Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4-day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae-larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.     

Is the parasitization capacity of Trichogramma cordubensis influenced by the age of the females?

We investigated the parasitization capacity of Trichogramma cordubensis Vargas & Cabello (Hymenoptera: Trichogrammatidae) females aged 24 h, 48 h, 72 h, 96 h, 120 h, and 144 h, using Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs as hosts. Wasps were held without hosts during the period of ageing, therefore being increasingly time-limited with respect to parasitization as they got older. The total number of parasitized hosts decreased as the age of the parasitoid increased. However, the proportion of lifetime parasitism carried out on the first day increased with wasp age, up to 120-h old females. These results show that the parasitization capacity of ageing T. cordubensis females changes as they become time-limited. The consequences of such changes for biological control programs are discussed.     

Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th) had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover, the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts (late instars) might be to superparasitize these hosts.     

Mating behaviour of the corn stalk borerSesamia nnonagrioides

The mating behaviour of the corn stalk borerSesamia nonagrioides (Lef.) [Lepidoptera:Noctuidae] was studied under laboratory conditions at 25 ± 1 °C, 65 ± 5% r.h. and 16:8 (L:D) regime. The females began calling during the first scotophase following emergence, the peak of calling occurred during the second scotophase and thereafter decreased. Maximum calling was observed between the fourth and sixth hour of the scotophase. The calling pattern varied with age. During the first and second scotophase most of the females were calling continuously, while during the third and fourth scotophase periodic calling was observed. The mean onset of calling was advanced and the mean length of calling per day was increased slightly as the female became older. Females held for 72 h in continuous darkness exhibited an endogenous circadian rhythm of calling. Matings began during the first scotophase following emergence and the peak of mating was observed during the second scotophase. Mated females did not remate. Few males mated more than once during the following scotophases.     

Daily rhythms in parasitization of the Angoumois grain moth <Emphasis Type="Italic">Sitotroga cerealella</Emphasis> Oliv. (Lepidoptera,Gelechiidae) eggs by the egg parasitoid <Emphasis Type="Italic">Trichogramma principium</Emphasis> Sug. et Sor. (Hymenoptera,Trichogrammatidae) females

Laboratory experiments conducted at L: D = 16: 8 have shown that the observed temporal pattern of parasitization of the Angoumois grain moth, Sitotroga cerealella eggs by Trichogramma principium females represents a resultant of arrhythmic age-related trends and circadian rhythms. Most of females delayed parasitization. The daily number of females starting to parasitize was maximal on the first day of contact with the host and then gradually declined. Practically all of the females started parasitization during the photophase. Moreover, when the first contact with the host fell on the scotophase, the total cumulative percentage of females that started parasitization during four days of the experiment significantly decreased. Oviposition activities of parasitizing females also occurred mainly during photophase. However, under constant light, these circadian rhythms were damped out after one cycle. In addition, anticipatory period of darkness during photophase directly inhibited parasitization. This suggests that the observed rhythms can be easily modified by the direct environmental influence. Under natural conditions, such a flexible oviposition rhythm may be of advantage for these parasitoids enabling them to use any opportunity for reproduction. In biocontrol practice, the lability of parasitization rhythms may enable Trichogramma females to adapt immediately to any new light-dark regimes, although darkness may have negative effects on their efficiency.     

Diel periodicity and influence of age and mating on female sex pheromone titre in Estigmene acrea (Lep., Arctiidae)

Abstract:  Calling behaviour, diel periodicity, and effect of age and mating on female sex pheromone titre in Estigmene acrea (Drury) were studied under laboratory conditions. Forty-five per cent of females started calling during the first scotophase, but the highest number of calling females was observed during the second, third and fourth scotophases. Calling behaviour occurred from the third hour after dark until just before the end of the scotophase. However, females exhibited a bimodal pattern of calling with the first peak occurring between 4 and 6 h and a second peak at 10 h after the onset of scotophase. The mean onset of calling time differed significantly with age. Older females showed a tendency to call longer, but there was no significant difference. The amount of (Z,Z)-3,6-cis-9, 10-epoxyheneicosadiene in females was quantified from the first scotophase following emergence, until the fifth scotophase. Glands of 0-day-old females presented a higher content of pheromone compared with that found in glands of 1-, 2-, 3- and 4-day-old females. Pheromone titre was determined at 2-h intervals throughout the third scotophase and photophase. (Z,Z)-3,6-cis-9,10-epoxyheneicosadiene was found in the gland during the scotophase as well as the photophase. However, there was no consistent pattern of pheromone production throughout the scotophase or photophase. Mated females of E. acrea produced significantly less pheromone than virgin females.     

