Effect Of Different Host Plants Research Articles

Influence of Host Plants and Tending Ants on the Cuticular Hydrocarbon Profile of a Generalist Myrmecophilous Caterpillar.

In myrmecophilous organisms, which live in symbiosis with ants, cuticular hydrocarbons (CHCs) play a pivotal role in interspecific communication and defense against chemical-oriented predators. Although these interactions form complex information webs, little is known about the influence of biotic environmental factors on the CHC profiles of myrmecophiles. Here, we analyzed the effect of different host plants and tending ants on the larval CHC profile of Synargis calyce (Lepidoptera: Riodinidae), a polyphagous species with facultative myrmecophily. Groups of caterpillars were fed individually with three host plant species (without tending ants), and with two tending ant species. Through gas chromatography analysis, we compared the cuticular profiles of treatments and found a high similarity between plants and caterpillars (65-82%), but a low similarity between caterpillars and their tending ants (30 - 25%). Cluster analysis showed that caterpillars, ants, and plants form distinct groups, indicating that S. calyce caterpillars have their own chemical profile. These results are similar to those observed for Lycaenidae caterpillars indicating that there is functional convergence in the chemical strategies used by myrmecophilous caterpillar species with similar ecology. Also, the results suggest that the cuticular compounds of S. calyce are primarily influenced by their host plants rather than their tending ants. Thus, we propose that these caterpillars present a trade-off between camouflage and directly informing their presence to ants, maintaining their unique chemical profile, though slightly affected by biotic environmental factors.

Effect of Different Host Plants on Biology of Tobacco Caterpillar, Spodoptera litura (Fabricius)

The tobacco caterpillar, Spodoptera litura (Fabricius) is present as an economically important and regular polyphagous pests in India and other countries. The knowledge of biology and ecology of an insect pests is a prerequisite for its management. An experiment was conducted on biology of Spodoptera litura (Fabricius) on different host plants in laboratory of the Department of Entomology, Rajasthan College of Agriculture, Maharana Pratap University of Agriculture and Technology, Udaipur, Rajasthan. The results revealed that the minimum and maximum incubation period of S. litura was 2.98 and 3.30 days recorded on castor and cauliflower, respectively. The minimum larval and pre pupal period was 12.96 and 1.00 days recorded on castor. The minimum and maximum pupal period were recorded on cotton (8.27 days) and cauliflower (6.44 days), respectively. The adult male and female moth survival maximum larvae reared on cauliflower 5.00 and 6.90 days whereas minimum on castor 3.95 and 6.00 days, respectively. The maximum percent adult emergence was recorded larvae reared on castor (87.50%) followed by cauliflower (85.00%) whereas minimum on cotton (67.50%). The maximum fecundity was recorded on castor (886.25) followed by soybean (870.00). The entire minimum life cycle was recorded on castor (29.05 days) whereas maximum on cotton (36.50days) followed by soybean (34.24 days). It was concluded that castor is best host plant for S. litura.

Effects of different host plants on the growth, development, and fecundity of Phthorimaea absoluta (Lepidoptera: Gelechiidae): an evaluation based on the age-stage two-sex life table.

This study aimed to investigate the growth and development parameters of Phthorimaea absoluta (Meyrick) population at each stage when feeding on 4 host plants: Lycopersicon esculentum, Solanum tuberosum, Solanum melongena, and Nicotiana tabacum. The objective was to predict population dynamics and develop appropriate control strategies. The age-stage sex-life table was used to evaluate survival rate, fecundity, life expectancy, reproductive value, population parameters, and population growth prediction of P. absoluta after feeding on the 4 Solanaceae plants. The results showed significant variations in the fecundity parameters of P. absoluta among the different host plants. The L. esculentum population exhibited the highest average egg-laying period (13.17 ± 0.61 days) and average egg production (219.31 ± 21.02 eggs), while N. tabacum had the lowest values (4.56 ± 0.26 days and 26.08 ± 2.53 eggs, respectively). The gross reproduction rate of P. absoluta feeding on L. esculentum was 146.43 ± 21.00, which was 1.80, 3.77, and 6.39 times higher compared to S. tuberosum, S. melongena, and N. tabacum, respectively. The average age period and population doubling time of P. absoluta feeding on L. esculentum were lower than those of the other 3 host plants. These results indicated that while P. absoluta can complete a generation on L. esculentum, S. tuberosum, S. melongena, and N. tabacum, L. esculentum is the most suitable host for its growth and development. Therefore, in the occurrence and adjacent areas of P. absoluta, relevant authorities should promptly monitor and control its population in the planting areas of Solanaceae plants to prevent further spread.

