Host Suitability Index Research Articles

Effects of host plants on spotted lanternfly (Hemiptera: Fulgoridae) nymphal survival and development.

Spotted lanternfly, Lycorma delicatula (White), is an invasive planthopper from China, which was first detected in Berks County, PA, in 2014 and has since spread to adjacent states including New Jersey in 2018. Lycorma delicatula is a polyphagous species that gregariously feeds on over 172 known hosts. We investigated development on key host plants Ailanthus altissima (Miller) (Sapindales: Simaroubaceae), Juglans nigra (L.) (Fagales: Juglandaceae), Acer rubrum (L.) (Sapindales: Sapindaceae), and Vitis vinifera (L.) (Vitales: Vitaceae) for each instar to elucidate potential host use throughout the season and target monitoring efforts. Our study indicated significant differences in survivorship and time spent in each nymphal life stage between host plants. We applied a host suitability index as a function of survivorship and development for each host plant and instar, which indicated A. altissima and J. nigra as suitable hosts for all 4 nymphal instars. Vitis vinifera was highly suitable for first and second instars but had low indices for the third and fourth instars, although suitability of V. vinifera may have varied based on variety and age of the vine. Lycorma delicatula nymphs had the lowest survivorship and longest development time on A. rubrum across all 4 life stages, despite this being a preferred oviposition host. Host had a significant effect on the morphometrics we measured within the first and second instars.

Fitness and cold tolerance of Spodoptera frugiperda fed on corn and two winter crops

AbstractFall armyworm (FAW) Spodoptera frugiperda is a major migratory and polyphagous pest. Overwintering, migrating and colonizing characters of FAW are closely related to vegetation and host adaptation. In this study, we investigated oviposition preference, feeding preference of FAW, as well as fitness, cold tolerance of FAW larvae fed on spring and summer crop (corn) and two winter crops (cabbage, Brassica campestris and rape, B. napus). The results showed that FAW could complete their life cycle by feeding on cabbage and rape, although fitness was not as good as corn. FAW fed on cabbage had higher survival, female pupal mass and host suitability index than rape while larvae preferred to feed on rape leaves and females preferred to lay eggs on rape plants. In addition, FAW larvae fed on cabbage had the shortest recovery time from chill coma compared to corn and rape, indicating that cold tolerance of FAW larvae was improved by feeding on cabbage. Consequently, cabbage could be an ideal host for FAW which needed to survive and reproduce in winter. These results improve our understanding of host selection and adaption of FAW, as well as lay a foundation for predicting winter breeding areas of FAW.

Seed storage proteins and seed coat compounds additively influence Callosobruchus maculatus Fab. tolerance in selected cowpea (Vigna unguiculata L. Walp.) varieties

AbstractThe cowpea weevil, Callosobruchus maculatus, is a major threat to stable cowpea production, especially in storage, and has been reported to facilitate postharvest losses in cowpea grains. Host resistance has been suggested as the best control method but with conflicting knowledge on the source of resistance. Hence, the study seeks to evaluate seed storage proteins (SSPs) and seed coat compounds (SCCs) associated with tolerance to C. maculatus. SSPs and SCCs were assayed and associated with C. maculatus tolerance in 19 cowpea varieties with varied tolerance levels using a stepwise multiple regression analysis. Top C. maculatus tolerants were TVu‐2027, TVu‐11952, TVu‐11953, and TVu‐145. The protein fraction with a mass of 51 kDa was a significant predictor associated with percentage adult insect emergence (PAE) and host suitability index (H.S.I.), and 57 and 71 kDa were associated with mean development period (MDP) whereas 59 and 131 kDa were associated with seed damage tolerance (TolSD). Several SCCs identified were associated with the C. maculatus tolerant measures used in the study. However, Thiazole, tetrahydro‐ and Undecane were consistently identified with C. maculatus tolerance. Higher phenotypic variability was accounted for by SCC than SSP fractions associated with C. maculatus tolerance in the study indicating that SCCs contributed more to the C. maculatus tolerance than the SSPs identified. These compounds can be incorporated into breeding for C. maculatus tolerant in cowpea and biopesticide formulations whereas cowpea varieties with the high or significant amount of these compounds can also be recommended to the farmers or to the cowpea producers.

