Hypervolume Niche Dynamics and Global Invasion Risk of Phenacoccus solenopsis under Climate Change

As a globally invasive quarantine pest, the cotton mealybug, Phenacoccus solenopsis, is spreading rapidly, posing serious threats against agricultural and forestry production and biosecurity. In recent years, the niche conservatism hypothesis has been widely debated, which is particularly evident in invasive biology research. Identifying the niche dynamics of P. solenopsis, as well as assessing its global invasion risk, is of both theoretical and practical importance. Based on 462 occurrence points and 19 bioclimatic variables, we used n-dimensional hypervolume analysis to quantify the multidimensional climatic niche of this pest in both its native and invasive ranges. We examined niche conservatism and further optimized the MaxEnt model parameters to predict the global invasion risk of P. solenopsis under both current and future climate conditions. Our findings indicated that the niche hypervolume of this pest in invasive ranges was significantly larger than that in its native ranges, with 99.45% of the niche differentiation contributed by niche expansion, with the remaining less than 1% explained by space replacement. Niche expansion was most evident in Oceania and Eurasia. The area under the receiver operating characteristic curve (0.83) and true skill statistic (0.62) indicated the model's robust performance. The areas of suitable habitats for P. solenopsis are increasing significantly and the northward spread is obvious in future climate change scenarios. North Africa, northern China, Mediterranean regions, and northern Europe had an increased invasion risk of P. solenopsis. This study provided scientific support for the early warning and control of P. solenopsis.

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The cotton mealybug, Phenacoccus solenopsis Tinsley and papaya mealybug, Paracoccus marginatus Williams and Granara de Willink (Hemiptera: Pseudococcidae) are becoming major threats to the production of Gymnema sylvestre R. Br. (Asclepiadaceae) in India. Management mainly depends on chemical insecticides which cause a serious problem of pesticide residue and insecticide resistance. The use of biorational insecticides such as biopesticides, botanicals, insect growth regulators, and microbial insecticides is important components of an Integrated Pest Management (IPM) program for successful management. We evaluated the bio-efficacy of twelve biorational insecticides, including entomopathogenic fungi (EPF), using the leaf spray method in laboratory conditions at 25 ± 1 °C, 70 % ± 5 % RH. The results revealed that the highest percent mortality was recorded by acetamiprid 20 % SP (100.00 %), followed by azadirachtin (98.27 %), Lecanicillium muscarium (2 × 109 spores/mL) (85.70 %) and Ocimum sanctum leaf extract (76.87 %) at 120 h after treatment (HAT) in P. solenopsis. In P. marginatus, 100.00 %, 96.39 % and 85.67 % and 74.90 % mortalities were achieved by acetamiprid 20 % SP, azadirachtin, L. muscarium (2 × 109 spores/mL) and O. sanctum leaf extract, respectively, at 120 HAT during the first spray. Various biorational insecticides showed a more or less similar trend of percent mortality in both species during the second spray. In both species, the lowest percent mortality was recorded by Andrographis paniculata leaf extract (46.29, 44.54) and (41.03, 46.39) at 120 Hours after treatment in the first and second spray, respectively. It was concluded that all the prescribed treatments are more effective than the control. Overall, azadirachtin recorded the highest percent mortality after acetamiprid and had the shortest LT50 (12.52 h) and (13.87 h) values in P. solenopsis and P. marginatus, respectively. Our study emphasizes that biopesticides like Azadirachtin 1 % EC (10000 ppm), L. muscarium (2 × 109 spores/mL) (5 mL/L) and O. sanctum leaf extract (5 %) may be recommended as alternatives to synthetic insecticides. Botanicals and EPF would be the most effective approach for sustainable integrated management of P. solenopsis and P. marginatus in the G. sylvestre ecosystem.

