Self-/conspecific discrimination and superparasitism strategy in the ovicidal parasitoid Echthrodelphax fairchildii （Hymenoptera： Dryinidae）

Superparasitism in solitary parasitoids results in fatal competition between the immature parasitoids, and consequently only one individual can emerge. In the semisoli- tary ovicidal parasitoid Echthrodelphaxfairchildii （Hymenoptera： Dryinidae）, 2 adults can emerge under superparasitism with a short interval （〈24 h） between the first and second ovipositions. We determined the female parasitoid＇s behavioral responses under self- and conspecific superparasitism bouts with first-to-second oviposition intervals of 〈2 h. The self- and conspecific superparasitizing frequencies increased up to an oviposition interval of 0.75 h, with the former remaining lower than the latter, particularly for oviposition intervals of _〈0.25 h, suggesting the existence of self-/conspecific discrimination. The superparasitizing frequency plateaued for oviposition intervals of _〉0.75 h, with no dif- ference between self- and conspecific superparasitism. The ovicidal-probing frequency did not differ under self- and conspecific superparasitism, and was usually 〈20%. The females exhibited no preference for the oviposition side （i.e., ovipositing on the side with or without the first progeny） and almost always laid female eggs for any oviposition in- terval under self- and conspecific superparasitism. The sex ratio was not affected by the type of superparasitism, oviposition sides, or the occurrence of ovicidal probing. These observed results about the oviposition side, ovicidal probing, and sex ratios differed from the predictions obtained assuming that the females behave optimally. Possible reasons for the discrepancies are discussed： likely candidates include the high cost of selecting oviposition sides and ovicidal probing, and, for the sex ratio, the low frequency of encountering suitable hosts before superparasitism bouts.     

Circadian rhythms of feeding, oviposition, and emergence of the boll weevil （Coleoptera： Curculionidae）

Circadian rhythm of feeding, oviposition, and emergence of boll weevil adults were determined at five different photophases （24, 14, 12, 10, and 0 hours） and a constant 27℃ temperature, 65% RH in the laboratory. Squares from Petri dishes, where they were exposed to boll weevil females, were removed and examined for feeding and oviposition punctures every 4 hours during daylight （0700-1900 h） and every 12 h at night （1900-0700 h） over eight consecutive days. Cohorts of randomly selected egg-punctured squares were sampled from ovipositing females at 0700, 1100, 1500, and 1900 during 24 hours and under different photophase treatments, and maintained in Petri dishes at 27 ＋ I℃, 65% RH. Dishes were observed twice daily （1900 and 0700 h） for adults emerging at day or night. Circadian rhythm of oviposition was not affected by the length of the photophase. The boll weevil has round-the-clock circadian rhythm of oviposition, with a daytime preference. We observed that 82.4%-86.0% of the boll weevil eggs were deposited between 0700 and 1900 h, and 14.0%-17.6% between 1900 and 0700 h during a 24-h period. Feeding of boll weevil females in photoperiods 24：0 h （complete light） and 0：24 h （complete darkness） did not significantly change between 0700-1900 h versus 1900-0700 h, while the d .ally cycle of light and darkness in other photoperiods significantly increased the feeding punctures from 0700-1900 compared with 1900-0700 h. The circadian rhythm of emergence depended significantly on the time of oviposition and the length of the photophase. Investigation of boll weevil circadian rhythm provides a better understanding of boll weevil ecology and reveals potential weak links for improving control technologies targeting their reproductive strategies.     

