Evaluation of turfgrass species and cultivars for potential resistance to twolined spittlebug (Hemiptera: Cercopidae)

Potential resistance to the twolined spittlebug, Prosapia bicincta (Say), was evaluated among 56 turfgrass genotypes. Greenhouse, laboratory, and field bioassays identified differences in spittlebug survival and development, host preference and damage levels, and turfgrass tolerance to and ability to recover from pest induced injury. All centipede grasses demonstrated high levels of susceptibility, followed by bermudagrasses, seashore paspalums, and zoysiagrasses. Average nymphal survival to the adult stage ranged from 1.5 to 78.1%. Development required 38.1-62.0 d under greenhouse conditions, depending on plant taxa. Among seashore paspalums, nymphal survival to the adult stage was lowest and duration of development was longest on HI-1, 'Sea Isle 2000', 561-79, and 'Mauna Kea'. Reduced spittlebug survival and increased developmental times were also observed on the bermudagrasses BERPC 91-15 and 'Tifway'. Although zoysiagrasses supported spittlebug development and survival to the adult stage, developmental times were extended on the zoysiagrass cultivars 'Emerald' and 'El Toro'. Spittlebug preference varied with generation evaluated. First-generation spittlebugs inflicted the greatest damage on TC201 (centipede grass), 'Primavera' (bermudagrass), and 'Emerald' (zoysiagrass) in choice tests. In the fall, second-generation spittlebugs damaged TC201 (centipedegrass) and 'Sea Isle 1' (paspalum) most severely, whereas 561-79 (paspalum) and 'Emerald'(zoysiagrass) were less severely affected. Among taxa included in field trials, HI-1, 'Mauna Kea', 'Sea Isle 2000',and AP-14 paspalums, 'Tifway' bermudagrass, and 'Emerald' zoysiagrass were most tolerant (demonstrated the best regrowth potential following twolined spittlebug feeding).     

Impact of Japanese beetle (Coleoptera: Scarabaeidae) feeding on seashore paspalum

Ten cultivars of seashore paspalum, Paspalum vaginatum Swartz, were compared for their response to Japanese beetle, Popillia japonica Newman, larval root feeding. Cultivars of Bermuda grass, Cynodon sp., and zoysiagrass, Zoysia sp., also were included for comparison. Turf grown in pots in the greenhouse was infested with second and third instars in this 2-yr study. Grub survival and weight gain, foliar growth, and root loss were compared among turfgrass species and cultivars. Few species-related differences were identified. Differences in grub tolerance were, however, observed to be a function of turfgrass cultivar. Some turf types demonstrating tolerance to grub feeding had rapid root growth and high root mass in control pots, but this was not consistent for all cultivars showing enhanced ability to maintain foliar growth despite grub feeding. The paspalum cultivars that seemed most tolerant of grub feeding were '561-79', 'Sea Isle 2000', 'Durban', 'HI-10', 'Kim-1', 'Sea Dwarf', and 'Sea Spray'.     

Influence of whorl region from resistant and susceptible corn genotypes on fall armyworm (Lepidoptera: Noctuidae) growth and development

The effect of diets prepared from whorl tissue of resistant and susceptible corn genotypes, Zea mays L., on the larval growth, development, and physiology of fall armyworm, Spodoptera frugiperda (J. E. Smith), was analyzed. Larvae reared on an optimized artificial diet had a higher growth rate and developed faster than those reared on lyophilized whorl tissue from resistant and susceptible genotypes. Larvae reared on the resistant material were smaller and had a longer developmental period. Larvae reared on yellow-green and green whorl sections from resistant plants were significantly smaller than those reared on the same sections of susceptible plants. There was no significant difference in weight when larvae were reared on the yellow whorl regions from either resistant or susceptible lines. Physiological indices were determined for larvae fed resistant and susceptible lyophilized and fresh whorl material. Larvae fed resistant lyophilized material had significantly lower growth rate (GW) and efficiency of conversion of ingested food to body substance (ECI) than those reared on artificial diet or susceptible material. However, there were no significant differences in consumption index (CI), approximate digestibility (AD) and efficiency of conversion of digested food to body substance (ECD) between larvae reared on lyophilized tissue from resistant and susceptible genotypes. Larvae reared on fresh yellow-green whorl sections from resistant plants had significantly lower GW, ECI, and ECD than those reared on susceptible material. In contrast, no significant differences in any of the estimated food consumption and utilization indices were observed between larvae reared on fresh yellow whorl sections from resistant or susceptible plants. These results suggest that some components of whorls from resistant plants, especially the yellow-green region, inhibit food utilization in fall armyworm larvae.     

