Behavioral and developmental effects of neem extracts on Clavigralla scutellaris (Hemiptera: Heteroptera: Coreidae) and its egg parasitoid, Gryon fulviventre (Hymenoptera: Scelionidae)

Extracts of neem, Azadirachta indica A. Juss, negatively affected feeding and development of Clavigralla scutellaris (Westwood), a coreid pest of pigeonpea, Cajanus cajan (L.) Millspaugh. Labial dabbing, pod wall penetration, and seed damage by fifth instars were significantly reduced on beans, Phaseolus vulgaris (L.), that had been dipped in aqueous, methanolic, or hexane extracts of neem seed kernel. When fourth instars were dipped directly into aqueous extract, developmental abnormalities of the wings occurred at all levels tested and fecundity dropped to zero at concentrations above 0.3125%. The LC50 value was 3.14% (220 ppm azadirachtin) at 8 d. The scelionid wasp Gryon fulviventre (Crawford) is an important natural enemy of Clavigralla spp.; egg mortality from this parasitoid ranged from 37 to 85% during the fall cropping season. Feeding by newly emerged wasps was dramatically reduced when honey was mixed with aqueous neem suspension, but 6-d survivorship of adults did not differ significantly from that of the control. Wasp oviposition behavior was altered slightly when coreid eggs were treated with neem: the period of antennation was significantly extended, but time for drilling, oviposition, and marking was unaffected. Neem-dipped eggs were accepted for oviposition and progeny emerged successfully from these treated eggs. Exposure of already parasitized eggs to neem did not interfere with progeny emergence, longevity, or sex ratio. Thus, neem extract and egg parasitoids seem to be compatible and promising control strategies for C. scutellaris. Our results suggest that use of neem against pod-sucking bugs will not interfere with natural control provided by G. fulviventre.     

Life history of Aptesis nigrocincta (Hymenoptera: Ichneumonidae) a cocoon parasitoid of the apple sawfly, Hoplocampa testudinea (Hymenoptera: Tenthredinidae)

Aptesis nigrocincta: Gravenhorst is a bivoltine ectoparasitoid of apple sawfly cocoons, hosts that must be found and parasitized by females at a depth of 10-25 cm in the soil. Females are significantly smaller than males and nearly wingless. After encountering a host, females needed 29.3 min at 20 degrees C and 19. 9 min at 25 degrees C to deposit an egg on the host. Development from egg to adult took 39.6 days for females and 38.0 days for males at 20 degrees C. This small difference was significant. At 20 degrees C, the longevity of females that had no opportunity to oviposit was on average 72.5 days, significantly higher than male longevity (50.6 days). The longevity of females given access to hosts throughout their lifetime averaged 58.6 days. Females were able to mate immediately after emergence and copulation lasted on average 21.7 s. After a pre-oviposition period averaging 5.8 days, females laid 20.2 eggs during their lifetime, thus less than one egg per day. Neither the fecundity nor longevity of individual females was correlated with body size. If females were deprived of food, longevity as well as lifetime fecundity were drastically reduced. Field studies were carried out in one organically managed apple orchard in Switzerland. Aptesis nigrocincta showed parasitism rates ranging from 12.1 to 39.7 % within single parasitoid generations, thereby constituting the most important mortality factor of apple sawfly cocoons.     

Refrigeration of Riptortus clavatus (Hemiptera: Alydidae) eggs for the parasitization by Gryon japonicum (Hymenoptera: Scelionidae)

