Spatial patterns of Trybliographa rapae parasitism of Delia radicum larvae in oilseed rape and cauliflower

Trybliographa rapae (Westwood) is an important parasitoid of Delia radicum (L.). Parasitism of D. radicum larvae by T. rapae in relation to host density on canola (oilseed rape) and cauliflower roots was examined at 10 field sites in Germany and Switzerland. For roots with host larvae, the proportion of roots with one or more parasitized hosts increased with increasing host density. However, for these infested roots, the parasitism of individual larvae was not consistently related to host density. When considering only roots on which there were parasitized larvae and the opportunity for multiple attacks, the proportion of larvae that were parasitized decreased with increasing host density in the field locations, and in a cage study under controlled conditions. A model of patch‐finding and number of attacks by female parasitoids suggests that patch‐finding is density‐dependent, but that low attack rate and interference effects limit numbers of attacks to three or less per visit to a host patch; the reduced number of attacks per visit leads to the inverse relationship of larval parasitism with host density in the host patches visited. The interplay of the density‐dependent and inversely density‐dependent processes appears to be responsible for the inconsistency of density dependence of overall larval parasitism in this and previous studies. In the laboratory, adult female T. rapae parasitized hosts at ≤4 cm deep in soil, but not at 6 cm deep. From the depth distribution of larval feeding sites in the field, we infer that between 4% and 20% of Delia larvae may be in a physical refuge from T. rapae parasitism, which may have a stabilizing influence on the host–parasitoid interaction.     

Evaluation of Fopius arisanus as a biological control agent for the olive fruit fly in California

1 The egg‐prepupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) was evaluated in quarantine facilities as a potential biological control agent for the olive fruit fly Bactrocera oleae (Diptera: Tephritidae) in California, U.S.A. 2 Nontarget testing of two weed biological control agents confirmed that F. arisanus will not attack Tephritidae that feed in inflorescences or galls. It may, however, pose risks to native Tephritidae that feed in fruit. 3 Females preferentially oviposited in eggs, although first‐instar B. oleae were also attacked. Low lifetime reproductive potential and high rates of direct mortality inflicted on host eggs indicate that rearing on B. oleae may prove difficult. 4 In multiparasitized B. oleae, F. arisanus prevailed in competition against two species of larval–pupal parasitoids, Diachasmimorpha kraussii and Psyttalia concolor (both Hymenoptera: Braconidae). 5 The broad host‐range of F. arisanus with respect to fruit‐feeding Tephritidae may preclude its introduction to California, as may its low fecundity and its intrinsic competitive superiority over larva l–pupal parasitoids, which include specialists on B. oleae that are currently being introduced to California. High rates of direct mortality, however, point to potential uses in augmentative biological control. Whether or not F. arisanus is released in California, its biology as a parasitoid of B. oleae has been little studied to date and the results herein may be applied in other regions worldwide where B. oleae is a problem.     

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

The olive fruit fly, Bactrocera oleae (Tephritidae), is a significant threat to California's 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.     

The Ability of Coptera haywardi (Ogloblin) (Hymenoptera: Diapriidae) to Locate and Attack the Pupae of the Mediterranean Fruit Fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), under Seminatural Conditions

In Latin America, the diapriid Coptera haywardi (Ogloblin) attacks the pupae of tephritid fruit flies. Anastrepha spp. are among its natural hosts, but in the laboratory it also develops in the exotic Mediterranean fruit fly, Ceratitis capitata (Wiedemann). Field cage tests demonstrated that C. haywardi could locate and parasitize Mediterranean fruit fly pupae under seminatural conditions as found in a Guatemalan coffee plantation. A mean of 18.3% of the pupae buried artificially at depths of 5 mm were parasitized by C. haywardi, while those buried at 15 mm suffered 3.2% parasitism. In a laboratory experiment, larvae that buried themselves to pupate were not significantly more likely to be parasitized than artificially buried pupae, although they may have left a physical or chemical trail that betrayed their presence. Thus, the artificial burial of pupae is unlikely to grossly underestimate C. haywardi efficacy in the field. Another field cage test found that mortality levels due to unsuccessful parasitoid attacks were similar to those resulting from successful parasitism. Thus, the actual effect of a mass-release might be considerably greater than that suggested from parasitism data alone. The results are considered sufficiently positive to encourage further testing of C. haywardi as a biological control agent of the Mediterranean fruit fly.     

