Body size is a main fitness component of insect parasitoids. We assessed the potential influence of maternal size of the parasitoid wasp Aphidius colemani Viereck (Hymenoptera: Braconidae: Aphidiinae) on its ability to parasitize the different instars of Aphis gossypii Glover (Hemiptera: Aphididae) on eggplant and cucumber. In the experiments "small" vs "large" parasitoid females were used. Females oviposited in all instars but more of the smaller hosts were parasitized. Host selection was affected by female size and the larger hosts were more frequently mummified by the large than the small females. Thus, parasitoid female size influenced host selection. This could affect the potential of the parasitoid to exploit populations of aphids that differ in their size structure. The importance of these results in terms of the ecological adaptations of the parasitoid and their implication for biological control are discussed.
This study investigates the thermal requirements, nymphal development rates and the fecundity of both alate and apterous adults of the giant willow aphid, Tuberolachnus salignus (Gmelin) at several temperatures. Nymphal development rate increased linearly with temperature. It was estimated that 196 ± 4 degree-days above a threshold temperature of 5.5 ± 0.3°C were required for apterae to complete development from birth to final ecdysis. The alate morph was significantly less fecund than the apterous morph and its fecundity did not vary with temperature. The apterous morph displayed highest fecundity at 20°C. Survival to reproduction was lower in the alate morph, but temperature had no effect on the proportion reproducing in either morph.
Functional responses of immature stages of Propylea quatuordecimpunctata (L.) to varying densities of Aphis fabae Scopoli
reared on Vicia faba L. were evaluated under laboratory conditions. All larval stages of the predator were starved for 12 h prior
to being placed individually for 24 h in plastic containers with different densities of its prey, A. fabae, on potted V. faba plants.
Logistic regression analysis of the proportion of aphids consumed as a function of initial density indicated that all larval instars of P.
quatuordecimpunctata exhibited a type II functional response when searching for A. fabae on V. faba plants. Attack rates (0.059,
0.057, 0.065 and 0.064) and handling times (6.18, 2.37, 1.06 and 0.44) for first to fourth instar larvae, respectively, were estimated
using Holling’s disc equation.
The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a serious pest of citrus in northern Iran, both because of the damaged caused by its feeding and as a vector of several viruses. The genetic structure of populations of A. gossypii on citrus trees at eight localities in Iran was surveyed using seven polymorphic microsatellite loci. Of 240 individuals tested, 142 multilocus genotypes (MLGs) were identified. The presence of multicopy genotypes and negative FIS values revealed that the major mode of reproduction in northern Iran is obligate parthenogenesis. The genotypic diversity of populations ranged between 0.24 and 0.93. Considerable genotypic diversity and a high frequency of unique MLGs, confirmed there is some cyclical parthenogenesis in the region. The analysis of molecular variance revealed high intrapopulation and weak interpopulation genetic differentiation (overall FST = 0.036) among the different populations. The UPGMA dendrogram of eight populations based on Nei's genetic distance indicated two clusters: genotypes from West of Mazandaran and Guilan provinces and those from East of Mazandaran. The same results were also obtained from the STRUCTURE analysis of these populations. This information on the genetic diversity of populations of A. gossypii in northern Iran could be useful for improving the Integrated Pest Management of this aphid.
Aphis fabae and Myzus persicae (Hemiptera: Aphididae) are insect pests that damage sugar beet and bean crops. Both are responsible for losses in yield and transmission of viral diseases, and may be present on the same host at the same time. Three parasitoid species, Aphidius colemani, Lysiphlebus testaceipes and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae) have the potential to be used as biological control agents against at least one of these species of aphids. As a first step prior to the implementation of a biological control program, our aim was to understand the host selection behaviour of the parasitoids, particularly when both aphids are present. We recorded the host acceptance (number of insertions of the ovipositor / number of antennal contacts), suitability (number of mummies / the number of insertions of the ovipositor) and emergence (number of adults emerging from mummies) of these three aphid parasitoids when parasitizing the two aphids. We also analyzed the effect of the host plant on the host preference of the parasitoid. Females of each parasitoid species (n = 15) were exposed to 20 aphids of A. fabae or M. persicae, or a mixture of these two species of aphids, for 15 min, on a leaf disc of each of the two host plants, sugar beet and bean. Higher host acceptance and suitability were recorded for A. colemani attacking both species of aphid: A. fabae (43 and 46%) and M. persicae (43 and 46%) on beet and bean plants respectively, compared to L. testaceipes and L. fabarum. L. testaceipes and L. fabarum showed a clear preference for A. fabae. L. fabarum accepted M. persicae on both plants only when it was mixed with A. fabae, probably due to a confusion effect. We found that the host plant played a significant role in host acceptance, host suitability. We conclude that A. colemani is the better of the three parasitoids studied for the biological control in bean, and particularly, sugar beet crops. and Loulou Albittar, Mohannad Ismail, Claude Bragard, Thierry Hance.
