The transgenerational consequences of maternal parasitism for aphid life history and suitability for subsequent parasitism.

Aphids parasitized in later instars can give birth to several nymphs before their reproduction is curtailed by the developing parasitoid. We examined the life histories of Aphis fabae Scopoli born to mothers parasitized by Lysiphlebus fabarum Marshall, and their suitability as subsequent hosts, to test the 'fecundity compensation' hypothesis. Maternal parasitism negatively impacted life history parameters, resulting in reduced estimates of population increase (rm, R0, and λ), and increased generation time (GT) and doubling time (DT). These impacts were greater when the larva developing in the mother turned out to be female rather than male, and greater still when mothers were superparasitized. Maternal parasitism produced aphids with shorter hind tibia (HTL), at birth and at maturity, but their developmental time was unaffected. Although female L. fabarum readily accepted such aphids for oviposition, rates of mummification and wasp emergence were lower, and more so when the maternal parasitoid was female. The resulting parasitoids took longer to develop than progeny from control wasps, had shorter HTLs, lower egg loads, smaller eggs, and produced fewer mummies with lower rates of adult emergence, all differences that were more pronounced when the maternal parasitoid was female. The progeny of these wasps exhibited similar impairments to these biological parameters as their parents, demonstrating that the negative impacts of development in maternally parasitized hosts extended for at least two generations. Thus, our results do not support fecundity compensation, but suggest that any benefits of post-parasitism reproduction will be offset by reduced fitness in both aphid progeny and the parasitoids that develop in them.

Functional Response of Hyperaspis polita (Coleoptera, Coccinellidae) to the Recently Invaded Mealybug Phenacoccus solenopsis (Hemiptera, Pseudococcidae).

Hyperaspis polita Weise is the major predator of Phenacoccus solenopsis Tinsley in southwestern Iran. The functional response of fourth instar larva, adult female and male of the ladybird, H. polita, preying upon different stages of the mealybug P. solenopsis was evaluated. All stages of H. polita exhibited type II functional responses against all stages of P. solenopsis with an exception that the functional response of the adult female stage of H. polita to first instar P. solenopsis nymphs was type III. Changing prey and predator stages did not result in significant differences in attack rates. Handling times, however, differed for different prey and predator stages. This parameter was the shortest for any stage of predator fed on first instar P. solenopsis nymphs and was estimated to be 0.1100, 0.1868, and 0.2939 h for fourth instar larval stage, adult females and males, respectively. Also, the handling time was the shortest for the fourth instar larval stage followed by adult females and males to different prey stages. Maximum predation rate (T/Th) decreased as P. solenopsis developed from one life stage to another, the lowest estimated value being obtained by feeding on adult female mealybug and the fourth instar larval stage was the most predatory. According to these results, the feeding potential of H. polita is noticeable with the fourth larval instar stage being considered the most efficient predatory stage for use in biological control programs. Further field-based studies are needed, however, before a comprehensive estimation of the biocontrol abilities of H. polita toward P. solenopsis can be made.

Cornicle secretions by Aphis fabae (Hemiptera: Aphididae) result in age-dependent costs and improved host suitability for Lysiphlebus fabarum (Marshall) (Hymenoptera: Braconidae).

We examined the life history consequences of cornicle secretion by Aphis fabae Scopoli in second and fourth instars, and its effects on host suitability for its parasitoid, Lysiphlebus fabarum (Marshall). Cornicle secretion did not affect aphid fecundity, but secretion in the second instar enhanced life table parameters, whereas secretion in the fourth instar affected them negatively, suggesting a higher cost of secretion in later instars. Secretion in either instar improved host suitability for L. fabarum. Although control and treated aphids were parasitized at similar rates, and with similar success, wasps developed faster and emerged as larger adults in aphids that had secreted, regardless of instar. Transgenerational effects were also evident. Progeny emergence was higher when parental wasps developed in fourth instars than in seconds, whether aphids secreted or not, and progeny were larger when parental hosts secreted in the second instar, but not in the fourth. Secreting fourth instars were preferred to controls by L. fabarum females in choice tests, but not secreting second instars, and fourth-instar secretion improved wasp emergence. When control aphids were attacked, second instars were more likely to secrete than fourth instars, whereas the latter were more likely to kick the parasitoid. Cornicle secretion reduced the probability of subsequent secretion events and the frequency of other aphid defensive behaviors, indicating energetic tradeoffs among defensive tactics. Overall, our results revealed that cornicle secretion by immature A. fabae exacts both physiological and behavioral costs and results in improved host suitability for its parasitoid.