Effect of Diachasmimorpha tryoni on two non-target flowerhead-feedingtephritids

Laboratory tests were conducted to evaluate the possible effect of a deliberately introduced fruit fly parasitoid, Diachasmimorpha tryoni, on 2 non-target flowerhead-feeding tephritid flies,Trupanea dubautiae and Ensina sonchi. The former is an nativecomposite endemic Hawaiian tephritid which feeds on flowerheads of the native composite shrub, Dubautia raillar dioides; the latter is an inadvertently introduced tephritid infesting flowerheads of the exotic weed, Sonchus oleraceus. Gravid females of D. tryoniwere confined in test cages with field-collected D.raillardioides and S. oleraceus flowerheads infested with late instars of T. dubautiae and E. sonchi,respectively. D. tryoni showed low levels of visiting and probing responses to D. raillardioides flowerheads and relatively higher responses to S. oleraceus flower heads in both the presence and absence of the parasitoid's normal host, the Mediterranean fruit fly, Ceratitis capitata. With 72-h exposure to D. tryoni, 13.9 and 2.6% of T. dubautiaewere attacked by test parasitoids in the absence and presence of C.capitata in the test cage, respectively; while 56.8 and34.2% of E. sonchi were attacked. In contrast, 94.0 and84.0% of C. capitata larvae presented in screened disheswith diet in test cages were attacked by D. tryoni in testswith T. dubautiae and E. sonchi, respectively. Attackof D. tryoni on flowerhead-feeding T. dubautiae andE. sonchi resulted in significant reduction in the emergence ofadult flies, especially in the absence of the parasitoid's normal host.While 8.8–12.8 adult D. tryoni per test (both males andfemales) successfully emerged from medflies, no adult D. tryoniprogeny emerged from T. dubautiae, and only 3 deformed males ofD. tryoni (much smaller than the normal wasp) emerged fromE. sonchi. The relevance of these findings to the safety offuture biological control programs against tephritid pests is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The biology of Bracon celer as a parasitoid of the olive fruit fly

A series of laboratory experiments was conducted on a colony of Bracon celer Szépligeti (Hymenoptera: Braconidae) reared on the olive fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae). Female B. celer preferentially probe and oviposit into olives containing late third-instar fly larvae. The parasitoid develops as a solitary, ectoparasitic idiobiont. Mean development time (oviposition to adult eclosion) at 22 °C was, for females, 36±1 (SE) days, and for males, 34±1 days. The mean longevity of adult female wasps when provided honey and water was significantly greater than when they were provided water alone, or nothing. The females produced an average of 9.7±7.2 progeny during their lifetimes, but production levels in the insectary colony suggested that this level of fecundity was artificially low and could be improved. The discrepancy may be a consequence of constraints on oviposition behavior imposed by the experimental design. The results are discussed with respect to insectary production methods and the potential use of B. celer as a biological control agent for olive fly in California.     

Mortality of olive fruit fly pupae in California

Efforts to control the olive fruit fly, Bactrocera oleae (Diptera: Tephritidae), in California have focused on insecticidal baits and biological control by parasitoids, which primarily target the adult and larval stages, respectively. The pupal stage, which occurs in the soil, has largely been overlooked. This study investigated mortality factors for olive fruit fly pupae in California olive orchards, using a combination of exclusion experiments and observation and trapping of potential predators. Results show predation and climatic factors contribute to pupal mortality. Ants (Formicidae) were the most numerous predators observed. Soil-borne pathogens caused no mortality in this study. Potential applications of these results in the development of a sustainable management program are discussed.