The aim of this work was to determine the impact of allelochemicals (glucosinolates/isothiocyanates) from Brassicaceae (Brassica napus and Sinapis alba) at two trophic levels in relation to biological control efficacy. The impact of these plants on aphid Myzus persicae (Sulzer) and Brevicoryne brassicae (L.) and ladybird Adalia bipunctata (L.) biology can be assessed by observation of several developmental parameters: mortality, development duration and adult weight. Sub-lethal toxicity can also be measured through the reproductive parameters of fecundity and/or egg viability. While both specialist and generalist aphids were positively influenced by Brassicaceae species, mixed effects are recorded in ladybird performances following the aphid species/host plant combinations. Significant differences appeared according to aphid host plant and aphid species. This work enhanced the influence of Brassicaceae plants either as cultivated species (B. napus) or as set-aside (S. alba) on both pests and beneficial insects. The allelochemical presence in plants must be taken into account in programs of integrated pest management due to their direct influence on biological control agents.
In a laboratory experiment, we investigated the preference of larvae and adults of Coccinella septempunctata (Coleoptera: Coccinellidae) for three aphid species: two essential prey, Acyrthosiphon pisum and Aphis philadelphi, and a toxic prey Aphis sambuci. Surprisingly, the toxic aphid was consumed at twice the rate of the two essential prey species. The stages and genders of the ladybirds did not differ in their preference for aphid species. In the tritrophic interaction, in the field, on the elder host plant Sambucus nigra, A. sambuci is usually avoided by C. septempunctata. To measure ladybird preference, apterous females of the three selected aphid species were released in a Petri dish followed by a ladybird. After four hours, we removed the ladybird, counted the number of aphids of each species that survived, and calculated the number of aphids of each species consumed in total. We examined preference by considering separately the first two aphids consumed by a predator (early feeding), and all remaining aphids consumed thereafter (late feeding). The consumption rates of the first two individuals did not deviate from expected values with no preference; i.e., ladybirds fed on aphids without choice in the beginning of experiment when they were hungry. The ladybirds did express preference thereafter, but our hypothesis that the ladybirds should be able to distinguish among the aphids during later phase of the experiment and choose the most profitable species, or at least distinguish between essential and toxic prey, was rejected.
In this study, aspects of the reproductive performance and behaviour of male Myzus persicae (Sulzer) (Hemiptera: Aphididae) were investigated. We report that males of clones possessing an autosomal 1,3 translocation conferring insecticide resistance show a weak trend for a reduction in reproductive potential. Clones with the translocation that can produce males but no mating females (androcyclic clones) did not have an additional disadvantage. The age of virgin males and females affected mating success. Young males and females, 0-5 days old, were the most successful with respect to the number of females mated and number of eggs produced. There was a decline in reproductive potential after 9-10 days into adult life for males and after 4-5 days for females. Mating behaviour was observed in the laboratory and described. Some pre-copulatory stroking behaviour by the fore and hind legs of the male was observed. Females occasionally walked in copula sometimes resulting in the disengagement of the male before the termination of mating. Average mating duration in the experimental conditions was 10.5 ± 4.0 minutes and both males and females readily mated more than once.
The predation rate of the polyphagous predator Macrolophus pygmaeus (Rambur) when offered two aphid species, Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas), was investigated. Equal or unequal numbers of nymphs of each instar of the aphids were offered to the predator alone or together. Aphids were placed on an eggplant leaf, together with a fifth instar nymph of the predator in a plastic Petri dish and kept in growth cabinets at 25°C, 65 ± 5% r.h., and a 16L : 8D photoperiod. The predation rate of M. pygmaeus was always higher on M. persicae than on M. euphorbiae. However, biomass consumption was highest when instars of M. euphorbiae were offered in unequal numbers. The predator showed a strong preference and higher biomass consumption of first and second instar M. persicae. In tests where M. euphorbiae was the prey, preference and biomass consumption were almost always higher for the first instar. Therefore, first and second instar M. persicae and first instar M. euphorbiae provide optimal prey for M. pygmaeus. The implication of the prey preference shown by M. pygmaeus for the biological control of these two aphid species is discussed.
The potential of the parasitoid Aphidius rhopalosiphi for controlling cereal aphids was tested in 16 m2 field cage experiments in 1998 and 1999. In the first year, aphids and parasitoids were released in cages containing naturally occurring populations of aphids and their natural enemies. In the second year, aphids and parasitoids were released in cages which had been cleared of insects by applying insecticide. The growths of the aphid populations in the different cages were analysed and compared. In 1998, the release of 50 pairs of parasitoids per cage had no significant effect on aphid population growth relative to that in the control cages. Even though the aphid population growth rates were less than 60% of that in the control cages, in the cages in which 100 pairs and 200 pairs of parasitoids were released, it was not possible to show they statistically differed. The aphid populations in these three cages were held below 10 aphids per tiller. In 1999, the aphid density was higher and the population grew faster than in 1998. The release of 100 and 200 parasitoids per cage significantly reduced aphid population growth. A. rhopalosiphi seemed to be a good control agent in field cages, provided they were released at the beginning of aphid population growth.