Infestation of Pink-Flesh Guava by Frugivorous Fruit Flies (Diptera: Tephritidae and Lonchaeidae) in an Orchard of Mixed Mandarin and Guava Trees at Morelos, Mexico

Guavas (Psidium guajava L.) are a main host of several Lonchaeidae and Tephritidae fruit flies. In Mexico, guavas are infested mostly by Anastrepha striata Schiner, A. fraterculus (Wiedemann), and occasionally by A. obliqua Macquart. We sampled 240 pink-flesh guavas from an orchard of mixed mandarin (Citrus reticulata Blanco) and guava trees at San Rafael de Zaragoza, Morelos. Fruit was collected biweekly during two fruiting periods [August-September 2021 (wet season) and January-February 2022 (dry season)]. Infestation rate, Host Suitability Index (HSI), and co-infestations by frugivorous fruit flies were assessed. We found 728 pupae (76% Anastrepha spp.), and an unusually large number of Neosilba spp. (24%). More infestation was detected during the dry season (432 pupae in the dry season versus 296 pupae in the wet season) probably caused by scarce availability of fruit. We reported for the first time, infestation of pink-flesh guavas by A. ludens from field-collected guavas picked from trees in mature-green stage. Using the HS Index, pink-flesh guavas were an inadequate host for A. ludens but were a good host for A. striata. We reported Neosilba spp. as a primary invader of guavas and discussed findings in the context of quarantine risk assessment.

Priority host plants for Ceratitis capitata, mediterranean fruit fly, based on the host reproduction number for surveillance, trade and eradication programs

Hosts of tephritids are known to vary in their capacity to support the life cycle from egg lay to adult. This capability is measured by the Host Reproduction Number (HRN) which the number of adults that emerge from one kg of fruit. Mediterranean fruit fly (Medfly) is one of the economically important fruit flies and is distributed worldwide. Many Medfly hosts are known but data to quantify their capacity to support the life cycle is scattered through many reports. Here, we reviewed published literature and found data on 146 potential hosts. We placed them in order of HRN and their Host Suitability Index. The HRN values ranged from bird plum (HRN = 1019) to three species of Syzygium which were non hosts (HRN = 0). The HRN order will help to inform and triage hosts for targeted surveillance and eradication programs and inform disinfestation activities associated with incursion response management, and for trade and risk mitigation.

The use of host reproduction number and host suitability index to rank hosts of fruit flies in Africa

The use of host reproduction number and host suitability index to rank hosts of fruit flies in Africa

Host Suitability Index for Polyphagous Tephritid Fruit Flies.

Tephritid fruit flies are major economic pests for fruit production and are an impediment to international trade. Different host fruits are known to vary in their suitability for fruit flies to complete their life cycle. Currently, international regulatory standards that define the likely legal host status for tephritid fruit flies categorize fruits as a natural host, a conditional host, or a nonhost. For those fruits that are natural or conditional hosts, infestation rate can vary as a spectrum ranging from highly attractive fruits supporting large numbers of fruit flies to very poor hosts supporting low numbers. Here, we propose a Host Suitability Index (HSI), which divides the host status of natural and conditional hosts into five categories based on the log infestation rate (number of flies per kilogram of fruit) ranging from very poor (<0.1), poor (0.1-1.0), moderately good (1.0-10.0), good (10-100), and very good (>100). Infestation rates may be determined by field sampling or cage infestation studies. We illustrate the concept of this index using 21 papers that examine the host status of fruits in five species of polyphagous fruit flies in the Pacific region: Bactrocera tryoni Froggatt, Bactrocera dorsalis (Hendel), Bactrocera latifrons (Hendel), Zeugodacus cucurbitae (Coquillett), and Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). This general-purpose index may be useful in developing systems approaches that rely on poor host status, for determining surveillance and detection protocols for potential incursions, and to guide the appropriate regulatory response during fruit fly outbreaks.

