Oviposition deterrence in spring wheat, Triticum aestivum, against orange wheat blossom midge, Sitodiplosis mosellana: implications for inheritance of deterrence

Some spring wheat lines are known to be antixenotic to ovipositing orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae). The genetic basis of antixenosis, expressed in the plant as oviposition deterrence to S. mosellana , was explored using a population of 92 doubled-haploid wheat lines from a cross between a susceptible parent and a deterrent parent which also had antibiosis resistance. Wheat midge egg densities on wheat spikes were obtained from a standardized laboratory cage test and from the field in 2006 and 2007. Compared to the susceptible parent, egg densities on 55–88% of the lines were reduced by more than half in the laboratory and both years in the field. Twenty-five of the 92 lines were consistently at least as deterrent as the deterrent parent in all three environments. Frequency distribution of egg densities compared to the parents indicated that deterrence was conferred by more than one gene, with complementary interaction among genes. Heritability of deterrence was estimated at 67%, showing that environment had a substantial effect on the phenotypic expression of the trait. Consistently deterrent lines had a larger proportion of eggs laid on the rachis compared to the other lines in all environments, suggesting that the presence of deterrence affects where on the spikelet the females lay their eggs. There was no evidence for linkage between deterrence genes and the antibiosis gene, Sm1 . Oviposition deterrence is a promising means for suppressing wheat midge oviposition in commercial wheat crops; however, the multigenic nature of oviposition deterrence in wheat to S. mosellana and the influence of environment on its expression will provide challenges for incorporating this trait into wheat breeding programs.     

Factors influencing oviposition behaviour of the sorghum midge, Contarinia sorghicola Coq.

Visual stimuli influence the orientation behaviour of the sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae). Yellow, red and white colours are attractive to the midge while blue and black are least attractive. Sorghum panicles covered with blue- or black-coloured bags in a headcage showed maximum midge damage, while the reverse was true for panicles covered with yellow, red, and white coloured bags.
Panicles at half-anthesis with viable pollen and receptive stigmata suffered higher damage than those at the pre- and post-anthesis. Physical removal of anthers and stigmata significantly reduced the oviposition by the sorghum midge. Reduced oviposition/adult emergence was also recorded in male sterile sorghum lines (2219A and 296A) or through chemically- (Ethrel) (2-Chloro ethyl-phosphonic acid) induced male sterility in panicles of the sorghum cultivar, Swarna. Chemical stimuli from viable pollen and receptive stigmata and to a limited extent physical stimuli, govern the oviposition behaviour of the sorghum midge.
Sorghum cultivars IS 12573C, S-GIRL-MR1 and IS 2816C showed antixenosis to adult midges. However, these cultivars became susceptible under no-choice conditions in the headcage. DJ 6514 and IS 12666C were attractive to the adult midges, but showed antixenosis to oviposition under natural and no-choice conditions. Genotypes with short florets showed antixenosis for oviposition. Ovary and anther breadth and tannin content of grain showed negative associations with oviposition. Cultivar antixenosis to adult midges and oviposition is an important component of resistance to the sorghum midge.     

Genetic control of different types of the aphid resistance in cereal crops

Inheritance of the two main types of the plant resistance to insects was investigated in the sorghum-greenbug (Schizaphis graminum Rond.) and wheat-bird cherry-oat aphid (Rhopalosiphon padi L.) interaction systems. The data obtained support the hypothesis that antixenosis (avoiding of the plant by the insect, given a choice) and antibiosis (adverse effect of the plant on the insect feeding on it) are pleiotropic manifestations of the same genes. This is confirmed by the following facts. (1) Identical patterns of segregation for antixenosis and antibiosis in different cases of sorghum resistance to the greenbug: monogenic control (gene Sgr4), digenic control (Sgr1, Sgr2 and Sgr7, Sgr8), and complementary action of the genes (Sgr9 and Sgr10). (2) Correlated changes in the levels of antibiosis and antixenosis during long-term reproduction of a greenbug clone on the resistant sorghum variety k-1206 (resistance controlled by one gene). (3) Simultaneous expression of antixenosis and antibiosis in F₃ wheat hybrid families to the bird cherry-oat aphid.     

