Biological Control Potential of Two Steinernematid Species Against the Date Fruit Stalk Borer (Oryctes elegans Prell, Coleoptera: Scarabaeidae).

The fruit stalk borer (Oryctes elegans) is an important pest of date palm (Phoenix dactylifera) trees in Saudi Arabia. This study was conducted to determine efficacy of using two species of entomopathogenic nematodes, Steinernema kushidai and Steinernema glaseri, against O. elegans under laboratory and field conditions. Under laboratory conditions, both species of nematodes showed a significant effect on the mortality of O. elegans larvae. Significant variations were observed when insects were exposed to nematodes for variable durations under laboratory conditions. They showed no differences in insect larval mortality when tested either in aqueous suspensions or in Galleria-infected cadavers. Insects exposed to nematode aqueous suspension for 4 d and those treated with Galleria-infected cadavers showed the same rates of mortality, which differed when insects were exposed to nematode-infected cadavers under field conditions. Mean percentages of corrected mortality varied between nematode species and number of infected cadavers. S. kushidai caused significantly higher mortality percentages ± SE (72.17 ± 5.57, 95.83 ± 4.17, 94.43 ± 5.57, and 100%) compared with S. glaseri when the fruit stalk borer, O. elegans, was treated for 6 wk with two, four, six, and eight infected cadavers, respectively.

Host-parasite interaction and impact of mite infection on mosquito population

ABSTRACT During the present study, the host-parasite relationship between mosquitoes and parasitic mites was investigated. The 8954 individuals of male and female mosquitoes belonging to 26 genera: seven each of Aedes and Culex, six of Anopheles and one each of Toxorhynchites, Coquillettidia and Uranotaenia were collected from 200 sites. The male and female mosquitoes were collected from the State of Uttar Pradesh, located at 26.8500° N, 80.9100° E in North India by deploying Carbon dioxide-baited and gravid traps. The intensity of mite's infection, type and number of mites attached to mosquitoes, mite's preference for body parts and host sexes were the parameters used to determine host-parasite relationship. Eight species of mites: Arrenurus acuminatus, Ar. gibberifrons, Ar. danbyensis, Ar. madaraszi, Ar. kenki, Parathyas barbigera, Leptus sp., and Anystis sp., parasitized mosquitoes. Parasitic mites preferred host's thorax for attachment as compared to the head, pre-abdomen or appendages. The present study suggests phoretic relationship between parasitic mites and mosquitoes. Wide occurrence, intensity of infection, parasitic load, and attachment preferences of the mites suggested their positive role in biological control of adult mosquitoes. The present study will set the path of future studies on host-parasite relationships of mites and mosquitoes and define the role of parasitic mites in the biological control of mosquitoes.

Comparative susceptibilities of different life stages of the red palm weevil (Coleoptera: Curculionidae) treated by entomopathogenic nematodes.

The red palm weevil, Rhynocophorus ferrugineus (Olivier) (Coleoptera: Curculionidae) has become the most important pest of the date palm trees in the world. It has been reported in the kingdom of Saudi Arabia since 1987 and in Egypt since 1992. Studies were conducted to compare preferences among red palm weevil life stages for infection by 12 entomopathogenic nematodes (EPNs), under no choice and five stage choice experiments, and curative trials by some of EPNs isolates. All EPN isolates proved to be pathogenic for the first instars of red palm weevil larvae. Some of the test EPNs exhibited a preference for larvae over pupae, and a lesser degree of preference for adults. In contrast some strains showed no preference for any stage. The local Egyptian isolates of EPNs were most efficient nematodes against red palm weevil than foreign strains. Field assessments using trunk injection resulted in a substantial decline in the population of red palm weevil after two successive applications within 3 wk. Efficacies ranging 48-88% were achieved in the curative assay resulting in a significant increase in palm survival compared with the untreated control. In conclusion, there is a great potential for the use of EPNs, in particular the Steinernema sp. (EGG4), against the red palm weevil when injected in the date palm.

Interaction of the koinobiont parasitoid Microplitis rufiventris of the cotton leafworm, Spodoptera littoralis, with two entomopathogenic rhabditids, Heterorhabditis bacteriophora and Steinernema carpocapsae.

Entomopathogenic nematodes are generally considered beneficial organisms. However, they can affect beneficial insects such as parasitoids. The interaction between the entomopathogenic nematodes Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) and Steinernema carpocapsae Weiser, and the parasitoid Microplitis rufiventris Kokujev (Hymenoptera: Braconidae) was investigated in the laboratory. In non-parasitized hosts, Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae) larvae exposed to H. bacteriophora showed a higher percent mortality than those exposed to S. carpocapsae. Both nematodes were able to invade and propagate in non-parasitized S. littoralis larvae and those parasitized by M. rufiventris. Both nematode species reproduced in Microplitis-parasitized hosts, but there was a higher number of nematodes in non-parasitized larvae. S. carpocapsae yielded higher numbers of infective juveniles than H. bacteriophora. Generally, the number of nematodes harvested increased as their host's size increased. The interaction between the nematodes and parasitoid favored the nematodes when the nematodes were inoculated during the parasitoid egg stage or the young parasitoid larvae, thus giving the nematodes a better chance to grow and reproduce, resulting in the death of the parasitoid larvae. Conversely, when the nematodes were inoculated during the late larval instar of the parasitoid, the competition partially favored the wasp, thus giving approximately 50% of the wasps a better chance to develop, emerge, and reproduce, providing evidence that both nematodes and wasps could reproduce in the same host. Egg maturation of female wasps derived from nematode-infected hosts was not significantly different than those from control hosts. The combined application of nematodes and parasitoids may be beneficial if the detrimental effects of the nematodes on the parasitoid could be avoided by precisely timing the application strategies. It is clear that Microplitis larvae and the nematodes share the host larva and engage in a trophic interaction with each other. Intraguild predation is briefly discussed.