褛裳夜蛾的交配行为及雄蛾对性腺提取物的反应节律

详细观察了褛裳夜蛾成虫的交配行为,利用风洞、触角电位技术研究了雄蛾对性腺提取物的反应节律,通过林间诱蛾试验进行了验证,旨在为褛裳夜蛾性信息素的精确提取及性信息素组份分离、鉴定提供依据。研究结果表明:成虫的求偶、交配行为均发生在暗期,有一定的节律性:雌蛾在羽化3d以后开始求偶,1周左右表现最为强烈,3-4日龄雌蛾在暗期4-6h开始求偶,最大求偶率在暗期6-8h;5-9日龄在进入暗期就开始求偶,最大求偶率出现在暗期4-6h。风洞试验表明,3-7日龄的雄蛾对性腺提取物均有明显的性行为反应,5日龄雄蛾在暗期4-6h对性腺提取物的反应最为强烈。3-6日龄的成虫在暗期4-6h开始交配,而7-8日龄的成虫于暗期2-4h开始交配,6日龄的成虫交配率最高,交配高峰在暗期4-8h。雄蛾对性腺提取物的触角电位反应也有一定的节律性:雄蛾对4日龄雌蛾性腺提取物开始有电生理反应,对6-7日龄暗期5h性腺提取物反应最为强烈。林间诱蛾试验测定了性腺提取物的引诱活性,7日龄雌蛾性腺提取物林间诱蛾量最高,引诱高峰在暗期4-6h,该结果也验证了褛裳夜蛾雄蛾对性腺提取物的反应节律。     

Flight initiation byProstephanus truncatus in relation to time of day, temperature, relative humidity and starvation

Studies were carried out in the laboratory on the influences of time of day, temperature, relative humidity and starvation on flight initiation byProstephanus truncatus (Horn) (Coleoptera: Bostrichidae). Flight occurred throughout the 12 h photophase and at the beginning of the scotophase but peaked at 2–0 h before darkness. Temperature exerted a significant effect on flight. The frequency of flight take-off increased with temperature over the range 20–30°C but declined sharply at 35°C. Flight activity increased with starvation up to a maximum at 2 days after which it began to decline.     

Long-term egg retention and parasitization in Trichogramma principum (Hym., Trichogrammatidae)

Laboratory experiments with Trichogramma principium Sug. et Sor. females that were offered Sitotroga cerealella Oliv. eggs demonstrated that less than half of the ovipositing females started oviposition during the first 2 days of the experiment, whereas the rest of the ovipositing females showed a delay in parasitization ranging from 2 to 10 days after contact with the host. Almost 10% of the wasps refused to parasitize the grain moth eggs over 12 days. The delay in parasitization may be as long as 6–8 days without any significant decrease in the number of mature ovarial eggs, in the number of eggs laid during the first 48 h of oviposition, and in the total lifetime fecundity. This egg retention is responsible for the fact that in spite of a relatively short mean duration of the oviposition period in each individual female (approximately 4 days), host parasitization by a group of simultaneously emerged wasps was almost uniformly distributed over 8–10 days. When induced, the parasitization state (i.e. the tendency to parasitize sequentially offered portions of host eggs) was stable both in the presence of a host and under host deprivation extended up to 8 days. These data provide further evidence for our hypotheses that the stability of the parasitization state in Trichogramma is based on endocrine mechanisms.     

Rhythmicity of mating and oviposition inCallosobruchus subinnotatus (Pic) (Coleoptera: Bruchidae)

Mating and oviposition behaviors were studied inCallosobruchus subinnotatus. Copulation was most frequent during the late scotophase, 2–3 h before onset of photophase. The females were less willing to mate during photophase, which increased the time to initiate mating while decreasing the duration of mating. Females exhibited increased movement prior to mating, resting immediately after mating, and remained stationary for 6 h when oviposition commenced. Multiple mating by both males and females affected the number of eggs laid, duration of mating, and uncoupling time at the end of mating. Females that mated two or three times laid more eggs than females that mated once or more than three times. Females that remainedin copula for less than 18 min showed greater readiness to remate than those that remainedin copula longer. There was a gradual decrease in the number of eggs females could lay with an increase in the number of previous matings by males.     