Seasonal changes of resistance to fenvalerate and cypermethrin in the larval parasitoid Cotesia plutellae （Hymenoptera： Braconidae）

The seasonal changes of insecticide resistance and stability in hymenopteran Cotesia plutellae, collected from Jianxin, Fuzhou-City, and Shangjie, Minhou-County, Fujian, China, were assessed by using a dry residual film method. The resistance to two insecticides in the field populations of C. plutellae was not stable under insecticide-free conditions in the insectarium. Compared with susceptible F11 progeny of C. plutellae in the insectarium, the resistance ratios （RR） in F0 parents were 18.4 for fenvalerate and 11.4 for cypermethrin based on LC50 at 9 hours, and 32.8 for fenvalerate and 28.5 for cypermethrin based on LC50 at 24 hours when the parasitoids were left in contact with the insecticides for 1 hour and mortalities were recorded at 9 and 24 hours, respectively. However, the RR in a field population of C. plutellae were 9.2 for fenvalerate and 12.7 for cypermethrin, if the parasitoids were left in contact with the insecticides for 24 hours. The resistances to the two pyrethroids in other field populations collected from Jianxin and Shangjie from November 2000 and July 2004 were also determined. Significant seasonal variations of resistance to the two insecticides in the field populations of C. plutellae were found. The RR were 3.0-18.4 for fenvalerate and 4.8-20.6 for cypermethrin in Jianxin populations from November 2000 to April 2002 based on LC50 at 9 h, and 2.3-13.6 for fenvalerate and 3.6-16.0 for cypermethrin in Shangjie populations from May 2002 to July 2004 based on LC50 at 24 hours. The resistance levels were high in spring and autumn and decreased sharply in summer. In addition, significant recovery from the knocked-down caused by the insecticides was found in the F0 and field populations of C. plutellae which were resistant to fenvalerate and cypermethrin if the parasitoids were left in contact with the pyrethroids for 1 hour. However, no recovery was found in susceptible F11 progeny.     

Influence of host age and host deprivation on longevity, egg load dynamics and oviposition rate in Microplitis rufiventris

Adult size, longevity, egg load dynamics and oviposition ofMicroplitis rufiventris Kok. which began their development in the first, second, third （preferred hosts） or fourth （non-preferred hosts） instar larvae of Spodoptera littoralis （Boisd.） were studied. The parasitoid size was largely determined by the initial host size at parasitism. Non-ovipositing females derived from older hosts lived for longer periods than those derived from younger ones. However, the ovipositing females, irrespective of their size, lived for almost the same periods. At emergence, the oviducts of adult females contain a significant amount of mature eggs available for oviposition for a few hours on eclosion day. Egg load increases during the early phase of adult life. The amount of additional mature eggs and rate of egg maturation per hour was greater for wasps derived from preferred hosts compared with those in females derived from non-preferred hosts. The pattern of egg production in M. rufiventris females depended on the availability of hosts for parasitization. Host-deprived females depleted the egg complement with aging; the longer the host deprivation, the lower the oviduct egg load. Marked reduction in both realized or potential fecundity of host-deprived females was observed following host availability. Host privation for more than 3 days induced a marked deficit fecundity pattern through the female＇ s life. The realized fecundity was determined by the interaction among host availability, the number of eggs that are matured over the female＇ s life span, oviposition rate and host size from which the female was derived. These results suggest that： （i） M. rufiventris wasp is a weak synovigenic species; （ii） the maturation of additional eggs is inhibited once the maximum oviduct egg load is reached; （iii） the egg load of the newly emerged female is significantly less than the realized fecundity; and （iv） because M. rufiventris females oviposit fewer eggs when they begin depleting their egg supply at 3 days, augmentative releases will require release immediately following emergence to ensure the highest parasitization rate in the field.     

