Comparison of detection ability of learned odors between males and females in the larval parasitoid Microplitis croceipes

Although female parasitic wasps are known to learn to associate odors with hosts and food, the ability of males to learn and detect odors has been neglected. We conducted laboratory experiments to compare the detection ability of learned odors between males and females in the larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). We first conditioned males and females to associate sucrose water with methyl benzoate, 3‐octanone, or cyclohexanone, and then observed their behavior toward various concentrations (40 ng l^?1?4 mg l^?1) of the trained odors. Conditioned male wasps responded as well as female wasps to various concentrations of the three odors. Response times by wasps to these three odors were not significantly different between sexes. For the three odors, response times of both sexes were longer at the intermediate concentrations (40–400 µg l^?1) than the higher or lower concentrations. The present study suggests that M. croceipes males can learn and respond to the three chemicals tested as well as the females, and conditioned males are as sensitive to learned odors as conditioned females. By using their sensitive learning and odor‐detection capabilities, M. croceipes males could search for food sources as efficiently as females under natural conditions.     

Learning of host searching cues by the larval parasitoid Microplitis croceipes

We conducted laboratory experiments using a wind tunnel to determine the effects of prior experience on the learning and retention of learned responses in the larval parasitoid Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). Although most females that had either antennated host frass or oviposited in a host in the presence of vanilla odor, made oriented flight to the odor from downwind in the wind tunnel at 30 min after experience, only those that had oviposited in a host with the odor responded to the odor at 24 h after experience. Females that had oviposited in the non‐natural host beet armyworm (BAW) larva with or without the odor did not respond to the odor at 30 min after experience. These results indicate that an oviposition in the host in the presence of odors strongly affects associative learning and the persistence of learned response to the odors. When females were allowed to antennate host frass in the presence of vanilla and to subsequently oviposit in a host within an interval of 5 min or less, their learned response to vanilla also persisted for 24 h. Similarly, when females were conditioned to link vanilla with host frass and then allowed to make an ovipositor contact with host hemolymph, their learned response persisted for 24 h. However, antennal contact with hemolymph after such conditioning of vanilla with host frass did not improve the persistence of learned response to the odor. These results indicate that ovipositor contact with host hemolymph during oviposition is partially responsible for an increased retention of learned response. Females responded to vanilla 48% of the time at 30 min after antennating host frass without the odor, but their response to the odor significantly decreased after oviposition in a BAW larva subsequent to the antennation of host frass. This result indicates that oviposition in a BAW larva decreases subsequent response to general odors. Based on the results, we discuss the foraging behavior of M. croceipes dependent on learning and subsequent experiences.     

The role of learning in adult food location by the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae)

Wind tunnel experiments were conducted to determine roles of odor learning in food foraging of the larval parasitoid,Microplitis croceipes (Hymenoptera: Braconidae). Females that had neither fed on sucrose water nor experienced any odor and females that had experienced an odor without feeding failed to respond to any odors in a wind tunnel. Most of the females that had fed without an odor also did not respond to odors. However, most of the females that had experienced an odor during feeding on sucrose water flew to the odor. These results indicate that when females experience an odor during feeding, they learn to associate the odor with food and subsequently respond to the odor. As age of females increased, their response to an experienced odor increased, peaked 2 to 5 days after emergence, and then decreased. With an increasing number of odor experiences while feeding, accuracy of females choosing the experienced odor increased. Females that experienced an odor while feeding three to five times chose the experienced odor 90% of the time. When females experienced an odor while feeding five times, the memory of food associated odor lasted at least 2 days. When they experienced food with two odors successively, they could memorize both odors, and multiple experiences did not cause memory interference. Even when females had learned a food-associated odor, their response to the learned odor ceased after several visits on patches containing the odor but no food. Such negative experience may cause switching of food searching to new odors by females.     

