Organic matter sources and size structuring in stream invertebrate food webs across a tropical to temperate gradient

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When good bugs go bad: intraguild predation by Jalysus wickhami on the parasitoid, Cotesia congregata

We report a case of direct intraguild predation involving an insect predator and parasitoid in an agricultural system. The spined stilt bug, Jalysus wickhami Van Duzee, feeds on eggs of the tobacco hornworm, Manduca sexta L., and also on prepupal and pupal stages of the gregarious hornworm parasitoid, Cotesia congregata (Say). In two separate trials, mean mortality of attached parasitoids was significantly lower (66%, 73%) than that of their detached siblings (97%, 96%) after a 3 day exposure to stilt bugs, demonstrating that attachment to the host offered some protection against predation. In no-choice experiments, prepupal parasitoids suffered greater mortality (0 day-old=61%, 1 day-old=65%) than pupal parasitoids (2 day-old=50%, 3 day-old=14%). When offered in combination with 0 or 2 day-old hornworm eggs, respective mortality of 0, 1, 2 and 3-day-old pupal parasitoids showed a similar pattern (67%, 63%, 33% and 23%). In another experiment, mortality of 0-day-old pupal parasitoids (64%) was greater than that of 3 day-old pupal parasitoids (38%). Mortality of pupal parasitoids was not affected by the availability of hornworm eggs, a highly acceptable food. Younger pupal parasitoids (=prepupae) probably suffered greater mortality because they were more easily fed on by stily bugs than older (pupated) ones. Because C. congregata overwinters in the prepupal stage, it may be particularly vulnerable to attack late in the season when stilt bug populations are large and hornworm eggs are relatively uncommon.     

Primary sex-ratio and differential progeny survivorship in solitary haplo-diploid parasitoids

ABSTRACT.

• 1 A method of partitioning emergence sex-ratio to give estimates of primary sex-ratio and male and female offspring survival from oviposition to emergence in solitary haplo-diploid parasitoids is presented.
• 2 This method is applied to sex-ratio data from a larval parasitoid, Aphidius ervi Haliday, and a pupal parasitoid, Coccygomimus turionella L., parasitizing a range of host types.
• 3 There was no evidence of facultative control of primary sex-ratio in either species. Parasitoid emergence sex-ratios were similar for all host sizes attacked by C. turionella. In contrast, emergence sex-ratios of A.ervi showed a significant male bias in smaller hosts. This shift in emergence sex-ratio was attributable to differential progeny survival.
• 4 Pre-emergence mortality in both species was a function of host size, with few offspring surviving from small hosts. This suggests that host size may be an important component in the dynamics of host-parasitoid interactions.
• 5 The evolution of sex-ratio regulatory mechanisms in solitary haplo-diploid parasitoids is discussed in the context of parasitoid life-history. We suggest that there is a constraint to the evolution of the facultative control of primary sex-ratio in parasitoids attacking larval stages as a result of the uncertainty of future host resource acquisition rates.

     

Diapause and cold tolerance in Asian species of the parasitoid Leptopilina (Hymenoptera: Figitidae)

Diapause and cold tolerance are essential for temperate insects to pass the winter, with the mechanisms controlling these two traits varying considerably among insects. In the present study, diapause and cold tolerance are compared among three Leptopilina species: Leptopilina japonica Novkovi? & Kimura, Leptopilina victoriae Nordlander and Leptopilina ryukyuensis Novkovi? & Kimura, all larval parasitoids of frugivorous drosophilid flies, with the aim of understanding their climatic adaptations. The first species is divided into the temperate (Leptopilina japonica japonica) and subtropical subspecies (Leptopilina japonica formosana), and the latter two species are distributed in the tropical and subtropical regions. The temperate subspecies of L. japonica enters prepupal diapause at low temperatures (15 or 18 °C), irrespective of photoperiod, and some individuals enter diapause when exposed to 0 °C for 1 or 2 day(s) or when placed at low humidity. Leptopilina victoriae also shows signs of diapause initiation at 15 °C, although L. ryukyuensis and L. j. formosana from the subtropical regions do not. Preimaginal viability at low temperature (13, 14 or 15 °C) is usually lower in L. victoriae from the tropical regions compared with L. japonica or L. ryukyuensis from the temperate or subtropical regions. Diapausing prepupae of the temperate subspecies appear to be cold tolerant. However, the cold tolerance of nondiapausing prepupae, pupae and adult females varies little among the tropical, subtropical and temperate species or subspecies, and adult males of the temperate subspecies of L. japonica are less cold tolerant than those of the tropical or subtropical species or subspecies. Cold tolerance may be unnecessary, except for diapausing individuals of the temperate species, because nondiapausing individuals appear in warmer seasons.     

