Host suitability and fitness-related parameters of Campoletis sonorensis (Hymenoptera: Ichneumonidae) as a parasitoid of the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae)

The seven age-classes of Trichoplusia ni (Hübner) larvae evaluated in this study as hosts of Campoletis sonorensis indicates that early 2nd larval instar (3–5 day-old larvae) of T. ni represents the most suitable host stage for the development of the larval endoparasitoid C. sonorensis. The higher suitability of early 2nd larval instar of T. ni resulted in more parasitised larvae, a higher rate of successful parasitoid emergence, a higher rate of female progeny, and a lower rate of immature parasitoid mortality. The fitness gain of C. sonorensis on late 1st larval instar (2 day-old larvae) and late 2nd larval instar –early 3rd instars (6–8 day-old larvae) stages of T. ni is negatively affected by the trade-offs between the different physiological and behavioral characteristics influencing their suitability as hosts of C. sonorensis.     

Fecundity and life table parameters of Campoletis sonorensis (Hymenoptera: Ichneumonidae), an endoparasitoid of the Cabbage Looper Trichoplusia ni Hübner (Lepidoptera: Noctuidae), under laboratory conditions

The fecundity and life table parameters of Campoletis sonorensis females were measured using thirty 4-day-old Trichoplusia ni larvae daily at 24°C, 60% RH and a photoperiod of 12 h L:12 h D. The mean longevity was 34.5±2.8 days, the mean oviposition period was 22.7±1.9 days, and the mean constant oviposition period and the mean post-oviposition period were 15.9±1.3 and 11.9±2.2 days, respectively. The mean realised fecundity and the mean fertility differed significantly at 66.9±7.8 and 60.4±7.8 parasitoids per female, respectively. The mean sex ratio for the mean oviposition period (23 days) was 0.13±0.07, indicating a highly female biased ratio. The life table parameters were: intrinsic rate of natural increase (r _m), 0.135 female/day; gross reproductive rate (GRR), 50.30; net reproductive rate (R _o), 49.96; finite capacity for increase (λ), 1.14 female/day; mean generation time (T), 28.97 days; doubling time (DT), 5.13; capacity for increase (r _c), 0.33; and cohort generation time (T _c), 11.69. Campoletis sonorensis may be a suitable candidate for a biocontrol program of T. ni populations mostly because the primary selection criterion, r_m , obtained for this parasitoid can be similar to or larger than the rate obtained for T. ni.     

Food web associations and effect of trophic resources and environmental factors on parasitoids expanding their host range into non‐native hosts

Trophic interactions and environmental conditions determine the structure of food webs and the host expansion of parasitoids into novel insect hosts. In this study, we investigate plant–insect–parasitoid food web interactions, specifically the effect of trophic resources and environmental factors on the presence of the parasitoids expanding their host range after the invasion of Chrysodeixis chalcites (Esper) (Lepidoptera: Noctuidae). We also consider potential candidates for biological control of this non‐native pest. A survey of larval stages of Plusiinae (Lepidoptera: Noctuidae) and their larval parasitoids was conducted in field and vegetable greenhouse crops in 2009 and 2010 in various locations of Essex and Chatham‐Kent counties in Ontario, Canada. Twenty‐one plant–host insect–host parasitoid associations were observed among Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), C. chalcites, and larval parasitoids in three trophic levels of interaction. Chrysodeixis chalcites, an old‐world species that had just arrived in the region, was the most common in our samples. The larval parasitoids Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae), Cotesia vanessae (Reinhard), Cotesia sp., Microplitis alaskensis (Ashmead), and Meteorus rubens (Nees) (all Hymenoptera: Braconidae) expanded their host range into C. chalcites changing the structure of the food web. Copidosoma floridanum (Ashmead) (Hymenoptera: Encyrtidae) was the most common parasitoid of T. ni that was not found in the invasive species. Plant species, host abundance, and agro‐ecosystem were the most common predictors for the presence of the parasitoids expanding their host range into C. chalcites. Our results indicate that C. sonorensis, C. vanessae, and C. floridanum should be evaluated for their potential use in biological control of C. chalcites and T. ni.     

Incidence of honeydew in southern pine-hardwood forests: implications for adult parasitoids of the Southern Pine Beetle,Dendroctonus frontalis (Coleoptera: Scolytidae)

The incidence of homopteran honeydew was measured under pines and hardwoods located within 10 Dendroctonus frontalis Zimmermann infestations on the Talladega National Forest (Alabama) during summer, 2000. There were more honeydew droplets beneath hardwood trees compared to pines, but no difference beween D. frontalis infested and uninfested pines. The number of honeydew droplets per tree differed between sampling dates, likely due to the effect of mean weekly temperature and rainfall on homopteran populations. The presence of honeydew on hardwoods may explain why D. frontalis parasitoids forage in areas that lack hosts and suggests that the fecundity of D. frontalis parasitoids may not be limited by adult nutrition.     