Importance of host plant species, Neotyphodium endophyte isolate, and alkaloids on feeding by Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae

Three grass host species--tall fescue, Festuca arundinacea Schreber; meadow fescue, Festuca pratensis Hudson; and perennial ryegrass, Lolium perenne L.--each infected with a number of different Neotyphodium endophyte isolates, were investigated for their effects on fall armyworm, Spodoptera frugiperda (J.E. Smith). Alkaloid profiles varied among associations. Choice and no-choice tests comparing feeding and early development of S. frugiperda larvae on endophyte-infected and endophyte-free leaf blade material were performed. Endophyte-mediated resistance to S. frugiperda was greatest in meadow fescue and weakest in tall fescue. Some endophyte isolates, particularly in perennial ryegrass and meadow fescue, had a major effect on feeding and development of S. frugiperda, whereas others had no effect or were only weakly efficacious. In tall fescue, some associations deterred S. frugiperda from feeding in choice tests but had no effect on development, whereas larvae reared on other associations weighed significantly more than control larvae fed endophyte-free grass. It was concluded that the deleterious consequences of endophyte infection were easily masked by other factors in tall fescue. Relative leaf age had no effect on feeding preferences in the three host species. Chemical analysis of herbage from the plants used, and results from a no-choice study using spiked artificial diets, failed to individually implicate any of the major known alkaloids (peramine, lolitrem B, ergovaline, and lolines) in the observed effects on S. frugiperda. Hypotheses explaining these observations, and their impact on creating desirable grass-endophyte associations for use in pastures, are discussed.     

Interaction of a solitary larval endoparasitoid, Microplitis mediator, with its host, Mamestra brassicae: host acceptance and host suitability

Abstract:  Microplitis mediator (Haliday) (Hym., Braconidae) is an important parasitoid of early instar larvae of the European cabbage moth, Mamestra brassicae L. (Lep., Noctuidae). In the laboratory, we examined attack responses of female M. mediator to the first three larval instars of M. brassicae . Females were presented with M. brassicae larvae either one individual at a time in a no-choice experiment, or three individuals, one from each instar, simultaneously in a choice experiment. Whether or not there was choice, naïve female parasitoids attacked a high proportion of larvae and did not discriminate among instars. In the no-choice experiment, attacked larvae were reared, and parasitoid cocoons were produced from about 76% of larvae attacked as first and second instars, but from only 19% of larvae attacked as third instars. Dissections of attacked larvae from the choice experiment showed that about 79% of attacks on first and second instars resulted in oviposition compared with only 49% for third instars. When given choice, frequency and number of attacks on first instar larvae increased with increasing parasitoid experience. Our results suggest that first and second instar larvae of M. brassicae are suitable hosts for M. mediator , but that third instar larvae are suboptimal both because oviposition attempts were frequently unsuccessful and because immature parasitoids failed to complete development. Nevertheless, naïve attacking parasitoids exhibited minimal discrimination among instars, although experienced parasitoids most frequently attacked first instar larvae. The host selection behaviour of M. mediator is discussed in the context of optimal foraging theory and implications for biological control.     

