Betty Benrey

THE SLOW-GROWTH-HIGH-MORTALITY HYPOTHESIS: A TEST USING THE CABBAGE BUTTERFLY

The slow-growth–high-mortality hypothesis predicts that prolonged development in herbivorous insects results in greater exposure to natural enemies and a subsequent increase in mortality. We tested this hypothesis using the cabbage butterfly Pieris rapae and its larval parasitoid Cotesia glomerata. We conducted a series of field and laboratory experiments to determine how variation in the larval development of P. rapae within and among four species of host plants (Brassica oleracea, Tropaeolum majus, Lunaria annua, and Cleome spinosa) influenced parasitism rates by C. glomerata. On the same host plant species, fast-developing larvae incurred less parasitism than slow-developing larvae of the same age, because once larvae reached the third instar they became much less vulnerable to attack due to the onset of encapsulation. Thus, the “window of vulnerability” was extended for slow-developing larvae. Similarly, the window of vulnerability was prolonged and larvae were susceptible to parasitism for a longer p...

Effects of plant metabolites on the behavior and development of parasitic wasps

Parasitoids are insects that spend their immature stages feeding from the tissues of other arthropods, eventually killing them. Many insects that serve as hosts for parasitoids are herbivorous, and...

Arthropod pest resurgence: an overview of potential mechanisms

Abstract The phenomenon of insecticide-induced resurgence of arthropod pests has long been known to occur in response to a reduction in natural enemy populations, releasing the pest population from regulation. However, studies of resurgent populations infrequently examine other mechanisms, although numerous alternative mechanisms such as physiological enhancement of pest fecundity, reduction in herbivore-herbivore competition, changes in pest behaviour, altered host-plant nutrition, or increased attractiveness may also cause, or enhance the probability of, resurgence. Additionally, many studies that have identified natural enemy mortality as the primary cause of resurgence do not document a priori regulation by natural enemies and, therefore, are correlative in nature. In this paper, a universal definition of resurgence is proposed and criteria for determining the occurrence of resurgence are listed. Both of these are essential to rigorous evaluation of this important phenomenon. Alternative mechanisms for resurgence and potential areas of future research are identified. It is argued that insecticide resistance is not a mechanism underlying resurgence; rather, it simply enhances the probability that resurgence may occur. The similarity of resurgence to some insect outbreaks is discussed. In some cases natural outbreaks differ only in the initiating factor. The importance of resurgence management to plant protection is that resurgence is totally contradictory to the intended outcome of insecticidal application. This conflict strengthens the need to identify specifically the causal factors for each case of resurgence in order to manage this detrimental phenomenon effectively.

Crop Domestication and Its Impact on Naturally Selected Trophic Interactions

Crop domestication is the process of artificially selecting plants to increase their suitability to human requirements: taste, yield, storage, and cultivation practices. There is increasing evidence that crop domestication can profoundly alter interactions among plants, herbivores, and their natural enemies. Overall, little is known about how these interactions are affected by domestication in the geographical ranges where these crops originate, where they are sympatric with the ancestral plant and share the associated arthropod community. In general, domestication consistently has reduced chemical resistance against herbivorous insects, improving herbivore and natural enemy performance on crop plants. More studies are needed to understand how changes in morphology and resistance-related traits arising from domestication may interact with environmental variation to affect species interactions across multiple scales in agroecosystems and natural ecosystems.

Host Species and Host Plant Effects on Preference and Performance of Diachasmimorpha longicaudata (Hymenoptera: Braconidae)

Abstract Naive female Diachasmimorpha longicaudata (Ashmead), a solitary endoparasitoid of tephritid fruit flies, exhibited positive responses toward volatiles of host fruits in olfactometer and wind tunnel bioassays. Although no significant preference for one of the test fruits, mango, Mangifera indica L., or grapefruit, Citrus paradisi Macfaden, was observed, the number of flights in the wind tunnel was higher in the presence of mangos. In the olfactometer trials, parasitoids preferred fly infested over noninfested grapefruits, and infested over noninfested mangos. Reproductive performance bioassays were conducted using Anastrepha ludens (Loew) larvae (Diptera: Tephritidae) reared in grapefruit, orange, mango, or artificial diet, and Anastrepha obliqua (Macquart) larvae reared in mango as parasitoid hosts. Parasitoid performance was compared for 2 Anastrepha species and 3 fruit species. Significant effects of fruit fly species and of the diet of fruit fly larvae on longevity, size, and progeny production of D. longicaudata were observed. Anastrepha ludens reared in grapefruit was the best host in terms of offspring longevity, size, and number of female progeny, but parasitoids that developed in A. ludens reared in mango had higher overall fecundity. Anastrepha ludens reared in mango was a better host than A. obliqua in the same fruit. No correlation between parasitoid size and demographic parameters was found. The results of this laboratory study showed that host preference and offspring performance are partially related.

