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The olive fruit fly, Bactrocera oleae, has been a key pest of olives in Europe and North America. We conducted the largest exploration for parasitoids associated with the fly across Sub-Saharan Africa (Kenya, Namibia, and South Africa) including some of the fly's adjoining regions (Canary Islands, Morocco, Réunion Island and Tunisia). From Sub-Saharan regions, four braconids were collected: Bracon celer, Psytallia humilis, P. lounsburyi, and Utetes africanus. Results showed that their regional dominance was related to climate niches, with P. humilis dominant in hot semi-arid areas of Namibia, P. lounsburyi dominant in more tropical areas of Kenya, and U. africanus prevalent in Mediterranean climates of South Africa. Psytallia concolor was found in the Canary Islands, Morocco and Tunisian, and the Afrotropical braconid Diachasmimorpha sp. near fullawayi on Réunion Island. Furthermore, we monitored the seasonal dynamics of the fly and parasitoids in Cape Province of South Africa. Results showed that fruit maturity, seasonal variations in climates and interspecific interactions shape the local parasitoid diversity that contribute to the low fly populations. The results are discussed with regard to ecological adaptations of closely associated parasitoids, and how their adaptations impact biocontrol.

Western grape leaf skeletonizer was first reported in southern California in 1941 and soon became a serious pest of commercially produced grapes in that region. Their gregarious larvae can easily defoliate vineyards and they remained a major problem for production of grapes until this pest was reunited with its host-specific natural enemies. Efforts to import into southern California effective natural enemies during the 1950s from southern Arizona succeeded in reducing populations of this moth to economically tolerable levels. We report for the first time on releases of natural enemies into central and northern California for control of western grape leaf skeletonizer. Over 600,000 parasitoids new to this region were released during late 1970s–1980s by the state's Biological Control Program. Foreign exploration by the California Department of Food and Agriculture (CDFA) into Mexico in 1978 resulted in additional parasitoids new to California: a new biotype of Ametadoria harrisinae and a new species of Chetogena sp. (Tachinidae). The high numbers of tachinids released throughout California is credited with aiding in the spread of a highly virulent strain of granulosis virus which in turn caused high levels of mortality to western grape leaf skeletonizer larvae. Reports of WGLS outbreaks in vineyards over the last 15 years are rare, in contrast to previous years. [ABSTRACT FROM AUTHOR]

The widespread and rapid establishment of the olive fruit fly in California required immediate changes in integrated pest management (IPM) programs for olives. After finding that resident natural enemies did not provide adequate control, researchers began a worldwide search for parasitoids, with exploration in the Republic of South Africa, Namibia, India, China and other countries. Parasitoids were shipped to California, and most were studied in quarantine to determine the best species for release. Two parasitoid species — Psyttalia lounsburyi and Psyttalia humilis — are now being released throughout the state’s olive-growing regions, and researchers are studying their effectiveness.

The role of generalist predators has long been considered an important component of mortality for many agricultural pests but can be difficult to quantify. We present the use of digital imaging as a means of both identifying key stink bug egg predators and measuring their relative impact on egg survivorship. Brown marmorated stink bug (BMSB), Halyomorpha halys and bagrada bug, Bagrada hilaris, two exotic stink bugs new to California, are now widely distributed throughout the state. A survey was conducted to identify resident natural enemies of their eggs. A field camera aided in the identification of arthropods attacking these eggs and their relative impact. Predation of BMSB eggs, which are naturally oviposited onto plant foliage, was less than for eggs of bagrada bug, which oviposit onto and into soil. The top ranked predators of BMSB eggs were the carabid Laemostenus complanatus (Coleoptera) the European earwig Forficula auricularia and ring-legged earwig Euborellia annulipes (Dermaptera), the oriental cockroach Blatta orientalis (Orthoptera), and the spider Trachelas spp. (Araneae). The two most common and important predators of bagrada bug were two ant species (Formicidae), Solenopsis xyloni and Monomorium ergatogyna, and species of Collembola (Entomobryidae). A Predation Index was developed to compare the relative importance of BMSB egg predators. Lastly, two striking, unanticipated results are reported: an apparent synergistic interaction between the spider Trachelas spp. and native ant M. ergatogyna in causing damage to sentinel eggs of BMSB, and the predaceous role for Collembola on bagrada bug sentinel eggs. [ABSTRACT FROM AUTHOR]

In 2013, cereal leaf beetle was reported for the first time in California. Most likely it moved south from Oregon into the state's northern region. In response, the gregarious larval endoparasitoid Tetrastichus julis (Hymenoptera: Eulophidae) was collected and transferred to a field insectary at the University of California Intermountain Research and Extension Center in Tulelake. From 2014 to 2018 the insectary was maintained to propagate T. julis for redistribution to commercial grain fields in northern California experiencing infestations by this pest. Sequential plantings of oats, preceded by winter wheat at this insectary provided a constant source of pre-head, lush oats throughout the summer. In turn, a reliable source of cereal leaf beetle hosts was produced for T. julis, which also increased in numbers. These parasitoids were released into infested commercial fields of wheat in the Klamath Basin region of northern California. Over four years beginning in 2016, annual surveys of the region showed that cereal leaf beetle populations declined while T. julis rapidly increased. Our releases, in addition to the natural spread of this parasitoid south from Oregon played a key role in the beetle population declining by nearly 90% over this period. [ABSTRACT FROM AUTHOR]