Endosymbiont Tremblaya phenacola influences the reproduction of cotton mealybugs by regulating the mechanistic target of rapamycin pathway

The intricate evolutionary dynamics of endosymbiotic relationships result in unique characteristics among the genomes of symbionts, which profoundly influence host insect phenotypes. Here, we investigated an endosymbiotic system in Phenacoccus solenopsis, a notorious pest of the subfamily Phenacoccinae. The endosymbiont, "Candidatus Tremblaya phenacola" (T. phenacola PSOL), persisted throughout the complete life cycle of female hosts and was more active during oviposition, whereas there was a significant decline in abundance after pupation in males. Genome sequencing yielded an endosymbiont genome of 221.1 kb in size, comprising seven contigs and originating from a chimeric arrangement between betaproteobacteria and gammaproteobacteria. A comprehensive analysis of amino acid metabolic pathways demonstrated complementarity between the host and endosymbiont metabolism. Elimination of T. phenacola PSOL through antibiotic treatment significantly decreased P. solenopsis fecundity. Weighted gene coexpression network analysis demonstrated a correlation between genes associated with essential amino acid synthesis and those associated with host meiosis and oocyte maturation. Moreover, altering endosymbiont abundance activated the host mechanistic target of rapamycin pathway, suggesting that changes in the amino acid abundance affected the host reproductive capabilities via this signal pathway. Taken together, these findings demonstrate a mechanism by which the endosymbiont T. phenacola PSOL contributed to high fecundity in P. solenopsis and provide new insights into nutritional compensation and coevolution of the endosymbiotic system.

Construction of a Banker Plant System via the Host Switch Trait of a Natural Enemy Aenasius bambawalei

Understanding the most effective host switch patterns in parasitic wasps, specifically Aenasius bambawalei (AB), is crucial for effectively controlling pests like Penacoccus solenopsis (PSS). This study aims to elucidate AB's ideal host switch pattern and assess its utility in maintaining synchronization between AB and PSS, thereby aiding in PSS control. We examined various host switch patterns and cycles to evaluate their impact on AB's offspring's parasitism rates and fitness in laboratory conditions. Concurrently, we assessed the fitness of both PSS and AB on tomato plants using different banker plant systems to maintain field synchronization. Results indicate that the three-repeat T1 host switch pattern of PSS-Penacoccus solani (PSI)-PSS was the most effective. Additionally, a specific banker plant system, "System B", which provided succulent plants hosting PSI, was optimal for synchronizing AB and PSS in a summer greenhouse setting. Our findings underscore the importance of employing specific host switch patterns and banker plant systems to effectively control PSS in the field. This research offers foundational data for incorporating a banker plant system into integrated pest management strategies for enhanced PSS control.

Antennal sensory structures of Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

BACKGROUND

The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) is one of the most devastating sap-sucking pests of cultivated plants. The success of P. solenopsis is attributable to its ecological resilience and insecticide resistance, making its control extremely difficult and expensive. Thus, alternative safe approaches are needed to prevent the pest population from reaching the economic threshold. One of these novel approaches is based on the fact that chemical communication via the olfactory system drives critical behaviors required for the survival and development of the species. This knowledge can be useful for controlling insect pests using traps based on semiochemicals. The antennae of insects are an invaluable model for studying the fundamentals of odor perception. Several efforts have been made to investigate the histological and ultrastructural organization of the olfactory organs, such as the antennae and maxillary palps, in many insect species. However, studies on the antennal sensory structures of Phenacoccus species are lacking. Furthermore, although enormous progress has been made in understanding the antennal structures of many mealybug species, the olfactory sensilla in the antennae of P. solenopsis have not yet been described. In this study, we describe, for the first time, the morphology and distribution of the antennal sensilla in male and female P. solenopsis using scanning electron microscopy.