Characteristics determining host suitability for a generalist parasite

Host quality is critical for parasites. The common cuckoo Cuculus canorus is a generalist avian brood parasite, but individual females show strong preference for a specific host species. Here, we use three extensive datasets to investigate different host characteristics determining cuckoo host selection at the species level: (i) 1871 population-specific parasitism rates collected across Europe; (ii) 14 K cases of parasitism in the United Kingdom; and (iii) 16 K cases of parasitism in Germany, with data collected during the period 1735–2013. We find highly consistent effects of the different host species traits across our three datasets: the cuckoo prefers passerine host species of intermediate size that breed in grass- or shrubland and that feed their nestlings with insects, and avoids species that nest in cavities. Based on these results, we construct a novel host suitability index for all passerine species breeding in Europe, and show that host species known to have a corresponding cuckoo host race (gens) rank among the most suitable hosts in Europe. The distribution of our suitability index shows that host species cannot be classified as suitable or not but rather range within a continuum of suitability.

Developmental and reproductive performance of a specialist herbivore depend on seasonality of, and light conditions experienced by, the host plant.

Host plant phenology (as influenced by seasonality) and light-mediated changes in the phenotypic and phytochemical properties of leaves have been hypothesised to equivocally influence insect herbivore performance. Here, we examined the effects of seasonality, through host plant phenology (late growth-season = autumn vs flowering-season = winter) and light environment (shade vs full-sun habitat) on the leaf characteristics of the invasive alien plant, Chromolaena odorata. In addition, the performance of a specialist folivore, Pareuchaetes insulata, feeding on leaves obtained from both shaded and full-sun habitats during autumn and winter, was evaluated over two generations. Foliar nitrogen and magnesium contents were generally higher in shaded plants with much higher levels during winter. Leaf water content was higher in shaded and in autumn plants. Total non-structural carbohydrate (TNC) and phosphorus contents did not differ as a function of season, but were higher in shaded foliage compared to full-sun leaves. Leaf toughness was noticeably higher on plants growing in full-sun during winter. With the exception of shaded leaves in autumn that supported the best performance [fastest development, heaviest pupal mass, and highest growth rate and Host Suitability Index (HSI) score], full-sun foliage in autumn surprisingly also supported an improved performance of the moth compared to shaded or full-sun leaves in winter. Our findings suggest that shaded and autumn foliage are nutritionally more suitable for the growth and reproduction of P. insulata. However, the heavier pupal mass, increased number of eggs and higher HSI score in individuals that fed on full-sun foliage in autumn compared to their counterparts that fed on shaded or full-sun foliage in winter suggest that full-sun foliage during autumn is also a suitable food source for larvae of the moth. In sum, our study demonstrates that seasonal and light-modulated changes in leaf characteristics can affect insect folivore performance in ways that are not linear.

The nocturnal larvae of a specialist folivore prefer Chromolaena odorata (L.) foliage from a sunny environment, but does it matter?

Increasing evidence suggests that the responses of insect herbivores to environment-mediated changes in the phenotypic and phytochemical traits of their host plants are more complex than previously thought. Here, we examined the effects of habitat conditions (shaded versus full-sun habitats) on plant traits and leaf characteristics of the invasive alien plant, Chromolaena odorata (L.) (Asteraceae). We also determined neonate larval preference of the specialist herbivore, Pareuchaetes pseudoinsulata Rego Barros (Lepidoptera: Erebidae) (a biological control agent) for shaded versus full-sun leaves. The study further evaluated the performance of the moth on C. odorata leaves obtained from both shaded and full-sun habitats. Leaves of C. odorata plants growing in the shaded habitat had higher water and nitrogen contents compared with full-sun leaves. Plants growing in shade had longer leaves but full-sun plants were taller and had greater aboveground biomass compared with shaded plants. Although neonate larvae of P. pseudoinsulata preferred to feed on full-sun foliage, development was faster when reared on shaded foliage. However, survival, pupal mass, growth rate, and Maw’s host suitability index of the moth did not significantly differ between full-sun and shaded foliage. Our inability to demonstrate significant differences in key insect performance metrics in P. pseudoinsulata between shaded and full-sun foliage, despite neonate larval preference for one of the foliage types, suggests that neither of the foliage types can be considered a superior host, and reiterate the fact that relationships between host plant quality (modulated by light intensity) and phytophagous insect performance are not simple.

