Whitefly Eggs Research Articles

Evaluation of Eruca Sativa and Capsicum annuum alcoholic extracts as pesticide against aphid and whitefly pests

The aphid (Aphidoidea family) and the whitefly (Aleyrodidae family) are closely related, quickly breeding insects that, when infected, render plants susceptible to diseases since they suck the juices of these plants. They damage the aerial parts of plants and even their roots. Their control is of high concern to limit the damage and minimize the loss of the crops with the use of the safest pesticides. The present study was conducted to assess the perished effect of the Eruca sativa (local name: arugula) leaves and the Capsicum annuum (local name: hot pepper) fruits on aphids and on the eggs and nymphs of whitefly by spraying their alcoholic extracts on tested species. Three pesticide concentrations (0.5, 1 and 1.5%) of either extract were prepared and tested. Adhesives, propellants and other materials were added to the extracts to enhance their effectiveness. The results indicated that the pesticide prepared from these extracts has a concentration- and time-dependent impact on the growth of all tested species; the highest mortality rate was achieved at 1.5% concentrations. The time required for that highest effect was 72 hours for Eruca sativa leaf extract on aphids (100%); and on the eggs (89%) and nymphs (94.1%) of whiteflies. Meanwhile, the highest mortality rates achieved by 1.5% Capsicum annuum fruit extract were after 48 hours on aphids (100%), on the nymphs of whiteflies (100%), and 72 hours on whitefly eggs (96.4%). These effects may be related to the presence of many bioactive substances that were detected in the extracts of these two plants, including tannins, glycosides, phenols, resins, flavonoids, saponins, alkaloids, coumarin, steroids and terpenes.

Susceptibility of Yellow Squash and Zucchini Cultivars to the Sweetpotato Whitefly, Bemisia tabaci Gennadius (MEAM1), in the Southeastern United States.

The sweetpotato whitefly, Bemisia tabaci (Gennadius) Middle East-Asia Minor 1 (MEAM1), causes significant losses to vegetable crops directly by sap-feeding, inducing plant physiological disorders, and elevating the build-up of sooty mold, and indirectly by transmitting plant viruses. In this study, we evaluated the susceptibility of 20 yellow squash and zucchini (Cucurbita pepo) cultivars to MEAM1, across three growing seasons in the southeastern United States. Weekly sampling of the numbers of MEAM1 adults, nymphs, and eggs were conducted from the fourth week after seed sowing and across 6 weeks during the summer and fall of 2021 and five weeks during the fall of 2022. In general, adult whitefly populations were high during the first week of sampling but decreased as the seasons progressed. The zucchini cultivar 'Black Beauty' harbored the most adults, while 'Green Eclipse Zucchini' was the least attractive zucchini cultivar to the adults in fall 2022. For yellow squash, 'Early Summer' (summer 2021) and 'Amberpic 8455' (summer 2021 and fall 2022) were the cultivars with the highest adult populations, while 'Lioness' (summer 2021) and 'Gourmet Gold Hybrid' (fall 2022) harbored the lowest adult counts. The whitefly egg counts across both vegetables trailed those of adults and peaked in the second week of sampling. The counts of nymphs increased as the seasons progressed, but there was a decline after the second week during fall 2021. For the yellow squash cultivars, 'Gourmet Gold Hybrid', (summer 2021 and fall 2022), 'Lioness', and 'Fortune' (summer 2021) recorded the highest yields. For zucchini, 'Golden Glory' (summer 2021) was the top performer. These results provide valuable information for whitefly management in yellow squash and zucchini based on host plant susceptibility and yield.

