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Barriers to gene flow can result in populations evolving into separate species, and understanding how these barriers evolve is a key step in understanding the process of speciation. This study investigates a major barrier to gene flow, mortality during development, of two parasitoid wasp species, Nasonia vitripennis Walker and N. giraulti Darling. Previous work has demonstrated high mortality in haploid hybrid males of these species and has shown potential rescue from this mortality in diploid hybrid females through backcrossing. However, this previous work did not directly measure egg clutch sizes in hybrids and also did not account for male eggs in these clutches. Here, we measure female-only egg and adult clutch sizes of both parent species and F2 hybrids, as well as F2 male egg and adult clutch sizes, in order to determine the impact of backcrossing on mortality in these hybrids. We find significant egg-to-adult mortality in diploid F2 hybrid females with a N. giraulti cytotype when backcrossed to N. vitripennis males; yet, these hybrids also experience less mortality than haploid F2 males. These results confirm the mortality and rescue in these F2 hybrid females and indicate that there is likely a combination of nuclear-cytoplasmic and nuclear-nuclear incompatibilities in these hybrids that lead to this mortality. This work provides a foundation for future studies to investigate the genetic basis of this mortality.
Coconut, Cocos nucifera L., in Tamil Nadu, India, was invaded by four whitefly (Hemiptera: Aleyrodidae) species between 2016 and 2019, increasing the total to six, along with Aleurodicus dispersus Russell and Aleurocanthus arecae David and Manjunatha. We examined the complexity and diversity of whiteflies in coconut across different agroclimatic zones of Tamil Nadu and found high and low damage levels by whiteflies at Veppankulam (70.4%) and Rameswaram (11.0%), respectively. The rugose spiraling whitefly, Aleurodicus rugioperculatus Martin, was the most dominant species but was effectively managed by the parasitoids Encarsia guadeloupae Viggiani and E. dispersa Polaszek, with the highest rate parasitism of 83.8% at Aliyar Nagar and the lowest (2.9%) in the Kanchipuram district. Aleurodicus rugioperculatus and Bondar's nesting whitefly, Paraleyrodes bondari Peracchi, have spread throughout Tamil Nadu. The population of A. rugioperculaus was high at Veppankulam and that of P. bondari was higher at Dharmapuri (28.6 and 31.1 adults/leaflet, respectively). All five invasive whitefly species in coconut were found only in 7 of 34 locations—Coimbatore, Sirumugai, Salem, Dharmapuri, Krishnagiri, Vellore, and Erode. Paraleyrodes minei Iaccarino and Aleurotrachelus atratus Hempel were distributed in the northwestern zone adjoining the western ghats of Tamil Nadu. Coconut plantations at Sirumugai (western ghats) supported the most diverse collection of whiteflies, with 0.61 and 1.09 Simpson and Shannon diversity indices. Among the 29 districts, adjoining Dindigul and Theni districts showed the highest Bray–Curtis Similarity Matrix. Butterfly palm, Dypsis lutescens H. Wendel, custard apple, Annona squamosa L., and guava, Psidium guajava L., are whitefly hosts in coconut landscapes.
Daniel López-Lima, Manuel Alejandro Tejeda-Reyes, Rafael Diego Rodríguez-Málaga, Everardo López-Bautista, Alejandro Salinas-Castro, Carlos Patricio Illescas-Riquelme
Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) is an insect of Asian origin and is currently distributed in several countries around the world. It has highly polyphagous habits and has been reported as a primary pest of different fruit, horticultural, and ornamental crops. This species was reported in Mexico in 2020, however, due to its invasive nature and its rapid adaptation to new ecosystems, it is probably present in other regions of the country. The lack of information on this pest has resulted in misidentifications and misdiagnosis at the field level by phytosanitary technicians. In the present work, we found that S. dorsalis is distributed in the states of Veracruz, Sinaloa, Jalisco, and Michoacán in Mexico occupying sites with different climates (warm and temperate) and elevations from 6 to 1,721 m above sea level. Plant reproductive hosts were blackberry (Rubus sp.), blueberry (Vaccinium sp.), Persian lime (Citrus latifolia Tanaka), mango (Mangifera indica L.), and pear (Pyrus communis L.). Through an evaluation of the response of adults toward chromatic traps, we found that this species greatly prefers yellow (×5.40) compared with blue color. More studies are needed on detection and control measures in order to reduce the distribution and economic impact caused by this insect pest in Mexico.
Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an economically important pest of variety of crops, including maize (Zea mays L.), rice (Oryza sativa L.), and cotton (Gossypium spp.). Conventional chemical insecticides are usually used for management of this pest; however, a viable alternative is the use of microbial agents or their biological products, such as entomopathogenic nematodes. Their efficacy, however, is affected by abiotic conditions including ultraviolet (UV) light and desiccation. It is therefore necessary to develop formulations that preserve or extend the viability of the agent or product while facilitating ease of application. This laboratory study was conducted to determine the pathogenicity of the nematode Heterorhabditis bacteriophora (Poinar) against S. frugiperda third-instar larvae. Infective juveniles (IJs) of the nematode were tested at a concentration of 350 IJs/ml in two substrates (water and 0.1% [w/v] agar suspension) with four periods of exposure (0, 5, 10 and 15 min) to UV radiation at 253.7 nm. Each of the eight treatments included 40 larvae, with each treatment replicated three times in a completely randomized design (two factors of type of medium and UV exposure time). We determined that the 0.1% (w/v) agar suspension, compared with the water substrate, protected the IJs from harmful UV light and thus improved the survival and pathogenicity of the IJs against third-instar S. frugiperda.
The contact toxicity activity of an essential oil extracted from Acorus calamus (L.) (Acoraceae) was evaluated against the phytophagous spider mites Tetranychus urticae Koch and Tetranychus macfarlanei Baker & Pritchard (Acari: Tetranychidae) and the predatory mite Amblyseius longispinosus (Evans) (Acari: Phytoseiidae). Adult mortality 24 h following application of 5% (v/v) concentration of the essential oil exceeded 90% for T. urticae and T. macfarlanei. Application of 1.2–5% concentrations of the essential oil to mite eggs reduced egg viability, with 0–54% hatch of T. urticae eggs and 0% hatch of T. macfarlanei eggs 6 d following treatment. At 2.5%, the essential oil was toxic to A. longipinosus by residual contact toxicity (58% mortality) and direct contact toxicity (0% mortality). No eggs and 47.6 eggs of A. longispinosus were oviposited with residual contact toxicity and direct contact toxicity, respectively. The chemical constituents of the essential oil, as determined with gas chromatography–mass spectrometry, showed that camphor (41.07%) and 5,5-dimethyl-2-ethynylcyclopent-2-en-1-ol (27.96%) were the major chemical compounds of the essential oil. These results indicate that this essential oil extracted from fresh A. calamus rhizomes could prove useful in controlling T. urticae and T. macfarlanei. Our findings also showed that the essential oil had no deleterious effects against A. longispinosus by direct contact toxicity test; however, A. longispinosus consuming spider mite eggs treated with essential oil were negatively impacted.
Plant tissue bioassays are a standard approach for bioassaying insects such as the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), an insect that specializes in systemic feeding on the phloem in leaves by using a piercing-sucking mouthpart apparatus. Systemic insecticides remain the most effective approach to whitefly management; however, little work has been done to quantify the amount of insecticide active ingredient that a species is exposed to when feeding. This study was conducted to estimate the imidacloprid and cyantraniliprole concentrations present in cotton (Gossypium hirsutum L.) leaves 24 h after a root drench for systemic toxicological bioassays. Insecticide active-ingredient quantification involved liquid chromatography–tandem mass spectrometry. Comparable concentration responses also were conducted to indicate the mortality of the sweetpotato whitefly at the tested concentrations. The results indicated significant active-ingredient retention with higher concentrations of insecticide treatments, which corresponded with higher sweetpotato whitefly mortality. Specifically, for imidacloprid and cyantraniliprole, the average slopes and intercepts of the log parts per billion of leaf tissue concentration to milligrams of active ingredient per liter of treatment solution were y = 4.08 x + 0.83 and y = 6.22 x + 0.47, respectively. These formulae estimate leaf tissue concentrations that can be linked to insect insecticide exposure in the leaves, with 50–73% of the overall variability explained. Significant correlations also were observed between the root drench concentrations, leaf tissue concentrations, and sweetpotato whitefly mortality.