The nocturnal larvae of a specialist folivore perform better on Chromolaena odorata leaves from a shaded environment

AbstractIncreasing evidence suggests that individuals of the same plant species occurring in different microhabitats often show a degree of phenotypic and phytochemical variation. Consequently, insect herbivores associated with such plant species must deal with environment‐mediated changes or variability in the traits of their host plants. In this study, we examined the effects of habitat condition (shaded vs. full‐sun habitats) on plant traits and leaf characteristics of the invasive alien plant, Chromolaena odorata (L.) King &amp; Robinson (Asteraceae). In addition, the performance was evaluated in two generations of a specialist folivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), on leaves obtained from both shaded and full‐sun habitats. The study was done in an area where the insect was introduced as a biological control agent. Leaves growing in shade were less tough, had higher water and nitrogen content, and lower total non‐structural carbohydrate, compared with leaves growing in full sun. Plants growing in shade had longer leaves and were taller, but above‐ground biomass was significantly reduced compared with plants growing in full sun. In both generations (parents and offspring), P. insulata developed faster and had larger pupal mass, increased growth rate, and higher fecundity when reared on shaded foliage compared with full‐sun foliage. Although immature survival and adult longevity did not differ between habitats, Maw's host suitability index indicated that shaded leaves were more suitable for the growth and reproduction of P. insulata. We suggest that the benefits obtained by P. insulata feeding on shaded foliage are associated with reduced toughness and enhanced nitrogen and water content of leaves. These results demonstrate that light‐mediated changes in plant traits and leaf characteristics can affect insect folivore performance.

Variation in host plant has no effect on the performance and fitness‐related traits of the specialist herbivore Pareuchaetes insulata

AbstractThe effect of host plant dissimilarity on insect preference and performance was tested using two morphological forms of Chromolaena odorata (L.) King &amp; Robinson (Asteraceae) (one from Florida, USA, another from South Africa), and a specialist herbivore, Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) from Florida, USA, that was introduced as a biological control agent in South Africa. Although this insect did establish at one site, of some 21 sites at which over 800 000 individuals were released, its population level in the field has remained low after an initial outbreak in 2006. To explain the poor performance of P. insulata, we hypothesised that P. insulata larvae prefer Floridian C. odorata to the southern African C. odorata, which is morphologically and probably genetically distinct, and that larvae reared on Floridian C. odorata should have higher fitness and performance. We tested this by comparing insect performance metrics on each of the two plant forms in laboratory experiments. Apart from pupal mass, which was significantly greater on southern African C. odorata, P. insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index, host suitability index, growth index, and fecundity between the Floridian and southern African C. odorata plants. In sum, we could not demonstrate that differences in plant forms in C. odorata are responsible for the poor performance of P. insulata in South Africa.

Antibiosis mechanism of resistance to pod borer, Helicoverpa armigera in wild relatives of chickpea