Evaluation of a low-cost staining method for improved visualization of sweet potato whitefly (Bemisia tabaci) eggs on multiple crop plant species

BackgroundThe sweet potato whitefly (Bemisia tabaci) is a globally important insect pest that damages crops through direct feeding and by transmitting viruses. Current B. tabaci management revolves around the use of insecticides, which are economically and environmentally costly. Host plant resistance is a sustainable option to reduce the impact of whiteflies, but progress in deploying resistance in crops has been slow. A major obstacle is the high cost and low throughput of screening plants for B. tabaci resistance. Oviposition rate is a popular metric for host plant resistance to B. tabaci because it does not require tracking insect development through the entire life cycle, but accurate quantification is still limited by difficulties in observing B. tabaci eggs, which are microscopic and translucent. The goal of our study was to improve quantification of B. tabaci eggs on several important crop species: cassava, cowpea, melon, sweet potato and tomato.ResultsWe tested a selective staining process originally developed for leafhopper eggs: submerging the leaves in McBryde’s stain (acetic acid, ethanol, 0.2% aqueous acid Fuchsin, water; 20:19:2:1) for three days, followed by clearing under heat and pressure for 15 min in clearing solution (LGW; lactic acid, glycerol, water; 17:20:23). With a less experienced individual counting the eggs, B. tabaci egg counts increased after staining across all five crops. With a more experienced counter, egg counts increased after staining on melons, tomatoes, and cowpeas. For all five crops, there was significantly greater agreement on egg counts across the two counting individuals after the staining process. The staining method worked particularly well on melon, where egg counts universally increased after staining for both counting individuals.ConclusionsSelective staining aids visualization of B. tabaci eggs across multiple crop plants, particularly species where leaf morphological features obscure eggs, such as melons and tomatoes. This method is broadly applicable to research questions requiring accurate quantification of B. tabaci eggs, including phenotyping for B. tabaci resistance.

Response of Whitefly Population to Rabbit Urine Foliar Spray on Tomato (Solanum lycopersicum L.)

Whiteflies greatly contribute to low yields and quality in tomato production. Continuous use of synthetic pesticides leads to whiteflies developing resistance to these pesticides. This research aimed at promoting the use of rabbit urine as a biopesticide against whiteflies in tomato production. Although rabbit urine is been used as a biopesticide against different pests, the best concentration to control whiteflies in tomato production is unknown. Six treatments compared in the two experiments of this study included: 2 L rabbit urine : 9 L water; 2 L rabbit urine : 6 L water; 2 L rabbit urine : 3 L water; 2 L rabbit urine : 0 L water; 0 L rabbit urine : 2 L water, and 20 mL Duduthrin 1.75EC : 20 L water. The first experiment was conducted in a randomized complete block design with six treatments and four blocks to investigate the effects of rabbit urine on the control of whitefly eggs, nymphs, and adults. The second experiment was conducted in a completely randomized design to determine the effect of rabbit urine on the bioactivity of adult whiteflies. Results indicated that plots treated with rabbit urine foliar spray registered reduced populations of whitefly eggs, nymphs, and adults, and lower LT50 values of repelling and killing compared to the negative control (0 L rabbit urine : 2 L water). However, a high ratio of rabbit urine caused significant scorching to tomato leaves. A solution of 2 L rabbit urine : 6 L water optimally controls whiteflies without scorching the plant foliage. Rabbit urine has both repelling and killing effects on whiteflies. In the future, further research can be conducted to investigate the effect of rabbit urine on populations of other important insect pests of tomato.

Biological control of sesame moth and tobacco whitefly in Antalya sesame fields

Sesame moth and tobacco whitefly cause significant damage to sesame plants, especially in the second-period sesame cultivation areas, if early intervention is not implemented. This greatly reduces efficiency. Chemical control is generally preferred for these pests in Türkiye. Today, the use of chemical control creates many harmful results. Therefore, in our study, the aim is to use biological control agents and preparations as an alternative to chemical control. In this study, applications of Nostalgist Bl biological insecticide containing 1.5% Beauveria bassiana strain Bb-1 1x108 CFU mil-1 spores, Nimbecidine biological insecticide containing 0.3 g L-1 Azadirachtin active ingredient, and Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae) an egg parasitoid and activities were determined. The application area (2 da) was divided into 3 blocks; each block was named with the letters A, B, and C. Each block was divided into four parcels. The above applicatios and biological insecticides were applied separately in each parcel, including the control parcels in each block. In the counts made according to the application results, there was a significant decrease in whitefly eggs and nymphs on the leaf surface. A very significant decrease was observed in the populations per plant in the sesame moth larvae counts. The highest efficiency was obtained with Nimbecidine and Nostalgist applications. The yield was moderate in the plots with parasitoid application.