Intrinsic competition and its effects on the survival and development of three species of endoparasitoid wasps

In natural systems, pre‐adult stages of some insect herbivores are known to be attacked by several species of parasitoids. Under certain conditions, hosts may be simultaneously parasitized by more than one parasitoid species (= multiparasitism), even though only one parasitoid species can successfully develop in an individual host. Here, we compared development, survival, and intrinsic competitive interactions among three species of solitary larval endoparasitoids, Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae), Microplitis demolitor Wilkinson, and Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), in singly parasitized and multiparasitized hosts. The three species differed in certain traits, such as in host usage strategies and adult body size. Campoletis sonorensis and M. demolitor survived equally well to eclosion in two host species that differed profoundly in size, Pseudoplusia includens (Walker) and the larger Heliothis virescens (Fabricius) (both Lepidoptera: Noctuidae). Egg‐to‐adult development time in C. sonorensis and M. demolitor also differed in the two hosts. Moreover, adult body mass in C. sonorensis (and not M. demolitor) was greater when developing in H. virescens larvae. We then monitored the outcome of competitive interactions in host larvae that were parasitized by one parasitoid species and subsequently multiparasitized by another species at various time intervals (0, 6, 24, and 48 h) after the initial parasitism. These experiments revealed that M. croceipes was generally a superior competitor to the other two species, whereas M. demolitor was the poorest competitor, with C. sonorensis being intermediate in this capacity. However, competition sometimes incurred fitness costs in M. croceipes and C. sonorensis, with longer development time and/or smaller adult mass observed in surviving wasps emerging from multiparasitized hosts. Our results suggest that rapid growth and large size relative to competitors of a similar age may be beneficial in aggressive intrinsic competition.     

Computational modeling and experimental validation of odor detection behaviors of classically conditioned parasitic wasp,Microplitis croceipes

A prototype chemical sensor named Wasp hound® that utilizes five classically conditioned parasitoid wasps, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), to detect volatile odors was successfully implemented in a previous study. To improve the odor‐detecting ability of Wasp Hound®, searching behaviors of an individual wasp in a confined area are studied and modeled through stochastic differential equations in this paper. The wasps are conditioned to 20 mg of coffee when associated with food and subsequently, tested to 5, 10, 20, and 40 mg of coffee. A stochastic model is developed and validated based on three positive behavioral responses (walking, rotation around odor source, and self‐rotation) from conditioned wasps at four different test dosages. The model is capable to reproducing the behaviors of conditioned wasps, and can be used to improve the ability of Wasp Hound® to assess changes in odor concentration. The model simulation results show the behaviors of conditioned wasps are significantly different when tested at different coffee dosages. We conjecture that the searching behaviors of conditioned wasps are based on the temporal and spatial neuron activity of olfactory receptor neurons and glomeruli, which are strongly correlated to the training dosages. The overall results demonstrate the utility of mathematical models for interpreting experimental observations, gaining novel insights into the dynamic behavior of classically conditioned wasps, as well as broadening the practical uses of Wasp Hound. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 31:596–606, 2015     

The role of herbivore‐ and plant‐related experiences in intraspecific host preference of a relatively specialized parasitoid

Parasitoids use odor cues from infested plants and herbivore hosts to locate their hosts. Specialist parasitoids of generalist herbivores are predicted to rely more on herbivorederived cues than plant-derived cues. Microplitis croceipes (Cresson)(Hymenoptera: Braconidae) is a relatively specialized larval endoparasitoid of Heliothis virescens (F.)(Lepidoptera: Noctuidae), which is a generalist herbivore on several crops including cotton and soybean. Using M. croceipes/H. virescens as a model system, we tested the following predictions about specialist parasitoids of generalist herbivores:(i) naive parasitoids will show innate responses to herbivore-emitted kairomones, regardless of host plant identity and (ii) herbivore-related experience will have a greater influence on intraspecific oviposition preference than plant-related experience. Inexperienced (naive) female M. croceipes did not discriminate between cotton-fed and soybean-fed H. virescens in oviposition choice tests, supporting our first prediction. Oviposition experience alone with either host group influenced subsequent oviposition preference while experience with infested plants alone did not elicit preference in M. croceipes, supporting our second prediction. Furthermore, associative learning of oviposition with host-damaged plants facilitated host location. I terestingly, naive parasitoids attacked more soybeathan cotton-fed host larvae in two-choice tests when a background of host-infested cotton odor was supplied, and vice versa. This suggests that plant volatiles may have created an olfactory contrast effect. We discussed ecological significance of the results and concluded that both plant- and herbivore-related experiences play important role in parasitoid host foraging.     