Odorant-binding proteins (OBPs) play an important role in specific recognition, binding, and transportation of odorants. In this study, the full-length complementary DNA (cDNA) sequence of AzanOBP7, a Minus-C OBP gene, from Agrilus zanthoxylumi Li Ming Lou (Coleoptera: Buprestidae) was cloned by rapid amplification of cDNA ends based on transcriptome data. The bioinformatic analysis showed that AzanOBP7 contains a 450-bp open reading frame encoding a 149-residue polypeptide, with a molecular mass of 17.176 kDa. It was predicted to be a nontransmembrane protein with an 18–amino acid signal peptide at the N terminus. The predicted three-dimensional structure of AzanOBP7 by AphadFold2 possesses seven α helices and two disulfide bridges. The multiple sequence alignment and phylogenetic tree revealed that AzanOBP7 reached the highest identity (94.70%) with Agrilus mali Matsumura (Coleoptera: Buprestidae) AmalOBP11; they also were closely aligned in a clade. Quantitative real-time polymerase chain reaction showed that AzanOBP7 exhibited the highest expression level in the abdomen of adult females. In the thorax, the expression level in adult males was significantly higher than that in other aged males (P < 0.01). Our study offers a theoretical foundation for further study on the functional characteristics of A. zanthoxylumi OBPs.
Entomopathogenic nematodes (EPNs) are important biological control agents of insect pests. Strains or isolates obtained in specific regions and utilized in situ might contribute to the success of EPNs, since they are adapted to local abiotic conditions. We isolated and identified three isolates each of Heterorhabditis bacteriophora Poinar and Steinernema carpocapsae (Weiser) from soils at Saltillo, Coahuila State, Mexico. These six isolates were bioassayed against larvae of Tenebrio molitor L., using six concentrations of infective juveniles (IJs) per larva (0, 10, 25, 50, 100, 200). EPN-induced mortality of the isolates ranged from 15.2% to 100%. The designated M5 isolate of S. carpocapsae caused 100% mortality after 72 h at concentrations ≥25 IJs/larva with a median lethal concentration of 4.99 IJs/larva. Comparison of mortality levels induced at the same concentration of the six EPN isolates indicated that the Steinernema isolates, in general, induced higher mortality levels than the Heterorhabditis isolates. IJ production in T. molitor larvae also was greatest with the M5 isolate of S. carpocapsae following exposure of larvae to a concentration of 100 IJs/larva with a mean of 17,320 IJs/larva. Based on induced mortality and IJ production, the S. carpocapsae M5 isolate appears to be a viable candidate for further study and possible development for use in insect pest management programs. This study indicates that naturally coexisting local nematode isolates possess different attributes critical for their use as biocontrol agents.
The ambrosia beetles, mainly Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae: Scolytinae), are serious pests of young trees in the ornamental industry and pecan orchards as infested trees develop branch dieback with occasional tree mortality. Surveys were conducted in the ornamental industry in 2020 and 2021 and the pecan industry in 2020 because clientele perspective on the extent of damage, phenology, monitoring, management, and loss related to the ambrosia beetle was unclear. Of 35 and 40 ornamental industry respondents, 68% and 82% indicated problems with this pest in 2020 and 2021, respectively. Of 66 pecan industry respondents, 52% reported beetle problems in 2020. About 85% of ornamental and 58% of pecan respondents indicated that 1–10 trees were attacked by ambrosia beetles and 1–30 or more trees were culled annually. The beetle problem persists throughout the growing season but appears greater during the spring than in other periods. About 73% of respondents indicated that current monitoring tools helped them with management decisions; however, a proportion did not use recommended monitoring tools but instead relied on visual signs to determine attacks on trees. In the 2020 surveys, only 37% of ornamental respondents and 43% of the pecan respondents used insecticide sprays, whereas in the 2021 survey, 71% of the ornamental clientele (mostly nurseries) sprayed pyrethroid insecticides for ambrosia beetle management. In 2020 surveys, about 48% and 56% of ornamental and pecan respondents, respectively, spent <$500 USD for ambrosia beetle management.
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