Samira A. Mohamed

Parasitoids of medfly, Ceratitis capitata, and related tephritids in Kenyan coffee: a predominantly koinobiont assemblage

Arabica coffee was sampled from two sites in the central highlands of Kenya (Rurima, Ruiru) and one site on the western side of the Rift Valley (Koru). Three species of ceratitidine Tephritidae, Ceratitis capitata (Wiedemann), C. rosa Karsch and Trirhithrum coffeae Bezzi, were reared from sites in the central highlands, and an additional species, C. anonae Graham, was recovered from the western-most site. Ten species of parasitic Hymenoptera were reared from these tephritids. The parasitoid assemblage was dominated by koinobionts. Eight of the species are koinobiont endoparasitoids, but only one idiobiont larval ectoparasitoid was reared, and only one idiobiont pupal endoparasitoid. The effects of sampling bias on determination of parasitoid assemblage size associated with concealed hosts are discussed. The potential for use of these parasitoids in biological control is also discussed. Most of the parasitoid species recovered during this study are capable of developing on C. capitata, while several also attack C. rosa. Both flies are notorious pests of tropical and subtropical fruits.

Taxonomic Identity of the Invasive Fruit Fly Pest, Bactrocera invadens: Concordance in Morphometry and DNA Barcoding

In 2003, a new fruit fly pest species was recorded for the first time in Kenya and has subsequently been found in 28 countries across tropical Africa. The insect was described as Bactrocera invadens, due to its rapid invasion of the African continent. In this study, the morphometry and DNA Barcoding of different populations of B. invadens distributed across the species range of tropical Africa and a sample from the pests putative aboriginal home of Sri Lanka was investigated. Morphometry using wing veins and tibia length was used to separate B. invadens populations from other closely related Bactrocera species. The Principal component analysis yielded 15 components which correspond to the 15 morphometric measurements. The first two principal axes contributed to 90.7% of the total variance and showed partial separation of these populations. Canonical discriminant analysis indicated that only the first five canonical variates were statistically significant. The first two canonical variates contributed a total of 80.9% of the total variance clustering B. invadens with other members of the B. dorsalis complex while distinctly separating B. correcta, B. cucurbitae, B. oleae and B. zonata. The largest Mahalanobis squared distance (D2 = 122.9) was found to be between B. cucurbitae and B. zonata, while the lowest was observed between B. invadens populations against B. kandiensis (8.1) and against B. dorsalis s.s (11.4). Evolutionary history inferred by the Neighbor-Joining method clustered the Bactrocera species populations into four clusters. First cluster consisted of the B. dorsalis complex (B. invadens, B. kandiensis and B. dorsalis s. s.), branching from the same node while the second group was paraphyletic clades of B. correcta and B. zonata. The last two are monophyletic clades, consisting of B. cucurbitae and B. oleae, respectively. Principal component analysis using the genetic distances confirmed the clustering inferred by the NJ tree.

Host specificity of Psyttalia cosyrae (Hymenoptera: Braconidae) and the effect of different host species on parasitoid fitness

Abstract Psyttalia cosyrae (Wilkinson) (Hymenoptera: Braconidae) is a synovigenic, koinobiont larval-pupal parasitoid of Ceratitis cosyra (Walker) (Diptera: Tephritidae), and possibly other tephritid fruit flies. Host acceptance and suitability of medfly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), mango fruit fly, Ceratitis cosyra , Natal fruit fly, Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi), Ceratitis anonae Graham, and melon fruit fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae), for oviposition and development of this parasitoid were investigated. The effect of different host species on traits widely used to assess parasitoid fitness was also evaluated. Psyttalia cosyrae accepted all host species tested, but acceptance varied. In no choice tests, C. cosyra and C. capitata were accepted at a significantly higher rate than the other four species. The parasitoid successfully developed only in C. cosyra and C. capitata . Eggs oviposited in C. rosa , C. fasciventris , C. anonae , and B. cucurbitae were encapsulated. Developmental time was shorter in C. capitata than in C. cosyra , but parasitoid progeny emerging from the latter host were more fit, as measured by percent female progeny, adult size, egg load, and adult survival.

