Effects of egg availability and egg maturity on the ovipositional activity of the parasitic wasp, Coccophagus atratus

ABSTRACT. Effects of egg availability on daily ovipositional activity were determined for Coccophagus atratus Compere (Hymenoptera: Aphelinidae). Females were observed for 6 h per day for their entire adult lives. Observed ovipositional activity was analysed in relation to egg maturation before and after emergence, egg depletion during oviposition and egg replenishment after oviposition. Ovipositional activity, including oviposition, inconsequential probes and searching for hosts, occurred predominantly in the first 30 min of exposure to hosts on the 2nd, 4th, 7th, 10th and 13th days after emergence. The remaining time was spent on non-ovipositional activities (preening, drinking honeydew and sitting on the glass of the experimental arena). Peaks of ovipositional activity were associated with high numbers of mature eggs in the ovaries. Eggs that remained in the ovaries after a bout of oviposition were apparently not mature even though they had attained their maximum size. Non-ovipositional activity continued until females had built up a reserve of about eighteen mature eggs. After each successive bout of oviposition, the rate of oogenesis slowed down. Consequently females took longer to accumulate a supply of eggs and periods of non-ovipositional activity increased.
We conclude that (1) the availability of eggs and the tendency of females to store mature eggs influences ovipositional activity, (2) full-sized eggs are not necessarily mature, (3) future experiments with C.atratus could be restricted to days of high ovipositional activity, and (4) the terms syn- and pro-ovigenic formulated by Flanders (1950) to describe apparent differences in oogenesis between various parasitic Hymenoptera do not apply to C. atratus and are therefore not universally applicable.     

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.

     

The dynamics of egg production, oviposition and resorption in a parasitoid wasp

1. The extent to which parasitoid wasps are limited by their egg supply is very important in understanding their reproductive strategies. Egg reserves are dynamic, with most wasps maturing new eggs throughout their life (synovigeny) and many species resorbing eggs that are not used in oviposition. We investigated the extent to which a parasitoid modulates its egg reserves in the light of its experience in finding hosts.
2. The egg dynamics of the Encyrtid Wasp Leptomastix dactylopii , a solitary parasitoid of mealybugs, were studied in the laboratory. This species is synovigenic and practises egg resorption.
3. We allowed newly emerged wasps to experience one of four environments of increasing value in terms of reproductive opportunities. We proposed that wasps that experienced good quality environments would maintain more mature eggs ready for oviposition. Dissection of wasps subject to different periods of host deprivation after the experimental treatment failed to confirm the hypothesis: egg load was independent of experience.
4. We also proposed that any adjustment of egg supply to make up for eggs oviposited would be effected through a reduction in egg resorption. Instead, we found that the wasp quickly made up for eggs oviposited by increased egg production.     

Oviposition and host-feeding patterns in Aphelinus asychis (Hymenoptera: Aphelinidae) at different aphid densities

Abstract. 1. The patterns of host-feeding and oviposition were examined in Aphelinus asychis Walker, which had been provided with second-instar pea aphids as hosts.
2. Female wasps responded to increasing host density (between one and forty aphids for 24 h) with an increasing tendency to oviposit rather than to feed. Superparasitism occurred at all aphid densities, even when unparasitized aphids were available.
3. Aphids intended for feeding were paralysed and died. Wasps did not feed on and oviposit in the same aphid.
4. Feeding to satiation lasted between 4 min and 42 min. Females that had starved for ≰18 h generally deposited one or more eggs before feeding again, while the reverse was true in wasps that had starved for 21 h.
5. The host-feeding behaviour of A. asychis is determined by a female's nutritional status. At low rates of host encounter, the anhydropic eggs may be resorbed. This reproductive strategy conforms to the destructive non-concurrent type among the Hymenoptera.     

Activity patterns and oviposition rates of Aphytis lingnanensis females,a parasitoid of California red scale Aonidiella aurantii: implications for successful biological control