RESULTS

Our results revealed that the entire antennae length and the number of flagellar segments were different between the sexes. Eight morphological types of sensilla were identified on male antennae: trichoid sensilla, chaetic sensilla (three subtypes), basiconic sensilla (two subtypes), and campaniform sensilla (two subtypes). Six morphological types of sensilla were found on female antennae. Sensilla chaetica of subtype 2 and campaniform sensilla of subtype 1 were distributed only on male antennae, suggesting that these sensilla are involved in the recognition of female sex pheromones. The subtype 1 of sensilla chaetica was significantly more abundant on female antennae than on male ones, while subtype 3 was only located on the terminal flagellar segment of the antenna in both sexes.

CONCLUSIONS

This study provides insightful information for future electrophysiological and behavioral studies on chemical communication in insects, particularly the cotton mealybug, P. solenopsis that could help in developing new strategies for controlling this economically important insect species.

Biology, ecology, and management of cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), is a highly invasive and harmful pest. It causes considerable loss of cotton crops in China, India and Pakistan. Little is known about its bionomics since it was first recorded in Pakistan and India in 2005. Rapid spread of this pest worldwide has accelerated research on its biology, ecology and management. The P. solenopsis has a short life cycle, and optimal temperatures lead to an increase in the number of generations per year, which is a serious threat to cotton crop production. Cotton mealybug is native to the USA, although it has now spread to >43 countries. Insecticidal control is the primary and dominant practice for this pest, and its resistance to commonly used insecticides is increasing. Biocontrol agents have strong potential for the management of nymphal instar stages. We read >250 articles related to our review title and finally reviewed recent advances in the understanding of P. solenopsis biology, ecology and control approaches, aiming to highlight integrated and biological management practices of this pest. © 2021 Society of Chemical Industry.

Cellulose Nanocrystals Loaded with Thiamethoxam: Fabrication, Characterization, and Evaluation of Insecticidal Activity against Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

Using smart nanopesticide formulations based on nanomaterials can offer promising potential applications for decreasing pesticide residues and their effects on human health and the environment. In this study, a novel nanoformulation (NF) of thiamethoxam (TMX) was fabricated using the solvent evaporation method through loading TMX on cellulose nanocrystals (CNCs) as the carrier. The synthesized TMX-CNCs was investigated through different techniques, such as Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and thermogravimetric analysis (TGA). The results revealed that the loading efficiency and entrapment efficiency were 18.7% and 83.7 ± 1.8% for TMX, respectively. The prepared nanoformulation (TMX-CNCs) had a width of 7-14 nm and a length of 85-214 nm with a zeta potential of -23.6 ± 0.3 mV. The drug release behavior study exhibited that the release of TMX from TMX-loaded CNCs was good and sustained. Furthermore, bioassay results showed that the insecticidal activity of TMX-CNCs against Phenacoccus solenopsis was significantly superior to that of the technical and commercial formulation, as indicated by the lower LC₅₀ value. The results indicate that the TMX nanoformulation has great potential for application in agriculture for pest control.

Interference Competition for Mutualism between Ant Species Mediates Ant-Mealybug Associations

Ant-hemipteran mutualism has been well documented, and many studies have reported the interference competition between ant species for the mutualism. However, little is known on how this interference competition impacts the reciprocally beneficial association. Previous studies demonstrated that the invasive mealybug Phenacoccus solenopsis (Tinsley) has established close mutual relationship with the ghost ant Tapinoma melanocephalum (Fabricius). The sympatric ants, Paratrechina longicornis (Latreille) and Tetramorium bicarinatum (Nylander) were frequently observed to compete for nutrient honeydew produced by P. solenopsis with T. melanocephalum. Herein, we investigated the effects of interference competition between the ant species on the ant-mealybug interactions. Phenacoccus solenopsis benefited from the tending by T. melanocephalum and P. longicornis. Interference competition between T. melanocephalum and P. longicornis interrupted the mutualism, suppressed the trailing activity of both species, but negligibly influenced the parasitism of Aenasius bambawalei Hayat, a solitary endoparasitoid of P. solenopsis. Harmonia axyridis, a predator of P. solenopsis, showed a significant avoidance when encountering with T. melanocephalum or P. longicornis, but not T. bicarinatum. Ant workers showed higher aggressiveness and lower exploratory activity when T. melanocephalum encountered P. longicornis. However, competition between T. melanocephalum and T. bicarinatum seldom influenced the trailing and exploratory activity of T. melanocephalum. It is concluded that interference competition for mutualism between ant species can mediate ant-mealybug associations and the fitness of mealybug colony. Our results also demonstrate that the effects of interference competition between ant species on ant-mealybug mutualism are varied among ant species.