Antagonistic Interactions between the African Weaver Ant Oecophylla longinoda and the Parasitoid Anagyrus pseudococci Potentially Limits Suppression of the Invasive Mealybug Rastrococcus iceryoides

The ant Oecophylla longinoda Latreille forms a trophobiotic relationship with the invasive mealybug Rastrococus iceryoides Green and promotes the latter’s infestations to unacceptable levels in the presence of their natural enemies. In this regard, the antagonistic interactions between the ant and the parasitoid Anagyrus pseudococci Girault were assessed under laboratory conditions. The percentage of parasitism of R. iceryoides by A. pseudococci was significantly higher on “ant-excluded” treatments (86.6% ± 1.27%) compared to “ant-tended” treatments (51.4% ± 4.13%). The low female-biased sex-ratio observed in the “ant-tended” treatment can be attributed to ants’ interference during the oviposition phase, which disrupted parasitoids’ ability to fertilize eggs. The mean foraging time, host handling time and number of successful oviposition in “ant-excluded” treatment were significantly higher compared to “ant-tended” treatments. When ant workers were allowed access to sterilized sand grains, mummified and unmummified R. iceryoides, they selectively removed the mummified mealybugs, indicating that they recognized the mummies as potential foods (1.2 ± 0.46 to 7.8 ± 1.17 mummies at 10 min intervals for 2 h). Percentage emergence from mummified R. iceryoides removed by the ants was significantly lower compared to emergence from mummies not exposed to ants. Although, host seeking parasitoids frequently evaded attacks, some were killed by the foraging ant workers (2.0 ± 0.38 to 6.0 ± 0.88 at 10 min intervals for 2 h). These results suggest for the first time that the presence of O. longinoda has a detrimental effect on the abundance, reproductive success and possibly oviposition strategy of female parasitoids, which might be a delimiting factor in field conditions if both natural enemies are to be recommended for use within the same agro-ecosystem.

Old and new host-parasitoid associations: parasitism of the invasive fruit fly Bactrocera invadens (Diptera: Tephritidae) and five African fruit fly species by Fopius arisanus, an Asian opiine parasitoid

Abstract Fopius arisanus (Sonan), a solitary koinobiont endoparasitoid of fruit flies, was introduced for testing and final release against the recently discovered species Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to assess host preference, host acceptability for oviposition, and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species, namely, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), C. cosyra (Walker), C. rosa Karsch, C. fasciventris (Bezzi), and C. anonae Graham. Females of F. arisanus visited all host egg patches, but showed a stronger preference to eggs of B. invadens, which was also most accepted for oviposition. Successful development of parasitoid progenies varied greatly across hosts, with B. invadens yielding the highest parasitoid progeny and C. fasciventris yielding no F. arisanus progeny. Most of the parasitoid eggs laid in C. rosa and C. fasciventris were encapsulated. Sex ratio was not influenced by host species and it was female biased in all hosts that produced parasitoid progeny. Fopius arisanus was able to establish a new association with C. capitata, C. cosyra and to a lesser extent C. anonae. The results are discussed in the light of the potential use of F. arisanus as a biological control agent of B. invadens.

Efficacy of soil application of Metarhizium anisopliae and the use of GF-120 spinosad bait spray for suppression of Bactrocera invadens (Diptera: Tephritidae) in mango orchards

Field trials were conducted for two seasons in mango orchards at Nthagaiya, Kenya, to evaluate the efficacy of soil inoculation with Metarhizium anisopliae (Hypocreales: Clavicipitaceae) and GF-120 spinosad bait sprays, applied either alone or in combination, for suppression of the invasive fruit fly, Bactrocera invadens (Diptera: Tephritidae). During the 2006/2007 season, average post-treatment samples showed that B. invadens catches from the control orchards were four times higher than the number of flies captured in the plots receiving M. anisopliae+GF-120. Fruit infestation was 16, 45, 30 and 60% in the M. anisopliae+GF-120, M. anisopliae alone, GF-120 alone and control orchards, respectively. In the 2007/2008 season, average B. invadens post-treatment samples in the control orchards were seven times higher than the treatment with M. anisopliae+GF-120; and fruit infestation was 11, 38, 28, and 52% in the orchards assigned to M. anisopliae+GF-120, M. anisopliae alone, GF-120 alone and control treatments, respectively. Enumeration of conidial densities from soil samples on agar plates showed initial densities of 1.1–2.1×105 colony forming units (cfu)/g of dry weight of soil but decreased to 1.0–1.4×103 cfu/g at the end of the experimental period. Exposure of laboratory-reared pupariating larvae to soil samples taken from fungus-treated fields showed significant reduction in B. invadens adult emergence (25–36%) compared with the control (80–82%). Our results suggest that the combined use of soil application of M. anisopliae and GF-120 spinosad bait spray is an effective IPM strategy for field suppression of B. invadens on mango.