The pod borer, Helicoverpa armigera, is one of the major constraints to chickpea production worldwide. The levels of resistance to pod borer in the cultivated chickpea germplasm are moderate, and therefore, we studied the reaction of 32 accessions of wild relatives of chickpea for resistance to H. armigera under greenhouse conditions. Accessions ICC 17257, IG 70002, IG 70003, IG 70012, (Cicer bijugum), IG 69948 (C. pinnatifidum), IG 69979 (C. cuneatum), IG 70032, IG 70033, IG 70038, and IG 72931 (C. judaicum) showed lower leaf feeding, a drastic reduction in larval weight, and poor host suitability index at the vegetative and/or flowering stages of crop growth as compared to the cultivated chickpeas. Based on percentage pods damaged by 5th day (< 52% pods damaged compared to 90% pods damaged in Annigeri), and percentage weight gain by the larvae (< 35% weight gain compared to 366% weight gain on ICCV 2); accessions IG 69979 (C. cuneatum), IG 70003, IG 70022, IG 70016, IG 70013, IG 70012, IG 70010, IG 70001, IG 70018, and IG 70002 (C. bijugum), and IG 72953 (C. reticulatum) showed high levels of resistance to H. armigera. Larvae of H. armigera weighed < 50 mg when reared on C. pinnatifidum (IG6 9948 and IG 70039), and C. judaicum (IG 72931) compared to 301.95 mg on C. arietinum (ICCC 37 – the cultivated chickpea). Larval weights on many accessions of the wild relatives of chickpea were much lower than those on the cultivated chickpeas, indicating the existence of different mechanisms of resistance to H. armigera. There was no pupation and adult emergence when the larvae were reared on accessions of C. pinnatifidum (IG 69948 and IG 70039), and C. judaicum (IG 69980, IG 70032, IG 70033 and IG 72931). The wild relatives of chickpea showing high levels of antibiosis to H. armigera can be used to introgress diverse resistance genes into cultivated chickpea to increase the levels and diversify the basis of resistance to this insect.

Suitability of clovers (Trifolium species and cultivars) as hosts of spotted clover aphid, a biotype of Therioaphis trifolii (Monell) (Hemiptera : Aphididae)

Summary. The performance of the spotted clover aphid, a biotype closely related to the spotted alfalfa aphid Therioaphis trifolii (Monell) f. maculata, was assessed on 18 accessions, all of which were cultivars of clover (Trifolium spp.) commonly grown in improved pastures in Australia. Aphids were reared on excised trifoliate leaves on agar containing a soluble fertiliser. Parameters measured were initial host acceptance by apterous adults, survival of first generation nymphs, incidence of alate adults produced, and the 4-day fecundity of apterous adults. A host suitability index was calculated for each of the cultivars tested. Most of the accessions were readily accepted by spotted clover aphid and nearly all proved to be suitable hosts. Mortality and alate production were generally low and fecundity of F1 apterae averaged more than 5 offspring per day on all cultivars in the 4-day fecundity study. Spotted clover aphid performed particularly well on 9 of the 10 cultivars of subterranean clover. The white clover cultivar Irrigation was the least suitable host. Spotted clover aphid has the potential to be a serious threat to improved pastures in Australia where clover is a major component.

Evaluation of Arachis hypogaea × A. cardenasii Interspecific Lines for Resistance to Insect Pests1

Abstract Fourteen lines from the interspecific cross Arachis hypogaea X A. cardenasii were evaluated in the field and seven lines from this cross were evaluated in the laboratory for resistance to insect damage. Laboratory evaluation of interspecific lines against major defoliators of peanut showed variable levels of resistance to the corn earworm, no resistance to the fall armyworm, and moderate resistance to the velvetbean caterpillar as noted by a reduced host suitability index in line IC 2–5. Damage ratings to plants in the field indicated no resistance in the interspecific lines to the tobacco thrips. However, a high level of resistance to the southern corn rootworm was observed in most of the lines. Resistance to the potato leafhopper was indicated by reduced damage ratings for all interspecific lines relative to damage on cv. Florunner. Resistance ratings for the potato leafhopper were highest in lines GP-NC WS 7 and IC 1–19 and was evident even under severe potato leafhopper pressure. The levels of resistance to the southern corn rootworm and potato leafhopper should prove useful in a breeding program to introgress resistance to these insects into elite cultivars.