高榕雌花期传粉榕小蜂和欺骗性小蜂的繁殖特点

榕树及其专一性传粉榕小蜂组成了动植物界最为经典的协同进化关系,传粉榕小蜂演化出欺骗性是非常罕见的。在雌雄同株的高榕隐头果内,共存着一种传粉榕小蜂Eupristina altissima和一种欺骗性的小蜂Eupristina sp.,两种小蜂在雌花期进入隐头果内繁殖,但有不同的繁殖特点。对比研究了两种小蜂从成虫羽化到产卵和传粉这个阶段的雌蜂个体大小、孕卵量及繁殖差异,结果表明:羽化期两种雌蜂的平均个体小,经飞行小个体的雌蜂易死亡,大个体雌蜂到达接受树,但通过苞片通道,一些个体较大的传粉榕小蜂被夹死导致进入果腔的雌蜂相对小,而欺骗性小蜂易通过苞片以至进入果腔的雌蜂个体较大。两种未产卵雌蜂均表现为个体大者孕卵量较多,但两种雌蜂的平均孕卵量没有差异。即使有充足雌花资源产卵,两种雌蜂均未产完所有卵,产卵后两种雌蜂卵巢中的卵量均显著减少,遗留下的卵量两种小蜂间没有差异。传粉榕小蜂只有部分个体传完所携带花粉,并表现为传粉越成功的雌蜂,产卵越多。存在种内竞争时,两种小蜂的产卵量均减少,传粉榕小蜂的传粉效率也降低。在种间竞争背景下,欺骗性小蜂产卵更成功,传粉榕小蜂的产卵和传粉量均受到极大抑制。研究结果说明雌花期隐头果内传粉榕小蜂只适量利用雌花资源产卵繁殖后代,更有效地传粉繁殖榕树种子,这可能是维持榕-蜂互惠系统稳定共存的重要机制之一;欺骗者稳定存在需降低与传粉者的直接竞争,而欺骗者和传粉者分散在不同果内,甚至是不同的树上繁殖是理想的繁殖策略。     

Daily rhythms in the sorghum shootfly, Atherigona soccata: oviposition, egg-hatch and adult eclosion

ABSTRACT. Daily rhythms controlling oviposition, egg-hatching and adult eclosion in the sorghum shootfly, Atherigona soccata Rondani, were investigated. Eggs were laid only during the photophase of a LD 12:12 cycle, in two peaks. Under continuous light, this oviposition was considerably attenuated but not made immediately arrhythmic. Egg-hatching and adult eclosion both commenced just before dawn. Some feature of the scotophase during or immediately after black-head formation apparently acts as a signal for hatching. Eclosion was controlled by light but its timing in the field was modified by temperature. The last 2–3 days of the pupal period constituted the most sensitive stage, and light signals received during this period determined the time of eclosion. Ecological advantages of these rhythms to the shootfly are discussed.     

Fecundity and Longevity of Green Vegetable Bug,Nezara viridula, Following Parasitism byTrichopoda giacomellii

The effects of parasitism by the ArgentinianTrichopoda giacomellii(Blanchard) on reproduction and longevity of its host,Nezara viridula(L.) are reported. Parasitoid larvae suppress egg maturation, reducing by 70% the fecundity of mature female hosts during the period of larval development. Egg viability was not affected, but mating frequency was reduced by approximately 50%. When parasitized as newly eclosed adults, 84% of females fail to reproduce. In male hosts, fertility and mating frequency were not affected during the period of larval parasitoid development. In male and reproductively immature female hosts, death was coincident with, or occurred shortly after parasitoid emergence (2–4 days); in mature females, death occurred on average 2 weeks after larval parasitoid emergence. Host mortality occurred as a consequence of tissue damage incurred as the parasitoid larvae emerged from the host. Some individuals survived parasitism though no further reproductive activity (mating or oviposition) occurred. The effectiveness ofT. giacomelliias a biological control agent is discussed in relation to its impact on reproduction and survival of its host and contrasted with the action of otherTrichopodaspecies.     