Bimodal cue complex signifies suitable oviposition sites to gravid females of the common green bottle fly

Gravid females of the common green bottle fly, Lucilia sericata Meigen (Diptera: Calliphoridae), readily locate recently deceased vertebrates as oviposition sites, particularly when these animals have been injured. We investigated semiochemical and visual cues that mediate attraction of gravid females to fresh rat carrion. Female flies were more strongly attracted to incised rat carrion than to intact carrion. They were also attracted to Porapak Q headspace volatile (HSV) extract of incised rat carrion. Analyzing aliquots of Porapak Q HSV extract by gas chromatographic‐electroantennographic detection revealed nine components [phenol, para‐ and/or meta‐cresol (could not be separated), guaiacol, dimethyl trisulfide (DMTS), phenylacetaldehyde, (E)‐2‐octenal, nonanal, and tetramethyl pyrazine] that consistently elicited responses from blow fly antennae. In laboratory experiments, a synthetic blend of these nine components was as attractive to gravid females as Porapak Q HSV extract, but blend attractiveness was due entirely to DMTS. In both laboratory and field experiments, increasing doses of DMTS attracted increasingly more flies. Coupled with DMTS, carrion‐type color cues (dark red, black) were more effective than bright color cues (white, yellow) in attracting flies. In field experiments, dark traps baited with DMTS captured a total of 214 calliphorid flies (200 L. sericata, 10 Lucilia illustris Meigen, three Calliphora vicina Robineau‐Desvoidy, one Calliphora vomitoria L.), all of which were gravid females. These results support the conclusion that DMTS and dark color represent a bimodal cue complex that signifies suitable oviposition sites to gravid calliphorid females, particularly L. sericata.     

Adult parasitoids of the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), feed on artificial diet on pine boles, pine canopy foliage and understory hardwood foliage

This study examined adult parasitoids of Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae) utilizing an artificial parasitoid food on locations with and without hosts. Eliminade™ was applied to bark on boles of infested pines, to pine canopy foliage and to understory hardwood foliage. Adult parasitoids were collected, identified and dissected to determine the presence of Eliminade™ within their guts. Individuals from eight parasitoid species were collected on pine boles within D. frontalis infestations in the Talladega National Forest (Alabama) in the summer of 1999 and 2000. Mean percentage of parasitoids feeding on Eliminade™ was 62±10% during both summers. Percentage of parasitoids feeding was the same 24 h after Eliminade™ application, regardless of food location or parasitoid species. Seven days later, level of parasitoid feeding on Eliminade™ was insignificant in the pine canopy and hardwood understory. In contrast, percent of parasitoid feeding on Eliminade™ applied to pine boles remained the same between 1 and 7 days of the application. Therefore, not only will adult parasitoids visit and feed on artificial food on pine boles with hosts, but also non-host locations such as pine canopy and understory hardwood foliage. These results have implications for potential sources of adult nutrition for parasitoids of D. frontalis.     

Does host plant quality affect the oviposition decisions of an omnivore?

Optimal oviposition theory predicts a positive relationship between female preference for oviposition hosts and offspring performance. Interspecies effects on oviposition preference have been widely investigated, especially for herbivores. However, intraspecies variation, such as nitrogen content, might also influence female preference for oviposition hosts and subsequent offspring performance. To evaluate this possibility, we investigated the oviposition preference of a zoophytophagous omnivore and the development and survival of its nymphs on a single species of host plant that varied in nitrogen content. In choice and no‐choice experiments without prey, female omnivores were allowed to oviposit on plants that had been fertilized using 4 rates of nitrogen fertilizer (39, 78, 156, and 311 mg/L nitrogen) for 72 h. After 72 h, the most females were found on tomato plants receiving high concentrations of nitrogen fertilizer and more eggs were laid on those plants. First instar nymphs developed more rapidly on high‐nitrogen plants and third instar nymphs developed faster on low‐nitrogen plants. Plant nitrogen did not affect nymph survival to the adult stage, or the probability of survival over time. Although female omnivores did discriminate between potential oviposition hosts based on plant nitrogen, their choices did not significantly impact nymph development or survival. This is the first study to show that intraspecies variation in nitrogen content between plants affects the oviposition preference of female omnivores, but not offspring performance.     

Cannibalism in a Zoophytophagous Omnivore is Mediated by Prey Availability and Plant Substrate

Cannibalism is a dietary option, the frequency of which, in most predator-prey systems, is inversely proportional to the abundance of primary prey. Under conditions of prey scarcity, in food webs involving plant-feeding omnivores, cannibals may choose to feed on either conspecifics or on the continuously-available but less nourishing plant substrate. We tested the effects of prey limitation and plant species on cannibalism in the omnivorous true bug, Dicyphus hesperus. Adult females preyed on first- and fourth-instar, and male conspecifics, and the rate of cannibalism increased under conditions of prey scarcity. Plant species affected cannibalism, with the highest cannibalism occurring on mullein, Verbascum thapsus and chrysanthemum, Chrysanthemum coronarium, and the lowest on tomato, Lycopersicon esculentum. Removal of leaf hairs from mullein reduced the rate of cannibalism. Host plant species affects the rates of cannibalism in D. hesperus and mechanisms other than the plant's value as food may contribute to this effect.     

Diel activity pattern and predation rate of the generalist predator Dicyphus hesperus

Abstract This study examined the diel activity pattern and the effect of diel activity pattern on predation rate and prey finding of Dicyphus hesperus Knight (Heteroptera: Miridae). To determine the diel activity pattern of D. hesperus, starved females were placed on tomato leaflets Lycopersicon esculentum Mill. (Solanaceae) under zero, low, or high light intensities at 02:00, 08:00, and 14:00 h, respectively, and the amount of time spent walking or resting during a 30‐min interval was recorded. Predation rates of D. hesperus females on Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) egg patches were determined under either a L16:D8 (long day) or L8:D16 (short day) diel period. Egg patches were removed from D. hesperus females after either 8 or 16 h of dark or 16 or 8 h of light, and the number of eggs consumed was counted. Dicyphus hesperus females spent more time searching for prey at night than during the day. Females ate eggs at a higher rate during the night than during the day. Overall, D. hesperus females had higher predation rates when reared under a long day diel cycle compared with females reared under a short day diel cycle. More females reared at the L16:D8 diel cycle found the egg patch during the night than during the day. There was no difference in egg patch finding between night and day for females reared at L8:D16. Overall, L16:D8 reared females found more egg patches than females reared at L8:D16. Therefore, D. hesperus females are more active and find and consume prey at a higher rate at night than day.