Development of Microplitis croceipes as a biological sensor

Classical conditioning, a form of associative learning, was first described in the vertebrate literature by Pavlov, but has since been documented for a wide variety of insects. Our knowledge of associative learning by insects began with Karl vonFrisch explaining communication among honeybees, Apis mellifera L. (Hymenoptera: Apidae). Since then, the honey bee has provided us with much of what we understand about associative learning in insects and how we relate the theories of learning in vertebrates to insects. Fruit flies, moths, and parasitic wasps are just a few examples of other insects that have been documented with the ability to learn. A novel direction in research on this topic attempts to harness the ability of insects to learn for the development of biological sensors. Parasitic wasps, especially Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), have been conditioned to detect the odors associated with explosives, food toxins, and cadavers. Honeybees and moths have also been associatively conditioned to several volatiles of interest in forensics and national security. In some cases, handheld devices have been developed to harness the insects and observe conditioned behavioral responses to air samples in an attempt to detect target volatiles. Current research on the development of biological sensors with insects is focusing on factors that influence the learning and memory ability of arthropods as well as potential mathematical techniques for improving the interpretation of the behavioral responses to conditioned stimuli. Chemical detection devices using arthropod‐based sensing could be used in situations where trained canines cannot be used (such as toxic environments) or are unavailable, electronic devices are too expensive and/or not of sufficient sensitivity, and when conditioning to target chemicals must be done within minutes of detection. The purpose of this article is to provide a brief review of the development of M. croceipes as a model system for exploring associative learning for the development of biological sensors.     

Influence of maternal age and host deprivation on egg production and parasitization byMicroplitis croceipes [Hym.: Braconidae]

The effect of maternal age and hostHeliothis virescens (F.) deprivation on egg production and allocation byMicroplitis croceipes (Cresson) was determined in the laboratory on 0.5, 1.0, 3.0, 6.0, 9.0, and 12.0 days old parasitoids. In host-deprived parasitoids, newly-emerged (0.5-day old) females produced significantly fewer eggs than older ones; egg production peaked 3 to 6 days after emergence and declined thereafter. However, the number of eggs found in undeprived parasitoids at various ages suggested a cyclical pattern of egg production. The rate of parasitization by host-deprivedM. croceipes was higher in 1.0 to 6.0 days old than in newly-emerged or older females and was correlated strongly with egg production (r=0.93). The first observation on premature larval hatching inM. croceipes was documented.      

Heritable differences in the response of the braconid waspMicroplitis croceipes to volatile allelochemicals

The heritable nature of differential responses by Microplitis croceipes(Cresson) (Hymenoptera: Braconidae) to airborne allelochemicals was investigated. Four isofemale lines were tested for three generations in a flight tunnel. Flight response was found to be strongly dependent on the familial origin, with two highly responsive lines being clearly differentiated from two less responsive ones. Each isofemale line could also be recognized by typical behaviors that suggested that M. croceipesfemales may inherit independent characters of sensory acuity to plant and to host chemicals and of learning ability.     

Species and sexual differences in antennal lobe architecture and glomerular organization in two parasitoids with different degree of host specificity, Microplitis croceipes and Cotesia marginiventris

The endoparasitic wasps (Hymenoptera: Braconidae), Microplitis croceipes (specialist) and Cotesia marginiventris (generalist), are parasitoids of lepidopteran larvae and differ in their degree of host specificity. Recent studies have reported key differences between the two species in the abundance of antennal olfactory sensilla and their response to host-related volatiles. Here, we have compared antennal lobe architecture and glomerular organization in the two parasitoid species by using a combination of axonal tract tracing techniques and confocal microscopy. In M. croceipes, the medial half of the antennal lobe is larger with a greater number of glomeruli compared with the lateral half, whereas in C. marginiventris, the lateral half is larger than the median half. The volume of the antennal lobe is approximately 2.5 times greater in M. croceipes than in C. marginiventris. However, the number of glomeruli per antennal lobe is only slightly higher in M. croceipes (females: 219–222; males: 220–224) than in C. marginiventris (females: 192–194; males: 193–196). A comparison of males and females within each species demonstrated a striking sexual difference in terms of an enlarged glomerulus (macroglomerulus or MG) at the entrance of the antennal nerve and of a complex of 3–4 MG (CMG) in the posterior region of the antennal lobe of males of both species. Being specific to males, both the MG and CMG might be involved in the detection of female-related odor.     