Photoperiodism of diapause induction in Thyrassia penangae (Lepidoptera: Zygaenidae)

Thyrassia penangae enters winter diapause as a prepupa in a cocoon. Photoperiodism of diapause induction was systematically investigated in this moth. The photoperiodic response curves under 24-h light-dark cycles showed that this insect is a typical long-day species. The critical daylength was 13 h 30 min at 25 °C, 13 h at 30 °C and 12 h 20 min at 28 °C. Transferring experiments from a short day (LD 12:12) to a long day (LD 15:9) or vice versa indicated that photoperiodic sensitivity mainly occurs during the larval period. In experiments using non-24-h light-dark cycles, when the length of photophase exceeded the critical daylength (13.5 h), was diapause inhibited effectively, even when the length of scotophase exceeded the critical nightlength (10.5 h). Only when a long scotophase was combined with a short photophase, diapause was induced effectively. This result suggests that daylength measurement is more important than nightlength measurement in T. penangae. Night interruption experiments under 24-h light-dark cycles exhibited two points of apparent light sensitivity, but the photosensitive position was highly influenced by temperature and the length of scotophase. Nanda-Hamner experiments failed to reveal the involvement of a circadian system in this photoperiodic time measurement. All light-dark cycles from LD 12:12 to LD 12:72 resulted in a short day response, and all cycles from LD 14:4 to LD 14:72 resulted in a long day response, suggesting that photoperiodic time measurement in this moth is performed by a day-interval timer or an hourglass-like clock.     

Nocturnal Calling Behavior in Mantids

Females of Mantis religiosa and Empusa pennata were video taped for several 24 h periods to determine if they showed behaviors associated with pheromone release. In the photophase the abdomen of both species was motionless and rested in continuous contact with the wings. However, at the beginning of the scotophase the females bent the abdomen ventrally so that the space between the abdomen and the wings increased significantly with respect to the daytime posture. Calling behavior (abdominal bending) was maintained throughout the 8 h scotophase and ended abruptly at lights on. Females of M. religiosa did not start calling until they were 30 days of age. Calling disappeared in mated females, but it reappeared two weeks later. Males stayed motionless in response to the odors emitted by other males or by noncalling females, but walked when a calling female was placed in the air flow. These observations suggest that female mantids bend their abdomens at night to release a sex pheromone. The adaptive function of nocturnal sex pheromone release in sexually cannibalistic species that rely strongly on visual cues for mating is discussed.     

Hunting for moving hosts: Cephalonomia tarsalis, a parasitoid of free-living grain beetles

The parasitic wasp Cephalonomia tarsalis parasitizes larvae of the saw-toothed grain beetle Oryzaephilus surinamensis, which feed on wheat grains. In contrast to most other host–parasitoid systems studied so far, the grain beetles are highly mobile within their habitat, bulk of grains in grain stores. This should increase the wasps’ problem to locate the hosts. To study the host-finding strategy of C. tarsalis females, the reaction of wasps to different grain and host-derived odour sources was tested in a four-chamber-olfactometer. These experiments revealed that wasps were attracted by healthy grains and mechanically damaged grains. In direct comparison, healthy and mechanically damaged grains are equally attractive. Both potential sources of host-derived odours, host faeces and trail-traces of larvae on filter paper were attractive to the wasps. The response to trail-traces vanished 30 min after larvae had been removed from the filter paper. With respect to the specificity of the odours, it turned out that wasps were attracted to odours from the seed–host complexes from O. surinamensis and Oryzaephilus mercator and the non-host complex of larvae of the granary weevil Sitophilus granarius in wheat grains. Odours from the seed–host complex were preferred. From these results, we hypothesize that host habitat location in C. tarsalis is achieved by using grain-derived odours. Within the habitat, wasps search for kairomones from host faeces and host trails. Following these larval trails finally leads wasps to their hosts.     

