Marshall W. Johnson

Olive Fruit Fly: Managing an Ancient Pest in Modern Times

Olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the major pest of commercial olives worldwide. Various aspects of its biology, ecology, management, and impact on olive production are highlighted. With the discovery of insecticidal resistance in some populations frequently treated with organophosphates, old and new control options are being investigated. The potential of biological control is examined. Surveys suggest that a small group of braconids in the Opiinae subfamily best represent the primary parasitoids attacking olive fruit fly in its native range. These species include Psyttalia lounsburyi, P. dacicida, P. concolor, P. ponerophaga, and Utetes africanus. Bracon celer, another braconid but in the Braconinae subfamily, is also reared from the fruit fly in its native range. The potential of these and other natural enemies is discussed with respect to olive fruit fly biology, commercial olive production, and biological constraints that may limit their success. We suggest that numerous species exist that should be further investigated as control agents for olive fruit fly in the many climatic regimes where the pest is found.

Impact of agricultural diversification on the insect community of cruciferous crops

Numerous studies have examined the responses of pest and beneficial arthropods to plant diversification in ephemeral cropping habitats. Cruciferous crops, mainlycabbage and broccoli, are probablythe most studied plants with respect to evaluating the impact of plant mixtures on insect population dynamics. This review examines the mechanisms influencing arthropod responses to floral diversification, specificallyfocusing on cruciferous crops. In manyinstances, mechanisms accounting for herbivores and natural enemyresponses to plant mixtures are not thoroughlytested. Biological parameters of herbivores impacted bycrop diversification were mainlyrelated to the behavior of the insects studied. Mechanisms accounting for herbivore responses to plant mixtures include reduced colonization, reduced adult tenure time in the marketable crop, and oviposition interference. Tactics used for choosing companion plants, and the future perspective for mixed-crucifer crops usage are discussed. Manipulative studies involving cruciferous crops provide some evidence that habitat manipulation techniques (e.g., intercropping, undersown nonhost plants, vegetation borders) impact crop growth. However, the indirect role habitat manipulation plays in the population dynamics of insect pests and natural enemies still remains unclear in manysy stems. Quantitative data are needed to determine the level of change in plant qualitybrought about bycompanion planting that alters arthropod behavior. r 2003 Elsevier Science Ltd. All rights reserved.

Fitness costs of resistance to Bacillus thuringiensis in the diamondback moth (Plutella xylostella)

Does adaptation to stress entail fitness costs in optimal environments? Antagonistic pleiotropy sometimes causes trade-offs in fitness across different environments in which the agent of stress is a pathogen (Lenski 1988) or a novel diet (Pashley 1988; Via 1991). It is commonly believed that evolution of resistance to insecticides also involves such trade-offs. Alleles conferring resistance are rare before exposure to insecticide and have been presumed to exert negative effects on fitness in the absence of insecticide (Crow 1957; Uyenoyama 1986; Hoffman and Parsons 1991). However, fitness costs associated with resistance to conventional synthetic insecticides appear to vary considerably among species and insecticides (Roush and McKenzie 1987; Roush and Daly 1990; Denholm and Rowland 1992). Moreover, little is known about fitness costs of resistance to insecticidal proteins from Bacillus thuringiensis, a common soil bacterium (McGaughey and Whalon 1992; Tabashnik 1994). Toxins from B. thuringiensis kill susceptible insects by binding to and disrupting the integrity of the midgut epithelium (Gill et al. 1992). Reduced binding of toxins is a primary mechanism of resistance in the diamondback moth, Plutella xylostella (Ferre et al. 1991), a major pest of cruciferous vegetables (Talekar 1992). The normal function of toxin-binding sites is not known but seems to be important because such sites are found in numerous insects (Feitelson et al. 1992). Several authors have suggested that alteration of toxin-binding sites may interfere with normal physiological functions (Van Rie et al. 1990; MacIntosh et al. 1991). Instability of resistance to B. thuringiensis in the absence of selection

Morphological variation in Bemisia endosymbionts.