Altered odor‐induced expression of c‐fos and arg 3.1 immediate early genes in the olfactory system after familiarization with an odor

In adult rats, repeated exposure to an odorant, in absence of any experimentally delivered reinforcement, leads to a drastic decrease in mitral/tufted (M/T) cell responsiveness, not only for the familiar odor but also for other novel odors. In the present study, using two different and complementary in situ hybridization methods, we analyzed the effect of familiarization with an odorant on c‐fos and arg 3.1 mRNA expression levels, and we examined the odor specificity of this effect. Odor exposure induces a specific increase in c‐fos and arg 3.1 expression in some particular olfactory bulb quadrants. Previous familiarization with the test odor results in a decreased expression of both IEGs in these quadrants, leading to the alteration of the odor‐specific pattern of c‐fos and arg 3.1 expression. In contrast, this odor‐specific pattern is not affected when different odors are used for familiarization and test. Similarly, an odor‐specific familiarization effect leading to a reduced c‐fos and arg 3.1 expression was also detected in the cingulate cortex and in the anterior piriform cortex. These results support our hypothesis that the decrease in M/T cell responsiveness following a preceding familiarization with an odorant may be related to a particular form of synaptic plasticity involving changes at the genomic level, and reveals further insight in olfactory information processing and the cellular mechanisms underlying familiarization in the olfactory system. © 2002 Wiley Periodicals, Inc. J Neurobiol 52: 61–72, 2002     

Comparative flight behavior of parasitoids Campoletis sonorensis and Microplitis croceipes

Flight behavior of parasitoids Microsplitis croceipes Cresson (Braconidae) and Campoletis sonorensis (Cameron) (Ichneumonidae) was examined in a wind tunnel. Both species exhibited odor directed, oriented flights to cotton, although flight frequency was related to variation in wind velocity or differential cotton volatile emission with changes in wind velocity, or both. Flight frequency at constant wind velocity was affected by illumination. Microplitis croceipes was attracted to the wind borne odor of Heliothis virescens (F.) frass and larvae, whereas C. sonorensis was not. Possible interaction of the wind borne odors from the habitat and host is suggested for parasitoids.

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Résumé Le comportement de vol de M. croceipes Cres. (Hym. Braconidae) et de C. sonorensis Cam. (Hym. Icheumonidae) a été étudié en olfactométrie dans un tunnel à vent. Les femelles des deux espèces, et non les mâles, ont un vol orienté par l'odeur des feuilles fraîches de coton (Gossypium hirsutum L.). La fréquence d'envol est liée aux changements de vitesse du vent, aux variations d'émissions, par le cotonnier, des substances volatiles, en fonction de la vitesse du vent, ou aux deux. La fréquence d'envol à vitesse de vent constante dépend de l'éclairage. La fréquence d'envol de C. sonorensis augmente avec des intensités lumineuses relativement fortes et diminue avec des intensités relativement faibles. L'inverse est observé avec M. croceipes. Le vent chargé d'odeurs de larves ou d'extréments d'Heliothis virescens F., attire M. croceipes et non C. sonorensis. Nous suggérons une éventuelle interaction des odeurs portées par le vent et provenant de l'habitat et de l'hôte.