1. Activity patterns of Aphytis lingnanensis Compere (Hymenoptera: Aphelinidae) females were determined. Females have a preovipositional period of 2–6.5 h and oviposit daily until they die. The average lifetime fecundity was 191 eggs (n = 10 females), with a maximum of 13 eggs per day, but usually far fewer. Females do not lay eggs at night as low light levels reduce the propensity to oviposit. 2. Aphytis lingnanensis females showed a repeatable pattern of activity during the course of the day, ovipositing actively during the first 1.5 h of their 7 h exposure to hosts. Thereafter, activity levels decreased sharply and females spent relatively long intervals resting. Activity occurred in fairly discrete bouts, with long periods of inactivity, ranging from 12 to 231 min between bouts. 3. Each day, females laid most eggs during their first bout of oviposition, with availability of mature eggs in the ovaries dictating the duration and intensity of ovipositional bouts. Once females completed a bout of oviposition in the laboratory, they moved away from the hosts even though many suitable hosts remained. They stood immobile, sheltering, until they matured more eggs. 4. These results suggest how general biological control models and dynamic state variable models of behaviour can be made more realistic. In particular, the behaviour of females does not remain constant over extended periods, particularly because of egg depletion, which suggests that the interaction between the ovipositional history of the individual and its physiological capabilities dictates the response of females to particular circumstances, and thus contributes to patterns of parasitism in the field. 5. It is predicted that A. lingnanensis females in the field are inactive at night and begin ovipositing when it becomes light enough in the morning. Egg depletion is likely if enough hosts are available, but should occur later in the day than was recorded in the laboratory. Egg-depleted females are likely to shelter while they mature more eggs, but may undertake interpatch movement.     

Taxon-specific multiplex-PCR for quick,easy, and accurate identification of encyrtid and aphelinid parasitoid species attacking soft scale insects in California citrus groves

Citricola scale, Coccus pseudomagnoliarum Kuwana (Hemiptera: Coccidae), is a serious pest of citrus in California’s San Joaquin Valley, but not in southern California where a complex of Metaphycus spp. Mercet (Hymenoptera: Encyrtidae) suppress it. This has created interest in using these (and other Metaphycus) species for biological control in the San Joaquin Valley. A critical step in assessing an organism’s potential for biological control is the ability to accurately identify it. For Metaphycus spp., this currently requires slide mounted adult specimens and expert taxonomic knowledge. We present a simple, quick and accurate method to identify any life stage of the ten major parasitoids of soft scales in California citrus, based on amplification of ribosomal DNA, using the polymerase chain reaction (PCR). Three multiplex-PCR protocols amplify products of taxon-specific sizes, allowing direct diagnosis of taxa accommodated by the PCR, and reducing identification time to a fraction of that of existing methods.     

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.     

Activity patterns in pregnant tsetse flies, Glossina morsitans

ABSTRACT. Actograph measurements of the spontaneous flight activity of isolated female Glossina morsitans morsitans Westw. were made through their first two pregnancy cycles in constant conditions under LD 12:12. Activity fell from a mean of c. 20 units/day to near zero during the 24 h preceding the day on which larvipositionoccurred. Activity on the day of larviposition rose significantly, to c. 35 units/day, then fell back to the baseline 20 units on subsequent days. The circadian pattern of activity was changed markedly by larviposition: 48 h before it, activity in the morning peak of the usual V-shaped diel pattern was twice normal; over 70% of the flies then fed, and the evening arm of their V disappeared; 24 h before larviposition, most flies were totally inactive, the few that did fly performing only 1 or 2 units/day, and only in the first and last hours of the photophase; on the day of larviposition, the morning peak of the V was reduced by c. 70%, and activity peaked instead during the post-noon 2–3 h, before and during the act of parturition. Almost all larvipositions occurred between noon and lights-out. It is suggested that the c. 48 h of pre-larviposition quiescence may play a role in the fact that pregnant G. morsitans females often survive non-residual aerosol insecticide campaigns.     

Activity patterns of springhares from the Eastern Cape Province, South Africa

The activity patterns of springhares Pedetes capensis ( Rodentia: Pedetidae ) from the Eastern Cape Province, South Africa, were investigated by counting the number of springhares active above ground at regular intervals throughout the night at different times of the year and under different weather conditions and phases of the moon. A combination of time of year, time of night and level of illumination best explained springhare activity, accounting for 43% of the variation in springhare numbers. Springhare activity generally reached its peak soon after dark, thereafter remaining fairly constant throughout most of the night and only decreasing in the 2–4-h period before sunrise. On those nights when the moon either rose or set during the night, this pattern was modified by the level of illumination. Springhares responded to moonlight by reducing above-ground activity, shifting activity to dark, moonless periods of the night, and by reducing their use of open space. Except for extremes, other weather conditions had no significant effect on springhare activity.     