Effects of different host plants on population fitness of pea aphid (Acyrthosiphon pisum)

BackgroundHost plants not only provide and living places and energy materials for insects, but also influence insect population parameters and population fitness. MethodsThis study examined the influence of various host plant species on the fitness of pea aphid (Acyrthosiphon pisum). The biological parameters and population parameters of pea aphid on 6 different host plants (Vicia fabae, Pisum sativum, Medicago sativa, Trifolium pratense, Onobrychis viciaefolia and Melilotus officinalis) were observed and counted by ecological experiments, which were carried out in a control chamber. ResultsThe results showed that the developmental duration of 1st and 2nd instar nymphs of pea aphids on T. pratense and P. sativum was significantly prolonged, whereas that of 3rd and 4th instar nymphs on O. viciaefolia and M. officinalis was significantly shortened. Compared with the pea aphid on the V. faba, the longevity of adults on M. officinalis and P. sativum was significantly prolonged, but only the generation time on P. sativum was significantly prolonged. Moreover, the survival rate of nymphs was significantly lower on O. viciaefolia and M. sativa than on others. Net reproductive rate and mean generation time on V. faba were significantly higher than in other host plants. The intrinsic rate of increase (rm) and finite rate of increase (λ) of pea aphid feeding of A. pisum on P. sativum and O. viciaefolia decreased. However, those on the double population time on P. sativum and O. viciaefolia were significantly higher than the others. ConclusionThe findings will clarify the population fitness of pea aphids on different hosts and guide the rational distribution of different host plants, and provide new references for aphid control strategies.

Divergent response of soil microbes to environmental stress change under different plant communities in the Loess Plateau

Soil microorganisms play a crucial role in the proper functioning and stability of grassland ecosystems, and are influenced by the nutrient acquisition strategies of their host plants. The Loess Plateau in China, is known for its severe soil erosion and distinctive loess deposits, with soil nutrient levels declining from southeast to northwest. However, little is known about the relative effects of different host plants on soil microbial communities under different environmental stress in the Loess Plateau. We investigated the microbial community within soil profiles (0–100 cm) under two types of grasses community (Agropyron cristatum and Stipa spp.) with different drought tolerances, which are widely distributed in three different climate regions of the Loess Plateau. The diversity, composition, community assembly, and predicted functions of the bacterial and fungal community were evaluated. We discovered that the climate-plant-soil microbe interactions were the most significant factor affecting the community composition of bacteria and fungi on the regional scale. In addition, the effects of edaphic factors (e.g., soil organic carbon [SOC], total nitrogen [TN], and total phosphorus [TP]) on the soil bacterial and fungal communities increased from the warm-temperate to the desert steppe environment. Furthermore, the microbial community and assembly processes were driven by TP content of Agropyron grass, which is more resistant to environmental stress, while the soil of Stipa grass was driven by SOC. This may have occurred because the soil microbes in the Agropyron grassland had a stronger ability to utilize refractory organic matter thus reducing dependence on SOC, compared to soil microbes in the Stipa grassland. Collectively, our results show that the soil microbes recruited by the different plant communities responded differently in microbial composition, assembly, and functions to adapt the environmental stress change.