     

Roles of odor, taste, and toxicity in the food preferences of lambs: implications for mimicry in plants

In the traditional sense, food ingestion consists of prehending, masticating, swallowing, and digesting plant matter. It is also possible to ingest plants without eating them. Volatile compounds are inhaled directly into the lungs and transported from the lungs into the bloodstream. Volatiles in high concentrations could presumably produce toxicosis, without an herbivore ever ingesting a plant in the customary sense. Volatile compounds may be aposematic, serving to warn potential predators of toxins in plants. We conducted three experiments to explore the roles of odor, taste, and toxicity in the food preferences of lambs. The first experiment determined if brief exposure to a novel odor followed by lithium chloride (LiCl)‐induced toxicosis caused lambs to avoid a familiar food that contained the odor. Lambs that sniffed coconut‐flavored barley and then received LiCl subsequently ate less coconut‐flavored barley than lambs that did not receive LiCl. The second experiment determined if lambs were deterred from eating a familiar food by the odor of Astragalus bisulcatus. A. bisulcatus is a malodorous (to humans) sulfur‐containing herb considered unpalatable and toxic. Neither odor nor intraruminal infusions of A. bisulcatus deterred lambs from feeding. The third experiment also determined how the degree of familiarity with the odor of A. bisulcatus, along with toxicosis, influenced preference of lambs for food with or without the odor of A. bisulcatus. Lambs with 8 d exposure to the odor but not given LiCl ate similar amounts of food, with and without the odor of A. bisulcatus, whereas lambs given LiCl showed a mild aversion to food with the odor during testing. Lambs with 1 d exposure to the odor but no LiCl ate similar amounts of food, with and without the odor, whereas lambs given LiCl showed a strong but transient aversion to food with the odor. Collectively, these findings show that lambs responded strongly to novel odors, but their response was transient and depended on the postingestive consequences of toxins and nutrients associated with odor inhalation. Thus, we submit that odor alone, in the absence of toxicosis or nociception, is not a deterrent to herbivores that continually sample foods and adjust intake based on the postingestive effects of toxins and nutrients. It also is unlikely that non‐toxic plants can mimic the odors of toxic plants to avoid herbivory (Batesian mimicry), unless the odors are indistinguishable by herbivores, again because herbivores constantly sample foods.     

Relaxin‐3 receptor (Rxfp3) gene deletion reduces operant sucrose‐ but not alcohol‐responding in mice

The pervasive use of refined sugars in highly accessible, palatable foods and persistent exposure to reinforcing food‐associated cues has contributed to overconsumption of sugar‐rich diets and the current obesity epidemic in Western society. We have shown previously that brain relaxin‐3 mRNA levels positively correlate with sucrose and alcohol intake, and that central antagonism of relaxin‐3 receptors (RXFP3) attenuates alcohol self‐administration and alcohol‐seeking in rats, but food‐seeking behaviour and palatable food consumption in mice. To further examine the relationship between motivated appetitive behaviours and relaxin‐3/RXFP3 signalling, we investigated the effect of Rxfp3 gene deletion in C57BL/6J mice on sucrose and alcohol self‐administration and cue‐induced reinstatement (RNST) of sucrose‐ and alcohol‐seeking. Acquisition and maintenance of sucrose and alcohol self‐administration was assessed in male wild‐type (WT) and Rxfp3 knockout (KO) (C57BL/6J^{RXFP3TM1/DGen}) littermate mice using fixed ratio (FR) schedules of reinforcement. Mice were subsequently challenged with a progressive ratio (PR) test to measure motivation and, following extinction training, re‐exposed to reward‐associated cues to evaluate RNST of active lever‐responding. Wild‐type and Rxfp3 KO mice displayed similar acquisition of FR1 sucrose self‐administration, but Rxfp3 KO mice responded less when the instrumental requirement was increased to FR3. These mice also showed a lower breakpoint for sucrose and attenuated cue‐induced RNST of sucrose‐seeking. Notably, no marked genotype differences in alcohol‐responding were observed. In mice, endogenous relaxin‐3/RXFP3 signalling promotes self‐administration of sucrose under high response requirements and cue‐induced RNST of sucrose‐seeking, but does not apparently regulate motivation to consume alcohol or alcohol‐seeking behaviour.     

