearly undetectable levels (<1 thrips/leaf) compared with predator‐free controls. There was no difference in the mean number of thrips on leaves between the two mite species treatments. Lower S. dorsalis numbers observed on roses when mites were present led to significantly reduced foliar damage assessed as the degree of tissue scarring from S. dorsalis feeding compared with the control. This study may provide rose growers in Florida an alternative option for managing S. dorsalis populations on roses, a typically unsuitable plant for maintaining mite populations.

Evaluation of insecticides and suitable trap containers for effective fruit fly catches

Fruit flies are quarantine pests and major impediments in horticultural production, domestic market, and export of fresh fruits and vegetables. Trapping with a lure is the best known method to monitor/ manage the fruit fly Bactrocera dorsalis populations. The fruit fly attraction and its mortality depend on the lure, type of killing agent, and design of the trap container. To make the trapping technology more robust, a study was conducted to find out the suitable killing agent amongst ten insecticides and the best trap design among the available six trap designs. The results revealed that emamectin benzoate 1.9EC was superior as killing agent with the maximum trap catches (648.75 to 1304.75 fruit flies/ trap) up to 12 weeks, followed by abamectin 1.9EC and profenophos 50EC. Among the trap designs, the CISH trap container was found to be superior (306.25 to 940.00 fruit flies/ trap/ week).

BdorOBP69a is involved in the perception of the phenylpropanoid compound methyl eugenol in oriental fruit fly (Bactrocera dorsalis) males

The oriental fruit fly (Bactrocera dorsalis) is a devastating fruit pest that infests more than 450 plant species. Methyl eugenol (ME) has been used as male attractant to monitor and eradicate B. dorsalis populations for 70 years, but the molecular basis of its activity remains largely unclear. Previously, BdorOBP83b and BdorOBP56f-2 as odorant binding proteins (OBPs) were identified responsible for ME perception. In this study, ME-induced expression profiles and in vitro binding assays revealed that BdorOBP69a is also produced in response to ME and binds directly to it with strong affinity (Kd = 9.54 μM). BdorOBP69a−/− null mutants generated by CRISPR/Cas9 mutagenesis showed significantly lower electroantennogram and behavioral responses to ME than wild-type controls. Molecular docking analysis followed by site-directed mutagenesis showed that residues Leu89 and Phe145 are essential for the interaction between BdorOBP69a and ME. BdorOBP69a is therefore an important component involved in the perception of ME in B. dorsalis and a promising molecular target for the development of new male attractants. The molecular docking and binding assay data also provide an important reference for future OBP gene manipulation and ME chemical engineering to improve the efficiency of male attractants.

Sublethal and transgenerational effects of six insecticides on Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

To clarify the effects of sublethal concentration of insecticide on the growth, development and reproduction of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), the sublethal and transgenerational effects of the LC 30 of six insecticides on adults and progeny (F 1 and F 2 generations) were studied using age-stage, two-sex life tables. Exposure to six insecticides had significant negative impacts on the life-history traits of B. dorsalis and led to reduced adult longevity and fecundity in F 0 , a longer larval stage duration in F 1 , and reduced fertility and survival. The intrinsic rate of increase ( r ), finite rate of increase ( λ ), and net reproductive rate ( R 0 ) were reduced in F 1 , with the greatest reduction observed in the chlorpyrifos treatment. In the F 2 generation, the adverse effects were weakened, only the cyantraniliprole treatment had lower values than the control, and the fecundity of other treatments returned to normal. Obvious “hormesis” phenomena were not observed in any of the generations. Based on the population hazard index, chlorpyrifos had the best control effect in the early stage, and cyantraniliprole had the best control effect in the long term. These results indicate that the LC 30 of the six insecticides exert different transgenerational effects on the B. dorsalis population.

The Short-Range Movement of Scirtothrips dorsalis (Thysanoptera: Thripidae) and Rate of Spread of Feeding Injury Among Strawberry Plants.

Scirtothrips dorsalis Hood infest strawberry (Fragaria x ananassa Duchesne, Rosaceae) fields from nearby crop fields and surrounding vegetation and cause injury to plants by feeding on young leaf tissues. Greenhouse and field studies were conducted to determine the short-range movement of S. dorsalis to assess the risk of an early S. dorsalis population to spread to adjacent plants. In a greenhouse, 25 potted strawberry plants were arranged in two concentric rows around a central plant, where plants in inner rows were 20 cm, and those in the outer rows were 40 cm from the central plant. In the field, 20 strawberry plants were arranged in two beds (90 cm apart), ten in each bed, and five plants in each row, with plants 30 cm apart. White sticky cards were placed at 60-120 cm from the central plant. Fifty S. dorsalis adults were released on a centrally located plant, and the numbers of S. dorsalis adults and larvae and feeding injury were recorded for 9-17 d on adjacent plants and sticky cards. Results showed that significantly more S. dorsalis adults and larvae remained on the initially infested plant compared to adjacent plants, although few adults were found up to 120 cm on sticky cards. The rate of spread of feeding injury was low with slight bronzing injury (<10% injury) on adjacent plants by 14-17 d. Since most S. dorsalis remained on initially infested plants for at least 2 wk, it is feasible to delay management actions and 'rescue' plants around a plant with minor injury symptoms.

Abundance and Diversity of Frugivorous Fruit Flies in Kandara, Murang’a County, Kenya

Fruits and vegetables are important source of livelihood to farmers and major horticulture sub sector with high contribution to agricultural GDP in Kenya. This study was conducted to determine diversity and abundance of frugivorous fruit flies in Kandara sub county, Murang’a County in 2018, at a place where first area of low pest population was created in Kenya for Bactrocera dorsalis. Three sets of pheromone traps (Methyl-Eugenol, Cuelure and Trimedlure) were set in six trap stations within farmers’ orchards in four agro-ecological zones (LH1 (Lower Highland Zone), UM1 (Upper Mid-land Zone), UM2, and UM3). The trap catch data was collected fortnightly and data analyzed. Six fruit flies species namely; Bactrocera dorsalis, Ceratitis cosyra, Ceratitis capitata, Zeugodacus cucurbitae, Dacus bivittatus and Perilampsis sp were identified. Bactrocera dorsalis population was significantly (P&lt;.001) different across the four agro-ecologies with lowest densities at LH1 and highest at UM3. Likewise, C. capitata recorded significant (P=0.042) difference densities across the agro-ecological zones, but no significant (P=0.386) difference was recorded for C. cosyra across the agro-ecological zones. Further, there was significant (P=0.012) difference in the number of Perilampsis sp across the agro-ecologies with the highest number recorded in UM1. Both Z. cucurbitae (P=0.061) and D. bivittatus (P=0.056) had low abundance across the agro-ecologies. The peak infestation period differed across the various fruit fly species, whereby B. dorsalis peaked in May, C. capitata in February and C. cosyra in January. The study shows that abundance for the fruit flies is probably related to their preferred hostplant and the weather patterns. We recommend continuous monitoring and intensifying trapping activities during peak periods in order to control the pest and protect fruits from damage. Farmers should be trained on the use of pheromone traps to reduce over-reliance on pesticides. Key words: Agro-ecologies, Bactrocera dorsalis, Ceratitis sp, fruit fly density, Pheromone