Gryon japonicum (Ashmead) (Hymenoptera: Scelionidae) is a solitary egg parasitoid of Riptortus clavatus (Thunberg) (Hemiptera: Alydidae) one of the most important pests in soybean in Korean and Japan. Refrigeration of R. clavatus eggs for up to 120 days was evaluated as a method of mass production of G. japonicum. The refrigeration reduced the eclosion of eggs, thus no nymph emerged after 30 days of egg refrigeration. Increased duration of host acceptance behaviors by G. japonicum and some detrimental effects on parasitism rate, developmental time, longevity, and adult size of the parasitoid were found in refrigerated host eggs. However, all the biological parameters of G. japonicum were unaffected by the refrigeration of up to 30 days. Gryon japonicum parasitized 16 and 14 host eggs daily that were refrigerated for 15 and 30 days, respectively, which did not differ from parasitization of fresh host eggs. Furthermore, refrigeration of host eggs did not reduce the reproduction of the emerged adult parasitoids and emergence and sex ratio of their progeny. Gryon japonicum also parasitized 14 and 13 refrigerated host eggs per day kept at 26.3°C and 78.7% RH for 2 and 4 days of post-refrigeration without significant reduction, respectively. These results show that refrigeration of R. clavatus eggs can be a good method for mass rearing of the parasitoid, and the host eggs killed by cold storage can be supplemented in the field to boost field parasitism.     

The biology of Diadromus collaris (Hymenoptera: Ichneumonidae), a pupal parasitoid of Plutella xylostella (Lepidoptera: Plutellidae), and its interactions with Oomyzus sokolowskii (Hymenoptera: Eulophidae)

The ichneumonid Diadromus collaris (Gravenhorst) has been recorded in many parts of the world as an important parasitoid of the diamondback moth, Plutella xylostella (Linnaeus), a serious pest of brassica vegetable crops worldwide. Some aspects of its biology and its interactions with Oomyzus sokolowskii (Kurdjumov), another major parasitoid of the same pest, were studied in the laboratory. At 25 degrees C, female wasps did not have mature eggs in their ovaries until about 12 h after emergence. Both males and females mated successfully 24-48 h after emergence, and females started to oviposit one to two days after emergence. Unmated females produced male progeny only; mated females produced progeny of both sexes. The development rate of the parasitoid increased linearly with temperature from 15 to 30 degrees C, with an estimated low temperature threshold of 7.4 degrees C and a thermal constant of 225.1 day-degrees for development from egg to adulthood. Rates of survival from larva to adulthood were about 90% between 20 and 28 degrees C and decreased as temperature decreased or increased. No immatures survived to adulthood at 35 degrees C. When provided with honey solution, the females lived on average 8.3, 11.5 and 7.0 days, and parasitized 26, 44 and 46 host pupae at 20, 25 and 30 degrees C, respectively. Female wasps could be stored at 15 degrees C for up to four weeks without detrimental effects on reproduction. Females of D. collaris attacked host pupae already parasitized by O. sokolowskii, inserting their ovipositor into the hosts at a similar frequency as into unparasitized host pupae, but they did not lay eggs inside the hosts.     

Reproductive biology of Fidiobia dominica (Hymenoptera: Platygastridae), an egg parasitoid of Diaprepes abbreviatus (Coleoptera: Curculionidae)

The reproductive biology of Fidiobia dominica Evans (Hymenoptera: Platygastridae) was studied in the laboratory (25.6 +/- 1 degrees C) using host eggs of Diaprepes abbreviatus L. (Coleoptera: Curculionidae). F. dominica readily parasitized D. abbreviatus eggs on both host plant and wax paper substrates. The number of egg masses parasitized and the number of offspring produced were higher when females were offered more than one host egg mass but did not differ when either two or three egg masses were offered. Female parasitoids that were provided with host eggs and a honey food source lived significantly longer than those that were not provided a food source; however, they did not parasitize more D. abbreviatus eggs. Oviposition occurred in host eggs from 0 to 7 d old, and host mortality was relatively consistent for eggs 0-5 d old and lower for eggs 6-7 d old. Successful parasitoid emergence seldom occurred after host eggs were 4 d old, and by 7 d, no adults successfully emerged. Developmental time from egg to adult was 19.3 +/- 0.2 d for males, significantly more rapid than the females (20.4 +/- 0.1 d). The mean longevity of adult females was 8.0 +/- 0.4 d, with a mean oviposition period of 2.7 +/- 0.3 d; males survived 8.1 +/- 0.4 d. The demographic parameters including intrinsic rate of increase (r(m)), generation time (T), and net reproduction (R(o)) were 0.142/d, 22 d, and 22.4 female eggs/d, respectively.     