The amount and chemistry of acylsugars affects sweetpotato whitefly (Bemisia tabaci) oviposition and development, and tomato yellow leaf curl virus incidence, in field grown tomato plants.

The objectives of this study were to ascertain the impact of endogenous production of trichome-exuded acylsugars on insects and insect transmitted virus by evaluating tomato lines and their hybrids bred for acylsugar production under field settings on whiteflies and the whitefly-transmitted tomato yellow leaf curl virus. Specifically, we utilized a diverse array of tomato lines and hybrids bred for changes in acylsugar amount or type, grown in three field trials under natural whitefly and virus pressure, to investigate whether the amount of accumulated acylsugars and or the chemical profile of the acylsugars were associated with greater resistance to whiteflies and reduced incidence of tomato yellow leaf curl virus. There was considerable variation in the abundance of whitefly eggs and nymphs and incidence of tomato yellow leaf curl virus across experiments and between entries. Increasing amount of acylsugars accumulated by the tomato entries was associated with a reduction in the abundance of whitefly eggs and nymphs and a reduction in the incidence of tomato yellow leaf curl virus. Additionally, we identified lines with changes in several acylsugar fatty acids that were associated with decreased abundance of whitefly eggs and nymphs and reduced incidence of tomato yellow leaf curl virus. These results inform the utility of acylsugars as a host plant defense system for improving resistance to whiteflies and their transmitted viruses, with potential for reducing insecticides as a control method for whiteflies and provide breeding targets for optimization of existing acylsugar tomato lines to create lines with the most efficacious amount and chemistry of acylsugars.

Eggsplorer: a rapid plant–insect resistance determination tool using an automated whitefly egg quantification algorithm

BackgroundA well-known method for evaluating plant resistance to insects is by measuring insect reproduction or oviposition. Whiteflies are vectors of economically important viral diseases and are, therefore, widely studied. In a common experiment, whiteflies are placed on plants using clip-on-cages, where they can lay hundreds of eggs on susceptible plants in a few days. When quantifying whitefly eggs, most researchers perform manual eye measurements using a stereomicroscope. Compared to other insect eggs, whitefly eggs are many and very tiny, usually 0.2 mm in length and 0.08 mm in width; therefore, this process takes a lot of time and effort with and without prior expert knowledge. Plant insect resistance experiments require multiple replicates from different plant accessions; therefore, an automated and rapid method for quantifying insect eggs can save time and human resources.ResultsIn this work, a novel automated tool for fast quantification of whitefly eggs is presented to accelerate the determination of plant insect resistance and susceptibility. Leaf images with whitefly eggs were collected from a commercial microscope and a custom-built imaging system. A deep learning-based object detection model was trained using the collected images. The model was incorporated into an automated whitefly egg quantification algorithm, deployed in a web-based application called Eggsplorer. Upon evaluation on a testing dataset, the algorithm was able to achieve a counting accuracy as high as 0.94, r2 of 0.99, and a counting error of ± 3 eggs relative to the actual number of eggs counted by eye. The automatically collected counting results were used to determine the resistance and susceptibility of several plant accessions and were found to yield significantly comparable results as when using the manually collected counts for analysis.ConclusionThis is the first work that presents a comprehensive step-by-step method for fast determination of plant insect resistance and susceptibility with the assistance of an automated quantification tool.

