EFFECT OF HOST-LARVAL DIET ON THE HOST ACCEPTANCE AND HOST SUITABILITY OF THE EGG PARASITOID Telenomus remus NIXON (Hymenoptera: Scelionidae) ON Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae)

Effect of host-larval diet on the host acceptance and host suitability of the egg parasitoid Telenomus remus Nixon (Hymenoptera: Scelionidae) on Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae). The life history of parasitoids is an important factor that can determine their ability to attack a host. The type of food consumed by the host can affect the ability of parasitoids such as host searching behavior, host suitability and host acceptance. In this research, we evaluate the effect of the S. frugiperda larvae diet on its suitability of the eggs produced by the adults for the egg parasitoid Telenomus remus. The research was studied on two types of egg masses of S. frugiperda that obtained from the moths that fed with natural or artificial diet during their larval stages. Parasitoid was reared from both types of hosts. An egg mass consisting of 50 S. frugiperda eggs from both types of hosts was exposed to one egg parasitoid female for 24 hours. S. frugiperda eggs then were reared until the parasitoid adult emerged. Each experiment was repeated 20 times. Host acceptance was observed through the host parasitism rate and its parasitization. Meanwhile, the host suitability was observed through the sex ratio of the emerging parasitoids. The results showed that S. frugiperda eggs reared using artificial diet had a higher parasitism rate (99.33%) than those of natural diet (82.53%). In contrast, the level of parasitization of S. frugiperda eggs reared using natural diet was higher (78.30%) than those of artificial diet (48.34%) because the number of emerging T. remus from S. frugiperda eggs reared using natural diet was also higher than those of artificial diet. However, the sex ratio (F:M) of emerging T. remus from S. frugiperda eggs reared using both of diet was female biased.

Host suitability of summer cover crops to Meloidogyne arenaria, M. enterolobii, M. incognita and M. javanica

Summary Cover crops can be a useful tool for managing plant-parasitic nematodes provided they are poor or non-hosts for the target nematode species. A glasshouse experiment was done to determine the host status of four common cover crops in Florida, sunn hemp, cowpea, sorghum sudangrass and sunflower, to pure populations of four common tropical root-knot nematode (RKN) species Meloidogyne javanica (Mj), M. incognita (Mi), M. enterolobii (Me) and M. arenaria (Ma). Tomato was included as a susceptible control. Eight weeks after nematode inoculation (WAI), tomato showed the highest root gall damage for all tested RKN species, with gall indices (GI) between 7 (Ma) and 8.5 (Me) and reproduction factor (RF) ranging from 20 (Ma) to 50 (Mj). No visible root galls were observed for any of the RKN species on sunn hemp and sorghum sudangrass at 8 WAI. However, Mj and Mi were able to reproduce slightly on sorghum sudangrass (RF = 0.02 and 0.79, respectively). Sunflower and cowpea were infected by all four tested RKN species, but host suitability varied. Sunflower root galling ranged from 1.1 (Me) to 4.5 (Mj) and RF = 3.2 (Me) to 28.7 (Mj), while cowpea root galling ranged from 0.6 (Mi) to 5.1 (Me) and RF = 0.8 (Mi) to 67.3 (Mj). Sunn hemp and, to a lesser extent, sorghum sudangrass were poor hosts to all four tested RKN species. Sunflower was a good host to all RKN species, but root gall damage and RF were lowest for Me. Cowpea was a good host to Mj, Me and Ma, but a poor host to Mi. Our results confirm and stress the importance of RKN species identification when selecting cover crops as an RKN management strategy.

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.