Embryonic Growth and Yolk Depletion during Incubation in the Chinese Skink,Plestiodon chinensis

We collected 24 gravid female Chinese skinks(Plestiodon chinensis) to study embryonic growth and yolk depletion during incubation. Females laid eggs between late May and mid-June. Eggs were incubated at 24(± 0.3) ℃. One egg from each clutch was dissected at 5-d intervals starting at laying. Embryonic stages at laying varied from Dufaure and Hubert's(1961) Stage 30-35, with a mean stage of 32.6. Incubation lengths at 24 ℃ varied from 35.1 to 48.3 d, with a mean of 41.5 d. Based on the derived functions describing instantaneous changes in embryo dry mass and yolk dry mass, we identified three phases of embryonic growth or yolk depletion in P. chinensis. Phase 1, from Day 0(at laying) to Day 15(～36% of the way through incubation), was one of minimal transfer of material from yolk to embryo. Phase 2, from Day 15 to Day 32-33(～77%-80% of the way through incubation), was characterized by increasingly rapid embryonic growth or yolk depletion. Phase 3, from Day 32-33 to hatching, was characterized by reduced embryonic growth or yolk depletion. The length of the last embryonic stage(Stage 40 = completely differentiated embryos) accounted for about 28% of incubation length, and the dry mass of the smallest embryos of Stage 40 accounted for only ～48% of the hatchling dry mass. Our study adds evidence to the idea that oviposition is not timed to coincide with the onset of rapid embryonic growth in oviparous reptiles, and is first to demonstrate that ～50% embryonic growth occurs in the last quarter of incubation in P. chinensis.     

Daily shoaling patterns in the zebrafish Danio rerio

Shoaling intensity in zebrafish Danio rerio is believed to vary throughout subjective day and night hours. This experiment examines long term variations in shoaling behavior. Adult zebrafish Dan io rerio were maintained under a 12：12 LD cycle （with dim red light serving as reduced visibility during subjective dark hours）, and their shoaling behavior was monitored every hour for a three-day period of time. Our results show that zebrafish perform shoaling behavior throughout subjective day and under reduced visibility conditions, although mean shoaling times during the light phase were significantly higher than mean shoaling times during the dark phase. However, on the 3^rd day of the experiment, mean shoaling times during the subjective night had increased and mean shoaling times during the subjective day had decreased. This shift in intensity was not seen on the first two days of the study, and may represent the influence of experience on the behavior of the test fish. We believe this study shows that shoaling behavior changes with light/dark cycles and that fish shoal even during reduced visibility conditions.     

Biology and life table parameters of the mushroom pest, Pediculaster fletchmanni （Acari： Siteroptidae）, at three constant temperatures

This paper is concerned with the bionomics and demography of Pediculaster fletchmanni Wicht （Acari： Siteroptidae） under controlled conditions （20 ± l, 22 ± 1 and 25 ± 1℃, 70% ± 5% relative humidity and a photoperiod of 16L ： 8D hours）. Glass Petri dishes inoculated with Trichoderma sp. mycelia were used as substrate and food source. The mean developmental time of the egg and the active larva did not differ significantly at the various constant temperatures, but these periods were significantly different for the quiescent larval stage. The preoviposition period ranged from 2.3 to 2.8 days, the ovipositional period increased with temperature increase, and all females died immediately after oviposition. The development of active larvae was the fastest of all life stages. The developmental threshold ranged between 5.25-14.22℃ the highest value being observed for the quiescent larval development. For immature development required 89.29 degree-days. Values of rm （intrinsic rate of increase） were 0.229, 0.398 and 0.386 for 20, 22 and 25℃ respectively. Finite rates of increase （λ） increased along with increasing temperature from 20-25℃ consequently the population doubling time （D） and mean generation time （T） showed significant differences with increasing temperature.     

Mobility affects copulation and oviposition dynamics in Pieris brassicae in seminatural cages