SummaryThe ultrastructure of the endosymbionts of several populations of whitefly (Homoptera: Aleyrodidae) was examined using transmission electron microscopy. Consistent differences in morphology and relative number of endosymbionts were observed between species and biotypes of whitefly within the Bemisia taxon.Bemisia argentifolii (=B. tabaci B biotype) individuals from Hawaii, Florida, and Arizona contained two morphological types of microorganisms housed within the mycetocyte cells of immature whiteflies. In contrast, individuals from populations ofB. tabaci A biotype from Arizona and Mexico, andB. tabaci Jatropha biotype from Puerto Rico, consistently contained three distinct morphological types of microorganisms within their mycetocytes. Organisms fromB. tabaci A and Jatropha biotypes differed from each other in the relative frequency of each type of microorganism. These observations suggest that different whitefly biotypes may have variable combinations of micro-fauna, with some possibly unique to each group, and furthers the hypothesis that variation in whitefly endosymbionts may be associated with the development of biotypes.

Leafminers in vegetables, ornamental plants and weeds in Indonesia: Surveys of host crops, species composition and parasitoids

Extensive surveys of vegetable, ornamental and weedy plant species were conducted in highland and lowland vegetable production areas in Indonesia with the aim of recording leafminer species present and their associated natural enemies. The most common dipterous species reared from samples was the pea leafminer, Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae). This introduced pest was particularly serious in highland vegetables in Java, Sumatra and South Sulawesi, causing yield losses as high as 60-70%. Another alien species, the vegetable leafminer, Liriomyza sativae Blanchard, contributed to problems in lowland areas on the north coast of West Java, where cucumbers were heavily damaged. An Asian leafminer species, Chromatomyia horticola Goureau, was more common in snow peas (Pisum sp.). Intensive sampling of leafminer-infested leaves from surveyed host plants yielded 11 species of hymenopteran parasitoids: 10 eulophids (Asecodes sp., Chrysocharis sp., Cirrospilus ambiguus (Hansson and LaSalle), Closterocerus sp., Hemiptarsenus varicornis (Girault), Neochrysocharis formosa (Westwood), Neochrysocharis sp., Pnigalio sp., Quadrastichus sp., Zagrammosoma sp.) and 1 eucoilid (Gronotoma sp.). The most abundant parasitoid species was H. varicornis. Levels of parasitism varied among crops and growing seasons, but were usually low, especially on potato (< 3%). Surveys revealed that most farmers (63%) attempted to control leafminers by applying insecticides twice weekly although these applications were neither effective nor economical according to responses of about 72% of the farmers. An integrated pest management approach is suggested that emphasizes IPM training for vegetable farmers and includes reductionor elimination of broad spectrum chemicals that would adversely affect parasitoids that may already be present as well as those that may be introduced. The initiation of a classical biological control programme is recommended to enhance the limited parasitoid complex present in Indonesia and increase levels of biological control.

High summer temperatures affect the survival and reproduction of olive fruit fly (Diptera: Tephritidae).

ABSTRACT The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is an invasive pest in California. Identifying environmental constraints that affect the geographic distribution and abundance of any invasive insect pest is fundamental to its effective management. Californias Central Valley, where most commercial olives are grown, is extremely hot during the summer, with maximum daily temperatures consistently >35.0°C. This study examined the effects of two diurnal temperature regimens (low 18.3°C, high 35.0 or 37.8°C) reflecting summer conditions in the valley, and one control temperature regimen (low 18.3°C, high 23.9°C) on the flys survival and reproductive success in the laboratory. The temperature regimen of 18.3–35.0°C resulted in delayed egg maturation and reduced production of mature eggs compared with the control temperature regimen. Egg maturation was possible at the higher temperature regimen when females were provided with water and food, and egg-laying occurred during the cold phase of the temperature cycle. Access to olive fruit and oviposition itself further promoted egg maturation. Under exposure to the 18.3–35.0°C temperature regimen, ≈50% of eggs died, and the remainder that hatched died as first instars. No egg hatch occurred at the temperature treatment of 18.3–37.8°C. We confirmed these laboratory results through field cage studies with adult B. oleae, conducted in the summer of 2007 and 2008. Under ambient summer temperatures, adult B. oleae survived for 1–2 wk, and females readily laid eggs when provided water and food. No offspring developed in midsummer of 2007, and <2% of the offspring developed to adults in summer 2008 trials. These results suggest that high summer temperatures limit the flys abundance in Californias Central Valley.