Genotypic variability and mode of action of Colorado potato beetle (Coleoptera: Chrysomelidae) resistance in seven Solanum species

Accessions from seven wild Solanum species were evaluated in the field for resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say). The multivariate insect population density data were analyzed using factor analysis. The factors extracted corresponded to relevant phases of the insect's life cycle and provided information on the mode of resistance (antixenosis and antibiosis) of the plant species. S. berthaultii, S. capsicibaccatum, S. jamesii, S. pinnatisectum, and S. trifidum demonstrated both antixenosis and antibiosis but expressed different levels of resistance. The mode of resistance of S. polyadenium seemed to be antibiosis and that of S. tarijense antixenosis. Genetic variability and heritability of insect resistance traits within accessions was trivial or inconsistent for all Solanum species studied.     

The relationship between morphological traits of the spring wheat spike and oviposition deterrence to orange wheat blossom midge

If morphological traits of a plant cause resistance to an insect pest or are strongly correlated with resistance levels, those traits can be used by plant breeders as phenotypic markers for indirect selection of resistance. To improve our understanding of antixenosis against the orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), expressed as oviposition deterrence in bread wheat, Triticum aestivum L. (Poaceae), 21 morphological traits of the wheat spike were studied in a genetically related wheat population and correlation of the traits with deterrence level was explored. The following traits had larger values in the deterrent parent of the population than the susceptible parent: ligule length, glume length, length of hair inside glume, palea length at post-anthesis stage, length of hair inside lemma, length of hair at spikelet base, inter-spikelet distance, and length of hair at rachis edge at post-anthesis stage. The highest correlation coefficient between mean egg density and a morphological trait of the wheat population was −0.287, which was for inter-spikelet distance. This represented 8% predictability from the point of view of crop breeding and explained one-twelfth of the variation in oviposition deterrence among lines. The morphological traits of bread wheat spikes were not highly correlated to deterrence. Therefore, no promising trait could be recommended for use in breeding programs. Studies of the fine-scale properties of the wheat plant surface, and their interactions with plant surface chemistry, with a greater focus on wheat midge oviposition behavior, may clarify the effect of the morphological traits on oviposition and deterrence.     

Antixenosis component of resistance to sorghum midge, Contarinia sorghicola Coq. in Sorghum bicolor (L.) Moench

Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is the most destructive pest of grain sorghum, and host-plant resistance is an effective method of controlling this insect. We studied the antixenosis component of resistance to sorghum midge using multi-, double- and no-choice cage tests, and under multi-choice field conditions to quantify and understand the nature of antixenosis component of resistance to this insect in Sorghum bicolor (L.) Moench. Midge response towards sorghum panicles was influenced by panicle size and cage type used to study the orientation behaviour. Maximum number of midges were recorded at 30 and 60 min after initiating the experiment. Antixenosis shown by C. sorghicola under multi-choice field conditions to ICSV 197 and TAM 2566 was not confirmed under cage tests, while DJ 6514, AF 28 and IS 3461 were non-preferred both under field and cage conditions. Midge-resistant female parents (PM 7061 and PM 7068) were less preferred than the midge susceptible (ICSA 42 and 296A) female parents. Male-sterility did not influence host finding and acceptance by the midge females, although in one out of two tests, the maintainer lines (B-lines) were preferred over the male-sterile lines (A-lines).     