Population Dynamics of Insect Pests and Beneficials on Different Snap Bean Cultivars

Snap bean is an important crop in the United States. Insecticides are commonly used against pests on snap bean, but many pests have developed resistance to the insecticides and beneficials are threatened by the insecticides. Therefore, host plant resistance is a sustainable alternative. Population dynamics of insect pests and beneficials were assessed on 24 snap bean cultivars every week for six weeks. The lowest number of sweetpotato whitefly (Bemisia tabaci) eggs was observed on cultivar 'Jade', and the fewest nymphs were found on cultivars 'Gold Mine', 'Golden Rod', 'Long Tendergreen', and 'Royal Burgundy'. The numbers of potato leafhopper (Empoasca fabae) and tarnished plant bug (Lygus lineolaris) adults were the lowest on cultivars 'Greencrop' and 'PV-857'. The highest numbers of adults were found in Week 1 (25 days following plant emergence) for B. tabaci and Mexican bean beetle (Epilachna varivestis); Week 3 for cucumber beetle, kudzu bug (Megacopta cribraria), and E. fabae; Weeks 3 and 4 for thrips; Week 4 for L. lineolaris; and Weeks 5 and 6 for bees. Temperature and relative humidity correlated with B. tabaci, E. varivestis, bee, and predator ladybird beetle populations. These results provide valuable information on the integrated pest management of snap beans.

Bemisia tabaci (Hemiptera: Aleyrodidae): Evaluation of Leaf Trichome Density based Resistance on Several Soybean Varieties

The whitefly Bemisia tabaci (Gennadius) is one of the important soybean pests which can reduce production up to 80 %. Soybean defense mechanism against B. tabaci is affected by the physical characteristics of the leaf surface, e.g. leaf thickness, density of trichomes, and sticky glandular trichomes. The objective of this research was to investigate B. tabaci population – trichome density relationship on ten soybean varieties. The experiment was carried out in Ngale Station, Ngawi District, East Java. The tested soybean varieties were Anjasmoro, Demas 1, Dena 1, Dering 1, Devon, Detam 3, Dewah, Gema, Grayak 1, and Wilis. The experiment was done by completely randomized design with three replications. Observation on the whitefly population was conducted weekly from 2 until 10 weeks after planting on 23 sample plants in each plot. The result showed that Devon was the variety with the highest population levels of B. tabaci, 10.89 (eggs), 14.48 (nymphs) individuals per leaf, respectively. The population of B. tabaci was affected by trichomes density. Devon was the highest density of trichomes (613.7 hairs per cm2). The density of trichomes and the number of whitefly eggs and nymphs relationship were significant (R2= 0,78 (egg) and 0.84 (nymph), n= 10, ?= 1 %, F Value= 0.00157, respectively).

Identification of Resistance Traits Against Whiteflies, Bemisia tabaci in Certified Varieties and Promising Strains in Field and Semi-Field Experiments

Al-Issa, Z., M.N. Salti, M. Nabahan and A. Khalifa. 2023. Identification of Resistance Traits Against Whiteflies, Bemisia tabaci in Certified Varieties and Promising Strains in Field and Semi-Field Experiments. Arab Journal of Plant Protection, 41(2): 173-182. https://doi.org/10.22268/AJPP-41.2.173182 Plants have developed defense systems to cope with pests’ challenge, especially insects to reduce their damage. In this study, some resistance traits in 30 cotton (Gossypium hirsutum) genotypes against cotton’s whitefly, Bemisia tabaci (Genn.) were evaluated through semifield experiments, where antixenosis of certified varieties and promising strains to the insect where studied by designing adhesive cage placed on leaves of the plant third upper, insect development from egg to adult were regularly observed and rates of development and survival, lifespan, sex ratio, and total emergence of adults were monitored. Preference test was conducted through recording numbers of different insect stages in 1cm2 area. Field experiments were carried out by planting cotton genotype for two successive seasons (2018, 2019). Insect density was evaluated by measuring whiteflies density every 15 days until the end of the growing season. During the 2020 season, trichome density in 1cm2 area was determined and their length and diameter were also determined at the 8 th node of cotton genotypes. The results showed that no significant differences among cotton genotype in relation to insect survival rate, lifespan, sex ratio, and emergence rate of adult. This study revealed that there were significant differences in trichome density in 1 cm2 of leaf area ranged between 86.33 to 160.7/cm2 . The correlation was significantly negative between egg and trichome density (R= -0.984). However, no significant correlation between length and diameter of trichome with nymph and egg density. The egg density varied from 32 to 54 egg/cm2 , whereas nymph’s density varied between 3.8 to 6.1 181 Arab J. Pl. Prot. Vol. 41, No. 2 (2023) nymphs/cm2 , and the variety Raqqa 5 had the highest density of whitefly nymphs and eggs during the two seasons. Whiteflies density peak was around mid-September and started to decline until mid-October. The results obtained suggested that there is a role for trichome density in resistance to whiteflies and there aren’t antixenosis between studied cotton’s genotypes. There is a need to investigate cotton genotypes from different cotton species such as G. arboreum, G. barbadens, G. thuberi for the presence of insect resistance traits. Incorporation of such resistance in cotton cultivars is a key for sustainable pest management. Keywords: cotton’s whiteflies, egg number, nymph number, resistance traits, preference, trichome