Evaluation of the impact of Diachasmimorpha longicaudata on Bactrocera invadens and five African fruit fly species

Diachasmimorpha longicaudata (Ashmead), a solitary koinobiont larval–prepupal endoparasitoid of fruit flies, was introduced into Kenya for testing and final release against the recently discovered invasive species, Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to determine host preference, host acceptability for oviposition and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species –Ceratitis capitata (Wiedemann), Ceratitis cosyra (Walker), Ceratitis rosa Karsch, Ceratitis fasciventris (Bezzi) and Ceratitis anonae Graham – for the development of D. longicaudata. Females of D. longicaudata visited all host‐larval patches, and were also attracted to these hosts at comparable levels. Acceptability, successful development of parasitoid progenies and their sex ratio varied widely across hosts. C. capitata yielded the highest parasitoid numbers whereas B. invadens was the only host that yielded a female‐biased sex ratio. Larvae of B. invadens, C. rosa, C. fasciventris and C. anonae mounted differential immune reaction towards D. longicaudata eggs. Although, the parasitoid performed poorly on the target host B. invadens, it was able to form new association with C. cosyra and C. capitata. The prospect of using this parasitoid in biological control of African indigenous fruit flies is discussed.

Cold Susceptibility and Disinfestation of Bactrocera invadens (Diptera: Tephritidae) in Oranges

ABSTRACT To develop a cold disinfestation treatment for the fruit fly Bactrocera invadens Drew, Tsuruta & White (Diptera: Tephritidae) that is rapidly spreading across Africa, research was conducted in Nairobi, Kenya, using flies from a laboratory culture and ‘Valencia’ orange (Citrus sinensis L. Osbeck) as the host. The developmental rate of B. invadens in Valencia oranges was determined at 28°C, and the third instar was found to be the least susceptible of the egg and larval life stages to cold treatment at 1.1°C in oranges. When 22,449 B. invadens third instars were exposed in oranges to a cold treatment with an approximate midpoint of 1.1 ± 0.5°C, the results suggested that a period of 16 d would be worthwhile verifying on a larger scale in oranges. Results from the first replicate of 16,617 larvae showed no survivors, but the second replicate of 23,536 larvae had three survivors. Because a longer cold treatment based on a mean temperature of 1.1°C would create logistical difficulties for some export markets, further replicates were conducted at an approximate midpoint of 0.5°C and at mean hourly maximum of 0.9 ± 0.5°C, for 16 d. After three replicates, in which 65,752 B. invadens third instars in total were treated with no survivors, the Japanese requirement of 99.99% mortality at the 95% confidence level was surpassed. The following treatment protocol for B. invadens larvae in oranges can therefore be recommended: fruit pulp to be maintained at temperatures of 0.9°C or lower for 16 consecutive days.

Cold Tolerance and Disinfestation of Bactrocera invadens (Diptera:Tephritidae) in ‘Hass’ Avocado

ABSTRACT Bactrocera invadens (Diptera: Tephritidae) has spread rapidly across Africa and currently poses a phytosanitary threat to the fruit industry of South Africa. In reaction a cold mitigating treatment to provide phytosanitary security to importing countries was developed in Nairobi, Kenya. Using laboratory reared fruit flies, the rate of development in ‘Hass’ avocado (Persea americana Miller) was determined at 28°C. Fruit ripeness or softness was found to be a factor improving larval fruit fly survival. Using this information the egg and larval developmental stages were subjected to 2°C cold treatment and it was found that the third instars were the most cold tolerant life stage and that it was expected that between 16 and 17 d treatment would provide phytosanitary security. There were no survivors in the treatment of an estimated 153,001 individuals in four replicates at an average fruit pulp temperature of 2°C satisfying the Probit 9 level of efficiency at a confidence of >95%. These data provide evidence that a continuous cold treatment of 1.5°C or lower for 18 d would provide phytosanitary security in that any consignment entering an importing country poses no risk of accidental importation of B. invadens.

The potential distribution of Bactrocera dorsalis: considering phenology and irrigation patterns.

A species in the Bactrocera dorsalis (Hendel) complex was detected in Kenya during 2003 and classified as Bactrocera invadens Drew, Tsuruta & White. Having spread rapidly throughout Africa, it threatens agriculture due to crop damage and loss of market access. In a recent revision of the B. dorsalis complex, B. invadens was incorporated into the species B. dorsalis. The potential distribution of B. dorsalis has been previously modelled. However, previous models were based on presence data and did not incorporate information on the seasonal phenology of B. dorsalis, nor on the possible influence that irrigation may have on its distribution. Methyl eugenol-baited traps were used to collect B. dorsalis in Africa. Seasonal phenology data, measured as fly abundance throughout the year, was related to each locations climate to infer climatic growth response parameters. These functions were used along with African distribution records and development studies to fit the niche model for B. dorsalis, using independent global distribution records outside Africa for model validation. Areas at greatest risk of invasion by B. dorsalis are South and Central America, Mexico, southernmost USA, parts of the Mediterranean coast, parts of Southern and Eastern Australia and New Zealands North Island. Under irrigation, most of Africa and Australia appear climatically suitable.