Role of Coccophagus sp. in the suppression of the soft green scale Coccus viridis (Green) (Hompoptera: Coccidae) on sapota

The soft green scale Coccus viridis (Green) (Homoptera: Coccidae) has become a major pest of sapota, Manilkara achras (Mill.) Forberg in India. A field study was conducted on the population dynamics of soft green scale Coccus viridis (Green) for 2 years (2004–2006) on sapota at the Indian Institute of Horticultural Research (IIHR) farm, Bangalore, India. The population of green scale declined from 30.72 per leaf in May 2004 to 1.62 per leaf in March 2006. Two coccinellid predators Chilocorus nigrita (Fab.) and Cryptolaemus montrouzieri (Muls.) and one aphelinid parasitoid Coccophagus sp. were recorded on C. viridis. Both the predators played a minor role in the population fluctuation of C. viridis. The parasitoid Coccophagus sp. was the dominant natural enemy observed throughout the study recording a mean of 10.24–94.67% parasitism. A significant positive correlation of the scale population with minimum temperature (r=0.54) and negative relationship with the parasitism by Coccophagus sp. (r=0.81) was recorded. Multiple regression analysis revealed that 75.7% of the variation present in the green scale population could be predicted by abiotic factors and parasitism by Coccophagus sp. Further, step-wise regression procedure employed to arrive at a multiple regression model showed that about 65.60% of the scale population could be predicted by one factor namely, parasitism by Coccophagus sp. These results showed that parasitism by Coccophagus sp. played a major role in regulating the population of the soft green scale infesting sapota.     

Life-history and oviposition behaviour of Amitus bennetti, a parasitoid of Bemisia argentifolii

Amitus bennetti Viggiani & Evans (Hymenoptera: Platygasteridae) is a recently described parasitoid of the silverleaf whitefly, Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae). Behaviour and life history of the parasitoid are described. The first nymphal instar of B. argentifolii is preferred by the parasitoid, but the 1st through 4th instar may be parasitised. Females first investigate hosts with their antennae, then walk over the host, and eventually step with their front legs on the leaf and insert their ovipositor inside the host facing away from the host, while the hind legs are still on the host. The time from encounter to oviposition (=latency to oviposition) is shortest on the 1st instar. Oviposition duration (mean=39 s) comprises 50% of the handling time. Development time from egg to adult decreases from 72 days at 15 °C to 42 days at 20 °C to 28 days at 25 °C. We estimate that 400 degree days is required for development, with a development threshold of 10 °C. Adult longevity in the absence of hosts was 29, 26 and 19 days and with hosts present 8, 8 and 5 days at 15, 20 and 25 °C, respectively. Amitus bennetti is proovigenic and oviposits most eggs shortly after adult emergence. During the first day of their adult lives females laid 1, 31 and 49 eggs at 15, 20 and 25 °C, respectively. Compared with other parasitoid species, the development time of A. bennetti is very long, and the implications of this for management of B. argentifolii are discussed.     

A comparison between the amino acid composition of an egg parasitoid wasp and some of its hosts

Amino acid compositions of the eggs of five lepidopteran hosts for Trichogramma minutum were compared with each other and with a non-host species, Rhodnius prolixus, in which T. minutum oviposits but does not develop. Host eggs are quite homogeneous, particularly when compared according to groupings of potentially interconvertible amino acids. Combined mole percent values for glycine, serine and alanine were higher in hosts (27.5–29.2 mole%) than in R. prolixus eggs (21.5 mole%), in bovine serum albumin (14.9%), which has been used as a protein source in artificial diets for T. minutum, or in many of the mixtures used in published diets for this species. Since these three amino acids make up 26.3 mole% of the adult amino acid content of T. minutum, their deficiency in diets could require metabolic compensation detrimental to development.Adult T. minutum arising from eggs of Manduca sexta, Choristoneura fumiferana, and Sitotroga cerealella are similar in amino acid composition to each other and, in general, to their hosts. Variability appears greater in hosts than in adult wasp composition, suggesting some interconversion of host amino acids to accommodate inflexible nutritional requirements of T. minutum.In the three host species tested, free amino acids constituted 15.8–19.3% by weight of the amino acid in egg contents. In M. sexta eggs, glycine, serine and alanine together make up 28.4% by weight of the total free amino acid, a much higher proportion than in many published diets. The four free amino acids (isoleucine, leucine, phenylalanine and histidine) reported to be oviposition stimulants in experiments on encapsulated diets are present in sufficient concentrations to induce oviposition in the host species tested and in R. prolixus. S. cerealella egg contents having approximately 1.8 g amino acid, yield one or rarely two adult T. minutum (1g amino acid/insect). In contrast, M. sexta eggs with 94 g amino acid each yield an average of 10–12 adults (8.2g amino acid/insect). This suggests that small hosts are allocated few eggs which can only develop into small adults because of nutrient supply (parasitoid size in metabolically restricted), whereas much larger hosts are allocated proportionately fewer eggs than the former resulting in larger, and presumably more viable and fecund, adults (parasitoid size is established behaviourally).     