Host Suitability for Crapemyrtle Bark Scale (Acanthococcus lagerstroemiae) Differed Significantly among Crapemyrtle Species

Crapemyrtle bark scale (CMBS, Acanthococcus lagerstroemiae), an invasive polyphagous sap-sucking hemipteran, has spread across 14 states of the United States since 2004. The infestation of CMBS has negatively impacted the flowering of ornamental plants and even the fruiting of some crops. Host identification is critical for determining potential risks in ecosystems and industries and helps develop strategic management. A host confirmation test was performed over 25 weeks using six Lagerstroemia species (L. caudata, L. fauriei ‘Kiowa’, L. indica ‘Dynamite’, L. limii, L. speciosa, and L. subcostata) and California loosestrife (Lythrum californicum). The 25-week observations confirmed all tested plants as the hosts. The repeated measures of analysis of variance (ANOVA; Tukey’s HSD, α = 0.05) indicated that the average number of CMBS females differed significantly between L. limii and L. speciosa. The highest number of the females observed on L. limii was 576 ± 25 (mean ± SE) at 17 weeks after inoculation (WAI), while the highest number was 57 ± 15 on L. speciosa at 19 WAI. In addition, L. subcostata and L. speciosa had significantly high and low numbers of males, respectively, among the Lagerstroemia species. Our results suggest that L. speciosa could be incorporated in developing new cultivars with low CMBS suitability.

Host suitability of Trichoplusia ni and Chrysodeixis chalcites (Lepidoptera: Noctuidae) for native and nonnative parasitoids expanding their host range

We evaluated the host suitability and related traits of Trichoplusia ni Hübner (Lepidoptera: Noctuidae) and Chrysodeixis chalcites Esper (Lepidoptera: Noctuidae), which is nonnative in North America, for the native parasitoids Campoletis sonorensis Cameron (Hymenoptera: Ichneumonidae) and Copidosoma floridanum Ashmead (Hymenoptera: Encyrtidae), and the nonnative parasitoid Cotesia vanessae Reinhard (Hymenoptera: Braconidae). For the larval parasitoid C. sonorensis and C. vanessae trials, three-day-old larvae of both hosts were used, whereas one-day-old eggs of both hosts were used for the egg–larval parasitoid C. floridanum trial. For suitability parameters on each host exposed separately to each of the three parasitoid species, we measured parasitoid emergence (parasitoid success), parasitoids that did not emerge (parasitoid cocoon mortality), the proportion of male offspring (parasitoid sex ratio), hosts that developed into moths (host success), hosts that died without developing into moths or producing a parasitoid (host mortality), parasitoids emerging from cocoon masses (brood size), and the developmental times of parasitoids and hosts. For C. sonorensis, the native host and the nonnative host were found to be similarly suitable. For C. vanessae, the native host was more suitable than the nonnative host. For C. floridanum, the native host was suitable, whereas the nonnative host was not; however, sublethal effects on both the native and nonnative hosts were observed. The differential suitability of the hosts observed in this study contributes to the understanding of this measure as a dynamic factor in the expansion of parasitoids into novel host species.

Quantitative Trait Loci Associated with Rotylenchulus reniformis Host Suitability in Soybean

Reniform nematode (Rotylenchulus reniformis) is a yield-limiting pathogen of soybean (Glycine max) in the southeastern region of the United States. A population of 250 recombinant inbred lines (RIL) (F2:8) developed from a cross between reniform nematode resistant soybean cultivar Forrest and susceptible cultivar Williams 82 was utilized to identify regions associated with host suitability. A genetic linkage map was constructed using single-nucleotide polymorphism markers generated by genotyping-by-sequencing. The phenotype was measured in the RIL population and resistance was characterized using normalized and transformed nematode reproduction indices in an optimal univariate cluster analysis. Quantitative trait loci (QTL) analysis using normalized phenotype scores identified two QTLs on each arm of chromosome 18 (rrn-1 and rrn-2). The same QTL analysis performed with log10(x) transformed phenotype data also identified two QTLs: one on chromosome 18 overlapping the same region in the other analysis (rrn-1), and one on chromosome 11 (rrn-3). While rrn-1 and rrn-3 have been reported associated with reduced reproduction of reniform nematode, this is the first report of the rrn-2 region associated with host suitability to reniform nematode. The resistant parent allele at rrn-2 showed an inverse relationship with the resistance phenotype, correlating with an increase in nematode reproduction or host suitability. Several candidate genes within these regions corresponded with host plant defense systems. Interestingly, a characteristic pathogen resistance gene with a leucine-rich repeat was discovered within rrn-2. These genetic markers can be used by soybean breeders in marker-assisted selection to develop lines with resistance to reniform nematode.