When, how often and for how long organisms mate can have strong consequences for individual fitness and are crucial aspects of evolutionary ecology. Such determinants are likely to be of even greater importance in monandrous species and species with short adult life stages. Previous work suggests that mobility, a key dispersal? related trait, may affect the dynamics of copulations, but few studies have investigated the impact of individual mobility on mating latency, copulation duration and oviposition latency simultaneously. In this paper, we monitored the copulation dynamics of 40 males and 40 females, as well as the oviposition dynamics of the females of the Large White butterfly Pieris brassicae, a facultative long-distance disperser butterfly. Individuals from a breeding were selected to create a uniform distribution of mobility and we recorded the timing, number and duration of all copulations in a semiexperimental system. We showed that mobility, measured as the time spent in flight under stressful conditions (a proxy of dispersal tendency), correlates with all aspects of copulation dynamics: mobile males and females mated earlier and for shorter periods than less mobile individuals. In turn, late mating females increased the time between copulation and oviposition. These results feed the previously described mobility syndrome of R brassicae, involving morphological and physiological characters, with life-history traits. We suggest that the reduction of mating latency and copulation duration has an adaptive value in dispersing individuals, as their life expectancy might be shorter than that of sedentary individuals.     

Influence of cornicle droplet secretions of the cabbage aphid,Brevicoryne brassicae,on parasitism behavior of na＇fve and experienced Diaeretiella rapae

Insects have evolved amazing methods of defense to ward off enemies. Many aphids release cornicle secretions when attacked by predators and parasitoids. These se cretions contain an alarm pheromone that alerts other colony members of danger, thereby providing indirect fitness benefits to the releaser. In addition, contact with cornicle se cretions could also threaten an attacker and could provide direct fitness to the releaser. However, cornicle secretions may also be recruited as a kairomonal cue by aphid natural enemies. In this study, we investigated the effect of the cornicle droplet volatiles of the cabbage aphid, Brevicoryne brassicae （L.）, on the hostsearching behavior of naive and experienced female Diaeretiella rapae （M＇Intosh） parasitoids in olfactometer studies. In addition, we evaluated the role ofB. brassicae cornicle droplets on the oviposition prefer ence of the parasitoid in a twochoice bioassay. Naive females did not exhibit any preference between volatiles from aphids secreting cornicle droplets over nonsecreting aphids, while experienced parasitoids exploited the secretions in their host location. Experienced females were also able to choose volatiles from both secreting and nonsecreting aphids over clean air, while this ability was not observed in naive females. Although secretion of cornicle droplets did not influence the percentage of first attack in either naive or experienced females, the success of attack （i.e. resulting in a larva） was significantly different between secreting and nonsecreting aphids in the case of experienced parasitoids.     

拟澳洲赤眼蜂和短管赤眼蜂在米蛾卵上的种间竞争

By means of single and mixed inoculation, this paper studied the interspecific competition between T. confusum and T. pretiosum on the factitious eggs of Corcyra cephaloica under different parasitoid densities, host densities and inoculated spaces. The results showed that for both singly and mixed inoculated groups, the parasitism increased with parasitoid density but decreased with host density, whereas the percentage of female progeny dropped with parasitoid density but enhanced with host density. No significant effect was observed on adult emergence for all parasitoid and host density treatments. In mixed inoculated group, the proportion of T. pretiosum in the progeny decreased with parasitoid density but increased with host density, and was more than 50% in all treatments, indicating that T. pretiosum had a stronger competitive ability than T. confusum. In the spaces ranging from 4cm^3 to 102cm^3, the parasitism decreased gradually in both singly and mixed inoculated groups. The percentage of female progeny and adult emergence had no significant difference among different inoculated spaces. In mixed inoculated group, the proportion of T. pretiosum in the progeny was more than 50% in all treatments except space 102 cm3, but decreased with space, which suggested that T. confusum could improve their competitive ability through increasing their search areas and looking for more hosts.     