Synthesis, Characterization, and Pesticidal Activity of Emamectin Benzoate Nanoformulations against Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

Using nanotechnology to develop new formulations of pesticides is considered a possible option in enhancing the efficiency, safety, and photostability of pesticides under various climatic conditions. In the present study, two novel nanoformulations (NFs) were successfully prepared based on nano-delivery systems for emamectin benzoate (EMB) by loading it on cellulose nanocrystals (CNCs) and silicon dioxide nanoparticles (SNPs) as carriers through a freeze-drying method. The synthesized nanoformulations were examined using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and dynamic light scattering (DLS). The results showed that SNPs and CNCs had a loading efficiency of 43.31% and 15.04% (w/w) for EMB, respectively, and could effectively protect EMB from photolysis under UV radiation. The LC50 values for EMB + SNPs, EMB + CNCs, and EMB commercial formulation against Phenacoccus solenopsis were 0.01, 0.05, and 0.31 μg/mL, respectively, indicating that both NFs were more effective than the EMB commercial formulation. This work seeks to develop new nano-carriers for potential applications of pesticides in plant protection, which will reduce the recommended dose of pesticides and thereby decrease the amount of pesticide residue in food and the environment.

Plant Defense Responses Induced by Two Herbivores and Consequences for Whitefly Bemisia tabaci

Diverse herbivores are known to induce various plant defenses. The plant defenses may detrimentally affect the performance and preference to subsequent herbivores on the same plant, such as affecting another insect’s feeding, settling, growth or oviposition. Here, we report two herbivores (mealybug Phenacoccus solenopsis and carmine spider mite Tetranychus cinnabarinus) which were used to pre-infest the cucumber to explore the impact on the plants and the later-colonizing species, whitefly Bemisia tabaci. The results showed that the whiteflies tended to select the treatments pre-infested by the mites, rather than the uninfected treatments. However, the result of treatments pre-infested by the mealybugs was opposite. Total number of eggs laid of whiteflies was related to their feeding preference. The results also showed that T. cinnabarinus were more likely to activate plant jasmonic acid (JA) regulated genes, while mealybugs were more likely to activate key genes regulated by salicylic acid (SA). The different plant defense activities on cucumbers may be one of the essential factors that affects the preference of B. tabaci. Moreover, the digestive enzymes and protective enzymes of the whitefly might play a substantial regulatory role in its settling and oviposition ability.

Molecular characterization and expression patterns of Phenacoccus solenopsis (Hemiptera: Pseudococcidae) heat shock protein genes and their response to host stress

As a polyphagous insect, little is known at the molecular level about the effects of different host plants on physiological changes in Phenacoccus solenopsis. In this study, four heat shock protein (Hsp) genes (PsHsp60, PsHsp70, PsHsp90, and PsHsp20.7) were identified from the transcriptome of P. solenopsis. Analysis of Hsp expression levels revealed significant differences in Hsp gene expression levels in P. solenopsis fed on different host plants. In host conversion tests, the expression levels of PsHsp90 and PsHsp60 were upregulated after transfer of second instar nymphs from tomato to cotton. The expression levels of PsHsp70 and PsHsp20.7 were, respectively, significantly upregulated at 9 and 48 hr after transfer from tomato to Hibiscus. The results of this study aid molecular characterization and understanding of the expression patterns of Hsp genes during different developmental stages and host transfer of P. solenopsis.