Biology and thermal requirements of Trichogramma atopovirilia Oatman & Platner (Hymenoptera: Trichogrammatidae) parasitizing eggs of Diaphania hyalinata L. (Lepidoptera: Pyralidae)

The development and parasitism of Diaphania hyalinata L. eggs by Trichogramma atopovirilia Oatman & Platner and its thermal requirements were studied at the temperatures of 18, 21, 24, 27, 30 and 33 degrees C. Thirty eggs of D. hyalinata were exposed to three females of T. atopovirilia for 5h at 25 degrees C and incubated at the different temperatures. The developmental time from egg exposure to adult, parasitism viability, number of adults per parasitized host egg and progeny sex ratio were monitored. The developmental time from egg to adult emergence of the parasitoid exhibited inverse relationship to the temperature, lasting 24.12 days at 18 degrees C and 7.36 days at 33 degrees C. Parasitism viability at 24, 27 and 30 degrees C was higher than 90%. The ratio of T. atapovirilia adult produced per egg and its sex ratio were not affected when using D. hialynata as host. The lowest threshold temperature (Tb) and estimated degree-days over Tb required by T. atopovirilia to develop on eggs of D. hyalinata was 11.99 degrees C and 130.42 masculine C, respectively. Considering the temperature regimes of two areas where cucurbitaces are cultivated in Bahia State (Rio Real and Inhambupe County) it was estimated that T. atopovirilia can achieve more than 32 generation per year. The results suggest that T. atopovirilia has potential to control D. hyalinata eggs with better chance of success under temperature regimes ranging from 24 to 27 degrees C that meets the suitable field conditions for cropping cucurbitaces.     

Trichogramma platneri (Hym.: Trichogrammatidae): Host choices between viable and nonviable codling moth,Cydia pomonella,and three-lined leafroller,Pandemis limitata (Lep.: Tortricidae) eggs

In laboratory host-preference studies,Trichogramma platneri Nagarkatti (Hym.: Trichogrammatidae) females, reared on viable codling moth,Cydia pomonella (L.) (Lep.: Tortricidae) eggs, parasitized significantly more viable than nonviable codling moth eggs produced by cobalt 60 irradiated adults. This ovipositional preference was maintained when competition increased per host egg. Similarly, one, three and fiveT. platneri females consistently oviposited more eggs into viable versus nonviable host eggs. A single femaleT. platneri parasitized a similar number of viableC. pomonella and three-lined leafroller,Pandemis limitata (Robinson) (Lep.: Tortricidae) eggs. However, as the number of females per host eggs increased, a significantly larger number of codling moth versus leafroller eggs were parasitized. One, three and fiveTrichogramma females parasitized significantly moreP. limitata versus nonviableC. pomonella eggs. NonviableC. pomonella eggs deflated to less than 25% of their original volume in four and ten days when held under dry and humid conditions respectively. The blackened prepupal stage of the parasitoid generally occurred in the nonviableC. pomonella eggs four days post-parasitization whereas the parasitized viable eggs blackened zero to one day earlier. Incubation under dry or humid conditions did not appear to influence the number of parasitized eggs that were able to blacken and show evidence of parasitism. Summerland Research Centre Contribution No. 938.     

The functional response of Uscana lariophaga under different egg distributions of its host Callosobruchus maculatus

The functional response of the egg parasitoid Uscana lariophaga Steffan (Hymenoptera: Trichogrammatidae) was tested under three different host distributions (even, clumped and random) within clusters of Callosobruchus maculatus Fab. (Coleoptera: Bruchidae) eggs. A Holling Type II functional response was found for all three distributions. Over low host densities, less than 50% of the host clusters was parasitized. At low host densities, U. lariophaga females parasitized significantly fewer eggs in random egg clusters with many beans than in clusters with fewer beans and an even or clumped egg distribution. At higher egg densities, plateau levels of maximum number of hosts parasitized were the same for all three egg distributions. Uscana lariophaga appears to be adapted to search for even or clustered egg distributions, as can be found in the field and under storage conditions.     

