Parasitoid developmental mortality in the field: patterns, causes and consequences for sex ratio and virginity.

1. Sex ratio theory predicts that developmental mortality can affect sex ratio optima under Local Mate Competition and also lead to 'virgin' broods containing only females with no sibling-mating opportunities on maturity. 2. Estimates of developmental mortality and its sex ratio effects have been laboratory based, and both models and laboratory studies have treated mortality as a phenomenon without identifying its biological causes. 3. We contribute a large set of field data on Metaphycus luteolus Timberlake (Hymenoptera: Encyrtidae), an endoparasitoid of soft scale insects (Hemiptera: Coccidae), which has sex allocation conditional on host quality and female-biased brood sex ratios. Developmental mortality within broods can be both assessed and attributed to distinct causes, including encapsulation by the host and larval-larval competition. 4. Thirty per cent of M. luteolus offspring die during development with 65% of this mortality because of encapsulation and 28% because of larval competition. The distributions of mortality overall and for each cause of mortality separately were overdispersed. 5. The probability of an individual being encapsulated increased with clutch size, while the probability of being killed by a brood mate declined with increasing clutch size and with increasing per capita availability of resources. 6. The sexual compositions of broods at emergence were influenced by both the degree and the type of mortality operating. At higher levels of mortality, single sex broods were more common and sex ratios were less precise. Overall, virginity was more prevalent than predicted and was more greatly affected by the occurrence of competition than by other sources of mortality, almost certainly because competition tended to eliminate males. 7. The reproductive and developmental biology of M. luteolus appears to be influenced by a complex interplay of maternal clutch size and sex allocation strategies, offspring-offspring developmental interactions, host defence mechanisms and postemergence mating behaviour. Despite the great sophistication of sex ratio theory, it has not yet evolved to the point where it is capable of considering all of these influences simultaneously.

Sequential hypothesis testing techniques for pest count models with nuisance parameters.

Sequential hypothesis testing in pest management applications are usually carried out using Wald's procedure or Iwao's procedure. Both of these procedures are applicable for one-parameter pest count models. The current practice for handling nuisance parameters when using the Wald procedure is to assume they are equal to specified values based on historical experience, and in the case of Iwao's procedure to assume a known mean-variance relationship such as Taylor's power law. In this article, we discuss the weaknesses of these practices, and advocate the use of Bartlett's sequential procedure as a better way to handle nuisance parameters. We also show how Bartlett's procedure can be implemented within three-hypothesis testing scenarios, where differentiation between three levels of infestation is desired.

Feasibility of tracking within-field movements of Homalodisca coagulata (Hemiptera: Cicadellidae) and estimating its densities using fluorescent dusts in mark-release-recapture experiments.

A mark-release-recapture technique was developed and tested for use in tracking the field movements of adult glassy-winged sharpshooters, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), in various agricultural and urban plantings. Greenhouse experiments in which adult H. coagulata were marked with one of five colored fluorescent dusts (Aurora Pink-All, Horizon Blue-A19, Blaze Orange-A15N, Saturn Yellow-A17, and Corona Magenta-A21) and released into cages with citrus seedlings showed that their mortality rates during a 30-d period were statistically similar to that of the undusted controls. Adults marked with a sixth dust color (Signal Green-A18N) suffered higher rates of mortality than did the undusted controls and thus were eliminated from further consideration. Adult H. coagulata marked with one of the five accepted colors of fluorescent dust were able to fly beyond 100 m in a field devoid of vegetation within minutes of their release, and the marking did not affect overall flight behavior significantly compared with that of the undusted controls. However, at wind speeds above 5 m/s, percentage recapture was significantly reduced, which indicates that both dusted and undusted adults were unable to orient their flight. In total, 41,124 marked and unmarked adults were released in the three field experiments in southern California (Riverside and Kern counties) during 2000 and 2001 to evaluate flight dispersal and estimate densities of H. coagulata. The mark-release-recapture and feral data obtained during the June, July, and August 2001 studies, when coupled with the Lincoln index, yielded estimates of adult H. coagulata of 1.2 and 2.2 million per ha, respectively, at a San Joaquin Valley (Kern Co.) and a southern California (Riverside Co.) citrus grove. The use of colored dusts to mark H. coagulata proved to be reliable, cost-effective, and time-efficient for mark-release-recapture studies with this insect within a citrus grove, but they are less likely to be useful for studies of adult H. coagulata movements among plantings.

Sex ratios in field populations of two parasitoids (Hymenoptera: Chalcidoidea) of Coccus hesperidum L. (Homoptera: Coccidae).