Mechanisms of Oryza sativa (Poaceae) resistance to Tagosodes orizicolus (Homoptera: Delphacidae) under greenhouse condition in Venezuela

Tagosodes orizicolus is one of the main plagues of rice in tropical America causing two types of damages, the direct one, feeding and oviposition effect, and an indirect one, by the transmission of the "Rice hoja blanca virus". During 2006-2007 we carried out research under greenhouse conditions at Fundaci6n Danac, Venezuela, in order to determine the mechanisms of antixenosis, antibiosis and tolerance to T. orizicolus, which could be acting in commercial varieties and advanced lines of the rice genetic breeding programs of INIA and Fundaci6n Danac. The method of free feeding was used for the antixenosis evaluation, whereas the method of forced feeding was used for antibiosis evaluation (effect on survival and oviposition). Additionally, we used the indirect method based on biomass depression to estimate the tolerance. Some of the evaluated traits included: grade of damage, number of insects settling on rice plants, percentage of sogata mortality at the mature state, number of eggs in the leaf midrib and an index of tolerance. The results showed that rice genotypes possess different combinations of resistance mechanisms, as well as different grades of reactions. The susceptible control 'Bluebonnet 50' was consistently susceptible across experiments and the resistant control 'Makalioka' had high antixenosis and high antibiosis based on survival and oviposition. The rest of the genotypes presented lower or higher degrees of antixenosis and antibiosis for survival and oviposition. The genotype 'FD0241-M-17-6-1-1-1-1' was identified with possible tolerance to the direct damage of sogata.     

Quantitative trait loci mapping of resistance to Laodelphax striatellus (Homoptera: Delphacidae) in rice using recombinant inbred lines

Laodelphax striatellus Fallén (Homoptera: Delphacidae), is a serious pest in rice, Oryza sativa L., production. A mapping population consisting of 81 recombinant inbred lines (RILs), derived from a cross between japonica' Kinmaze' and indica' DV85' rice, was used to detect quantitative trait loci (QTLs) for the resistance to L. striatellus. Seedbox screening test (SST), antixenosis test, and antibiosis test were used to evaluate the resistance response of the two parents and 81 RILs to L. striatellus at the seedling stage, and composite interval mapping was used for QTL analysis. When the resistance was measured by SST method, two QTLs conferring resistance to L. striatellus were mapped on chromosome 11, namely, Qsbph11a and Qsbph11b, with log of odds scores 2.51 and 4.38, respectively. The two QTLs explained 16.62 and 27.78% of the phenotypic variance in this population, respectively. In total, three QTLs controlling antixenosis against L. striatellus were detected on chromosomes 3, 4, and 11, respectively, accounting for 37.5% of the total phenotypic variance. Two QTLs expressing antibiosis to L. striatellus were mapped on chromosomes 3 and 11, respectively, explaining 25.9% of the total phenotypic variance. The identified QTL located between markers XNpb202 and C1172 on chromosome 11 was detected repeatedly by three different screening methods; therefore, it may be important to confer the resistance to L. striatellus. Once confirmed in other mapping populations, these QTLs should be useful in breeding for resistance to L. striatellus by marker-assisted selection of different resistance genes in rice varieties.     

Marker-trait association analysis for gall midge (Orseolia oryzae) resistance in a diverse rice population

Damage caused by insect herbivores, notably Asian rice gall midge, Orseolia oryzae is more prevalent in the rice-growing belts of India's southern and north-eastern states. As a prelude to resistant cultivar development, the identification of genomic regions for resistance in the source population is crucial. In the present investigation, 202 rice genotypes were phenotyped and assayed with genomic markers reported for gall midge resistance. Positive skewness and platykurtic distribution of response scores suggested the inheritance of gall midge resistance in the study population. The marker gm3del3 contributed the most genetic variation, followed by RM28574 and marker RM22709 explained minimal variation. A marker-trait association analysis with a single marker-trait linear regression approach was performed to discover gall midge resistant genomic region/genes. The marker RM17480 on chromosome 4 reported to be linked with gm3 gene was found significantly associated with the gall midge resistance genomic region with allelic effects in a negative direction favouring resistance reaction. The allelic effects of significantly associated markers were correlated significantly with the phenotypic variation of gall midge damage scores. Genes identified in the vicinity of this marker contribute to stress response reactions in rice plants. The 200 bp allele of the marker was associated with susceptibility, while the 250 bp allele was associated with resistance expression. This allelic association with trait variation suggests the importance of associated marker for utilisation in marker-assisted selection programmes to incorporate resistance alleles into elite rice genotypes.     

