Effects of growing resistant potatoes with gene H1 from Solarium tuberosum ssp. andigena on populations of Heterodera rostochiensis British pathotype A

Pure pathotype A populations of Heterodera rostochiensis produce a few females on ex andigena hybrids with the H₁ gene for resistance. As the proportion of larvae able to become female on ex andigena hybrids was not increased by reproducing the nematodes on such hybrids for 3 years, these females seem not to be genetically different from the rest of the population. The proportion increased rapidly when the initial population contained a few pathotype (species) E nematodes but again no increase in the proportion of pathotype (species) A larvae able to become female on ex andigena was detected and pathotype E replaced pathotype A.     

Histochemistry and Senescence of Colleters of Allamanda cathartica (Apocynaceae)

Allamanda have colleters on the adaxial bases of petiole, bractsand bracteoles. Each colleter is finger shaped, differentiatedinto a long head on a short stalk. Vasculature to the colleteris absent but branched laticifers are present among the centralcells. Secretion of the colleter contains glucose and rhamnose.The major elements present in the exudate are Na, Fe and Zn.Starch, protein and lipids were identified, with lipids themajor component. Petiolar colleters are persistent and becomestiff due to the lignification occurring in the walls of epithelialand central cells. Because of over-lignification in the centralcells, the cell lumen is highly reduced. Allamanda, colleter, laticifer, secretion, senescence     

Diel biting activity of Culex (Melanoconion) caudelli in Trinidad, West Indies

The diel biting periodicity of the arbovirus vector Culex (Melanoconion) caudelli Dyar and Knab (Diptera; Culicidae) in the Aripo-Wallerfield forest, Trinidad, was studied by collecting mosquitoes attracted to mouse-baited traps at 2-hourly intervals during eight 24 h periods. Biting females of Cx caudelli were collected during all night-time hours, 18.00-06.00 hours, with an overall unimodal pattern, i.e. one well-defined peak between 22.00 and 04.00 hours. This contrasts with previous reports that Cx caudelli is diurnally active. During the four moon phases, the period of peak biting activity varied from 22.00 to 24.00 hours at fullmoon, from 22.00 to 04.00 hours at first quarter, and from 24.00 to 02.00 hours at new moon and last quarter phases. The number of mosquitoes collected varied significantly with moon phases, the highest (152/24 h) being collected in the first lunar quarter and the lowest (71/24 h) in the last lunar quarter. Cloud cover and rainfall had no significant effect on the diel biting periodicity of Cx caudelli.     

Morpho-histogenic studies on tendrils of Passiflora

The ontogenetic development of the tendril and its associatedorgans is investigated in 17 species of Passiflora. The shootapex shows a single tunica layer though the second layer simulatestunica. The cytohistological zonation is not a constant feature.In P. caerulea Linn., it is distinct at leaf initiation butin P. pruinosa Mast., P. vespertilio Linn., and P. watsonianaMast., it is indistinct. The main axillary bud differentiatesfrom the peripheral meristem of the shoot apex. The differentiationof this bud into floral and tendril menstems occurs at a nodeimmediately below the shoot apex in P. minima Blanco. and Pracemosa Brot. In other species this differentiation generallyoccurs at the lower nodes. The floral meristem is initiatedas an accessory bud from this bud, thus forming a bud complex.The residuum of the bud complex develops as a tendril. The thirdaccessory bud which does not originate from this bud complex,develops into a vegetative branch. The fundamental nature ofthe vascular relationship between the flower, tendril, accessorybud, subtending leaf, and the axis is similar in most of theinvestigated species.     