Stochastic nuclear organization and host-dependent allele contribution in Rhizophagus irregularis

BackgroundArbuscular mycorrhizal (AM) fungi are arguably the most important symbionts of plants, offering a range of benefits to their hosts. However, the provisioning of these benefits does not appear to be uniform among AM fungal individuals, with genetic variation between fungal symbionts having a substantial impact on plant performance. Interestingly, genetic variation has also been reported within fungal individuals, which contain millions of haploid nuclei sharing a common cytoplasm. In the model AM fungus, Rhizophagus irregularis, several isolates have been reported to be dikaryotes, containing two genetically distinct types of nuclei recognized based on their mating-type (MAT) locus identity. However, their extremely coenocytic nature and lack of a known single nucleus stage has raised questions on the origin, distribution and dynamics of this genetic variation.ResultsHere we performed DNA and RNA sequencing at the mycelial individual, single spore and single nucleus levels to gain insight into the dynamic genetic make-up of the dikaryote-like R. irregularis C3 isolate and the effect of different host plants on its genetic variation. Our analyses reveal that parallel spore and root culture batches can have widely variable ratios of two main genotypes in C3. Additionally, numerous polymorphisms were found with frequencies that deviated significantly from the general genotype ratio, indicating a diverse population of slightly different nucleotypes. Changing host plants did not show consistent host effects on nucleotype ratio’s after multiple rounds of subculturing. Instead, we found a major effect of host plant-identity on allele-specific expression in C3.ConclusionOur analyses indicate a highly dynamic/variable genetic organization in different isolates of R. irregularis. Seemingly random fluctuations in nucleotype ratio’s upon spore formation, recombination events, high variability of non-tandemly repeated rDNA sequences and host-dependent allele expression all add levels of variation that may contribute to the evolutionary success of these widespread symbionts.

Host plant-mediated effects on Buchnera symbiont: implications for biological characteristics and nutritional metabolism of pea aphids (Acyrthosiphon pisum).

The pea aphid, Acyrthosiphon pisum, is a typical sap-feeding insect and an important worldwide pest. There is a primary symbiont-Buchnera aphidicola, which can synthesize and provide some essential nutrients for its host. At the same time, the hosts also can actively adjust the density of bacterial symbiosis to cope with the changes in environmental and physiological factors. However, it is still unclear how symbionts mediate the interaction between herbivorous insects' nutrient metabolism and host plants. The current study has studied the effects of different host plants on the biological characteristics, Buchnera titer, and nutritional metabolism of pea aphids. This study investigated the influence of different host plants on biological characteristics, Buchnera titer, and nutritional metabolism of pea aphids. The titer of Buchnera was significantly higher on T. Pretense and M. officinalis, and the relative expression levels were 1.966±0.104 and 1.621±0.167, respectively. The content of soluble sugar (53.46±1.97µg/mg), glycogen (1.12±0.07µg/mg) and total energy (1341.51±39.37µg/mg) of the pea aphid on V. faba were significantly higher and showed high fecundity (143.86±11.31) and weight (10.46±0.77µg/mg). The content of total lipids was higher on P. sativum and T. pretense, which were 2.82±0.03µg/mg and 2.92±0.07µg/mg, respectively. Correlation analysis found that the difference in Buchnera titer was positively correlated with the protein content in M. officinalis and the content of total energy in T. pratense (P < 0.05). This study confirmed that host plants not only affected the biological characteristics and nutritional metabolism of pea aphids but also regulated the symbiotic density, thus interfering with the nutritional function of Buchnera. The results can provide a theoretical basis for further studies on the influence of different host plants on the development of pea aphids and other insects.

Host preference and biology of Spodoptera frugiperda (J.E. Smith) on different host plants under laboratory conditions

Effects of different host plants (castor, maize, bajara, mung bean, groundnut and cotton) on developmental period, pupal weight, sex ratio, longevity and oviposition of S. frugiperda (Lepidoptera: Noctuidae), were studied under laboratory conditions. All of the biological parameters included in the study were affected by the host plants. S. Frugiperda larvae developed differently on the different host plants, from shortest to longest in the following order: maize, castor, groundnut, mungbean, bajara and cotton. Pupal development was shorter on maize and castor than on the other host plants, and males generally developed longer than the females. A pupal weight of females was recorded highest on maize and castor. Female pupae were generally heavier than their male counterpart. More females than males were found among emerged adults. In a choice test, S. Frugiperda females oviposited most on maize and castor, least on cotton, and intermediate on groundnut, mungbean and bajara. It can be inferred from the above parameters that maize and castor are suitable hosts for S. frugiperda and it may also be used as a trap crop to prevent the attack of economically important crops.