We tested several assumptions and predictions of host-quality-dependent sex allocation theory (Charnov et al. 1981) with data obtained for the parasitoid Metaphycus stanleyi Compere on its host, brown soft scale (Coccus hesperidum L.), in a California citrus grove and in the laboratory. Scales ceased growing after parasitization by M. stanleyi. Thus, M. stanleyi may gauge host quality (=size) at oviposition. Host size positively influenced adult parasitoid size, and parasitoid size in turn influenced adult longevity of M. stanleyi. However, parasitoid fitness gains with host size and adult size were similar in males versus females. Sex allocation to individual hosts by M. stanleyi depended on host size; females consistently emerged from larger hosts than males. Host size was important in a relative sense; the mean host sizes of females versus males, and of solitary versus gregarious parasitoids varied with the available host size distribution. The offspring sex ratio of M. stanleyi reflected the available host size distribution; the sex ratio of emerging parasitoids varied with the available host size distribution. We did not detect a "critical host size" below which males emerged, and above which females emerged; rather, only females emerged from hosts in the upper size range, and a variable ratio of males and females emerged from hosts in the lower size range. We conclude that the sex ratio of field populations of M. stanleyi is driven largely by the available size distribution of C. hesperidum. In addition, we tested predictions resulting from theoretical analyses of sex allocation in autoparasitoids with data obtained on Coccophagus semicircularis (Förster) parasitizing brown soft scale in the field. The sex ratio of C. semicircularis was consistently and strongly female biased (ca. 90% females). Based on available theoretical analyses, we suggest that this sex ratio pattern may have resulted from a very low encounter rate of secondary hosts coupled with a strong time limitation in C. semicircularis females. This explanation was the most plausible given constraints stemming from the detection of secondary hosts, their variable location within primary hosts, and their handling times. Finally, the size of hosts which yielded single versus multiple parasitoids, and the sizes of these parasitoids, were compared. These comparisons suggested that: (1) M. stanleyi females gauge host sizes precisely, and in terms of female offspring; thus a fitness penalty is not incurred by females which share a host, while males benefit from sharing a host, and; (2) instances where multiple C. semicircularis emerged from a single host were probably the result of parasitism by different females, or during different encounters by a single female.

Seasonal variation and infestation incidence by Marmara gulosa (Lepidoptera: Gracillariidae) on grapefruit in the Coachella Valley, California.

The population dynamics of citrus peelminer, Marmara gulosa Guillén and Davis, were investigated in 1996-1999 in commercial grapefruit groves in the Coachella Valley, CA. The first generation of the peelminer on new fruit was observed in early June 1998; larval densities of peelminer increased at the beginning of summer and peaked in late July to early August in most years, then decreased, remaining low by the end of the summer and rest of the year. Three parasitoids were identified, with Cirrospilus coachellae Gates in highest numbers in all groves and years. Numbers of larvae parasitized by C. coachellae increased by midsummer in most groves, coinciding with the decline in densities of the citrus peelminer. Miners continued to develop on fruit left from previous harvest in June. Miners preferred the lower half canopy of the trees. Parasitism and availability of fruit for development are major components in the dynamics of the citrus peelminer.

Augmentative releases of Metaphycus sp. nr flavus against citricola scale on oranges in the San Joaquin Valley of California: are early releases better than late ones?

We conducted an augmentative release trial with the encyrtid parasitoid Metaphycus sp. nr flavus (Howard) against citricola scale, Coccus pseudomagniolarum (Kuwana), in three citrus orchards in the San Joaquin Valley of California. Three parasitoid release timings (14 October-13 November, 4 January-5 February, and 26 February-16 March; hereinafter "early," "intermediate," and "late") were compared with a no-release check. Approximately 2,400 female parasitoids were released per central release tree. Late releases were associated with reduced scale survival on the release trees but no evidence of scale suppression was found on adjacent trees. Early and intermediate releases resulted in less pronounced scale suppression than late releases. Intermediate and late, but not early, releases were associated with an increase in the numbers of recovered female M. sp. nr flavus. Early releases, however, increased the numbers of recovered male Metaphycus spp. Thus, at the time of early releases, the scales may have been too small for the production of female parasitoids. A multiple regression model relating the degree of scale mortality in one orchard to the levels of recovered female Metaphycus helvolus (Compere), M. sp. nr flavus, or M. luteolus (Timberlake) (these latter two species are morphologically indistinguishable), and Coccophagus spp., suggested that the number of Coccophagus spp. females followed by M. helvolus females, were most strongly associated with scale mortality.

Effect of host availability and egg load in Trichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) and its consequences on progeny quality

Experimentos foram conduzidos para determinar se fêmeas de Trichogramma platneri Nagarkatti (Hymenoptera: Trichogrammatidae) têm a habilidade de direcionar a alocação de recursos (reprodução/longevidade) e se esse comportamento é afetado pela disponibilidade e pelo tamanho dos hospedeiros. Fêmeas de parasitóides grandes, oriundas de ovos de Trichoplusia ni Hübner (Lepidoptera: Noctuidae), expostas a cinco ou 15 ovos de T. ni, diariamente, produziram número similar de descendentes que aquelas fêmeas que tiveram acesso a número ilimitado de hospedeiros desde a emergência. Resultados similares foram obtidos quando elas foram mantidas temporariamente sem ovos de T. ni durante um, três, cinco ou dez dias, e então providas com um suplemento ilimitado de hospedeiros. Contrariamente, fêmeas pequenas, oriundas de ovos de Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), mantidas temporariamente sem ovos de T. ni durante um período de um a três dias, apresentaram uma redução significativa no número de descendentes produzidos. Independentemente do tamanho da fêmea, o número de ovos presentes no ovário aumentou significativamente com o transcorrer do tempo.Além disso, existiu uma relação positiva entre longevidade e a duração do período em que as fêmeas foram mantidas na ausência do hospedeiro.