Impact of avian and arthropod predation on lepidopteran caterpillar densities and plant productivity in an ephemeral agroecosystem

Abstract.  1. Most studies evaluating the combined impact of spiders and other predators on herbivore densities in agroecosystems have focused primarily on their trophic connections with invertebrate predators (e.g. carabids, chrysopids); however linkages among spiders and vertebrate predators may also help structure the population dynamics of insect herbivores. A field experiment was conducted to examine the impact of avian and spider predation on lepidopteran caterpillar densities and plant productivity within a Brassica agroecosystem.

CHAPTER 13 – Enhanced Biological Control through Pesticide Selectivity

This chapter discusses direct and indirect effects of pesticides on natural enemies, the consequences of disrupting biological control, and approaches to reduce the negative impact of chemicals on natural-enemy populations. Direct effects include short- and long-term impacts on natural enemies due to direct contact with pesticides or pesticide residues, and indirect effects are those in which the impact of the pesticide is mediated through the natural enemys host or prey. Indirect effects may be caused by reduction of host or prey populations that serve as food sources for natural enemies, a change in the host or prey distribution, and ingestion of pesticide-contaminated prey or hosts. Unilateral chemical control of arthropod pests can result in population explosions of both target and nontarget organisms due to various reasons, including hormoligosis, pesticide resistance, and the destruction of natural enemies. The best method for reducing the overall negative impact of chemicals on natural enemies is to avoid pesticide applications altogether. Pesticides used in the management of pests should be applied only when necessary and economically justifiable.

The Genetic Properties of the Primary Endosymbionts of Mealybugs Differ from Those of Other Endosymbionts of Plant Sap-Sucking Insects

ABSTRACT Mealybugs (Hemiptera, Coccoidea, Pseudococcidae), like aphids and psyllids, are plant sap-sucking insects that have an obligate association with prokaryotic endosymbionts that are acquired through vertical, maternal transmission. We sequenced two fragments of the genome of Tremblaya princeps, the endosymbiont of mealybugs, which is a member of the β subdivision of the Proteobacteria. Each of the fragments (35 and 30 kb) contains a copy of 16S-23S-5S rRNA genes. A total of 37 open reading frames were detected, which corresponded to putative rRNA proteins, chaperones, and enzymes of branched-chain amino acid biosynthesis, DNA replication, protein translation, and RNA synthesis. The genome of T. princeps has a number of properties that distinguish it from the genomes of Buchnera aphidicola and Carsonella ruddii, the endosymbionts of aphids and psyllids, respectively. Among these properties are a high G+C content (57.1 mol%), the same G+C content in intergenic spaces and structural genes, and similar G+C contents of the genes encoding highly and poorly conserved proteins. The high G+C content has a substantial effect on protein composition; about one-third of the residues consist of four amino acids with high-G+C-content codons. Sequence analysis of DNA fragments containing the rRNA operon and adjacent regions from endosymbionts of several mealybug species suggested that there was a single duplication of the rRNA operon and the adjacent genes in an ancestor of the present T. princeps. Subsequently, in one mealybug lineage rpS15, one of the duplicated genes, was retained, while in another lineage it decayed. These results extend the diversity of the types of endosymbiotic associations found in plant sap-sucking insects.

Diachasmimorpha longicaudata and D. kraussii (Hymenoptera: Braconidae), potential parasitoids of the olive fruit fly

Abstract The olive fruit fly, Bactrocera oleae (Tephritidae), is a significant threat to Californias olive industry. As part of a classical biological control program started in 2002, the parasitoids Diachasmimorpha kraussii and D. longicaudata (Hymenoptera: Braconidae) were imported to California from laboratory colonies in Hawaii. Studies on their biology and behavior as parasitoids of the olive fruit fly were conducted in quarantine. Both species tend to oviposit into 2nd and young 3rd instars, with the offspring completing development in the flies’ puparia. Most eggs are deposited in the first two weeks of adult life. Observed lifetime fecundity was low, possibly as a consequence of the relatively poor quality of the harvested olives used as a host substrate. Both pre-imaginal development and adult longevity were limited at constant temperatures above 30°C, which may indicate that these species will have difficulty establishing in the warmest regions of California.