Development of novel microsatellites for population genetic analysis of Phenacoccus solenopsis Tinsley (Hemipeta: Pseudoccoccidae) based on genomic analysis

The cotton mealybug, Phenacoccus solenopsis Tinsley (Hemipeta: Pseudoccoccidae), is an aggressively invasive pest causing huge economic losses of crops around the world. In this study, we developed genome-wide microsatellites for population genetic analysis of P. solenopsis. We obtained a random genome of P. solenopsis with a size of 267.07 Mb and scaffold N50 of 14.12 Kb. In total 115,639 microsatellites were isolated from the genome, of which those with trinucleotide motifs were the most abundant. Forty-two polymorphic loci were selected for primer validation based on three populations. Allele numbers varied from 2 to 5 with an average value of 2.5 per locus, and allelic richness ranged from 1.00 to 4.48. The observed heterozygosity (H₀) and expected heterozygosity (H_E) ranged from 0.00 to 0.92 and 0.00 to 0.73, respectively. Population genetic structure analysis based on the developed markers revealed strong differentiation between three populations of P. solenopsis collected from its invasive range in China. The microsatellites developed in our study should provide efficient genetic markers for population level studies of P. solenopsis to reveal invasion history and patterns of dispersal.

Sex Pheromone of the Cotton Mealybug, Phenacoccus solenopsis, with an Unusual Cyclobutane Structure

The cotton mealybug, Phenacoccus solenopsis, the distribution of which was formerly limited to Nearctic and Neotropical regions, recently invaded many countries in various regions including Asia, Africa, and the Pacific. More recently, P. solenopsis was newly recorded in Japan and is currently an emerging pest of agricultural crops. In this study, we determined the structure of a sex pheromone of P. solenopsis in order to develop an effective lure for monitoring this pest. From volatiles emitted by virgin adult females, we isolated a compound attractive to males. By means of coupled gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy, we identified this as (2,2-dimethyl-3-isopropylidenecyclobutyl)methyl 3-methylbut-2-enoate. This compound was synthesized and shown to be attractive to male P. solenopsis. Analysis by gas chromatography using an enantioselective stationary phase and polarimetry analyses of the natural pheromone and synthetic enantiomers showed the natural compound to be the (R)-(-)-enantiomer. This compound is an ester of maconelliol, which has an unusual cyclobutane structure found in sex pheromones of other mealybug species, and senecioic acid, also found in the pheromones of other mealybug species. However, this is the first example of the ester of maconelliol and senecioic acid as a natural product.

Molecular Characterization of Two Fatty Acyl-CoA Reductase Genes From Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

Fatty acyl-CoA reductases (FARs) are key enzymes involved in fatty alcohol synthesis. Here, we cloned and characterized full-length cDNAs of two FAR genes from the cotton mealybug, Phenacoccus solenopsis. The results showed PsFAR I and PsFAR II cDNAs were 1,584 bp and 1,515 bp in length respectively. Both PsFAR I and PsFAR II were predicted to be located in the endoplasmic reticulum by Euk-mPLoc 2.0 approach. Both of them had a Rossmann folding region and a FAR_C region. Two conservative motifs were discovered in Rossmann folding region by sequence alignment including a NADPH combining motif, TGXXGG, and an active site motif, YXXXK. A phylogenetic tree made using MEGA 6.06 indicated that PsFAR I and PsFAR II were placed in two different branches. Gene expression analysis performed at different developmental stages showed that the expression of PsFar I is significantly higher than that of PsFar II in first and second instar nymphs and in male adults. Spirotetramat treatment at 125 mg/liter significantly increased the expression of PsFar I in third instar nymphs, but there was no effect in the expression of PsFar II Our results indicated these two FAR genes showed different expression patterns during insect development and after pesticide treatment, suggesting they play different roles in insect development and detoxification against pesticides.