Aggregation facilitates larval growth in the neotropical nymphalid butterfly Chlosyne janais

1. Larvae of Chlosyne janais (Lepidoptera: Nymphalidae) feed gregariously as early instars on the shrub Odontonema callistachyum (Acanthaceae). During the fourth instar, aggregations break up and larvae feed as solitary individuals.

Functional Response and Superparasitism by Diachasmimorpha longicaudata (Hymenoptera: Braconidae), a Parasitoid of Fruit Flies (Diptera: Tephritidae)

Abstract The functional response and the effect of superparasitism of Diachasmimorpha longicaudata (Ashmead) in larvae of Anastrepha ludens (Loew) was determined under laboratory conditions. Adult parasitoids were tested individually and in groups of 5. Third-instar A. ludens larvae were exposed for 3 h to experienced, 5-d-old females at the ratios of 1, 5, 20, 30, 40, 50, and 60 host larvae per wasp. For individual females, functional response was type III, whereas for females in groups, a type II curve was observed. In the presence of conspecifics, females increased their parasitization activity. Females showed a strong tendency for self-superparasitism (the same female laying >1 egg in the same host) with a range of 38.9–57.9% of larvae superparasitized, even when there was no competition and a high availability of host larvae. In the superparasitism experiment, when the parasitoid/host ratio was 1 or greater, larval mortality was consistently high but never exceeded 90%. Successful parasitoid emergence decreased as the parasitoid/host ratio increased. We discuss and question the detrimental effects that have been attributed to superparasitism in solitary endoparasitoids.

The influence of plants on insect parasitoids: Implications for conservation biological control

Publisher Summary The chapter discusses the impact that plants have on insect pests and weed pests. Generally, the survival of the pests depends on the habitat in which they live. If the environment is unfavorable, they cannot survive. Whether it is insect pests or weed pests, all need favorable environment to survive. For pests, the most important part of their habitat is the plants on which they live and eat and on which depends their survival. In the agroecosystem in which one lives, 22% of all known species are green plants and about 26% are plant-feeding insect species. As plant-feeding insect species are so huge in number, one needs to adopt suitable measure to protect ones crops. Plants provide important information about the host location; so one needs to be very attentive in identifying the cues through which host location can be identified. The chapter provides an overview on ways in which plants are directly or indirectly influenced by parasitoids. It illustrates the interactions that take place between parasitoids and their environments.

Ancient and recent evolutionary history of the bruchid beetle, Acanthoscelides obtectus Say, a cosmopolitan pest of beans

Acanthoscelides obtectus Say is a bruchid species of Neotropical origin, and is specialized on beans of the Phaseolus vulgaris L. group. Since the domestication and diffusion of beans, A. obtectus has become cosmopolitan through human‐mediated migrations and is now a major pest in bean granaries. Using phylogeographic methods applied to mitochondrial DNA (mtDNA) and nuclear microsatellite molecular markers, we show that the origin of this species is probably further south than Mesoamerica, as commonly thought. Our results also indicate that A. obtectus and its Mesoamerican sister species Acanthoscelides obvelatus, two morphologically close species differing principally in voltinism, speciated in allopatry: A. obtectus (multivoltine) arising in Andean America and A. obvelatus (univoltine) in Mesoamerica. In contrast to Mesoamerica where beans fruit once yearly, wild beans in Andean America fruit year‐round, especially in regions showing little or no seasonality. In such habitats where resources are continuously present, multivoltinism is adaptive. According to existing hypotheses, multivoltinism in A. obtectus is a new adaptation that evolved after bean domestication. Our data suggest the alternative hypothesis that multivoltinism is an older trait, adapted to exploit the year‐round fruiting of wild beans in relatively aseasonal habitats, and allowed A. obtectus to become a pest in bean granaries. This trait also permitted this species to disperse through human‐mediated migrations associated with diffusion of domesticated beans. We also show that diversity of Old World A. obtectus populations can be quite well explained by a single colonization event about 500 bp. Human‐mediated migrations appear not to be rare, as our results indicate a second more recent migration event from Andean America to Mexico.

Grape variety affects female but also male reproductive success in wild European grapevine moths

Abstract 1. For insect herbivores the quality of the larval host plant is a key determinant of their fitness. Only little attention, however, has been given to the effects of plants on mating success of males and its consequence for the reproductive output of their mates. In addition, almost all the studies that have investigated the influence of host plants on herbivore fitness components have been done in the laboratory, and less is known of these effects in natural conditions.