Host Deprivation Effect on Reproduction and Survival of Wolbachia-Infected and Uninfected Trichogramma kaykai Pinto & Stouthamer (Hymenoptera: Trichogrammatidae) / Efeito da Suspensão de Hospedeiros sobre a Reprodução e Sobrevivência de Trichogramma kaykai Pinto & Stouthamer (Hymenoptera: Trichogrammatidae) Infectados e Não Infectados com Wolbachia

Comparou-se o efeito da suspensão temporária do fornecimento de hospedeiros sobre a reprodução e sobrevivência de Trichogramma kaykai Pinto & Stouthamer infectado e não infectado com Wolbachia. Ovos de Trichoplusia ni Hübner (Lepidoptera: Noctuidae) foram utilizados como hospedeiro. A progênie de fêmeas arrenótocas e telítocas foi reduzida com o aumento do período de ausência de hospedeiros, contudo fêmeas arrenótocas produziram significativamente mais progênie independentemente do período de ausência de hospedeiros (0 a 10 dias). Essas fêmeas produziram também um número maior de filhas. A ausência de hospedeiros não afetou o número de indivíduos emergentes por hospedeiro quando se consideraram as duas formas reprodutivas isoladamente. Por outro lado, menor número de parasitóides emergiu em ovos parasitados por fêmeas telítocas. Uma relação positiva existiu entre a duração da ausência de hospedeiros e a longevidade. Fêmeas arrenótocas viveram significativamente mais que fêmeas telítocas. Os resultados revelaram que as duas formas reprodutivas responderam de forma similar quando sujeitas a períodos de ausência de hospedeiro (de até 10 dias). Fêmeas arrenótocas, contudo foram mais fecundas e viveram mais que fêmeas telítocas em todos os tratamentos avaliados.

The effect of temporary host deprivation on the reproduction and survival of Trichogramma kaykai Pinto & Stouthamer was determined by comparing a Wolbachia-infected (thelytokous) and an arrhenotokous line of T. kaykai when reared on Trichoplusia ni Hübner (Lepidoptera: Noctuidae) eggs. The progeny produced by both arrhenotokous and thelytokous females decreased with increasing periods of host deprivation, but arrhenotokous females produced significantly more progeny than thelytokous females regardless of the period of host deprivation (0 to 10 days). They also produced more daughters. Host deprivation did not affect brood size within arrhenotokous or thelytokous lines. However, fewer wasps emerged from hosts parasitized by Wolbachia-infected than by uninfected T. kaykai. A direct relationship existed between longevity and the length of time an arrhenotokous or a thelytokous wasp was deprived of hosts. The longer the deprivation period, the longer they lived. However, arrhenotokous females lived longer than their thelytokous counterparts. These findings showed that temporary host deprivation (up to 10 days) affected both reproductive forms similarly. However, in all conditions studied arrhenotokous wasps produced more progeny and lived longer than their thelytokous counterparts.

Effect of Wolbachia on the Survival and Reproduction of Trichogramma kaykai Pinto & Stouthamer (Hymenoptera: Trichogrammatidae) / Efeito de Wolbachia na Sobrevivência e Reprodução de Trichogramma kaykai Pinto & Stouthamer (Hymenoptera: Trichogrammatidae)

Infecções causadas por Wolbachia resultando em indivíduos paternogenéticos são comuns dentro do gênero Trichogramma. Contudo, os efeitos do microrganismo sobre a fecundidade e sobrevivência dos parasitóides têm sido relativamente pouco estudados. O objetivo desse estudo foi determinar os efeitos da bactéria na sobrevivência e reprodução de Trichogramma kaykai Pinto & Stouthamer, comparando indivíduos infectados (telítocos) com indivíduos curados através de antibiótico (arrenótocos), ambos criados em ovos de Trichoplusia ni Hübner. Fêmeas curadas produziram significativamente mais progênie, além de maior número de filhas que as fêmeas infectadas. Um número significativamente maior de indivíduos emergiu de ovos parasitados por fêmeas arrenótocas do que de ovos parasitados por fêmeas telítocas. As fêmeas não infectadas, contudo, viveram menos que as fêmeas infectadas. Fêmeas curadas apresentaram maturação de ovos mais rápida que fêmeas infectadas.

Parthenogenetic inducing Wolbachia infections are particularly common in the genus Trichogramma, but the influence of the microrganism on parasitoids' fitness has received relatively little attention. The aim of this study was to determine the effects of the bacteria on the survival and reproduction of Trichogramma kaykai Pinto & Stouthamer, comparing an infected line (thelytokous) with an antibiotically cured (arrhenotokous) line, both reared on Trichoplusia ni Hübner eggs. Cured wasps produced significantly more progeny and more daughters than Wolbachia-infected wasps. Significantly more wasps emerged per host when parasitized by the arrhenotokous females than by the thelytokous females. Cured females, however, lived significantly less than infected females. Eggs of cured females matured faster than infected ones.