Longevity-fertility trade-offs in the tephritid fruit fly, Anastrepha ludens, across dietary-restriction gradients

Although it is widely known that dietary restriction (DR) not only extends the longevity of a wide range of species but also reduces their reproductive output, the interrelationship of DR, longevity extension and reproduction is not well understood in any organism. Here we address the question: ‘Under what nutritional conditions do the longevity‐enhancing effects resulting from food restriction either counteract, complement or reinforce the mortality costs of reproduction? To answer this question we designed a fine‐grained DR study involving 4800 individuals of the tephritid fruit fly, Anastrepha ludens, in which we measured sex‐specific survival and daily reproduction in females in each of 20 different treatments (sugar : yeast ratios) plus 4 starvation controls. The database generated from this 3‐year study consisted of approximately 100 000 life‐days for each sex and 750 000 eggs distributed over the reproductive lives of 2400 females. The fertility and longevity‐extending responses were used to create contour maps (X‐Y grid) that show the demographic responses (Z‐axis) across dietary gradients that range from complete starvation to both ad libitum sugar‐only and ad libitum standard diet (3 : 1 sugar : yeast). The topographic perspectives reveal demographic equivalencies along nutritional gradients, differences in the graded responses of males and females, egg production costs that are sensitive to the interaction of food amounts and constituents, and orthogonal contours (equivalencies in longevity or reproduction) representing demographic thresholds related to both caloric content and sugar : yeast ratios. In general, the finding that lifespan and reproductive maxima occur at much different nutritional coordinates poses a major challenge for the use of food restriction (or a mimetic) in humans to improve health and extend longevity in humans.     

Electroantennogram responses of a parasitic wasp, Microplitis croceipes, to host-related volatile and anthropogenic compounds

The parasitic wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) showed its own characteristic electroantennogram (EAG) response profiles to 13 host‐related (cis‐3‐hexenol, α‐pinene (R)‐(+)‐limonene (S)‐(–)‐limonene, trans‐β‐ocimene (±)‐linalool, (–)‐trans‐caryophyllene, α‐humulene, nerolidol, trans‐nerolidol, cis‐nerolidol, methyl jasmonate and indole) and four anthropogenic (2‐diisopropylaminoethanol, 2,2′‐thiodiethanol, 2‐methyl‐5‐nitroaniline and cyclohexanone) volatile compounds. These profiles were similar between males and females except for 2‐diisopropylaminoethanol, which elicited significantly larger EAG responses in males. Among the compounds tested, cis‐3‐hexenol, linalool and cyclohexanone elicited the largest EAG responses. EAG responses were not influenced by the age of wasps between 1 and 13 days after emergence. EAG responses were dose‐dependent, and highly EAG‐active compounds elicited significant EAG responses with less than 10 μg of the compounds at source. Quantification of compounds released from an odour cartridge indicates that release rate is highly dependent on the chemical nature of stimuli, showing up to 10 000‐fold differences in the amount released between different compounds when the same amount was loaded in the odour cartridge. Wasps having undergone a behavioural training regime to be attracted to either cyclohexanone or methyl jasmonate did not show any differences in EAG responses from those of untrained wasps.     

Effects of methoxyfenozide-treated surfaces on the attractiveness and responsiveness of adult leafrollers

Abstract The attractiveness and responsiveness of the adult redbanded leafroller, Argyrotaenia velutinana (Walker), and obliquebanded leafroller, Choristoneura rosaceana (Harris), exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide were investigated in wind tunnel and orientation tube assays. For both species, when males were exposed to water‐treated surfaces for 48 h, and regardless of what treatment surfaces the females had been exposed to, the mean percentage recaptures of such treated males in the wind tunnel assays were always significantly greater than the recaptures of males that had been exposed to methoxyfenozide. However, exposure to surfaces treated with surfactant (Latron B‐1956) also negatively affected the responsiveness (or attractiveness) of both moth species. In the orientation tube assays, males exposed to methoxyfenozide‐treated surfaces always had significantly lower mean levels of individuals exhibiting sexual excitability, and the mean distances traveled upwind, regardless of females’ exposure. In addition, exposure to surfactant‐treated surfaces did not affect mean levels of sexual excitibility and distances traveled upwind. The two bioassays demonstrated that male A. velutinana and C. rosaceana exposed to methoxyfenozide‐treated surfaces were not as responsive to calling females (treated and non‐treated) as were the non‐treated males. Conversely, females exposed to methoxyfenozide‐treated surfaces were just as attractive to non‐treated males as water‐treated females. It appears that a male's ability to respond to a calling female is more negatively affected by the ecdysone agonist than a female's ability to call and attract males.     

