Female antennal sensilla of Epidinocarsis lopezi and Leptomastix dactylopii (Hymenoptera: Encyrtidae), parasitoids of pseudococcid mealybugs

Antennal sensilla were compared in females of two encyrtid Hymenoptera, Epidinocarsis lopezi and Leptomastix dactylopii, parasitoids of adults and larvae of Pseudococcidae. The external morphology of these sensilla was studied using scanning electron microscopy and their ultrastructure observed under transmission electron microscopy using ultrathin sections. Female antennae have seven different types of sensilla, morphologically very similar in the two species: trichoid sensilla, which are putative mechanosensilla, sensilla chaetica types 1 and 2, which are presumably contact chemosensilla, and sensilla chaetica types 3 and 4, basiconic sensilla, and placoid sensilla, which are all presumed to be olfactory sensilla. Sensilla chaetica types 2 and 4 are thought to be directly involved in host discrimination. The only differences between the two species are in the number and distribution of some types of sensilla. These differences might be related to the varied tritrophic ecological context of the two species rather than to their similar biology.

The hemocytes of the mealybugs Phenacoccus manihoti and Planococcus citri (Insecta: Homoptera) and their role in capsule formation

Hemocytes of Phenacoccus manihoti and Planococcus citri were studied to determine general ultrastructure, phenoloxidase activity, and the presence or absence of a glycocalyx. Prohemocytes, oenocytoids, and granular hemocytes of types 1 (GH1), 2 (GH2), and 3 (GH3) were observed in P. manihoti. In P. citri we observed only GH2 and GH3 (macrophage-like cells). In addition to these hemocyte types, other cells that we believe to be fat-body cells were also observed free in the hemolymph. There was evidence of phenoloxidase activity in GH2 and GH3. The intensity of this reaction increased after parasitization of P. manihoti by the wasp Epidinocarsis lopezi. In most hemocyte types the glycocalyx was very little developed. In P. manihoti, lysis of hemocytes was observed in the vicinity of the parasitoid larva, leading to the formation of a capsule.

Interference by ants in biological control of the cassava mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae) in Ghana

In surveys of cassava fields in the coastal savanna and rain forest zones of Ghana, eight species of ants, mostly in the genera Camponotus, Crematogaster and Pheidole (Hymenoptera: Formicidae), were found attending cassava mealybug, Phenacoccus manihoti Matile-Ferrero. Ant densities were much higher in the rain forest than in the savanna and, in most zones, positively correlated to mealybug population densities. Pheidole megacephala (Fabricius) was the only species more abundant in the interior of fields, whereas the other species preferred the edges of fields or, like Camponotus spp., did not respond to edge effects. Weediness of the fields did not clearly influence the presence of ants. Crematogaster sp. and P. megacephala spent most of the time on cassava tips, where they built carton tents. Ants of the three genera reduced parasitism rates by the exotic Epidinocarsis lopezi (De Santis) (Hymenoptera: Encyrtidae) to half, compared to the rates observed on mealybug colonies of equal size that were not attended. Hyperparasitism by Prochiloneurus insolitus (Alam) (Hymenoptera: Encyrtidae) and Chartocerus hyalipennis Hayat (Hymenoptera: Signiphoridae) and predation by the indigenous Exochomus troberti Mulsant (Coleoptera: Coccinellidae) were similarly reduced. Where ants were excluded experimentally by insectcide barriers, parasitism was 32%, compared to only 10% in the control, and predator densities were reduced three-fold. In a 24 h experiment, Pheidole megacephala was observed to remove about half the E. troberti larvae; Crematogaster sp. and Camponotus spp. were less efficient. The results show the locally strong interference of ants with biological control of the cassava mealybug. Despite this interference, mealybug populations in the rain forest were judged to be below damaging levels.

FECUNDITY, LONGEVITY, AND INTRINSIC NATURAL RATE OF INCREASE OF EPIDINOCARSIS LOPEZ1 (DE SANTIS) (HYMENOPTERA: ENCYRTIDAE)

A laboratory study of the fecundity, longevity, and intrinsic natural rate of increase of Epidinocarsis lopezi (De Santis) (Hymenoptera: Encyrtidae) was performed at 26 °C, the average temperature observed in the Congo during pullulation of its host Phenacoccus manihoti Mat.-Ferr. (Homoptera: Pseudococcidae). With 30 mealybugs per female per day, the parasitoid lives for an average of 41.4 days and lays 558.5 eggs. The net reproduction rate (R0) was calculated to be 269.9 females per female per generation, the average duration of a generation (T) was 33.9 days, and the intrinsic natural rate of increase of the parasitoid (rm) was 0.213. The fecundity observed in E. lopezi in this study was much higher than the figures previously reported. The rm of the parasitoid appeared to be higher than that determined by other authors for the mealybug. The limits of such a comparison are discussed.