Analysis of microbial diversity and community structure of rhizosphere soil of Cistanche salsa from different host plants.

Host plants influence rhizosphere microorganism composition through root secretions, and rhizosphere associated microorganisms influence Cistanche seeds germination. At present, little is known about effects of different host plants on soil bacteria and fungi in the rhizosphere of Cistanche salsa. High-throughput sequencing was used here to reveal the similarities and differences in the structural composition of the soil microbial community of C. salsa from six host plants (i.e., Halocnemum strobilaceum, Atriplex patens, Kalidium foliatum, Caroxylon passerinum, Anabasis aphylla, Krascheninnikovia ceratoides). We discovered that Krascheninnikovia ceratoides-parasitizing C. salsa (YRCR6) had the highest diversity of rhizosphere bacterial communities, and Anabasis aphylla -parasitizing C. salsa (YRCR5) had the highest diversity of rhizosphere fungal communities. Fungal communities were more influenced by the host plant than bacterial communities. In addition, we discovered certain rhizosphere microorganisms that may be associated with Cistanche seeds germination, including Mortierella, Aspergillus alliaceus, and Cladosporium, which are account for a relatively high proportion in Halocnemum strobilaceum, Atriplex patens and Anabasis aphylla -parasitizing C. salsa. Redundancy analysis results also revealed that AP, HCO3–, pH, Ca2+, SO42–, and K+ had a highly significant impact on the bacterial community structure (P < 0.01), while pH and SO42– had a significant impact on the fungal community structure (P < 0.05). Conclusively, differences were noted in the structure of rhizosphere bacterial and fungal communities of C. salsa parasitizing different plants in the same habit and the difference may be related to the host plant. This result can provide a new ideas for the selection of host plants and the cultivation of C. salsa.

Effect of host plants on the oviposition preference of pink bollworm, Pectinophora gossypiella (Lepidoptera: Gelechiidae)

Abstract Pink bollworm (Pectinophora gossypiella (Saunders, 1843)) (Lepidoptera: Gelechiidae) is an important pest of cotton. We aimed to study the effect of different host plants on the oviposition preference of pink bollworm under laboratory conditions. Cotton (Bt and non-Bt), okra and hibiscus plants were used, which vary in morphological characteristics. Significant differences were observed in the density of trichomes and it is positively correlated with oviposition behaviour of pink bollworm. In a no-choice test, we recorded a higher number of eggs on Bt and non-Bt cotton plants. In two-, three- and four-choice experiments, pink bollworm preferred to deposit the maximum number of eggs on non-Bt cotton among other host plants. A substantially higher number of eggs were laid on Bt cotton in combinations with okra and hibiscus and a considerably lower number on non-Bt cotton. We recorded fewer numbers of eggs on hibiscus in all combinations. Overall, pink bollworm moths showed greater affinity towards non-Bt cotton plants and deposited the maximum number of eggs there. From the practical point of view, the development of cotton genotypes which are devoid or have a lesser density of trichomes may be a possible solution to reduce the pink bollworm egg load on cotton.