Effects of temperature and host stage on the parasitization rate and offspring sex ratio of Aenasius bambawalei Hayat in Phenacoccus solenopsis Tinsley

Temperature and host stage are important factors that determine the successful development of parasitoids. Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae) is a primary parasitoid of the newly invasive mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae). The effects of temperature on the parasitic characteristics of A. bambawalei have seldom been investigated. In the study, we explored the effects of temperature, exposure time, and host stage on the parasitization rate and offspring sex ratio (female to male) of A. bambawalei under laboratory conditions. The laboratory results showed that the successful parasitization rate of A. bambawalei increased with higher temperatures and older host stages. When the parasitoids were exposed to 36 °C for 24 h, the parasitization rate of female adults (52%) was nearly two times that of 3rd instar nymphs. Additionally, heat stress duration and host stage resulted in an increase in the offspring sex ratio of A. bambawalei. When A. bambawalei was exposed to 36 °C for 24 h, the offspring sex ratio increased dramatically to 81.78% compared with those exposed for 12 h, and it increased to 45.34% compared with those exposed for 16 h. The offspring sex ratio was clearly higher when the host stage was an adult female mealybug Our findings provide important guidance for the mass rearing and field releases of A. bambawalei for the management of P. solenopsis in the future.

Analysis of expressed sequence tags (ESTs) from a normalized cDNA library and isolation of EST simple sequence repeats from the invasive cotton mealybug Phenacoccus solenopsis

The cotton mealybug, Phenacoccus solenopsis Tinsley, is a serious and invasive pest. At present, genetic resources for studying P. solenopsis are limited, and this negatively affects genetic research on the organism and, consequently, translational work to improve management of this pest. In the present study, expressed sequence tags (ESTs) were analyzed from a normalized complementary DNA library of P. solenopsis. In addition, EST-derived microsatellite loci (also known as simple sequence repeats or SSRs) were isolated and characterized. A total of 1107 high-quality ESTs were acquired from the library. Clustering and assembly analysis resulted in 785 unigenes, which were classified functionally into 23 categories according to the Gene Ontology database. Seven EST-based SSR markers were developed in this study and are expected to be useful in characterizing how this invasive species was introduced, as well as providing insights into its genetic microevolution.

Inoculation of Nicotiana tabacum with recombinant potato virus X induces RNA interference in the solenopsis mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

OBJECTIVES

The chitin synthase 1 (CHS1) gene in Phenacoccus solenopsis (PsCHS1) was evaluated as a potential target of RNA interference (RNAi) by using Potato virus X (PVX) as a vector (recombinant PVX) for expressing RNAi triggering elements in Nicotiana tabacum L.

RESULTS

RT-PCR analysis confirmed the expression of PsCHS1 in N. tabacum inoculated with recombinant-PVX-PsCHS1 (treated). RT- and multiplex-PCR further showed a reduction in mRNA levels of the target gene in mealybugs feeding on treated plants. Mortality in parent adults and emerging nymphs (21 and 29%) exposed to the treated plants was significantly higher (P < 0.05) than those exposed to uninoculated (-ve control) or inoculated with non-recombinant PVX (PVX-control). The number of surviving adults and the combined number of adults and nymphs (47 and 60%) was significantly (P < 0.05) lower on the treated plants than the -ve (76%) or PVX (74%) control. The visual observations verified the physical deformities in mealybugs exposed to the treated plants.

CONCLUSION

chitin synthase 1 is a potential RNAi target in P. solenopsis and the recombinant PVX can be used as a tool to evaluate candidate RNAi triggering elements in plants.