Effects of egg age of Spartocera dentiventris (Berg) (Hemiptera: Coreidae) on parasitism by Gryon gallardoi (Brethes) (Hymenoptera: Scelionidae)

To evaluate the effect of egg age of Spartocera dentiventris (Berg) on the parasitism by Gryon gallardoi (Brethes), groups of 12 eggs of 2, 3, 4, 5, 6, 7, 8, and 12 days old were exposed to one female of G. gallardoi on a test tube, with the wasp observed for 2h subsequently. Later, the eggs were individualised and incubated (25 +/- 1 degrees C; 12h photoperiod) until adult emergence. To identify the preferred age, groups of 12 eggs of 1, 3, 5, 7 and 12 days of age were simultaneously exposed to a parasitoid female on an arena for 2h. These groups were also individualised and incubated until parasitism was confirmed. On all ages tested parasitism was at about 88.5 +/- 2.64%, with a reduction in adult parasitoid emergence with age increasing (P < 0.01). The development time increased with increasing egg age (P < 0.01), with males developing faster. Parasitoid sex ratio for all ages tested was female-biased (0.49:1), with the proportion of males invariant with host age (P > 0.05). When the egg groups were exposed simultaneously, the female preferred eggs one and three days old. The results indicate a preference of G gallardoi for younger eggs of S. dentiventris, with host egg age exerting a negative effect on development time and offspring emergence of the parasitoid.     

Reproductive Biology of Celatoria compressa (Diptera: Tachinidae), a Parasitoid of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

The tachinid Celatoria compressa, a parasitoid of adult Diabrotica species in North America has been studied as a candidate classical biological control agent for the western corn rootworm, Diabrotica virgifera virgifera, in Europe. Prior to its potential importation, a thorough understanding of the parasitoid's reproductive biology is essential, and is an important component in the evaluation of a species as a biological control agent. In this study it has been clarified that C. compressa belongs to a group of a few tachinid species characterised by having eggs that contain fully developed larvae which are laid directly into the host. After mating, the egg load of females increased steadily from day 1 to a maximum egg load on day 4. Thereafter eggs containing fully developed first instar larvae reached a maximum of 31 in 69 eggs. At the first day of larviposition, females laid on average only five eggs into multiple hosts, which is in contrast to the availability of 18 eggs containing fully developed first instars in the uterus per female at that time. During a mean female's larviposition period of 23 days, a total of 33 first instars were larviposited into the hosts, which is only half of the female's egg load. Lifetime fecundity of C. compressa was significantly correlated with longevity. However no relationship was found between body size and either lifetime fecundity or longevity. In this study, an inverse host density-dependent pattern of percent parasitism was shown for C. compressa under 24-h fixed-time laboratory conditions, reflecting a Holling type II response. The number of host parasitized per C. compressa female reached an upper limit of 10 hosts with an increasing host density, which can be explained by the long host handling time of C. compressa.     

Biology of a thelyotokous biotype of Eretmocerus mundus (Hymenoptera: Aphelinidae) on Bemisia tabaci (Homoptera: Aleyrodidae)

Abstract Thelyotokous biotype of Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae), a parasitoid of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), was recently recorded in northern Iran. Reproductive biology of this biotype was studied as part of an evaluation of its potential for biological control of B. tabaci. The parasitoid deposited more eggs under 2nd and 3rd nymphal instars than 1st or 4th instars. Adult females fed honey, with no access to whitefly nymphs, lived significantly longer (13.6 ± 4.7 d) than those given access to nymphs, but not fed honey (7.6 ± 2.21 d). Lifetime fecundity averaged 81.7 ± 26.9 female progeny per female parasitoid, ranging from 11–132. Daily fecundity, measured as the number of whitefly nymphs parasitized by per female each day for 10 d, averaged 18.06 ± 3.95 for the first 6 d of life, and then declined to < 11. Developmental time from oviposition to parasitoid emergence was significantly shorter in the 3rd instar of the host (15.9 ± 1.06 d) than in the 1st instar (18.7 ± 2.3 d), but not in the 2nd instar (16.4 ± 1.3 d).     