Effect of Different Host Plants on the Biology of Diamond-Back Moth, Plutella Xylostella Under Laboratory Conditions in Northern Punjab, Pakistan

Plutella xylostella is an oligophagous pest of several host plants belonging to the family Cruciferae (cauliflower, cabbage, canola). This is widely distributed in all those areas where its hosts exist and cause severe crop losses. The current study was conducted to check the effect of host plants such as cabbage, cauliflower and canola on the biology of P. xylostella. The effect on incubation period, growth, development time, fecundity, oviposition, % survival and % egg viability was studied on canola, cabbage and cauliflower. The developmental time from 1st instar to adult emergence was longest (18 days) on canola while shortest on cauliflower (15 days). Fecundity was recorded maximum (259 eggs) on cauliflower and minimum (159 eggs) on canola. Percentage survival of each stage was recorded maximum on cauliflower (84%) followed by cabbage (73%) and canola (69%). A significant difference was observed intheintrinsic rate of increase, rm with host plants. The intrinsic rate of increase(0.290) and finite rate of increase values (1.35) were obtained on cauliflower while 0.283, 1.30 and 0.239, 1.23 on cabbage and canola, respectively. Cauliflower was found to be the most preferable host for P. xylostella due to higher percentage of survival, higher fecundity, higher % egg viability and shorter developmental period. The study provides knowledge about the host plants that prove helpful in enhancing the P. xylostella population.

Effect of Different Host Plants on The Different Haemocyte Counts and Haemocyte Viability of Larvae of Spodoptera littoralis and Agrotis ipsilon

The present study aimed to investigate the effect of different six host plants namely, Cabbage, alfalfa, Jaw’s mallow, lettuce, turnip, and castor leaves on the total haemocyte count (THC), percentage of haemocyte viability, and the percentage of each type of haemocyte (differential haemocyte count, DHC) in Spodoptera littoralis and Agrotis ipsilon fourth instar larvae. There are five types of haemocytes in A. ipsilon and S. littoralis larvae; Prohaemocyte, Plasmatocyte, Granulocyte, Spherocytes, and Oenocyte. Results recorded the highest value 13.3±0.68 of Prohaemocyte at lettuce and the lowest value 9.3 for Cabbage, alfalfa and turnip. On the other hand, Prohaemocyte recorded the highest value 12.6 ± 0.9 in the case of castor feeding and 8.7 ± 0.3 for turnip for S. littoralis. Plasmatocyte recorded 45.3 ± 2.9 cells/mm3for A. ipsilon feed on turnip and 47.3 ± 1.8 cells/mm3for S. littoralis feed on lettuce as the highest value while Granulocyte recorded 33 ± 4.1 and 35 ± 0.7 for A. ipsilon feed on Jaw’s mallow, respectively. Spherocytes recoded 15.3 ± 0.9 and 12.3 ± 0.9 for A. ipsilon and S. littoralis feed on alfalfa. Finally, Oenocyte recorded 7.7 ± 1.5 and 7.3 ± 1.4 for A. ipsilon and S. littoralis feed on castor. Total haemocytic count recorded 29 ± 0.3 and 36 ± 0.75 cells/mm3 as the highest value when both A. ipsilon and S. littoralis feed on Alfalfa. Also, the haemocyte viability % recorded the highest value 91.5 ± 2.6 and 96.2 ± 0.8 % for A. ipsilon and S. littoralis feed on feed on Alfalfa. The result recorded increasing DHC level after feeding of the fourth larval instar of S. littoralis and A. ipsilon on different plant hosts such an increase in DHC gives an impression that blood cells may share in detoxifying. The most obvious activity of haemocyte is phagocytosis. In this context, the most active phagocytes are the Plasmatocyte, Plasmatocyte which was implicated in the encapsulation of necrotic tissues.

Quantity and transmission efficiency of an isolate of the Potato virus Y–Wilga (PVYN−Wi) by aphid species reared on different host plants