Calling behaviour ofMamestra brassicae: effect of age and photoperiod

Die periodicity of calling and the effect of age and photoperiod on calling behaviour were studied in virgin females of the cabbage moth,mamestra brassicae L. (Lepidoptera: Noctuidae). No calling activity was observed during the first scotophase. Most females called for the first time during the 2nd or 3rd scotophase after emergence, regardless of the photoperiod. Moths maintained under 16L: 8D started calling significantly later in the scotophase than those maintained under 18L: 6D. With increasing age, moths initiated calling significantly earlier. Under the 16L: 8D photoregime, the mean onset calling time decreased from scotophases 2 to 3, after which it stabilized around ca. 260 min after the start of the scotophase. With 18L: 6D, the onset of calling decreased until scotophase 4, and subsequently stabilized around ca. 130 min after lights off.Present address: Nodus Information Technology bv, University Business & Technology Center Vadaring 51, 6702 EA Wageningen, The Netherlands     

The effect of host size on quality attributes of the egg parasitoid,Trichogramma pretiosum

In a study of the quality ofTrichogramma pretiosum Riley (Hymenoptera: Trichogrammidae), we compared female wasps emerging from natural hosts, parasitized in the laboratory or the field with those emerging from factitious hosts used for commercial mass production. Females from the natural hosts were larger, more fecund, and longer lived than those from the factitious hosts. Compared to small females, large female wasps are substantially more fecund when honey (carbohydrate) is available but marginally more fecund when honey is unavailable. The size of a femaleT. pretiosum depends on two factors: the size of the host egg from which it emerges even when the wasp was gregarious, and the number of conspecifics that emerge with it. The similarities in the size distribution of female wasps emerging from natural hosts, in conjunction with the mechanism by whichTrichogramma measure host size and allocate eggs accordingly, suggests the hypothesis that size related components of fitness in femaleT. pretiosum are under strong selection in the field.     

Life history studies of <Emphasis Type="Italic">Prorops nasuta</Emphasis>, a parasitoid of the coffee berry borer

Life history studies were conducted in the laboratory on the African parasitoid Prorops nasuta Waterston (Hymenoptera: Bethylidae), a parasitoid of the coffee berry borer, Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae). The female wasp enters an infested coffee berry, kills the adult borer and seals the entrance of the berry with the body of the borer, impeding the entry of other organisms into the berry. The preoviposition period ranges from 3 to 14 days (mean 5.42 ± 0.37 SE). During this time females feed on the immature stages and paralyse fully grown larvae and pupae of the CBB. P. nasuta is an idiobiont solitary ectoparasitoid. Eggs are laid externally on the last instar larvae and pupae. Mean development time (egg to adult) for males and females was 27.7 (±0.37 SE) and 30 (±0.12 SE) days, respectively. Median survival for wasps fed on final instar CBB larvae was 27.7 days, significantly longer than any other treatment, while for females without food it was 2.5 days. In culture, females produced an average of 4.3 (±0.39 SE) progeny during their lifetimes. Adults began emerging at 30.6 days (±0.28 SE) after cultures were started and peak production was reached at 36 days, declining thereafter. Males normally emerged from coffee beans 2–3 days before females. Males usually emerged from 07:00 to 09:00h and females from 10:00 to 14:00 h. The culture sex ratio (proportion of males) was 0.21. Virgin females produced only male offspring.     

Interacting effects of photophase and scotophase on the diapause response of the Indian meal moth, Plodia interpunctella

The diapause-programming response to photoperiod in Plodia interpunctella was analyzed by exposing larvae to various 24-h and non-24-h regimes of light and darkness. The response to 24-h regimes indicated three photoperiodic parameters—a critical scotophase, a minimal photophase, and a minimal scotophase for a full expression of the response. The critical response was based on dark-time measurement, because disruption of the scotophase abolished the response and the diapause incidence varied as a function of scotophase in non-24-h regimes. The critical scotophase varied with the duration of the preceding photophase. Prevention of diapause by single or double-night interruptions of long scotophases could be explained by resetting of the dark-time measurement. The effect of a light pulse was modified by the quantitative interaction of light and dark reactions. The sensitivity to resetting by a light pulse seemed to be decreased in the early scotophase with an increasing duration of the preceding light period. Therefore, the significance of light in the photoperiodic response was something more than delimiting scotophase for the time measurement.