Temperature‐dependent development of the great European spruce bark beetle Dendroctonus micans (Kug.) (Coleoptera: Curculionidae: Scolytinae) and its predator Rhizophagus grandis Gyll. (Coleoptera: Monotomidae: Rhizophaginae)

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Response of maize stemborers and associated parasitoids to the spread of grasses in the rainforest zone of Kisangani,DR Congo: effect on stemborers biological control

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Plankton dynamics under different climate conditions in tropical freshwater systems (a reply to the comment by Sarmento,Amado & Descy, )

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Drosophila parasitoids (Hymenoptera) of Japan

The Drosophila parasitoid system is an excellent model for the study of biological and ecological interactions. In Japan, extensive studies have been carried out on Drosophila parasitoids since the early 2000s. Here we provide up-to-date information on their diversity, distributions, host use and reproductive mode. Until now, 45 wasp species have been recorded. In addition, four genetically distinct groups (tentatively assigned as “races”) have been found in Ganaspis brasiliensis (Figitidae). Most of them are larvo-pupal parasitoids belonging to the families Figitidae and Braconidae, and some are pupal parasitoids of the families Pteromalidae and Diapriidae. A species of Encyrtidae was also recorded. Their major hosts are indicated with information on the host's breeding sites. Except Ganaspis xanthopoda and two races of G. brasiliensis that are distributed both in tropical and temperate regions, they are divided into tropical and temperate species. The tropical species are mainly distributed in Southeast Asia, and their distributions in Japan are restricted to the Ryukyu islands, particularly Iriomote-jima. The temperate species have been recorded from the main islands of Japan and surrounding islands but not from the Ryukyu islands, except two braconid species, Asobara japonica and Phaenocarpa sp. TK1. Some of the temperate species have also been recorded from Korea, China, Europe and/or North America. Among the 45 Japanese parasitoid species, at least seven are assumed to be thelytokous.     

Parasitoid assemblages of soybean defoliator Lepidoptera in north-western Buenos Aires province, Argentina

1 The objective of this study was to examine the structure of parasitoid assemblages attacking soybean defoliator Lepidoptera in north-western Buenos Aires province, Argentina. 2 Through larvae sampling from 1992 to 1996, and laboratory data plus the known biology of the species recorded during the study, parasitoid species composition, richness, number of guilds per host species, and levels of parasitism, were determined. 3 Total species richness was 23, all species were primary endoparasitoids, and categorized as koinobionts. They belonged to Hymenoptera (11 species) and Diptera (12 species). Rachiplusia nu (Noctuidae) hosted the highest number of parasitoid species. 4 Four parasitoid guilds were recorded for R. nu (egg–prepupal endoparasitoid, early larval endoparasitoid, late larval endoparasitoid, and larval–pupal endoparasitoid); two for Spilosoma virginica (Arctiidae) (late larval endoparasitoid and larval–pupal endoparasitoid) and Colias lesbia (Pieridae) (early larval endoparasitoid and larval–pupal endoparasitoid); and one for Anticarsia gemmatalis (Noctuidae) and Loxostege biffidalis (Pyralidae) (early larval endoparasitoid). 5 Only four out of seven potential parasitoid guilds defined for Lepidoptera were recorded in a soybean agroecosystem located in north-western Buenos Aires province, suggesting that potential host niches were not totally utilized. 6 Soybean lepidopteran defoliators supported a mean species richness of 4.8 parasitoids, a result that is similar to that reported for exophytic hosts in the Neotropics. 7 Parasitoid assemblages from each host differed in species composition, richness, number of guilds, and levels of parasitism.     