Host range of rugose spiraling whitefly, (Aleurodicus rugioperculatus) martin and its incidence and damage on coconut plant in coastal region of Bangladesh

Rugose spiraling whitefly, Aleurodicus rugioperculatus Martin (Hemiptera: Aleyrodidae) is an invasive pest causing severe damage to several plant species. Surveys were conducted in the farmers’ orchards of 11 coastal districts of Bangladesh namely Patuakhali, Barguna, Barishal, Khulna, Bagherhat, Pirojpur, Jhalokathi, Bhola, Laxmipur, Noakhali and Cox’s Bazar to know the host range of rugose spiraling whitefly and its incidence and damage in coconut during July 2021 to June 2022. Results revealed that a total of 22 plant species from 16 families were recorded as hosts of A. rugioperculatus. Among the host plants 4 hosts were infested by A. rugioperculatus in which all the life stages such as egg spirals, nymphs and adults of whitefly were noticed whereas in other 18 host plants only the egg stages were observed. The highest incidence of whitefly egg spirals, nymphs and adults per leaflet of coconut was observed in September 2021 at Bagherhat followed by October, November and May 2022 while the lowest was in July 2021 at Cox’s Bazar followed by June, January, February 2022 and December 2021. The highest percent (97%) infested tree was recorded in Bagherhat district while the lowest percent infested tree (68%) was in Cox’s Bazar. The highest percent (96.23%) of infested fronds per tree were recorded in Bagherhat district and the lowest percent infested fronds per tree (67.23%) was in Cox’s Bazar. The highest percent (84%) of leaflet area occupied by this insect was recorded in Bagherhat and the lowest percent was in Cox’s Bazar (48%). SAARC J. Agric., 20(2): 183-197 (2022)

Detection and classification of whiteflies and development stages on soybean leaves images using an improved deep learning strategy

This paper presents a novel strategy to detect and classify adult whiteflies and five important related stages on images of detached soybean leaves. The whitefly Bemisia tabaci is a major pest in soybean crops, and by detecting, counting and differentiating its related life stages in field collected leaves control management decisions can be made. The proposed solution is based on a deep learning object detection algorithm (YOLOv4), modified into an specific new learning strategy with innovations on data augmentation, image mosaicking, and fusion of hypothesized object categories. A real and annotated dataset of images is provided from a controlled experiment infected with whitefly eggs having 121 images and 973 annotated objects. The experimental results showed a promising performance of the proposed system, reaching an f1-score of 0.87, in comparison with a single YOLOv4 algorithm that reached f1-score of 0.80. The overall strategy could be extended to work in other similar tasks for image based pest management.

Selection of F2RC1 saladette-type dwarf tomato plant populations for fruit quality and whitefly resistance

ABSTRACT This study aimed to select promising F2RC1 populations of saladette-type dwarf tomato plants for the development of breeding lines based on agronomic characteristics, fruit quality, and whitefly resistance. The experimental design was randomized blocks containing 13 treatments (10 F2RC1 populations of dwarf tomato plants, both parents, and a commercial hybrid) with four replicates. The evaluations were performed included weight, length, diameter, shape, pulp thickness, number of locules, soluble solids, β-carotene, and lycopene concentration of the fruit; plant internode length; acylsugars concentration; and number of whitefly eggs, nymphs, and adults on the leaflets. The data were analyzed using ANOVA, selection indices, and multivariate analysis. The first backcross increased the agronomic characteristics of the populations in relation to the donor parent, especially for fruit weight (169.1%), fruit length (26.1%), and fruit diameter (16.6%). The UFU SDi 7, UFU SDi 9, and UFU-SDi 17 populations were selected using two selection indices and were therefore considered promising.