Potato virus Y (PVY) is a destructive plant virus causing important damage in different crops, particularly in potato. PVY is transmitted in a non-persistent manner by many aphid species, and the distal part of the stylet plays an important role in virus transmission by these aphids. Among other possible factors, the type of host plant on which the aphids develop could also affect virus transmission efficiency, yet little is known about this. Furthermore, the quantification of potyviruses in individual vectors has mainly focused on intact whole aphid body and not the stylet alone, whereas an even more precise indicator that could correlate with vector efficiency in non-persistently transmitted viruses is the quantity of the virus in the stylet. Therefore, this study aims to verify the effect of different host plants on which an aphid vector was reared on its ability to acquire and transmit the PVY, and whether the quantity of PVY in the aphid vector stylet could be used as a useful trait for evaluating vector efficiency. A key finding in this study indicates that when the aphid Myzus persicae was reared on broad bean and then exposed to acquire PVY, it transmitted PVY less efficiently (50%) compared to when it was reared on Brussels sprout (81%). Additionally, the transmission percentage correlated directly with the virus quantity in the stylet (r = 0.7) and not in the intact whole aphid body (r = 0.06). This could be exploited as a useful index for virus transmission efficiency in epidemiological studies or predictive schemes.

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.

Effect of host plants on life history traits of Phenacoccus solenopsis (Homoptera: Pseudococcidae)

AbstractCotton mealybug,Phenacoccus solenopsisTinsley is an important polyphagous insect pest and causes severe losses to different crops worldwide. In the current study, we investigated the effect of different host plants, such asCaesalpinia pulcherrima,Plumeria rubra, Anthurium andraeanum, Jasminum sambac, andHibiscus rosasinensis, on the biological parameters ofP. solenopsis. The survival rate from crawler to adult, female nymphal duration, development time from crawler to female adult, and female adult weight were significantly different on the different hosts. Male nymphal duration, development time from crawler to male adult, pupal weight, emergence rate of male adults, and mean relative growth rate for male were similar on all the tested host plants. Pupal duration and generation time of male and female onH. rosasinensiswere significantly shorter than on the other hosts. Adult male and femaleP. solenopsislongevity was significantly shorter onH. rosasinensiscompared to other hosts. The fecundity was lower onC. pulcherrimaandA. andraeanumand hatchability was lower onC. pulcherrimathan on the other hosts. The net reproductive rate, the intrinsic rate of natural increase, and biotic potential and mean relative growth rate for female ofP. solenopsiswere significantly different on the tested hosts. Our results point to the role of host plants in increasing the populations ofP. solenopsisand could help to design cultural management strategies.

Effect of Different Host Plants on the Sugar Beet Fly Pegomyia mixta vill. and its Associated Parasitoid Opius nitidulator (Nees)

Effect of Different Host Plants on the Sugar Beet Fly Pegomyia mixta vill. and its Associated Parasitoid Opius nitidulator (Nees)

Effect of host plants on developmental and population parameters of invasive leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the most serious pests of tomato, capable of causing 100% crop losses under favourable conditions. We studied the effect of different host plants on developmental and population parameters of this pest at 25 ± 0.5 °C temperature, 70 ± 5% relative humidity and 12 L: 12D photoperiod. Host plant had significant effect on the developmental biology and the population growth parameters of the pest. The leafminer developed fastest on tomato leaves and slowest on potato tubers. Population growth parameters like intrinsic rate of increase, net reproductive rate, finite rate of increase, doubling time and weekly multiplication rate of T. absoluta were highest on tomato leaves and lowest on potato tubers. Mean generation time was minimum on tomato leaves and maximum on potato tubers. Females developed on tomato leaves were more fecund than other hosts. Though, tomato was found to be the most suitable host plant of T. absoluta, yet, the pest developed and grew successfully on other alternate hosts like potato (Solanum tuberosum L.), brinjal (Solanum melongena L.) and pepino (Solanum muricatum Aiton). These hosts can, therefore, play an important role in the survival, population build up and overwintering of the miner. Further, under favourable conditions the miner can become a serious pest on these crops and need to be monitored on these crops as well.