Larval parasitoids and pathogens of the fall armyworm in honduran maize

Parasitism by natural enemies of all larval instars of the fall armyworm (FAW),Spodoptera frugiperda, was quantified in 5 Honduran maize fields during the 1984 growing season. Overall, 42.0% of the host larvae were killed by the natural enemy complex. The braconid parasitoidChelonus insularis was the most common natural enemy accounting for 36.8% of the complex and causing 15.5% mortality of FAW larvae. Other important natural enemies included the nematodeHexamermis sp., the tachinidLespesia sp. and the imperfect entomopathogenic fungusNomuraea rileyi. Distinct ranges of larval instars were attacked by several natural enemy species.Chelonus insularis was an important FAW natural enemy at all larval densities observed. Florida Agricultural Experiment Station Journal Series No. 8650 and MIPH-EAP No. 146.     

Rearing of ectoparasitoid Diapetimorpha introita on an artificial diet: supplementation with insect cell line-derived factors

We investigated the use of two insect cell lines to improve an artificial diet (DI) for the pupal ectoparasitoid Diapetimorpha introita. DI was supplemented with Grace's culture medium conditioned with IPL-LdFB, a cell line derived from fat body of the gypsy moth, Lymantria dispar (FBCell diet), and with Grace's medium conditioned with Sf9, a cell line derived from ovaries of the fall armyworm, Spodoptera frugiperda (Sf9Cell diet). The diets were also chemically analyzed for nutrients and any deficiencies were filled by the addition of nutrients. One-half ml aliquots of each diet were encapsulated in paraffin domes and newly hatched larvae of D. introita were placed on each diet (one larva/dome) and allowed to develop to the adult stage. Providing fresh diet on day four when the larvae were in the third instar did not improve parasitoid production. Compared with DI, only Sf9Cell had a positive effect on the parasitoid's growth, increasing the size of male parasitoids. The parasitoids, however, took longer to develop to the adult stage than those reared on the natural host. Neither cell line significantly enhanced the average weight of female parasitoids, shortened developmental time, nor increased % cocoons produced and % adult emergence. Providing additional nutrients (amino acids, vitamins, cations and anions, fatty acids and milk/egg protein) to both diets (based on chemical analyses of the cell line-supplemented diets) enhanced the average weight of the females on Sf9Cell and males and females on FBCell. The nutritional additions, however, did not improve the developmental time, pupation and adult emergence.     

Comparison of callus induction and plant regeneration from different explants in triploid and tetraploid turf-type bermudagrasses

The turf-type bermudagrasses are genetically variable and do not respond uniformly to tissue culture and plant regeneration protocols. We evaluated the callus induction response of two explant types, young inflorescences and nodes, from multiple genotypes including triploid TifSport, TifEagle, and Tift97-4 and tetraploid Tift93-132, Tift93-135, Tift93-156 and Tift93-157 on MS medium supplemented with 1–1.5 mg l⁻¹ 2,4-D + 0.01 mg l⁻¹ BA + 1.16 g l⁻¹ proline. Four types of callus were observed. Type I was fluffy, soft, and white non-embryogenic callus, common to all cultures. Type II was globular, transparent, and hard, but sticky callus, which was pre-embryogenic and could be selected for subculture. Type III callus was transparent, compact, and embryogenic. Type IV callus was opaque white and compact. Both Type III and Type IV calluses were embryogenic and regenerative. A combination of gelling agents in the medium (2 g l⁻¹ Gelrite and 5 g l⁻¹ agar) improved callus quality and increased the rate of compact callus formation during subculture. Embryogenesis from compact callus was observed in TifEagle, TifSport and Tift93-132, and shoots were regenerated on MS medium with 0.1 mg l⁻¹ 2,4-D + 0.5–4.0 mg l⁻¹ BA. Low intensity light treatment (30 μmol m⁻2 s⁻¹ of cool white fluorescence) to callus before regeneration greatly enhanced regeneration frequency from 6.7% to 40% in recalcitrant TifSport.     