Influence of urbanisation on the prevalence of protozoan parasites of bumblebees

1. Increasing urbanisation is often cited as a cause of declining biodiversity, but for bumblebees there is evidence that urban populations of some species such as Bombus terrestris L. may be more dense than those found in agricultural landscapes, perhaps because gardens provide plentiful floral resources and nesting opportunities. 2. Here we examine the influence of urbanisation on the prevalence of the main protozoan parasites of bumblebees in west central Scotland. We would expect transmission rates and prevalence of parasites to be higher in high density host populations, all else being equal. 3. Workers of two bee species, B. terrestris and B. pascuorum, were sampled over a 45‐day period in mid to late summer, and parasites were detected in faeces and via dissection. A comparison of the two methods suggests that faecal sampling is considerably less sensitive than dissection, failing to detect infection in 27.8%, 55.1%, and 80% of cases of infection with the parasites Crithidia bombi, Nosema bombi, and Apicystis bombi, respectively. 4. For all three parasites, broad patterns of prevalence were similar, with prevalence tending to increase with urbanisation in B. terrestris but not in B. pascuorum. The different patterns of seasonal prevalence in the two bee species suggest that intraspecific transmission is more important that interspecific transmission. 5. Our observation of greater parasite prevalence among B. terrestris in urban compared with rural areas suggests that urban habitats may present greater opportunities for parasite transmission. Greater bee densities in urban areas may be the driving factor; however, further study is still needed. For example, differences in disease prevalence between habitats could be driven by differences in the types and abundance of flowers that are available, or in exposure to environmental stressors.     

Evidence for hilltopping in bumblebees?

1. Male bumblebees are known to exhibit a range of mate‐location behaviours, including perching on prominent objects and darting at passing queens, patrolling of scent‐marked flight routes, and waiting outside nest entrances for virgin queens to emerge. Here we provide evidence for a fourth strategy, known as hilltopping. This behaviour is widely known from a range of invertebrates, but has not previously been described in bumblebees. 2. We studied the distribution of bumblebees along transects ascending four hills in Scotland and demonstrate that, relative to workers, males of four bumblebee species or species groups (Bombus lapidarius, B. monticola, B. pascuorum, and B. lucorum/magnus/cryptarum/terrestris) tend to congregate at or near the tops of hills. This is, to our knowledge, the first evidence for hilltopping in bumblebees and the first record of any putative mate‐locating behaviour for male B. pascuorum, a very common species in Europe. 3. We note that, in common with most previous studies of mate‐locating behaviour in bumblebees, attraction of virgin queens and mating were not observed.     

An improved method for detecting substrate preferences shown by mosquitoes that exhibit 'skip oviposition'

Abstract. A new method is described for detecting and characterizing ovi-position-substrate preferences among insects (e.g. Aedes aegypti ) that customarily disperse the eggs of a single batch among several sites (i.e. that exhibit 'skip oviposition'). The method entails recording the distribution of eggs by individual females provided initially with an array of identical sites, thus eliminating possible effects of position preference and female density, and then placing one test site into the array. A preferred substrate can be identified promptly in this way without having to count eggs.     

Oviposition habitat preferences of Toxorhynchites moctezuma mosquitoes in four types of tropical forest in Trinidad

1. Oviposition of the mosquito Toxorhynchites moctezuma Dyar & Knab was investigated in four types of tropical forest in Trinidad, West Indies, using surrogate and natural ovitraps. Larvae of Tx. moctezuma are obligate predators that might be useful for the biological control of Aedes aegypti (L). 2. Significantly more oviposition occurred in seasonal-deciduous forest than in either montane or evergreen-seasonal forest. 3. Oviposition in surrogate containers (black-painted polystyrene cups, 90 mm diameter) was compared with that occurring in typical natural containers (nutpots of Lecythis zapucajo Aublet). Surrogate ovipots were relatively insensitive indicators of oviposition activity, and would be an inefficient means of harvesting Tx. moctezuma eggs. 4. Implications for the collection, culture and mass release of Tx. moctezuma are discussed.     

Distribution and seasonality of Culex (Melanoconion) caudelli, a vector of arboviruses in Trinidad

Seasonal and spatial distributions of the arbovirus vector mosquito Culex (Melanoconion) caudelli Dyar and Knab (Diptera: Culicidae) in the Aripo-Wallerfield forest, Trinidad, were studied by collecting mosquitoes attracted to mouse-baited traps in forest, ecotone and savannah, one day per week throughout the year, 98% of the Cx caudelli mosquitoes were collected during the wet season, with a significant positive correlation between rainfall and mosquito catch. The reverse occurred during the dry season. Cx caudelli displayed a preference for the ecotone where 67% were collected, while 32% and 1% were collected in the forest and savannah respectively.