Suitability of pollen as an alternative food source for different developmental stages of Amblyseius herbicolus (Chant) (Acari: Phytoseiidae) to facilitate predation on whitefly eggs

Alternative food sources could sustain predator populations by influencing their performances including predation, development, and reproduction in periods of shortage or scarcity of prey under laboratory or fields conditions. The aim of this study was to explore suitability of cattail pollen (Typha orientalis) as an alternative food source for different stages of Amblyseius herbicolus (Chant) (Acari: Phytoseiidae) on their predation capacity against the eggs of whitefly Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae), and the developmental and reproductive responses of the predators to different diet switching regimes under laboratory conditions (T1: nymphs and early adults fed pollen; T2: nymphs fed pollen but early adults fed whitefly eggs; T3: nymphs fed whitefly eggs but early adults fed pollen; T4: nymphs and early adults fed whitefly eggs). Results in the diet switching experiment revealed that although A. herbicolus could prey on whitefly eggs in all the treatment groups, the predatory mites obviously differed in their capacity to prey on the target pest whitefly eggs when fed on cattail pollen and whitefly eggs during different developmental stages. A. herbicolus in group T2 revealed the highest average predation rate, being 1.31, 1.17, and 1.49 times those in groups T1, T3, and T4, respectively. Our results indicated that food sources including cattail pollen and whitefly eggs were suitable for A. herbicolus, because it was able to develop from egg to adult females in all the treatment groups. The mixed diets (T2 and T3 groups) revealed positive effects on the developmental and reproductive parameters of A. herbicolus females, leading to higher oviposition rates and shorter developmental durations when compared with those of groups T1 and T4. A. herbicolus in group T2 revealed the highest average oviposition rates (1.32, 1.26, and 1.81 times those in groups T1, T3 and T4, respectively); however, no significant differences were observed between the T1 and T3 groups. All the eggs of A. herbicolus succeeded in reaching adulthood, but the duration of egg to adult developmental time of A. herbicolus was different among the four treatment groups. The longest and shortest developmental times were obtained in groups T4 and T3, respectively. All the results in the present study demonstrated that A. herbicolus adult females can prey on T. vaporariorum eggs, and cattail pollen was suitable as an alternative or additional food source with high nutritional value for this predatory mite to enhance the predation capacity towards whitefly eggs because A. herbicolus can successfully complete its immature development as well as reproduction.

Effects of Mulch Type, Plant Cultivar, and Insecticide Use on Sweet Potato Whitefly Population in Chili Pepper.

One of the most devastating pests of chili pepper is the sweet potato whitefly (SPW), Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). It sucks plant sap, emits honeydew on which sooty mold fungi grow, and transmits the pepper yellow leaf curl Indonesia virus (PepYLCIV), the most damaging viral disease of chili in Indonesia. Farmers rely mainly on insecticide to control the insect with two to three sprays in a week. To reduce the insecticide use, an integrated approach needs to be developed. Therefore, the current study evaluated the effectiveness of the integration of reflective mulch, host plant resistance, and insecticide use for managing the sweet potato whitefly on the chili pepper. In 2018, a complete randomized block design was used in three separate trials to assess the effects of mulch, cultivar, or insecticide application frequency on the numbers of whitefly eggs, nymphs, and adults. In 2019, a split-split plot design was used to evaluate the effects of the integration of mulch, cultivar, and insecticide application frequency on the numbers of whitefly eggs, nymphs, and adults. The results showed that the reflective silver mulch had significantly lower numbers of whitefly eggs, nymphs, and adults, in comparison to the rice straw mulch and bare ground treatments. Chili plants cv. Bara was more resistant than Bhaskara against B. tabaci in the field; however, in the no-choice trial, no significant difference was detected between both cultivars. Insecticide applications twice per week and once per week were equally effective in controlling the whitefly on the susceptible cultivar (Bhaskara). Overall, the integration of reflective mulch, resistant cultivar, and insecticide application every two weeks effectively suppressed B. tabaci populations on the chili pepper. This approach could substantially reduce the number of insecticide applications from twice per week (commonly practiced by chili farmers in the area) to one application only in two weeks.