Temperature- and Relative Humidity-Dependent Life History Traits of Phenacoccus solenopsis (Hemiptera: Pseudococcidae) on Hibiscus rosa-sinensis (Malvales: Malvaceae)

Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), a worldwide distributive invasive pest, originated from the United States, and it was first reported in Guangdong province, China, in 2008. The effects of temperature and relative humidity (RH) on the life history traits of P. solenopsis on Hibiscus rosa-sinensis L. (Malvales: Malvaceae) were studied at seven constant temperatures (15, 20, 25, 27.5, 30, 32.5, and 35°C) and three RHs (45, 60, and 75%). The results showed that temperature, RH, and their interactions significantly influenced the life history traits of P. solenopsis. First instar was the most sensitive stage to extreme temperatures with very low survival rates at 15 and 35°C. At 25-32.5°C and the three RHs, the developmental periods of entire immature stage were shorter with values between 12.5-18.6 d. The minimum threshold temperature and the effective accumulative temperature for the pest to complete one generation were 13.2°C and 393.7 degree-days, respectively. The percentage and longevity of female adults significantly differed among different treatments. It failed to complete development at 15 or 35°C and the three RHs. Female fecundity reached the maximum value at 27.5°C and 45% RH. The intrinsic rate for increase (r), the net reproductive rate (R0), and the finite rate of increase (λ) reached the maximum values at 27.5°C and 45% RH (0.22 d(-1), 244.6 hatched eggs, and 1.25 d(-1), respectively). Therefore, we conclude that 27.5°C and 45% RH are the optimum conditions for the population development of the pest.

Inheritance, realized heritability and biochemical mechanism of acetamiprid resistance in the cotton mealybug, Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae)

The cotton mealybug, Phenacoccus solenopsis Tinsley (Homoptera: Pseudococcidae) is a serious pest in many countries of the world because of its polyphagous nature and has caused huge losses to the cotton crop. The aim of present study was to explore the mode of inheritance and mechanism of acetamiprid resistance in P. solenopsis. After five rounds of selection with acetamiprid, P. solenopsis developed a 315-fold resistance compared with the laboratory susceptible population. The LC50 values of progenies of both reciprocal crosses (F1 and F1') showed no significant difference and degree of dominance values were 0.56 and 0.93 for F1 and F1', respectively. Monogenic model of inheritance and Lande's method revealed that more than one factors were involved in acetamiprid resistance. Realized heritability (h(2)) value was 0.58 for acetamiprid resistance. A synergism study of piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) with acetamiprid also showed the significant presence of P-450 mono-oxygenase and esterase in the acetamiprid resistance. Hence, acetamiprid resistance in the P. solenopsis was autosomal, incompletely dominant and polygenic. These results are a source of basic information to design and plan fruitful management programmes to control P. solenopsis.

Cross-resistance, the stability of acetamiprid resistance and its effect on the biological parameters of cotton mealybug, Phenacoccus solenopsis (Homoptera: Pseudococcidae), in Pakistan

BACKGROUND

Acetamiprid is a neonicotinoid insecticide that is effective against both soil and plant insects, including insects of the orders Lepidoptera, Coleoptera, Homoptera and Thysanoptera. In order to estimate the effects associated with insecticide exposure and devise better pest management tactics, a field population of Phenacoccus solenopsis was exposed to acetamiprid in the laboratory. Subsequently, cross-resistance and the effects of acetamiprid on the biological parameters of P. solenopsis were investigated.

RESULTS

Following five rounds of selection with acetamiprid, P. solenopsis developed a 315-fold greater resistance to this chemical compared with an unexposed control population. The selected population also demonstrated very high to moderate cross-resistance to other tested insecticides. Furthermore, acetamiprid resistance remained unstable when the acetamiprid-selected population was not exposed for a further five generations. The acetamiprid-selected population had a relative fitness of 0.22, with significantly lower survival rate, pupal weight, fecundity, percentage hatching, net reproductive rate, intrinsic rate of natural increase, biotic potential and mean relative growth rate, with prolonged male and female nymphal duration, developmental time from egg to female adult and male and female longevity compared with the control population.

CONCLUSION

P. solenopsis biological parameters are greatly affected by acetamiprid, and it is of significant cost for the insects to counter these effects. This study will be a valuable source of information for further understanding of acetamiprid resistance and for assisting the development of resistance management programmes.