Effects of deltamethrin on the reproduction of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae)

The influence of deltamethrin on the reproduction of Trichogramma cordubensis, a thelytokous egg parasitoid, was investigated by studying egg maturation and daily fecundity of insecticide treated wasps and offspring emergence rates. The insecticide was applied to the parasitoids at the prepupal stage within its host eggs (Ephestia kuehniella). The total number of parasitized eggs per female during the first 7 days was not significantly influenced by the tested concentrations of deltamethrin. Prevalence of parasitism during this period had a similar pattern between deltamethrin treatments and the control. In addition, the mean number of mature eggs observed per female per day was significantly correlated to mean daily fecundity, regardless of the treatments. Offspring emergence was significantly influenced by the insecticide treatments experienced on their progenitors, decreasing significantly at 48 and 72 h for the highest tested concentration of deltamethrin (23.6 mg [a.i.]/L). Despite that, deltamethrin had no adverse effects on the reproduction of treated wasps, particularly when was applied at the concentration recommended by the manufacturer (12.5 mg [a.i.]/L).     

Aging and changes in fecundity of the flea Leptopsylla segnis (Siphonaptera: Leptopsyllidae)

In experiment, the mean diurnal fecundity of Leptopsylla segnis females increased during the first five days since the beginning of feeding on white mice and reached the maximum in the second five-day period (15.7-16.7 eggs per 1 female during a day). In subsequent period of stay on a host, an activity of egg laying gradually decreased. In flea females, which had lived on hosts for 40 days and more this index was 3.7 eggs. During the mean life longevity (23 days), the flea females lay about 260 eggs; the females, which have lived more than 40 days, produce above 400 eggs.     

Ontogeny and reproductive biology of Diadegma semiclausum (Hym.: Ichneumonidae), a larval endoparasitoid of Diamondback Moth,Plutella xylostella (Lep.: Plutellidae)

In this article, the ontogeny and reproductive biology of Diadegma semiclausum (Hym.: Ichneumonidae), an important parasitoid of Plutella xylostella (Lep.: Plutellidae) are described in detail. We did dissect parasitized P. xylostella larvae in phosphate-buffered saline and determine the external morphology of its parasitoid at all developmental stages. The developmental duration of its immature stages, adult longevity, total oviposition period and fecundity of the parasitoid are determined at 24 ± 1 °C, 65  ±  5% R.H., and a photoperiod of 16:8 h L:D. The mean duration of egg and larval stages is 9.56 days and the prepupa and pupa stages last for 8.27 days. In average, female longevity is 1.31 times longer than that of males, and females lay 300 eggs in total. The peak of D. semiclausum oviposition is on the eighth day after mating. The egg loading pattern of D. semiclausum was investigated to determine the parasitoid ‘ovigeny index’ throughout the female's parasitoid lifetime. Initial egg load in immature females (<2 h age) is 1.45 per female and the mean lifetime potential fecundity (total immature and mature oocytes), at four interval ages, is 34. With an ovigeny index value of 0.038, D. semiclausum is considered moderately to strongly synovigenic. In the absence of the host, after 3 days, the number of eggs is decreased in D. semiclausum. Our results demonstrated that there is a negative relation between the ovigeny index and egg resorption in this parasitoid.     

Effect of temperature on parasitism and host-feeding of Trichogramma turkestanica (Hymenoptera: Trichogrammatidae) on Ephestia kuehniella (Lepidoptera: Pyralidae)

The egg parasitoid Trichogramma turkestanica Meyer is being evaluated as a biological control agent against the Mediterranean flour moth, Ephestia kuehniella Zeller, in flour mills. The longevity, parasitism and host-feeding of the parasitoid at four constant temperatures (15-30 degrees C) has been determined in the laboratory. The highest fecundity occurred at intermediate temperatures. The number of host eggs killed by host-feeding per female was highest at the two lower temperatures. A very conservative estimate of host-feeding showed that it accounts for approximately half of the mortality of host eggs at 20 and 25 degrees C and thus could constitute a major mortality factor for the flour moth population.     