辽宁水稻品种抗灰飞虱鉴定及其抗性机制研究

为探明辽宁地区水稻品种对本地灰飞虱Laodelphax striatellus(Fallén)的抗性水平及其抗虫机制,本研究利用改进的苗期集团鉴定法,以IR36为抗虫对照品种、武育粳3号为感虫对照品种,对42份辽宁地区主栽水稻品种和研究待推广品种进行了水稻苗期对灰飞虱抗性鉴定,并从中选取20份不同抗性水平的品种进行了排趋性和抗生性的测定。结果表明:从42份水稻材料中仅筛选出1份抗虫材料辽优5218,中抗品种11份,其余均为感虫或高感品种。在不同水稻类型中,杂交稻的抗虫性普遍较常规稻强,而从水稻株型上看,抗性品种大多为披散型。抗虫机制研究发现,抗虫品种辽优5218和中抗品种港育129兼具排趋性和抗生性,是非常理想的抗性种质资源,中抗品种港源8号和粳优558具有很强的排趋性,也是较为理想的抗性资源,为抗性机制的深入研究提供了材料。但大部分省内主栽主推品种不具备对灰飞虱的抗性,应引起重视。     

Determining the host‐plant resistance mechanisms for Mamestra brassicae (Lepidoptera: Noctuidae) pest in cabbage

Six cabbage (Brassica oleracea var. capitata) varieties with different levels of resistance to Mamestra brassicae (Lepidoptera: Noctuidae) were investigated in order to assess whether antibiosis and antixenosis mechanisms are involved in the resistance to this pest or not. Four experiments were conducted to determine the effect of variety and plant ontogeny on larval behaviour, adult oviposition and leaf damages in non‐choice and choice tests. Larval survival, time to development and larval weights differed depending on the varieties and plant stages that we tested. At the pre‐head stage, larval mortality was higher, larvae died faster, time to pupation was shorter, pupae were lighter and the percentage of viable pupae and growth index (GI) values were lower than larvae reared from plants at the head stage. The commercial hybrid ‘Corazón de buey’ and the local variety named ‘BRS0535’ exhibited antibiosis to M. brassicae as they reduced its survival and growth and delayed its development time. In addition, these varieties were the most resistant after artificial infestation in terms of head foliage consumption and number of larvae per plant. Oviposition tests demonstrated that resistance found in ‘Corazón de buey’ and BRS0535 could be also based on antixenosis mechanisms as they resulted in fewer egg batches on plants, whereas BRS0402 could be classified as resistant because M. brassicae larvae showed less preference for it. Thus, resistance to M. brassicae found in cabbage crops may be due to the joint action of several factors involving antibiosis and antixenosis. We found significant differences in the resistance of BRS0535 depending on the plant ontogeny as it loses its resistance while developing. Further studies are required to identify the mechanism of antibiotic resistance which is present in this variety at the pre‐head stage and the changes that occur in plant defence as it grows.     

Seed yield of near-isogenic soybean lines with introgressed quantitative trait loci conditioning resistance to corn earworm (Lepidoptera: Noctuidae) and soybean looper (Lepidoptera: Noctuidae) from PI 229358