Olive fruit fly, Bactrocera oleae Rossi, is a worldwide pest of olives. To discover new parasitoids for a biological control program in California, olives were collected from various locations in the Himalayan foothills (China, Nepal, India, Pakistan) as part of a comprehensive search for B. oleae throughout its range. Wild olives, Olea europaea ssp. cuspidata, were sparsely distributed and B. oleae-infested olives were scarce. Wild olives were most widespread in Pakistan where fly infestation reached 30%. Infested olives in southwestern China were rare, reaching only 5%. Flies were identified morphologically as B. oleae, the first record from China. No B. oleae were recovered from India or Nepal. Mitochondrial gene sequences from NADH dehydrogenase (ND1), cytochrome oxidase subunit 1 (COX1), and 16S rRNA were obtained from flies and compared with B. oleae sequences in GenBank. A single mitochondrial haplotype was found in Chinese flies. Chinese B. oleae represent a maternal lineage based on ND1 and COX1 that is highly divergent from other B. oleae. Phylogenetic analysis by maximum likelihood and Bayesian inference based on the concatenated dataset of B. oleae sequences with sequences of two close subcongeners, Bactrocera biguttula (Bezzi) and Bactrocera munroi White, and analysis of delineation of species boundaries using the genealogical sorting index, supported the idea that Chinese flies share recent common ancestry with B. oleae. Flies were parasitized by braconid wasps, Psyttalia ponerophaga (Silvestri) in Pakistan, and a Diachasmimorpha species in China. Our survey reinforces the possibility of finding new biocontrol agents of olive fruit fly in the Himalayan region. [ABSTRACT FROM AUTHOR]

Alfalfa trap crops are currently used to manage Lygus spp. in organic strawberry fields on the California Central Coast. The retention of Lygus spp. in alfalfa creates aggregated distributions that provide improved opportunities for biological control by the introduced parasitoid Peristenus relictus (Ruthe). The abundance and distribution of P. relictus between two trap crops separated by 50 strawberry rows were analyzed in 2008 and 2010. Parasitism of Lygus spp. nymphs by P. relictus (measured by larval abundance and % parasitism) was greatest in alfalfa trap crops compared with strawberry rows. A significantly positive correlation between host nymphs and P. relictus larvae in and between trap crops was found. Movement of P. relictus adults from a marked alfalfa trap crop into adjacent strawberry rows or trap crops was also studied in 2008 and 2009 using a chicken egg-albumin enzyme-linked immunosorbent assay mark-capture technique. In 2008 and 2009, 85 and 49% of protein-marked wasps were captured from central trap crops, respectively, indicating that alfalfa trap crops act as a concentrated "host-density anchor" in organic strawberry fields. [ABSTRACT FROM AUTHOR]

Lygusspp. (Heteroptera: Miridae) are serious pests of numerous field and fruit crops in North America. In an effort to reduce crop damage, parasitoids known to attack these species in Europe were introduced into the USA beginning in the 1970s. Permanent populations of the nymphal endoparasitoidPeristenus relictus(Hymenoptera: Braconidae) were established at two locations in California during the 2000s. Both populations are associated with significant reductions in lygus bugs attacking alfalfa, commercially produced strawberries grown organically and in wild vegetation. Beginning in 2009, in an effort to determine the extent to whichP. relictushas spread from the Sacramento Valley and Monterey Bay region, populations of lygus bug were sampled at increasing distances from their original release sites.P. relictushas dispersed at least 213 km in the central region of California and 150 km along the coastal mountains. These respective populations have averaged 16.6 km/year and 17.7 km/year since they were released. While not directly examined, the spread ofP. relictussouth into the central and major growing region of California, the San Joaquin Valley, where previous releases have failed, suggests this population may be evolving greater heat tolerance, relative to the populations originally introduced into California. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) is a highly attractive plant host to Lygus spp. and is used as a trap crop in California organic strawberries to influence the dispersion and dispersal of these pests, particularly Lygus hesperus Knight. The abundance and distribution of Lygus spp. nymphs between two trap crops separated by 50 strawberry rows was analyzed in 2008 and 2010. Nymphs demonstrated a bimodal distribution in strawberries between trap crops, where nymphs were most abundant and aggregated in alfalfa, when compared with interior strawberry rows, where nymphs were less abundant. The majority of nymphs were concentrated in trap crops and nymphal densities in interior strawberry rows were well below economic thresholds. The movement of Lygus spp. from a marked alfalfa trap crop into adjacent strawberry rows or trap crops was also studied in 2008 and 2009 using a chicken egg albumin enzyme-linked immunosorbent assay mark-capture technique. The majority of marked-captured L. hesperus adults and Lygus spp. nymphs remained in alfalfa trap crops, rather than dispersing out into strawberry rows at 24 h, 48 h, and 2 wk, postprotein application. The attenuation of Lygus spp. movement in alfalfa associated with organic strawberries is a key component of successful trap cropping. A small percentage of marked adults and nymphs were captured in neighboring alfalfa trap crops, located 62 m from the point of protein application, highlighting the dispersal capacity of this key pest. [ABSTRACT FROM AUTHOR]