Profitable self-superparasitism in an infanticidal parasitoid when conspecifics are present: self-superparasitism deters later attackers from probing for infanticide

Abstract.  1. To reveal the profitability of self-superparasitism when conspecifics are present, the total combined fitness returns from the first and second ovipositions under triple parasitism were compared with fitness returns from the first oviposition under double parasitism, using the small brown hopper Laodelphax striatellus and its semi-solitary infanticidal parasitoid Echthrodelphax fairchildii .
2. The total combined survival rate of the first and second comers under triple parasitism with oviposition intervals of 1/24 h (where 1 and 24 h represent the first-to-second and second-to-third oviposition intervals respectively) was nearly double the survival rate of the first comer under double parasitism with a 25-h oviposition interval, although there was no difference between these triple and double parasitisms in terms of head width and developmental time. Under the conditions of other oviposition intervals, self-superparasitism produced null (1/1- and 24/24-h intervals) or negative fitness returns (24/1-h intervals). This suggests that self-superparasitism on hosts that were self-parasitised 1 h previously is profitable when conspecifics are present.
3. When the female parasitoid laid an egg on a host harbouring the earlier comer(s) on the non-oviposition side, she often probed the non-oviposition side for infanticide, i.e. killing the first offspring. When the first and second comers were on different sides, the probing frequency at the third oviposition in triple parasitism with 1/24-h oviposition intervals was lower than that at the second oviposition in double parasitism with a 25-h oviposition interval. This difference was responsible for the above difference in survival rate between the triple and double parasitisms.     

Evidence for adaptive self-superparasitism in the dryinid parasitoid Haplogonatopus atratus when conspecifics are present

Self-superparasitism – ovipositing in or on a host that was previously parasitized by the same individual – had generally been considered maladaptive for solitary parasitoids. Recently, however, some researchers have suggested that self-superparasitized hosts produce higher fitness returns per host than singly parasitized hosts when these hosts are parasitized by conspecifics. The present study is the first to verify this possibility in the parasitoid Haplogonatopus atratus . Fitness returns from the first and second ovipositions under triple parasitism were compared with those from the first oviposition under double parasitism. Fitness returns were assessed in terms of survival rate, adult size, and developmental time. No differences were found between the two groups in adult size and developmental time. When the interval between the second and third ovipositions was 1 h, the total survival rate of the first and second comers under triple parasitism was higher than the survival rate of the first comer under double parasitism, and as high as the total survival rate of two first comers under double parasitism. This suggests that the value of self-parasitized hosts is as high as that of unparasitized hosts. When the second-to-third interval of triple parasitism was 24 h, self-superparasitism produced no fitness returns. Moreover, fitness returns from ovipositing into self-superparasitized hosts were similar to those from ovipositing into singly parasitized hosts.     

Adaptive significance of facultative infanticide in the semi-solitary parasitoid Echthrodelphax fairchildii

Abstract.  1. This is the first work to show how imperfect kin recognition influences the behavioural strategy of parasitoids.
2. The female of Echthrodelphax fairchildii lays an egg on the right or left side of the host thorax. When superparasitising on the side without the first offspring, it often probed the opposite side with its sting and killed the first offspring more than 50% of the time. The frequency of probing increased with increasing inter-oviposition interval, and was higher in conspecific superparasitism than in self superparasitism.
3. The adaptiveness of probing was assessed by the difference in fitness returns between superparasitism with probing and superparasitism without probing. Fitness returns from self‐superparasitism and those from conspecific superparasitism were assessed by the fitness performance of both first and second comers, and that of second comers respectively.
4. In terms of the survival rate of immatures (one fitness component), probing under conspecific superparasitism guaranteed higher fitness returns than not probing for longer oviposition intervals, but under self‐superparasitism not probing guaranteed higher fitness returns for shorter intervals because superparasitism for such intervals often resulted in two-adult emergence.
5. In terms of head width (another fitness component), probing produced higher fitness returns for shorter oviposition intervals for both self and conspecific superparasitism.
6. Assuming that offspring quantity contributes more to fitness returns than does offspring quality, the observed frequencies of probing were considered adaptive for parasitoids whose abilities to distinguish between self and conspecifically parasitised hosts and to estimate inter-oviposition intervals are imperfect.     

