Hannah Nadel

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.

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.

Ingestion of spinosad bait GF-120 and resulting impact on adult Chrysoperla carnea (Neuroptera: Chrysopidae)

Abstract The spinosad bait spray GF-120 Naturalyte F® (Dow AgroSciences LLC, Indianapolis, IN, USA) is widely used in commercial olives in California. Because of concern about its non-target effects on beneficial insects, we studied its impact on feeding behavior, mortality, and reproductive parameters of adult green lacewings, Chrysoperla carnea (Stephens), under laboratory conditions. Male and female feeding rate and quantity, and subsequent mortality, were compared over a 5-day period following a 24-h exposure to honey, GF-120, or the bait component (without spinosad) in two-choice and no-choice assays. All treatments were ingested equally when offered alone. Spinosad did not impart repellency or preference to GF-120 relative to the bait. Honey was preferred in choice tests with GF-120 or bait. Significant mortality occurred when GF-120 was offered alone, but was not significant when it was offered in choice with honey or bait. In a separate assay of female longevity and reproduction, mortality rate as a function of time was similar in all treatments, except for some significantly earlier mortality due to GF-120 compared with honey. GF-120 ingestion significantly reduced fecundity compared with bait during the first week after treatment. Egg hatch was not significantly affected. The preference of adult C. carnea for food should ameliorate the potential negative effect of GF-120 on adult C. carnea mortality in the field. The laboratory study finds that GF-120 is a potentially safer choice for C. carnea than an aqueous suspension of spinosad, and provides no new evidence for definitive risk to field populations.

Non-target host risk assessment of the idiobiont parasitoid Bracon celer (Hymenoptera: Braconidae) for biological control of olive fruit fly in California

Abstract Non-target risk posed by an African parasitoid, Bracon celer Szépligeti (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 parasitoids 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.

Fruit fly parasitoids in coffee in Mpumalanga Province, South Africa

Abstract Bracon celer, Psyttalia perproxima, Psyttalia humilis (all Hymenoptera: Braconidae) and Tetrastichus giffardianus (Hymenoptera: Eulophidae) were reared from fruit flies (Diptera: Tephritidae) infesting Coffea canephora in Mpumalanga, South Africa. Psyttalia perproxima and T. giffardianus were recorded for the first time from southern Africa. Ceratitis capitata was likely the main tephritid host.