Effect of tinopal LPW on the insecticidal properties and genetic stability of the nucleopolyhedrovirus of Spodoptera exigua (Lepidoptera: Noctuidae)

The influence of an optical brightener, Tinopal LPW, on the activity of a purified genotype of the nucleopolyhedrovirus (SeMNPV) of the beet armyworm, Spodoptera exigua (Hübner), was determined in second to fifth instar (L2-L5) S. exigua. When mixed with viral occlusion bodies (OB) 1% Tinopal LPW significantly reduced the median lethal dose (LD50) of the virus in all instars compared with insects treated with SeMNPV alone. Levels of enhancement, as determined by LD50 values, ranged from 2.6- to 580-fold, depending on the instar. The greatest enhancement occurred on the two later instars, L4 (70-fold) and L5 (580-fold), which show a much higher resistance to SeMNPV infection than earlier instars. The median time to death (MTD) values were not significantly different in any instar among larvae treated with SeMNPV + Tinopal LPW and those treated with SeMNPV alone. Larval development in SeMNPV + Tinopal LPW treated larvae was retarded, in second and fourth instars, compared with controls or larvae treated with SeMNPV alone. The OB yields from SeMNPV treated larvae were almost 1.6-fold greater in second instars (9.3 x 10(6) OBs/larvae), and 1.9-fold greater in fourth instars (1.9 x 10(8) OBs/larvae), than those obtained in larvae treated with SeMNPV + Tinopal LPW. The addition of 1% Tinopal LPW to the virus suspension did not alter the genotypic composition of viral progeny during four successive passages of the virus.     

Effect of group size on parasitism in a natural population of the Baltimore checkerspot Euphydryas phaeton

Summary The effect of group size of early instars on parasitism of Euphydryas phaeton (Nymphalidae) was examined. Different numbers of larvae were stocked per web to determine the effect of group size on parasitism. Larval aggregations of moderate size (the size occurring naturally) had the least parasitism. Larger larval groups had a disproportionately high rate of parasitism. The major larval parasitoids located vulnerable larvae within webs, instead of attacking larvae available on the outside of webs. Parasitism rates were similar for larvae of damaged and undamaged webs, a consequence of the behavior and location of larvae in the webs. Lower limit to group size was a function of facilitation of larval numbers in reaching the first feeding site, the top of the host plant. Feeding facilitation by larval aggregations was not a factor in larval survival or growth.     

穴蚁蛉的自然种群动态

本文主要报道了穴蚁蛉 Myrmeleon(Morter) sagax(Walker)幼虫的野外自然种群数量动态。穴蚁蛉 1年发生 1代 ,在自然界其幼虫 3～ 5月份数量平稳略有下降 ,5、6月间数量迅速下降 ,6月初数量最少 ;7～ 9月份数量迅速上升 ,而后下降 ;新一代穴蚁蛉幼虫 (蚁狮 )在 6月份出现。其种群 ,秋季以 1龄幼虫数量为多 ,冬季主要以 2龄幼虫为主越冬 ,春季以 3龄蚁狮占优势。春季野外采集来的蚁狮 ,在每日光照 14小时、每周两饲 (每次饲 1头米蛾 Corcyra cephalonica成虫 )的条件下饲养 ,结果发现 ,采集回时处于 3龄期的蚁狮比自然界大约提前 1个月结茧化蛹和羽化 ;而采集回时处于 2龄期的蚁狮则和自然界中的情况基本一致。     

Suitability of various turfgrass species and cultivars for development and survival of black cutworm (Lepidoptera: Noctuidae)

Black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), feeding bioassays were conducted on young and mature turfgrass species to determine their potential resistance. Measures of resistance included larval weight, survival rate, instar development, pupal weight, duration of pupation, and days to pupation and adult emergence. Black cutworm reared on Poa pratensis 'Midnight', Poa arachnigera 'Tejas', and Poa pratensis X Poa arachnigera 'Reveille' exhibited slower development, lower weight, and higher overall mortality than those fed upon other turfgrasses tested. Larvae reared on Reveille did not survive to pupation and all died within 14 d. Black cutworm larvae reared on Midnight died within 17 d in trial 1 but attained pupation in trial 2. However, development of black cutworm larvae was slower on Poa pratensis Midnight compared with other susceptible turfgrass species such as Agrostis stolonifera 'Penncross', Poa annua ('DW194', 'Q98-4-6', and 'Q98-6-18'), Lolium perenne, and Poa supina 'Supranova'. Generally, larval performance on young plant tissues was better than on mature plant tissues. Larvae reared on P. pratensis 'Midnight' exhibited the most distinctive difference on young versus mature plant tissue. These results suggest that plant age may play an important role in turfgrass susceptibility and resistance.     