The development of superior soybean, Glycine max (L.) Merr., cultivars exhibiting resistance to insects has been hindered due to linkage drag, a common phenomenon when introgressing alleles from exotic germplasm. Simple-sequence repeat (SSR) markers were used previously to map soybean insect resistance (SIR) quantitative trait loci (QTLs) in a'Cobb' X PI 229358 population, and subsequently used to create near-isogenic lines (NILs) with SIR QTL i n a 'Benning' genetic background. SIR QTLs were mapped on linkage groups (LGs) M (SIRQTL-M), G (SIRQTL-G), and H (SIRQTL-H). The objectives of this study were to 1) evaluate linkage drag for seed yield by using Benning-derived NILs selected for SIRQTL-M, SIRQTL-H, and SIRQTL-G; 2) assess the amount of PI 229358 genome surrounding the SIR QTL in each Benning NIL; and 3) evaluate the individual effects these three QTLs on antibiosis and antixenosis to corn earworm, Helicoverpa zea (Boddie), and soybean looper, Pseudoplusia includens (Walker). Yield data collected in five environments indicated that a significant yield reduction is associated with SIRQTL-G compared with NILs without SIR QTL. Overall, there was no yield reduction associated with SIRQTL-M or SIRQTL-H. A significant antixenosis and antibiosis effect was detected for SIRQTL-M in insect feeding assays, with no effect detected in antixenosis or antibiosis assays for SIRQTL-G or SIRQTL-H without the presence of PI 229358 alleles at SIRQTL-M. These results support recent findings concerning these loci.     

Antibiosis component of resistance in sorghum to sorghum midge, Contarinia sorghicola

Sorghum midge, Contarinia sorghicola Coq. (Diptera: Cecidomyiidae) is an important pest of grain sorghum, and host-plant resistance is one of the most effective means of controlling this pest. We studied the antibiosis mechanism of resistance in sorghum to C. sorghicola in a diverse array of midge-resistant and midge-susceptible genotypes. Data were recorded on adult emergence, postembryonic developmental period, number of mature eggs in the ovary, fecundity, larval survival from artificially implanted eggs; and the tannins, soluble sugars, and protein content of 10-day old and mature grains during the 1982-91 rainy and post-rainy seasons. Adult emergence was significantly lower in the midge-resistant genotypes compared with the susceptible controls. Initiation of adult emergence was delayed by 4–8 days on DJ 6514, IS 8571, IS 9807, IS 10712, IS 19474, IS 19512, ICSV 830 and ICSV 197. Postembryonic developmental period was prolonged on DJ 6514, IS 15107, IS 3461, IS 7005, IS 19474, ICSV 831 and ICSV 197. However, the delay in adult emergence or the extended developmental period was not observed during the post-rainy season in some genotypes. These differences in the expression of antibiosis to midge in resistant genotypes over seasons may be attributed to the effect of environmental conditions on the insect development and chemical composition of sorghum grain. Amounts of tannins and proteins were generally greater in the midge-resistant lines compared with the susceptible ones (except tannins in DJ 6514) while the soluble sugars were low in the midge-resistant lines (except TAM 2566). These differences in chemical composition of the grain between genotypes and variations over seasons have been discussed in relation to the expression of antibiosis mechanism of resistance to the sorghum midge. Antibiosis to sorghum midge was also evident in terms of smaller size of larvae, lower number of eggs in the ovary, reduced fecundity, and larval survival. Midge-resistant lines have diverse effects on the biology of this insect. Antibiosis along with other components of resistance can be used to develop cultivars with stable resistance to C. sorghicola.     

Aphis pomi (Hemiptera: Aphididae) population development, shoot characteristics, and antibiosis resistance in different apple genotypes

In high-value crops such as apple, Malus X domestica (Borkh.), insecticidal pest control is of high relevance. The use of resistant apple cultivars can increase the sustainability of pest management in apple orchards. Besides variation in plant chemistry that may influence plant resistance by antibiosis or antixenosis, plant growth characteristics also can affect plant susceptibility to pests such as aphids. Variable susceptibility to the apple aphid, Aphis pomi De Geer (Hemiptera: Aphididae), has been described for different apple cultivars. These observations were based on phenotypic surveys and no information on genetically based apple resistance to A. pomi is yet available. The objective of this study was to relate shoot growth characteristics with aphid population development, and to assess the genetic background of apple antibiosis-based resistance to A. pomi by quantitative trait loci (QTL) analysis. Aphid population development was repeatedly studied in the field in sleeve cages attached to 200 apple trees of different genotypes. Aphid population development was positively correlated to shoot length and growth, and it also was affected by climatic conditions. Indications for antibiosis-based resistance to A. pomi remained weak in the studied apple genotypes, and the only detected putative QTL on linkage group 11 of'Fiesta' apples was not stable for the different replications of the experiment. This lack of quantifiable resistance may be partly explained by environmental conditions related to aphid development in sleeve cages.     