Fall Armyworm (Lepidoptera: Noctuidae) Consumption and Utilization of Nine Bermudagrasses

Nine bermudagrass varieties and strains were evaluated to determine their effects on consumption, utilization, preference, and host suitability of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). The established varieties, ‘Coastal,’ ‘Tifton 44,’ ‘Tifton 78,’ and ‘Tifton 292,’ a newly released variety, ‘Grazer,’ and the experimental strains, #1 R12P5, OSU 71 × 6-7, OSU 74 × 11-2, and OSU 74 × 12-1 were included in this study. ‘Tifton 292’ was the grass most preferred by neonate larvae, and OSU 74 × 11-2 was the least preferred. A host suitability index indicated that ‘Tifton 78’ was the most suitable host for FAW development, and OSU 71 × 6-7 was the least suitable. The nine bermudagrass varieties and strains were categorized as susceptible (‘Tifton 78,’ OSU 74 × 12-1, and ‘Grazer’), intermediately resistant (#1 R12P5, ‘Coastal,’ ‘Tifton 292,’ OSU7 4 × 11-2, and ‘Tifton 44’), and resistant (OSU 71 × 6-7). The mechanism of resistance to FAW feeding is believed to be antibiosis rather than nonpreference.

Consumption and Utilization of Bermuda Grass by Fall Armyworm (Lepidoptera: Noctuidae) Larvae

Fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae were reared on seven Bermuda-grass, Cynodon dactylon (L.) Pers., clones. Consumption, utilization, preference, and suitability were determined for sixth instar larvae on all clones tested. Low nitrogen and digestibility levels found in ‘Alicia’ and ‘OSU 6-7’ leaves limited larval growth and development. A host-suitability index showed that ‘Coastal’ and ‘GA. 77-56’ were less resistant to fall armyworm than were ‘Alicia’ and ‘OSU 6-7.’ ‘Coastal,’ ‘GA. 77-26,’ and ‘GA. 77-56’ Bermuda grasses were preferred over the other clones, while ‘Alicia’ and ‘OSU 6-7’ were the least preferred.

Bermudagrass Resistance to the Fall Armyworm (Lepidoptera: Noctuidae) 1

Nine bermudagrass, Cynodon dactylon (L.) Pers., clones were evaluated for fall armyworm, Spodoptera fruġiperda (J. E. Smith). survival, developmental rate, pupal weight, leaf consumption, and preference. By using a host-suitability index, ‘Tifton 44’ was rated intermediately resistant and ‘Tifton 292’ was rated highly resistant to larval feeding. Preference tests showed that ‘Coastcross I’ was preferred over all other clones. The resistance in ‘Tifton 292’ is primarily antibiosis.

Fall Armyworm (Lepidoptera: Noctuidae) Larval Development and Adult Fecundity on Five Grass Hosts 1

Fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae were reared in the laboratory on five host plants and on artificial bean diet. The most suitable hosts for fall armyworm development, as determined by a host suitability index, were goosegrass, Eleusine indica (L.) Gaertn., and coastal bermudagrass, Cynodon dactylon (L.) Pers. The least suitable host was yellow nutsedge, Cyperus esculentus L. Significant differences were noted in larval duration, consumption, pupal weight, pupal duration, adult longevity, and fecundity between larvae reared on the various host plants. Additionally, pupal duration (five of six treatments) and adult longevity (one of six treatments) were sex dependent. Females reared on all diets except artificial diet oviposited the greatest number of eggs on day 1 of oviposition. Those reared on artificial diet exhibited peak oviposition on day 2.

Resistance of Arachis Species to the Fall Armyworm, Spodoptera frugiperda1

Abstract Fourteen species of Arachis were evaluated for survival, leaf consumption, development rate, and preference by the fall armyworm, Spodoptera frugiperda (J. E. Smith). Using a host-suitability index, A. monticola, A. hypogaea, cv. ‘Florunner,’ A. stenosperma, and A. batizogaea were the most suitable hosts and were classified susceptible to the fall armyworm. A. burkartii and A. villosa were the least suitable hosts and were classified resistant. These classifications were also supported, in general, by preference of the insect for the species of Arachis.