草地贪夜蛾幼虫对常用杀虫剂相对敏感基线的建立

【目的】本研究旨在建立草地贪夜蛾Spodoptera frugiperda对常用杀虫剂的相对敏感基线,为我国草地贪夜蛾的抗药性系统性监测提供依据。【方法】从玉米田采集草地贪夜蛾在室内不接触任何杀虫剂连续饲养5~7代,采用浸叶法和点滴法测定了草地贪夜蛾3龄幼虫以及采用饲料药膜法测定了草地贪夜蛾2龄幼虫对6大类共7种常用杀虫剂(甲维盐、乙基多杀菌素、虫螨腈、茚虫威、四氯虫酰胺、虱螨脲和氯虫苯甲酰胺)的敏感性,并据此建立了草地贪夜蛾幼虫对这7种杀虫剂的相对敏感基线。【结果】浸叶法测得上述7种药剂对草地贪夜蛾幼虫的LC₅₀值在0.054~12.131 mg/L之间;点滴法测得上述6种药剂(不含虱螨脲)对草地贪夜蛾幼虫的LD₅₀值在0.355~4.707 μg/g之间;饲料药膜法测得上述7种药剂对草地贪夜蛾幼虫的LC₅₀值在0.003~0.238 μg/cm²之间。【结论】采用3种生测方法建立了草地贪夜蛾幼虫对几种常用杀虫剂的相对敏感基线,为我国草地贪夜蛾的抗药性监测和化学防治提供了依据。     

Influence of parasitism by Chelonus insularis Cresson (Hymenoptera: Braconidae) on the susceptibility of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) to insecticides

The egg-larval parasitoid Chelonus insularis Cresson is a key parasitoid of the fall armyworm Spodoptera frugiperda (J. E. Smith) during the second field generation in the upper Magdalena River Basin, Colombia. In spite of selection pressure, the higher susceptibility of the second generation fall armyworm larvae to insecticides, compared with that of the first generation, suggests that the parasitism may be responsible for the apparent difference in susceptibility. Parasitized and non-parasitized 2nd-instar larvae of the fall armyworm were tested for susceptibility to chlorpyriphos, methomyl, cypermethrin, and Bacillus thuringiensis in the laboratory, using the leaf dip test. Parasitized larvae were up to 3.93 times more susceptible to chlorpyriphos, 3.71 times to methomyl, and 14.11 times to cypermethrin than non-parasitized larvae. The least effect of parasitism on susceptibility was found for B. thuringiensis. We discuss the negative influence of synthetic insecticide on the parasitoid population dynamics and its impact on insecticide resistance.     

Hymenopteran parasitoids of diamondback moth (Lepidoptera: Ypeunomutidae) in northern Thailand

Larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Ypeunomutidae), cause severe economic damage to cabbage, Brassica oleracea L. variety capitata (Brassicaceae) and related vegetables in Thailand. Overuse of broad-spectrum insecticides for diamondback moth control is a serious problem and has obscured the contributions of indigenous parasitoids. Our objectives were to identify indigenous diamondback moth parasitoids in northern Thailand and to assess their potential for natural control. Six parasitoid species were reared from diamondback moth larvae and pupae collected in 1990 and in 2003-2004. These included the larval parasitoid Cotesia plutellae Kurdjumov (Braconidae), a larval-pupal parasitoid Macromalon orientale Kerrich (Ichneumonidae), and pupal parasitoids Diadromus collaris Gravenhorst (Ichneumonidae) and Brachymeria excarinata Gahan (Chalcididae). Single specimens of Isotima sp. Forster (Ichneumonidae) and Brachymeria lasus Walker (Chalcididae) also were reared from diamondback moth hosts. C. plutellae was the dominant larval parasitoid and was often reared from host larvae collected from fields sprayed regularly with insecticides; parasitism ranged from 14 to 78%. Average parasitism by M. orientale was only 0.5-6%. Parasitism of host pupae by D. collaris ranged from 9 to 31%, whereas B. excarinata pupal parasitism ranged from 9 to 25%. An integrated pest management (IPM) protocol using simple presence-absence sampling for lepidopterous larvae and the exclusive use of Bacillus thuringiensis (Bt) or neem resulted in the highest yields of undamaged cabbage compared with a control or weekly sprays of cypermethrin (local farmer practice). IPM programs focused on conservation of local diamondback moth parasitoids and on greater implementation of biological control will help alleviate growing public concerns regarding the effects of pesticides on vegetable growers and consumers.     

Differences in worker caste behaviour of Oecophylla smaragdina (Hymenoptera: Formicidae) in response to larvae of Anthene emolus (Lepidoptera: Lycaenidae)

The larvae of Anthene emolus (Lycaenidae) cannot survive in the wild without their associated ant Oecophylla smaragdina (Formicidae) . The ants groom the lycaenid larvae for secretions and, in turn, protect them from parasitoids and predators. Both major and minor worker ants tend larvae, although, in the present study, the frequencies of tending by different castes proved to be significantly different. Ants also tended late instars significantly more than young larvae. O. smaragdina ants of the same colony were observed fighting when A. emolus larvae were present. Aggression was exhibited by the major workers against the minor workers that tried to tend secreting larvae. Major ants precluded the minors from the most nutritious secretions, leaving minors to tend the less productive, early instars. On a few occasions, aggression was unchecked and major workers killed the larvae they were tending (presumably accidentally). When larvae were experimentally reared with only one caste of ant, the resulting butterflies showed no differences in dry weight. Mortality was high when larvae were reared with only minor ants or in the absence of ants.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 391–395.     

Plant resistance and its effect on the peritrophic membrane of southwestern corn borer (Lepidoptera: Crambidae) larvae

The southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), is a serious pest of corn, Zea mays L., in the southern United States. Corn germplasm lines with conventional genetic leaf-feeding resistance to this pest, the fall armyworm, Spodoptera frugiperda (J.E. Smith), and other lepidopterans have been released to the public by USDA-ARS scientists located in Mississippi. Recent studies suggest the insect resistant lines disrupt the integrity of the peritrophic membrane of the fall armyworm. The objectives of this study were to investigate any morphological differences in the structure of the peritrophic membrane of southwestern corn borer larvae feeding on resistant and susceptible corn hybrids and to quantify the damage. Larvae were reared under field and laboratory conditions on three corn hybrids (two resistant and one susceptible). Scanning electron microscopy was used to examine the peritrophic membrane for abnormalities such as holes or tears and to count the holes or tears in the membrane. Differences in the degree of damage to peritrophic membrane of larvae fed on resistant and susceptible plants were not detected. Up to five distinct layers of the membrane were observed in each larva. Variation in the amounts of damage to the peritrophic membrane observed from larvae feeding on all plant material was high. Plant resistance adversely affects growth and development of southwestern corn borer larvae, and further investigations are needed to explain the role of plant resistance and its relation to peritrophic membrane in southwestern corn borer larvae.     