The developmental strategy of an idiobiont ectoparasitoid, Dendrocerus carpenteri : influence of variations in host quality on offspring growth and fitness

Dendrocerus carpenteri (Curtis) (Hymenoptera: Megaspilidae) is a solitary hyperparasitoid, which attacks prepupal and pupal stages of hymenopteran parasitoids inside mummified aphids. The larva feeds externally on the host, which is envenomed by the female at oviposition. To evaluate the influence of variations in host quality on the growth, development and fitness of D. carpenteri, we varied the size and developmental stage of the primary parasitoid host (Aphidius ervi Haliday), which was reared on different instars of pea aphid [Acyrthosiphon pisum (Harris)] and English grain aphid [Sitobion avenae (F.)]. Within each kind of host, females eclosed from the relatively larger mummies, while males eclosed from the smaller mummies. Host size and hyperparasitoid size were correlated, and females were larger than males. In hyperparasitoids developing on prepupal and pupal hosts, development time from oviposition to adult eclosion was proportional to size; females required more time for development than males. The mean relative growth rate was the same in males and females and increased with host quality, as predicted by the growth model of Mackauer and Sequeira (1993) for idiobiont parasitoids. Larvae developing on late-pupal stages and pharate adults of A. ervi were unable to consume sclerotized host tissues; they were smaller and needed more time for development. The average number of mature eggs at eclosion was six, except in females developing on suboptimal hosts, which contained only one egg or none. Egg volume was correlated with female size, possibly reflecting differences in larval ontogeny. We provide equations describing the relationship between host quality as indexed by hind-tibia length of the mummified aphid and adult body size in terms of dry mass, development time and mean relative growth rate of D. carpenteri. We discuss the usefulness of host size as a proxy of host quality for idiobiont parasitoids, and provide examples of exceptions. Received: 14 December 1997 / Accepted: 23 July 1998     

Some factors affecting the composition of tropical ichneumonid faunas

An increasing accumulation of data shows that tropical ichneumonid faunas are no more species-rich than extra-tropical ones, despite the fact that most of their host groups show increased tropical species-richness. This lack of increase in ichneumonid species-richness can be attributed to the absence of groups whose hosts are not present (e.g. Ctenopelmatinae) and poor tropical representation by many groups of diurnal koinobionts (e.g. Campopleginae). Low host density has been postulated as a barrier to tropical koinobiont species-richness, but it is here suggested that this is not the only limiting factor as groups of nocturnal koinobionts, such as the Ophioninae, show increased tropical species-richness. It is postulated that koinobionts have the capability of being able to locate sparse hosts, but as they host-search in flight, a prolonged daytime host-searching period in the tropics would expose them to a high level of predation pressure. By being active at night koinobionts can avoid diurnally active predators. It is also postulated that sparse hosts may be located more easily at night and more habitats may be climatically suitable for ichneumonid activity when they are not subject to direct sunlight. Idiobionts, such as the Mesostenini and Pimplini, are more species-rich and morphologically diverse in the tropics than they are in extra-tropical regions. It is suggested that this results from the fact that tropical idiobionts can be active during the whole of the diapausing period, when their hosts are available, whereas activity by temperate idiobionts is prevented by inclement weather. Although many idiobionts are probably less exposed to predators than koinobionts, many have evolved obvious protective devices.     

蓖麻蚕个体发育中蜕皮甾类滴度的变化

用放射免疫分析法(RIA)测定了蓖麻蚕(Philosamia cynthia rieini)从卵期到成虫个体发育整个过程的蜕皮甾类(MH)水平.卵期在6天时有一个MH峰.一龄到四龄各龄均有一个MH峰,出现在停食前一天,导致幼虫蜕皮.五龄期有两个MF峰.第一个小峰出现在第三天,使进食的幼虫向预蛹转化;第二个高峰在上簇两天后,导致蛹表皮的形成.与其它鳞翅目昆虫一样,蛹期只有一个MH峰,发生在蛹期的前半段.成虫期血淋巴内MH含量很低.     

Parasitoids of the arctiid mothPareuchaetes pseudoinsulata (Lep.: Arctiidae), an introduced biocontrol agent against the weedChromolaena odorata (asteraceae), in asia and Africa

The leaf-feeding arctiid mothPareuchaetes pseudoinsulata has been released widely in tropical countries for the control of the weedChromolaena odorata. P. pseudoinsulata is now widespread and locally abundant in Ghana, Indonesia, India, Sri Lanka, Malaysia, Micronesia and the Philippines. In the West Indies where it is native,P. pseudoinsulata is host to 2 species of egg parasitoids, 4 species of tachinid larval parasitoids, 1 larval-pupal parasitoid, and 1 pupal parasitoid, as well as a virulent nuclear-polyhedrosis virus.P. pseudoinsulata is not significantly parasitised where it is established in south-east Asia, Oceania or Africa. No egg parasitoids have been reported, and only 3 larval or larval-pupal parasitoids. Only one of these, the larval-pupal tachinidExorista xanthaspis, is regularly encountered, and rarely exceeds 10% parasitism in the field. These results confirm the pattern that herbivorous insects from families with exposed larvae are unlikely to be heavily parasitised in a new geographic range.     