Effect of Different Host Plants on the Onion Thrips, Thrips tabaci Lind. and the Land Snail, Monacha spp. Population Abundance According to Intercropping some Vegetable Crops and the Final Yield

Field experiments were carried out at El-Riad district, Kafr El-Sheikh governorate during three successive seasons, 2014/15, 2015/16 and 2016/17. To study host preference and the effect of intercropping each of lettuce (Roman), onion (Buheirah red) and garlic (sids 40) cultivars, on the onion thrips, Thrips tabaci Lind.andthe land snail,Monacha spp.population abundance and the resulting yield. T. tabaci was the high attractive to onion followed by garlic, while lettuce was least attractive during the three successive seasons. It can be noticed the highest monthly average number of T. tabaci were recorded in March on onion plantations alone and onion intercropping, with lettuce, followed by garlic plantations alone, garlic (intercropped with lettuce) in the three seasons, while lettuce plantations alone and lettuce intercropping, with onion and with garlic were recorded in February in 2015 and 2016 but it was in March in 2017 season. Also, the highest monthly average number of Monacha spp. were recorded in March on lettuce plantations alone and followed by lettuce intercropping, with onion and garlic, while garlic plantations alone, garlic (intercropped, with lettuce) and onion plantations alone and onion (intercropped, with lettuce) were recorded in February or March. It can be noticed that, Monacha spp. was the high attractive to lettuce, while garlic and onion were the least attractive during the three successive seasons. The population abundance of thrips and snails differed according to host plant, there were significant differences among host plants (p≤ 0.05).The rate of infestation was higher in the sole crops than in those intercropped crops which caused reduction of T. tabaci and Monacha spp., and almost, significant differences were found (p≤0.05).The resultant yield, due to intercropping, was also affected. The lettuce, onion and garlic plants intercroppe reduced the resultant yield when compared with control.

BIOLOGICAL STUDIES ON THE CITRUS MEALYBUG, Planococcus citri (RISSO) (HEMIPTERA: PSEUDOCOCCIDAE) UNDER LABORATORY CONDITIONS

Biological studies were carried out in the laboratory of Scale Insects and Mealybugs Department, Plant Protection Research Institute, Sharkia Branch, Egypt during the period extended from 2010–2016 years on the citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae) to study the effects of different host plants and temperatures on some biological aspects of the pest to use these useful information for mass rearing and designing a comprehensive pest management program and prediction models for the citrus mealybug. The accumulated degrees days (ADD) for male and female stages were also calculated. The obtained results obviously showed that there were significant effects on developmental periods, adult longevity, life cycle and generation period of P. citri when reared on pumpkin fruits compared with those reared on potato sprouts. The periods of citrus mealybug stages were significantly reduced gradually by increasing of rearing degree of the tested temperatures i.e. 20, 25 and 30˚C. The mathematical method showed that the accumulated degree days which required for completing one generation for females was 418.11 ADD unit.

Switching among natal and auxiliary hosts increases vulnerability of Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) to insecticides.

The role of insecticidal application and host plant resistance in managing Spodoptera exigua has been well documented, but the effect of different host plants, on which the pest cycles its population in the field, has seldom been investigated. Therefore, we have studied the vulnerability of S. exigua against commonly used insecticides (cypermethrin, chlorpyrifos, lufenuron, and emamectin benzoate) with different mode of actions when it switches its generations from natal to auxiliary hosts and vice versa. Different field populations being established on different host plants including castor, cauliflower, cotton, okra, and spinach were collected and reared in the laboratory before insecticidal bioassays. The role of larval diet and host plant switching on their response to tolerate applied insecticides was studied using leaf‐dip bioassay methods. Host switching demonstrated a significant role in altering the vulnerability of S. exigua populations to tested insecticides. Spodoptera exigua sourced from castor, when switched host to okra and spinach, exhibited 50% higher mortality when treated with emamectin benzoate. This trend in mortality was consistent upon complete host switch cycle (natal—auxiliary—natal host). However, the highest increase (92%) in vulnerability was recorded when the larvae were shifted to spinach from cotton. In general, chlorpyrifos and lufenuron had highest efficacies in terms of larval mortality. The findings of present studies provide insights to a better understanding the behavior of polyphagous pests and the role of different host plants in altering the susceptibility of these pests against applied insecticides. Ultimately the results warrant that due consideration should be given to cropping patterns and time of host switching by pest population during planning and executing chemical control.