Host-plant susceptibility to the carrot fly, Psila rosae. 3. The role of oviposition preferences and larval performance

The acceptability of various plant species to ovipositing carrot flies was weakly, but significantly correlated with the host's suitability for larval development. Both adult host-plant preferences and larval performance as determined in laboratory experiments explained a part of the variation in susceptibility among the various test plants observed in the field. Across the whole set of plant species examined, antixenosis contributed more substantially to resistance than antibiosis, while the reverse seemed to be true for carrot cultivars.     

Host-plant preference and oviposition responses of the sorghum midge, Stenodiplosis sorghicola (Coquillett) (Dipt., Cecidomyiidae) towards wild relatives of sorghum

Sorghum midge, Stenodiplosis ( Contarinia ) sorghicola (Coquillett) is an important pest of grain sorghum world-wide. Considerable progress has been made in screening and breeding for resistance to sorghum midge. However, some of the sources of resistance have become susceptible to sorghum midge in Kenya, in eastern Africa. Therefore, the wild relatives of Sorghum bicolor were studied as a possible source of new genes conferring resistance to sorghum midge. Midge females did not lay eggs in the spikelets of Sorghum amplum , Sorghum bulbosum , and Sorghum angustum compared to 30% spikelets with eggs in Sorghum halepense when infested with five midge females per panicle under no-choice conditions. However, one egg was laid in S. amplum when infested with 50 midges per panicle. A larger number of midges were attracted to the odours from the panicles of S. halepense than to the panicles of Sorghum stipoideum , Sorghum brachypodum , S. angustum , Sorghum macrospermum , Sorghum nitidium , Sorghum laxiflorum , and S. amplum in dual-choice olfactometer tests. The differences in midge response to the odours from S. halepense and Sorghum intrans were not significant. Under multi-choice conditions, when the females were also allowed a contact with the host, more sorghum midge females were attracted to the panicles of S. bicolor compared with S. amplum , S. angustum , and S. halepense . In another test, numerically more midges responded to the panicles of IS 10712 compared with S. halepense , whereas the differences in midge response to the panicles of ICSV 197 ( S. bicolor ) and S. halepense were not apparent, indicating that S. halepense is as attractive to sorghum midge females as S. bicolor . The wild relatives of sorghum (except S. halepense ) were not preferred for oviposition, and they were also less attractive to the sorghum midge females. Thus, wild relatives of sorghum can prove to be an alternative source of genes for resistance to sorghum midge.     

Identification of quantitative trait loci associated with small brown planthopper (Laodelphax striatellus Fallén) resistance in rice (Oryza sativa L.)

F(2) and BC(1) populations derived from the cross between 02428 / Rathu Heenati were used to investigate small brown planthopper (SBPH) resistance. Using the F(2) population, three QTLs for antixenosis against SBPH were located on chromosomes 2, 5 and 6, and accounted for 30.75% of the phenotypic variance; three QTLs for antibiosis against SBPH were detected on chromosomes 8, 9 and 12. qSBPH5-c explaining 7.21% of phenotypic variance for antibiosis was identified on chromosome 5 using the BC(1) population. A major QTL, qSBPH12-a1, explained about 40% of the phenotypic variance, and a minor QTL, qSBPH4-a, was detected by the SSST method in both the F(2) and BC(1) populations. The QTLs indentified in the present study will be useful for marker assisted selection of SBPH resistance in rice.     