Intrinsic and extrinsic competitive interactions between two larval parasitoids of Heliothis virescens

1. Competition between parasitoid species may be a key factor in the community dynamics of plant–herbivore-parasitoid systems and is an important consideration in the selection and management of effective biological control agents. 2. Interspecific competition can occur between adult parasitoids searching for hosts (extrinsic competition) and between multiple parasitoid larvae developing within a single host individual (intrinsic competition). A model system comprising the lepidopteran pest Heliothis virescens and two key hymenopteran endoparasitoids, Microplitis croceipes and Cardiochiles nigriceps, was employed to explore parasitoid host-location strategies and the consequences of intrinsic and extrinsic competitive interactions between parasitoid species. 3. The less specialised of the two parasitoids, M. croceipes, was found to have a shorter hatching time and to dominate intrinsic competition, except when its oviposition followed that of the more specialised parasitoid, C. nigriceps, by 16 h or more. This interval corresponded to the differential in hatching time between the two species. 4. Cardiochiles nigriceps, however, displayed superior host-searching efficiency that may compensate for its disadvantage in intrinsic competition. This parasitoid was more effective at detecting host infestation sites via airborne odours and at locating and attacking early instar host larvae than was M. croceipes.     

Disruptive Sublethal Effects of Insecticides on Biological Control: Altered Foraging Ability and Life Span of a Parasitoid after Feeding on Extrafloral Nectar of Cotton Treated with Systemic Insecticides

Predictions in integrated pest management on the compatibility of an insecticide with biological control often are based on incomplete screening tests. While measuring levels of mortality from direct insecticide exposure is a very common screening method, possible sublethal effects as a result of either direct or indirect insecticide exposure remain relatively unknown. The impact of sublethal effects on the success of biological control can be as deleterious as mortality. Here, we report the reduced host foraging ability and longevity of the parasitoid Microplitis croceipes Cresson (Hymenoptera: Braconidae) after feeding on extrafloral nectar from cotton (Gossypium hirsutum L., Malvaceae) plants that were treated with systemic insecticides. The insecticides used in this study are regularly applied in cotton-growing areas in the United States. For all tested insecticides, longevity of M. croceipes females that fed on nectar from cotton was affected for at least 10 days after plants were treated with insecticides. Moreover, the parasitoid's host foraging ability was severely affected for periods ranging from 2 days (imidacloprid) to 18 days (aldicarb) after insecticide application. The consequences of these sublethal effects on the success of biological control are discussed.     

Embryo and early larval stages of the Humboldt Current krill Euphausia mucronata (Crustacea: Euphausiacea)

The Humboldt Current krill, Euphausia mucronata (Crustacea: Euphausiacea), is an endemic and keystone species in the food web of this highly productive eastern border current ecosystem. The morphology and ontogeny of E. mucronata is known from calyptopis I to the adult phase, but the embryonic and early‐life stages (nauplius and metanauplius) of this broadcast spawning species are unknown. We describe the morphology and development time of these life stages to complete the knowledge of its life cycle. Embryos were obtained from purple‐gonad gravid females collected off Dichato, central Chile, during November 2012. Eight gravid females (mean=16 mm total length) were incubated in seawater at 12°C under laboratory conditions. The average development time from single‐cell embryos to the metanauplius stage was 2.2 d and hatching occurred between 20 and 25 h. The average growth rate was 0.35 mm d^?1 from the late limb bud to the metanauplius stage (range=0.21–0.48 mm d^?1). Embryos of E. mucronata had a mean chorion diameter of 0.460 mm, embryo diameter of 0.343 mm, and perivitelline space of 0.056 mm. Our biological information reported here constitutes a baseline for future ecological studies on distribution and temporal variability of spawning activity and reproductive strategies of E. mucronata in the highly variable and productive Humboldt Current ecosystem.