Facilitation, competition, and vegetation patchiness: from scale free distribution to patterns

A new technique for the modeling of perennial vegetation patchiness in the arid/semiarid climatic zone is suggested. Incorporating the stochasticity that affects life history of seedlings and the deterministic dynamics of soil moisture and biomass, this model is flexible enough to yield qualitatively different forms of spatial organization. In the facilitation-dominated regime, scale free distribution of patch sizes is observed, in correspondence with recent field studies. In the competition controlled case, on the other hand, power-law statistics is valid up to a cutoff, and an intrinsic length scale appears.     

Influence of host deprivation on egg load and oviposition behaviour of Brachymeria intermedia, a parasitoid of gypsy moth

Abstract. Mated female Brachymeria intermedia (Hymenoptera: Chalcididae) deprived, since emergence, from pupae of their host Lymantria dispar (Lepidoptera: Lymantriidae), accumulated eggs but had a very low rate of hostacceptance. Parasitoids that were host-deprived after encountering pupae early in life also accumulated eggs, but maintained a high acceptance rate. Thus early exposure to hosts promoted active reproductive behaviour. Total egg production depended on the total number of pupae encountered, indicating that B.intermedia adjust their egg production to host availability. Hence, in B. intermedia both the physiological state of the parasitoid (age and egg load) and the informational state (in this case host-availability and experience) interact to shape oviposition behaviour.     

Activity and ranging patterns in relation to fruit utilization by Brown Capuchins (Cebus apella) in French Guiana

I studied brown capuchins (Cebus apella)in primary forest in French Guiana. They displayed different feeding and ranging patterns in response to changes in fruit availability and distribution. When fruit was scarce and patchily distributed, foliage/stem feeding and invertebrate foraging was high, and capuchins limited their daily movement to <2 km, focusing on large fruit patches. When fruit was in average supply and scattered throughout the forest, the proportions of foliage/stems and invertebrates in the diet decreased, and the day range length increased to 2.8 km. When fruit was abundant and widespread, foliage/stems were rarely eaten, while invertebrate foraging increased, and. the daily locomotor distance was reduced to 2 km.     

Activity patterns of females of the solitary bee Anthophora plumipes in relation to temperature, nectar supplies and body size

Abstract.

• 1 Patterns of activity at a large nesting aggregation and at foraging sites are described for females of the solitary bee Anthophora plumipes (Pallas). Changes in the quality and quantity of the resource collected by females provisioning cells are related to variation in female body mass and microclimate.
• 2 Activity at the nest site demonstrated relationships with aspects of the thermal environment experienced by A.plumipes. Measures of temperature showing significant relationships differed for females in different stages in the nesting cycle exhibiting characteristically different behaviour patterns.
• 3 Larger females emerged from nest tunnels earlier in the morning and provisioned cells at lower ambient temperatures than smaller individuals. Body size therefore predicts reproductive success at low ambient temperatures.
• 4 Pollen and nectar loads carried by females increased with ambient temperature. Because only one cell is completed per day and the size of offspring is determined by the quality and quantity of resource provided by the mother, the body size of individuals emerging in the following season will depend on interactions between climate and body size, in addition to any heritable component.
• 5 Variation in activity levels at foraging sites is attributed not only to thermal considerations, but also to variation in the quality of rewards available at different floral sources.

     

Sex allocation and egg distribution of an autoparasitoid, Encarsia pergandiella (Hymenoptera: Aphelinidae)

Abstract. 1. Encarsia pergandiella Howard females develop as primary parasitoids on immature whiteflies, and males develop as secondary parasitoids on females of their own or a related species. The hypothesis that the sex ratio reflects the relative abundance of the two host types was tested in the laboratory using petri dish arenas with varying proportions of early fourth instar greenhouse whitefly (Trialeurodes vaporariorum (West.)) (primary hosts) and pupal female E.pergandiella (secondary hosts). Egg distribution was analysed with respect to sex ratio, super-parasitism and host discrimination.
2. The proportion of primary and secondary hosts parasitized in each treatment reflected the relative availability of each host type. Thus females presented with 75% primary hosts laid more female eggs than male. However, in all treatments, a greater proportion of secondary hosts were parasitized than would be expected from the proportion of secondary hosts available. This indicates that more male eggs were laid than expected.
3. More secondary hosts than primary hosts were superparasitized.
4. Host discrimination analysis using a new test statistic showed that females generally laid eggs at random with regard to previous parasitism of primary or secondary hosts. However, females in one treatment with 50% of each host type appeared to preferentially oviposit in secondary hosts which did not contain any eggs.