Are galling insects better protected against parasitoids than exposed feeders?: a test using tenthredinid sawflies

ABSTRACT.

• 1 Data mostly from the published literature were used to assess the effect of galling on the number of parasitoid species per host species in the phylogeny of nematine sawflies from free external feeders (colonial and solitary) to leaf gallers and shoot gallers.
• 2 The strongest effects of galling were the total elimination of the species-rich cocoon-attacking guild of parasitoids, and eonymphal parasitoids, from the parasitoid community on shoot gallers, all of which are in the genus Euura.
• 3 All tachinid larval parasitoids were also eliminated by the galling habit.
• 4 The cumulative effects of these exclusions resulted in a decline in mean number of parasitoid species per host species from almost sixteen species on external colonial feeders to 4.0 species on shoot gallers.
• 5 General patterns in per cent parasitism by non-tachinid and tachinid larval parasitoids, eonymphal and cocoon parasitoids, on exposed feeders to shoot gallers, showed declines in non-tachinid attack and elimination of tachinid, eonymphal and cocoon parasitoids. But leaf gallers tended to be attacked more than exposed feeders by non-tachinid larval parasitoids.
• 6 The galling habit had a long-term impact by reducing the number of parasitoid species attacking nematine sawfly gallers and per cent mortality inflicted, so that natural enemies may have been important as a selective factor in the evolution of galling nematine sawflies.

     

Brood sex ratios of the solitary parasitoid wasp, Coccophagus atratus

Abstract.

• 1 Female eggs of Coccophagus atratus are deposited within the haemolymph of coccoid scale insects. Male eggs are deposited on to late larval and prepupal stages of parasitoids of scale insects, including conspecifics.
• 2 When presented with either one host type or a combination of both host types, female C.atratus deposit all their available eggs, assigning the appropriate sex egg to each host encountered. Brood sizes are not adjusted for different combinations of hosts.
• 3 Behavioural observations show that females do not move away from patches of hosts until all their eggs are laid, regardless of the host type.
• 4 Brood sex ratios varied with changes in the relative availability of hosts for males and hosts for females. When both host-types were present in equal numbers, male biased sex ratios resulted (mean ±SEM =0.71 ± 0.009) and when 70% of hosts provided were suitable for female eggs, mostly female-biased sex ratios resulted (mean ± SEM = 0.37±0.01).
• 5 Our results do not fit predictions based on the assumption that a sex ratio of 0.5 should be expected in C.atratus. Observed sex ratios indicate that the unusual life histories of these parasitoids need to be taken into account in explanations of their sex ratios.

     

Parasitism and predation as agents of mortality of winter moth populations in neglected apple orchards in Nova Scotia

Abstract.

• 1 This study compared the roles of pupal mortality and parasitism in winter moth (Operophtera brumata) population dynamics in Nova Scotian apple orchards and assessed the importance of beetles as pupal predators.
• 2 The component of pupal mortality termed predation accounted for greater stage-specific mortality of winter moth than parasitism by Cyzenis albicans in four neglected orchards.
• 3 Parasitism by Cyzenis albicans was not spatially density-dependent in any orchard, whereas the predation component of pupal mortality was spatially density-dependent in the two orchards most densely populated by winter moth.
• 4 Field experiments indicated that over 60% of pupal predation may be attributed to beetles, and that about 46% of pupal predation occurred within 4 weeks after pupal drop.
• 5 Mortality of introduced populations of winter moth in Nova Scotia resembles that of native populations in England where density-dependent predation regulates the winter moth population and reduces the parasitoid population to minimal levels. The situation in Nova Scotia appears to have changed appreciably since the establishment of parasitoids into the system in the 1950s.

     

The Species and Size Composition of Tropical Freshwater Zooplankton with Special Reference to the Oriental Region (South East Asia)

A contrast between temperate and tropical Cladocera, Copepoda and Rotifera zooplankton fauna shows a markedly different size composition and species diversity. There are fewer species, and these are generally smaller in the tropics than in either the North or South Temperate Zones. Larger species of the genera Daphnia and Simocephalus are relatively rare in the tropics, while members of Eurycerus and Saycia are absent. Members of the families Holopedidae, Leptodoridae and Polyphemidae increase in abundance toward the temperate regions. Two small cyclopoid copepods are common in tropical zooplankton, while many of the common larger species of other regions are absent or very rare. The chief rotifer components are Keratella tropica and species of Brachionus.     