Superparasitism strategy in a semisolitary parasitoid with imperfect self/non-self recognition, Echthrodelphax fairchildii

To assess the adaptiveness of self‐ and conspecific superparasitism in the parasitoid Echthrodelphax fairchildii Perkins (Hymenoptera: Dryinidae), we measured the rate of superparasitism avoidance and fitness returns from superparasitism for different intervals between the first and second ovipositions. We also tested for any preference in oviposition side and whether any such preference was adaptive. The rate of superparasitism avoidance in both self‐ and conspecific superparasitism was about 10% for oviposition intervals of 2–8 h, and higher for intervals of 1 and ≥24 h (but did not exceed 35%). When conspecifically superparasitizing (but not self‐superparasitizing), females exhibited a slight preference for the side without the first‐comer. Under conspecific superparasitism, the survival rate of second comers was independent of the oviposition side and interval, but slightly lower than that of immature parasitoids for single parasitism. The adult size of second‐comers on the side harboring the first‐comer was larger than that of second‐comers on the side without it, when the oviposition interval was <24 or 96 h. These results explained the overall low rate of avoidance of conspecific superparasitism, but not the variation in avoidance rate or the preference for side without the first‐comer when conspecifically superparasitizing. Assuming that fitness returns are influenced more by offspring quantity than by their quality, self‐superparasitism produced positive fitness returns only when the oviposition interval was <24 h and the side without the first‐comer was selected. This suggests that the observed behavior was not adaptive. Possible reasons for the discrepancies between observed and optimal behaviors, including an imperfect ability for self/non‐self recognition, are discussed.     

Host Stage Selection and Sex Allocation by Gyranusoidea tebygi (Hymenoptera: Encyrtidae), a Parasitoid of the Mango Mealybug, Rastrococcus invadens (Homoptera: Pseudococcidae)

Host stage selection and sex allocation by Gyranusoidea tebygi Noyes (Hym,, Encyrtidae) were studied in choice and no-choice experiments in the laboratory. The parasitoid reproduced on first, second, and third instars of the mango mealybug, Rastrococcus invadens Williams (Hem., Pseudococcidae), and it avoided hosts that were already parasitized. Host feeding was occasionally observed. Sex ratios of the offspring produced by individual wasps were highly biased in favor of females, whereas the sex ratio of groups of wasps foraging under crowded conditions varied from male biased in smaller hosts to female biased in larger hosts. Females had longer developmental times than males, developed faster in larger mealybugs than in smaller ones, and were always larger than males emerging from the same host instar. Their size increased with the instar of the host at oviposition. About 90% of all ovipositions in second and third instar nymphs resulted from an attack with multiple stings, starting with a sting in the head of the host for the most part. The function of these head stings is either to assess quality of the host or to subdue hosts prior to oviposition. Encounter rates, number of attacks, and number of stings during one attack increased, while ovipositions decreased with host instar. Time investment per oviposition and time spent preening increased with increasing host age because older hosts defended themselves more vigorously than younger ones. Thus, while fitness of the parasitoid increased with host size, fitness returns per time decreased. The implications of this host selection behavior for the biological control of the mango mealybug are discussed.     

The relative fitness of Drosophila melanogaster (Diptera,Drosophilidae) that have successfully defended themselves against the parasitoid Asobara tabida (Hymenoptera,Braconidae)

Drosophila melanogaster larvae defend themselves against parasitoid attack via the process of encapsulation. However, flies that successfully defend themselves have reduced fitness as adults. Adults which carry an encapsulated parasitoid egg are smaller and females produce significantly fewer eggs than controls. Capsule-bearing males allowed repeated copulations with females do not show a reduction in their number of offspring, but those allowed to copulate only once did. No differences were found in time to first oviposition in females, or in time to first copulation in males. We interpret the results as arising from a trade-off between investing resources in factors promoting fecundity and mating success, and in defence against parasitism. The outcome of this investment decision influences the strength of selection for defence against parasitism.     