The overwintering survival and development of olive fruit fly, Bactrocera oleae (Rossi), and the endoparasitoids, Psyttalia humilis Silvestri and P. lounsburyi (Silvestri), were investigated at sites in California's interior valley and coastal region. In the interior valley, adult flies survived up to 4-6 mo during the winter when food was provided. Adult female flies could oviposit in late fall and early winter on nonharvested fruit and, although egg survival was low (0.23-8.50%), a portion of the overwintered cohort developed into adults the following spring; percentage of survival was negatively correlated to daily minimum temperature. P. humilis and P. lounsburyi successfully oviposited into host larvae in late fall, and their progeny developed into adults the following spring, although with a low percentage (0-11.9%) survivorship. Overwintering survival of puparia of the olive fruit fly and immature larvae of P. humilis and P. lounsburyi (inside host puparia), buried in the soil, were tested at an interior valley and coastal site. Survival of olive fruit fly ranged from 0 to 60% and was affected by the trial date and soil moisture. Overwintering survival of both the fruit fly and tested parasitoids was lower at the colder interior valley than the coastal site; P. humilis immature stages had the highest mortality levels while B. oleae pupae had the lowest mortality levels. The spring emergence pattern of the tested insects was well predicted by a degree-day model. We discuss factors potentially impeding establishment of introduced olive fruit fly parasitoids in California and elsewhere. [ABSTRACT FROM AUTHOR]

Psyttalia lounsburyi (Silvestri) and P. humilis (Silvestri) (Hymenoptera: Braconidae) were evaluated in California for their potential to control the invasive olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae). Psyttalia lounsburyi is a specialist on B. oleae while P. humilis also attacks other tephritid species. Field cage trials, conducted from 2006 to 2009, were used to compare P. lounsburyi and two populations of P. humilis (Kenya and Namibia) in California's interior valley and coastal regions. Both parasitoid species reproduced on B. oleae in all trials. Under similar abiotic conditions, offspring production per female was higher in P. humilis than in P. lounsburyi, suggesting that host specificity by P. lounsburyi does not confer a higher efficiency on B. oleae in cultivated olives. Two abiotic factors were shown to impact parasitoid efficiency. First, adult parasitoid survival was poor during periods of high summer temperatures, common to the olive production areas in California's interior valleys. Second, parasitism levels were lower on B. oleae larvae feeding in larger Ascolano cv. fruit than in smaller Manzanillo cv. fruit. Results are discussed relative to biological control of B. oleae in commercial olives and the usefulness of natural enemies specialized to attack fruit flies in wild olives compared with the larger cultivated olive fruit. [ABSTRACT FROM AUTHOR]

The article offers information on the effort of California researchers to provide adequate control of olive fruit fly in the state. The started a worldwide search for parasitoids with exploration in several countries such as Republic of South Africa, Namibia,and India. It mentions that parasitiods were shipped to California and studied in quarantine to determine the best species for release. It notes that two best species are already released and are being studied for their effectiveness.

Non-target risk posed by an African parasitoid, Bracon celer Szepligeti (Hymenoptera: Braconidae), was assessed for a classical biological control program against olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae: Dacinae), in California, USA. Behavioral and reproductive responses to non-target tephritid species were tested with beneficial (Chaetorellia succinea [Costa] and Parafreutreta regalis Munro) (Tephritidae: Tephritinae) and native (Rhagoletis fausta [Osten Sacken]) (Tephritidae: Trypetinae) fruit fly species in successive no-choice and choice experiments under close confinement in quarantine. Non-target host-plant substrates exposed to B. celer were yellow-starthistle flower heads containing C. succinea, Cape ivy stem galls containing P. regalis, and bitter-cherry fruit containing R. fausta. The parasitoid probed all three infested non-target plant substrates, but significantly less than olives infested with B. oleae. It produced offspring from P. regalis in Cape ivy stem galls, but appeared unable to penetrate yellow-starthistle flower heads with its ovipositor. Bracon celer killed some B. oleae and R. fausta larvae without parasitism. Reproduction on P. regalis indicates that B. celer has a broad physiological host range, which, combined with the parasitoid's acceptance of all three host-plant substrates, indicates a strong potential to negatively impact non-target species. Although physical and temporal barriers to host attack may reduce risk to most non-target tephritids by B. celer in California, the parasitoid should not be released due to its risk of harming the beneficial P. regalis. Release of P. regalis is still under consideration, however, and final risk assessment should depend on whether the fly proves useful for weed control. [ABSTRACT FROM AUTHOR]