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.     

Parasitism capacity of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) reared under different temperatures on Bonagota salubricola (Meyrick) (Lepidoptera: Tortricidae) eggs

The parasitism capacity of Trichogramma pretiosum Riley strain bonagota on Bonagota salubricola (Meyrick) eggs was studied under the temperatures of 18, 20, 22, 25, 28, 30 and 32 degrees C. The number of days with parasitism, accumulated parasitism, total number of eggs parasitized per female and parasitoid longevity was evaluated. In the first 24h, parasitism ranged from 1.6 (32 degrees C) to 8.8 (22 degrees C) eggs of B. salubricola. Accumulated egg parasitism of B. salubricola reached 80% in 1st to 4th day at 20 degrees C to 32 degrees C, respectively, and in the 7th day at 18 degrees C. Temperatures from 18 degrees C to 22 degrees C were the best suited for the total eggs parasitized for female, resulting in 35.4 and 24.6 eggs/male respectively. T. pretiosum female longevity ranged from 7.8 to 2.5 days, at 18 degrees C and 32 degrees C, respectively. The results showed that T. pretiosum strain bonagota is better adapted to temperatures from 18 degrees C to 22 degrees C.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Superparasitism in the solitary ectoparasitoid Aptesis nigrocincta: the influence of egg load and host encounter rate

Theory predicts that the acceptance of hosts already parasitized by a conspecific will depend both on egg load and the availability of hosts. In the present laboratory study, we tested the effect of egg load and host encounter rate on the propensity of superparasitism in the solitary parasitoid Aptesis nigrocincta Gravenhorst (Hymenoptera, Ichneumonidae), a synovigeneous ectoparasitoid of prepupae of the European Apple Sawfly. Parasitoid females carry few voluminous eggs at a time and the egg maturation rate is less than one egg per day. Egg load was manipulated by giving females access to hosts one week prior to the start of treatments and host availability by giving females access to either one host cocoon every day or every other day. In the first treatment where females had a high egg load of 5.3 egg in their ovaries and encountered host cocoons at low rates, we found that parasitized hosts were accepted to the same degree as healthy hosts. In females with significantly decreased egg load (3.8 eggs) encountering hosts at the same rate we found a slight but non-significant decrease in the acceptance of parasitized hosts compared with healthy hosts. In contrast, A. nigrocincta females accepted significantly fewer parasitized hosts at a high host encounter rate that would lead them to the point of egg limitation in the near future. Within the range of egg loads tested, the host encounter rate appears to be the most important determinant for a females decision to oviposit onto hosts already parasitized by a conspecific.     

Factors affecting sequential sex allocation in the parasitoid wasp Gryon japonicum

Female wasps of the solitary egg parasitoid Gryon japonicum (Hymenoptera: Platygastridae) allocate male and female offspring in a particular sequence to successive hosts. Male eggs are typically laid in the second host, and the sex allocation sequence is reset after a certain period of time. The present study aimed to examine the underlying mechanism to hold information and reset the sequence by using eggs of Riptortus pedestris (Heteroptera: Alydidae) as hosts. After completion of initial oviposition, a female wasp was treated by cold anesthesia for 1 h, exposure to a parasitized host for 3 h, or being kept at 15°C in darkness for 24 h, and then presented with three host eggs. Cold‐anesthetized females did not reset the sex allocation sequence, indicating that cold anesthesia did not block the mechanism of holding information about oviposition order. Frequent encounters with parasitized hosts were also insufficient to reset the sequence. However, being kept in cool, dark conditions significantly affected resetting, suggesting that low temperature lengthened the time required to reset the sequence. This implies that it is probable that the mechanism to hold information and reset sex allocation sequence in G. japonicum involves metabolism.