Oviposition Behavior and Conspecific Host Discrimination in Diachasmimorpha longicaudata (Hymenoptera: Braconidae), a Fruit Fly Parasitoid

We studied conspecific host discrimination and oviposition behavior of Diaschasmimorpha longicaudata (Ashmead), in third instar Anastrepha ludens (Loew) under laboratory conditions. The complete process of oviposition in D. longicaudata required an average of 29±11.7 s (Mean±SE), during which time the female remained completely immobile. This contrasts with attempts to oviposit for lesser durations (2-4 s), during which the female constantly moved her antennae and abdomen. In order to determine the host discrimination ability of this species (i.e., the capacity to distinguish between parasitized and non-parasitized hosts), third-instar A. ludens non-parasitized or parasitized 24 h earlier, were exposed simultaneously to individual female wasps with or without previous oviposition experience. An identical test was performed using larvae parasitized 48 h earlier. Both types of females showed a similar behavioral pattern of oviposition, but with significant differences in the number of eggs laid in parasitized and non-parasitized larvae. Experienced females showed reduced incidence of oviposition in parasitized larvae as well as a greater number of probes that did not lead to parasitism (rejection), although this difference was only significant in the 24-h test. This suggests that the host discrimination capacity of this parasitoid is innate and that previous oviposition experience increases the discrimination ability of females.     

Imperfect preference for singly parasitized hosts over doubly parasitized hosts in the semisolitary parasitoid Echthrodelphax fairchildii: implications for profitable self-superparasitism

Self‐superparasitism can be profitable (i.e., a fitness gain) when conspecific female adult parasitoids prefer singly parasitized hosts over doubly parasitized hosts. This preference is expected to evolve when the value (i.e., the fitness gain from oviposition) of doubly parasitized hosts is lower than that of singly parasitized hosts. We examined whether such a preference is found in the small brown planthopper, Laodelphax striatellus (Fallén) (Homoptera: Delphacidae), and its semisolitary infanticidal parasitoid Echthrodelphax fairchildii Perkins (Hymenoptera: Dryinidae). We compared the preferences and host values between each of four pairs of double and triple parasitism, each of which had the same time interval between the first and last oviposition bouts. Ovipositions on doubly and singly parasitized hosts occurred with similar frequencies in each of the four pairs, even though the doubly parasitized hosts were of lower value than the singly parasitized hosts. However, the value of doubly parasitized hosts with the first and second parasitoid offspring on the same side of the host was higher than that of hosts with the two offspring on different sides, and the value of the former did not differ significantly from that of singly parasitized hosts. The preferences between singly and doubly parasitized hosts with the two offspring on the same or different sides were as expected from differences in their values, except for one pair of double and triple parasitisms. This exception is considered attributable to an imperfect ability to evaluate hosts.     

Reproductive biology and small-scale rearing of cherry bark tortrix and its candidate biological control agent

Abstract:  The larval parasitoid, Campoplex dubitator (Hym.,: Ichneumonidae), is under consideration as an agent for classical biological control of cherry bark tortrix (CBT), Enarmonia formosana (Lep.,: Tortricidae), in North America. A comprehensive risk analysis of the candidate agent will require prosperous cultures of both the pest and its parasitoid. We present a rearing method for small-scale production of both species using a bean-based artificial diet, with additional information on the reproductive biology of C. dubitator . Based on estimated survivorship probabilities, a CBT egg had a 70% chance of developing completely to the adult stage under this system. The success of parasitism, however, was very dependent on the instar of the CBT host larva at the time of oviposition. All parasitised first instar larvae died shortly after the attack, rendering them unsuitable for oviposition, while 50% of parasitised second instar larvae died prematurely. In contrast, early mortality was 15–30% for larvae parasitised in the third to fifth instars. Regardless of the instar at oviposition, approximately 90% of the surviving hosts yielded parasitoids, showing a high acceptance by C. dubitator of second to fifth instars for oviposition.