Functional response of the tiger beetle Megacephala carolina carolina (Coleoptera: Carabidae) on twolined spittlebug (Hemiptera: Cercopidae) and fall armyworm (Lepidoptera: Noctuidae)

The functional response of the tiger beetle Megacephala carolina carolina L. (Coleoptera: Carabidae) was determined on adult twolined spittlebug, Prosapia bicincta (Say) (Hemiptera: Cercopidae), and fourth instars of fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), in single-prey and two-prey systems. In the laboratory, M. carolina carolina demonstrated a type II functional response for P. bicincta and S. frugiperda in both single- and two-prey systems. Search efficiency of M. carolina declined for both prey as the initial number of prey increased. Of the total prey consumed, M. carolina carolina killed significantly more S. frugiperda than P. bicincta in the single-prey system (8.0 and 4.5, respectively) and the two-prey system (5.0 and 2.0, respectively). Estimates of attack coefficient, a, were not significantly different for P. bicincta and S. frugiperda in the single-prey (0.07 and 0.02) and two-prey systems (0.04 and 0.06), respectively. The handling time, T(h), was significantly greater for P. bicincta (5.02 and 10.64 h) than for S. frugiperda (2.66 and 4.41 h) in single- and two-prey systems, respectively. Estimations of attack coefficient and handling time in the single-prey system were used to predict prey preference of M. carolina carolina. No strong prey switching response was observed. M. carolina carolina showed no preference for either prey. However, in the presence of S. frugiperda, the functional response of the predator for P. bicincta was reduced. M. carolina carolina is a potential predator of one or more turfgrass pests and should be considered in conservation efforts.     

Influence of fall armyworm previous experience with soybean genotypes on larval feeding behavior

Previous experience on host plants can modify insect feeding behavior. Because insect habituation and induction of preference to host plants are variable across species of plants and insects, it is necessary to investigate each insect-plant interaction to determine whether this phenomenon occurs or not in the system. In this study we investigated the potential occurrence of habituation and induction of preference in fall armyworm (FAW) Spodoptera frugiperda to soybean genotypes. Neonate FAW larvae reared on artificial diet were divided into four treatment groups and fed for one generation with either the resistant soybeans PI 227687 or IAC 100 or the susceptible soybeans BRS Valiosa RR or IGRA RA 626 RR. Biological parameters of FAW were recorded. Eggs obtained from FAW of each genotype group were separated, and the newly hatched larvae were fed on the same genotypes experienced by their parents for additional 8 days. FAW larval preference and leaf area consumed were evaluated in choice feeding assays with the four soybean genotypes within a 24-h period. Genotypes PI 227687 and IAC 100 negatively affected FAW development, demonstrating they are FAW-resistant. FAW larvae exposed to both resistant genotypes consumed more foliage of genotype IGRA RA 626 RR in the choice assays, whereas larvae reared on both susceptible genotypes did not show any preference. From our preliminary study, FAW does not show habituation and induction of preference toward the experienced soybean genotypes. The importance of our findings to host plant resistance and insect-plant biology fields is discussed.     

Conventional resistance of experimental maize lines to corn earworm (Lepidoptera: Noctuidae), fall armyworm (Lepidoptera: Noctuidae), southwestern corn borer (Lepidoptera: Crambidae), and sugarcane borer (Lepidoptera: Crambidae)

Plant resistance is a useful component of integrated pest management for several insects that are economically damaging to maize, Zea mays L. In this study, 15 experimental lines of maize derived from a backcross breeding program were evaluated for resistance to corn earworm, Helicoverpa zea (Boddie); fall armyworm, Spodoptera frugiperda (J. E. Smith); southwestern corn borer, Diatraea grandiosella Dyar; and sugarcane borer, Diatraea saccharalis (F.). Experimental line 100-R-3 was resistant in the field to leaf feeding by fall armyworm and line 116-B-10 was resistant in the field to leaf feeding by fall armyworm and leaf and stalk feeding by southwestern corn borer. When corn earworm larvae were fed field harvested silks from experimental line 81-9-B in the laboratory, their pupal weights were significantly lower than the pupal weights of larvae that were fed silks from the resistant control, Zapalote Chico. Maysin levels lower than those commonly associated with corn earworm resistance were present in the resistant experimental line, 107-8-7, indicating a new basis confers resistance to corn earworm in this line. These resistant experimental lines will provide plant breeders with new sources of resistance to lepidopterous insects for the development of improved maize breeding populations.