Biopesticides for Management of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) and Tomato Yellow Leaf Curl Virus.

The sweetpotato whitefly, Bemisia tabaci MEAM1 Gennadius, is a global pest of tomato, transmitting Tomato yellow leaf curl virus (TYLCV). Management of B. tabaci is challenging in part because of its ability to develop resistance to insecticides. Biopesticides include materials that control B. tabaci via mechanisms that do not select for resistance. Field experiments were conducted in the spring and fall of 2016 and 2017 at the University of Florida's Gulf Coast Research and Education Center in west central Florida to compare biopesticides to conventional insecticides for management of B. tabaci and TYLCV. Insecticide rotations were designed in part around the concept that conventional insecticide programs should group modes of action according to 5-wk treatment intervals, corresponding to an estimated 5-wk generation time for the pest. In 2016, when tomato was treated during the first 5-wk treatment interval with either biopesticides or neonicotinoid insecticides, insecticidal soap contributed to a reduction in whitefly egg numbers and percentage TYLCV that was comparable to results achieved with dinotefuran. In contrast, egg numbers and virus incidence in plants treated with kaolin clay tended to be numerically higher than the untreated control. In spring 2017, comparisons of biopesticides and conventional ovicides/nymphicides during the second 5-wk treatment interval showed that biopesticides can provide comparable reduction in nymph numbers to conventional insecticides. While data from these trials confirm that biopesticides can reduce numbers of whitefly eggs and nymphs, they indicate that season-long programs of the biopesticides evaluated may not reduce transmission of TYLCV below economically acceptable levels.

Functional response and prey stage preference of Delphastus catalinae and D. pallidus (Coleoptera: Coccinellidae) on Bemisia tabaci (Hemiptera: Aleyrodidae)

ABSTRACTConsidering the importance of natural enemies in the integrated management programme of Bemisia tabaci (Gennadius), in the current study we evaluated the biocontrol potential of two predatory beetles Delphastus catalinae Horn and D. pallidus LeConte against Middle Eastern Asia Minor 1 (MEAM1 or biotype B) and Mediterranean (MED or biotype Q) whiteflies, the two most notorious representatives of the B. tabaci species complex. The functional responses of two predators at prey densities ranging from 20 to 120 whitefly eggs/leaf disc, and prey-stage preferences with different ratios of whitefly eggs and nymphs of two predatory beetles were investigated under laboratory conditions. Both beetle species showed Type II functional response with respect to MEAM1 and MED eggs, determined by the logistic regression model. Based on the observed predation parameters (handling time, attack rate, and the number of eggs consumed), D. catalinae seemed to be a more suitable biocontrol candidate for whitefly pests. Results indicated that both the beetle species preferred whitefly eggs over the early nymphal instars and they could consume >50 eggs per day. Although these findings are promising, their feeding potential needs to be evaluated further under greenhouse and semi-field conditions to confirm their efficacy against MEAM1 and MED whitefly.

Preference for Oviposition by Sweetpotato Whitefly, Bemisia tabaci (Gennadius)1, in Two Soybean Genotypes, and Volatile Release