Detection and analysis of QTLs for resistance to the brown planthopper, Nilaparvata lugens, in a doubled-haploid rice population

 We used a mapping population of 131 doubled-haploid lines, produced from a cross between an improved indica rice variety (IR64) and a traditional japonica variety (Azucena), to detect quantitative trait loci (QTLs) for resistance to the brown planthopper (BPH), Nilaparvata lugens. We evaluated the parents and mapping population with six tests that measure varying combinations of the three basic mechanisms of insect host plant resistance, i.e., antixenosis, antibiosis, and tolerance. To factor-out the effect of the major resistance gene Bph1 from IR64, the screening was done with two BPH populations from Luzon Island, The Philippines, that are almost completely adapted to this gene. A total of seven QTLs associated with resistance were identified, located on 6 of the 12 rice chromosomes. Individual QTLs accounted for between 5.1 and 16.6% of the phenotypic variance. Two QTLs were predominantly associated with a single resistance mechanism: one with antixenosis and one with tolerance. Most of the QTLs were derived from IR64, which has been shown to have a relatively durable level of moderate resistance under field conditions. The results of this study should be useful in transferring this resistance to additional rice varieties. Received: 10 May 1998 / Accepted: 4 June 1998     

Good mothers,bad mothers,and the nature of resistance to herbivory in <Emphasis Type="Italic">Solidago altissima</Emphasis>

Evidence of poor correspondence between an insect herbivore’s oviposition preferences and the performance of its offspring has generally been attributed either to maladaptive behavior of the insect mother or inadequate measurement by the researcher. In contrast, we hypothesize that many cases of “bad mothers” in herbivores may be a byproduct of the hierarchical way natural selection works on resistance in host plants. Epistatic selection on the components of resistance (i.e., antixenosis and antibiosis) may generate negative genetic correlations between the resistance components, which could counteract the efforts of herbivores to oviposit on the best hosts for the performance of their offspring. In common garden and greenhouse experiments, we measured aspects of antixenosis and antibiosis resistance in 26 genets of tall goldenrod, Solidago altissima, against two common herbivores: the gall-inducing fly Eurosta solidaginis and the spittlebug Philaenus spumarius. Goldenrod antixenosis and antibiosis were positively correlated against E. solidaginis and negatively correlated against P. spumarius. Analogously, population-wide preference–performance correlations were positive for the gall flies and negative for the spittlebugs. Several natural history differences between the two insects could make gall flies better mothers, including better synchrony of the phenologies of the flies and the host plant, the much narrower host range of the gall flies than the spittlebugs, and the more sedentary lifestyle of the gall fly larvae than the spittlebug nymphs. If these results are typical in nature, then negative genetic correlations in antixenosis and antibiosis in plants may often result in zero or negative population-wide correlations between preference and performance in herbivores, and thus may be an important reason why herbivorous insects often appear to be bad mothers.     

Characterization of greenbug (Homoptera: Aphididae) resistance in synthetic hexaploid wheats

Twelve greenbug (Schizaphis graminum (Rondani)) biotype E-resistant synthetic hexaploid wheats synthesized by crossing Triticum dicoccum Schrank. and Aegilops tauschii (Coss.) Schmal. were evaluated for the three known insect resistance categories, including antibiosis, anti-xenosis, and tolerance. Different methods were evaluated for calculating antibiosis and tolerance. Calculating intrinsic rate of population increase and measuring leaf chlorophyll content with a SPAD chlorophyll meter proved to be time- and labor-efficient for antibiosis and tolerance determination, respectively. The resistance in all synthetic hexaploids proved to be the result of a combination of antibiosis, antixenosis, and tolerance, which makes them valuable sources of greenbug resistance. To assist plant breeders in selecting the best germplasm for greenbug resistance, a plant resistance index was created that revealed differences among the synthetic hexaploid wheats.