Gamma irradiation on canola seeds affects herbivore-plant and host-parasitoid interactions.

As an agricultural modernization, gamma irradiation is an important method for enhancing crop yield and quality. Nevertheless, its use can alter other plant traits such as nutrition and resistance to different biotic/abiotic stresses that consequently affect plant-insect interactions. A tritrophic system was utilized based on two canola mutant lines produced through gamma irradiation (RGS 8-1 and Talaye 8-3). Plutella xylostella (L.), as a worldwide pest of Brassicaceae and Cotesia vestalis (Holiday) as a key biocontrol agent of P. xylostella were examined for the potential indirect effects of canola seed irradiation on the experimental insects' performance when acting on the respective mutant lines. This study showed that physical mutation did not affect plant nitrogen and herbivore-damaged total phenolics; however, phenolic compounds showed greater concentration in damaged leaves than undamaged leaves of both mutant and control plants. The relative growth rate and pupal weight of P. xylostella reared on RGS 8-1 were significantly higher than those reared on the control RGS. There was no significant difference by performance parameters of the parasitoid, C. vestalis, including total pre-oviposition period, adult longevity, adult fresh body weight of males and females, pupal weight, forewing area, and total longevity of both sexes on tested canola cultivars in comparison with their mutant lines. Life table parameters of C. vestalis on mutant lines of both cultivars, RGS and Talaye, were not significantly different from their control treatments. Comprehensive studies should be conducted to find out the mechanisms under which gamma rays affect plant-insect interactions.

The persistence toxicity of three insecticides against adult of a thelytokous parasitoid, Lysiphlebus fabarum (Hymenoptera: Aphidiidae).

In order to investigate the effects of three insecticides on three day-old L. fabarum females (Hymenoptera: Aphidiidae), the parasitoid of Aphis fabae, an experiment was carried out using IOBC/wprs method. Persistence toxicity of insecticides has been evaluated in the semifield condition. The trials were laid out in randomized complete block design (RCBD) with 3 replicates and an untreated check. The insecticides abamectin 1.8 EC, imidacloprid 350 SC, and pymetrozine 25 WP were used at recommended field rates. The insecticides were applied on broad bean foliage using a hand sprayer, until run-off. Contact toxicity of semi field-aged residues of insecticides on adult parasitoids was evaluated using the cage-method. The mortality of adult parasitoid, after 24 h contact with 1-day old residues of abamectin, imidacloprid and pymetrozine were 53, 90 and 57%, respectively. After 5 days the effect of residues decreased so that the adult mortality diminished to 28, 77 and 18% for mentioned above insecticides. 16-day old residues lead to 9, 22 and 14%; and 30-day old residues lead to 0, 3 and 1% mortality for these insecticides, respectively. Based on this study, abamectin and pymetrozine with persistence less than 5 d are classified as short lived (Class A) and imidacloprid with persistence between 5 to 15d, classified as slightly persistent (Class B) compounds.

Predictors of conversion to sinus rhythm using ibutilide for atrial fibrillation or flutter.

To determine what factors can predict conversion to sinus rhythm, we retrospectively studied 201 consecutive patients who received ibutilide for treatment of atrial fibrillation or flutter. On multivariate analysis, the following factors were significantly associated with conversion: recent onset of arrhythmia, an underlying atrial flutter rhythm, lack of a history of congestive heart failure, and lack of concomitant digoxin therapy.

Cryoablation of incessant ventricular tachycardia: case report and long-term follow-up.

We report the case of a 52-year-old man who had incessant ventricular tachycardia despite treatment with antiarrhythmic agents. Placement of an implantable cardioverter/defibrillator, radiofrequency ablation, and antitachycardia pacing were ineffective. He underwent intraoperative arrhythmia mapping and cryoablation at our institution. Eighteen months later, he remained free of arrhythmia. He was in New York Heart Association functional class II with an ejection fraction of 30%.