Soybean, Glycine max (L.), in the field is very susceptible to infestation by sweetpotato whitefly, Bemisia tabaci (Gennadius). Preference for oviposition by whitefly in two soybean genotypes was evaluated, and a profile of volatile compounds in healthy plants was obtained. The average number of eggs per square centimeter was 4.1 to 13.7 in ‘Nainari’ variety and 15.1 to 28.4 in an experimental line. Trichome averaged 6.5 per square centimeter in Nainari and 6.8 in the experimental line. The average length of trichomes of Nainari was 311 microns and in the experimental line was 342. Solid-phase microextraction and gas chromatography-mass spectrometry were used to obtain the profile of volatile compounds in two Nainari soybean genotypes and one experimental line: cis-3-hexenyl acetate; cis-3-methyl-1,3-pentadiene; 4-methyl-1,3-pentadiene; cis-3-hexenyl valerate; cis-2-hexen-1-ol; 9-ethyl-9-heptyloctadecane; tetradecane; tridecane; and 2,6-bis(1,1-dimethylethyl)-4-(1-oxopropyl) phenol. In plants infested with whitefly eggs and nymphs, eight compounds were identified in Nainari and seven in the experimental line: M-xylene; 1-octen-3-ol; d-limonene; cedrene; propanoic acid, 2-methyl-, 2-methyl propyl ester; 3-methylnonane; longifolene; caryophyllene; 2,5-cyclohexadiene-1,4-dione, 2,6-bis (1,1-dimethylethyl)-; alpha-farnesene; pentanoic acid, 2,2,4-trimethyl-3-carboxyisopropyl, isobutyl ester, and 2,6-bis(1,1-dimethylethyl)-4-(1-oxopropyl) phenol. Differences in the profile of volatile compounds in healthy Nainari plants might explain oviposition repellency.

Functional responses of two predatory bugs (Hemiptera: Anthocoridae) to changes in the abundance of Tetranychus urticae (Acari: Tetranychidae) and Bemisia tabaci (Hemiptera: Aleyrodidae)

Orius spp. (Hemiptera: Anthocoridae) is well-known genus of generalist predators, which feed on numerous pest insects and mites infesting crops. In this study, the functional responses of the predatory bugs, Orius laevigatus (Fieber) and Orius vicinus (Ribaut), to different densities of the eggs of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and red spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), were determined under laboratory conditions. Different numbers of eggs (2, 4, 6, 8, 16, 32, 64 and 128) of both species of prey were offered to females of the above predators for 24-h in a controlled environment of 25 ± 1°C, 60 ± 10% RH and under a 16L : 8D photoperiod. The parameters of the functional responses were assessed using Holling's Disc Equation. Both predators showed a Type II response to both prey. The attack rates (a) and handling times (Th) of the predators were computed for spider mites eggs: O. laevigatus (a: 0.972, Th: 0.007) and O. vicinus (a: 1.113, Th: 0.005), and whitefly eggs: O. laevigatus (a: 1.022, Th: 0.002) and O. vicinus (a: 0.772 Th: 0.006). Furthermore, the average number of B. tabaci eggs consumed by O. laevigatus females was greater than by those of O. vicinus. In contrast, O. vicinus was a more efficient predator of T. urticae eggs than O. laevigatus. Consequently, these results indicate that together these predators might be effective biological control agents in regulating populations of B. tabaci and T. urticae in agricultural ecosystems.

Three Release Rates of Dicyphus hesperus (Hemiptera: Miridae) for Management of Bemisia tabaci (Hemiptera: Aleyrodidae) on Greenhouse Tomato.

The sweetpotato whitefly, Bemisia tabaci, is a pest of greenhouse-grown tomato. Restrictions on insecticides in enclosed structures and the presence of commercial pollinators limit the options for the chemical control of whiteflies in greenhouses, increasing the importance of biological controls. Dicyphus hesperus is a zoophytophagous mirid predator native to North America. Three release rates of D. hesperus were evaluated on greenhouse tomato for control of the sweetpotato whitefly. The release rates were one, two or three adult D. hesperus per tomato plant each week for three weeks in cages containing four tomato plants and one mullein banker plant. There were fewer whitefly eggs in cages receiving predators than untreated cages one week after the third release, and fewer whitefly nymphs in cages receiving predators two weeks after the third release. There were no statistical differences in whitefly eggs or nymphs among predator release treatments. The highest release rate resulted in a 60% reduction in whitefly nymphs. Forty-two days after the first predator releases, there were no differences among release treatments in the number of D. hesperus. Our results indicate that D. hesperus can contribute management of B. tabaci on greenhouse tomato, but that it may be insufficient as a sole strategy.