Phytoplankton and its dynamics in two tropical lakes: a tropical and temperate zone comparison

Temporal patterns of phytoplankton biomass and community structure are described for two Kenyan lakes and subsequently compared with patterns reported in other tropical and temperate lakes. Lake Naivasha had a lower and more seasonally variable (10×) biomass, with a seasonal shift between diatoms and blue-greens, while the L. Oloidien biomass was less variable (3.7×) and dominated by blue-greens. Biomass and chlorophyll a were strongly correlated and in turn were coupled to the level of total phosphorus. A total of 143 and 94 taxa were described for L. Naivasha and L. Oloidien, respectively.The comparative analysis showed: a) a paucity of exclusively tropical species; b) that more than 30 percent of the species in two highly saline Kenyan lakes were also present in the two freshwater lakes; c) no evidence for a postulated decline of phytoplankton species abundance with latitude from the temperate zone to the tropics; d) that the low fraction of chrysophyte biomass in tropical lakes is a function of trophy rather than of latitude; e) that the fraction of chlorophyte biomass in tropical lakes is generally higher than in temperate lakes; f) that the proportion of nannoplankton in the two Kenyan freshwater lakes is not different from that in temperate lakes of the same trophy; g) that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone; h) evidence for large inter-year difference in the max.:min. biomass ratio in the only tropical lake (L. Naivasha) for which such data are available; i) that an average biomass ratio appears predictable for tropical lakes from the proportion of the sediment surface in contact with epilimnetic water. Overall, no evidence was found that the freshwater tropical phytoplankton composition or dynamics differ in any fundamental fashion from that observed in the temperate lakes during the summer.Contribution number 147 of the Limnology Research Centre, McGill University.     

日本佳盾蜾蠃的生物学特性观察

日本佳盾蜾蠃Euodynerus nipanicus（Schulthess）是一种重要的独栖捕食性天敌昆虫,对我国南方林区鳞翅目蛾类害虫的控制具有一定作用。本文报道了日本佳盾蜾蠃的形态特征、生活史及幼虫和成虫的行为等生物学特性。该蜂在江西赣州地区 1 年发生 4 代,以滞育的老熟幼虫在巢管虫室内越冬,滞育期约 190 d。翌年的4月下旬成虫开始外出活动,主要包括交配、筑巢、产卵、捕食等行为。通过野外收集筑巢巢管,室内饲养观察等,发现该蜂的卵近似微弯的长圆柱形,长 2.912 ± 0.127 mm,卵期2-4 d,平均 2.5 ± 0.99 d;非越冬幼虫期 8. 1 ± 0. 99 d;预蛹期4.3 ± 0. 48 d;蛹期7. 4 ± 0.84 d;雌雄比约为 2. 95:1。本研究丰富了日本佳盾蜾蠃的生物学基础知识,为进一步利用该蜂防治南方林区鳞翅目蛾类害虫提供了依据。     

Population regulation of a mosquitoArmigeres theobaldi with description of the animal fauna in zingiberaceous inflorescences

1. Inflorescences of some Curcuma and Zingiber (Zingiberaceae) in tropical Asia provide an unique aquatic habitat being discrete, small, and made of numerous smaller compartments (the bracts).
2. The aquatic community in inflorescences of Curcuma in northern Thailand was composed of immature Diptera, of which the biting midge Dasyhelea and the mosquito Armigeres theobaldi were the commonest. No important competitors, predators or pathogenic parasites for the mosquito were confirmed.
3. Inter-inflorescence distribution of the mosquito was contagious. Within each inflorescence, the fourth-instar larvae or pupae usually occupied bracts singly.
4. The k-value analysis detected density-dependent mortality due to contest competition in the mosquito larvae.
5. Variations in the larval and pupal mosquito size were density-independent and remarkably small as compared with size variations known for other mosquitoes.
6. These population attributes (large density-dependent mortality with density-independent, minimally variable individual size) appear unique among mosquitoes, arising from conspecific killing, efficient foraging (inter-bract movement by crawl and single occupation of bracts), and availability of host plant tissues as supplementary food.
7. A simple population model suggested that a small proportion of adult females lay eggs.