Genetic variation and the performance of a mass‐reared parasitoid,Trichogramma pretiosum (Hymenoptera: Trichogrammatidae), in laboratory trials

During mass rearing, adaptation of biological control agents to the rearing environment is a potential problem. Using the parasitoid wasp Trichogramma pretiosum, the performance of 26 highly inbred lines, five composite ‘populations’ (created from the inbred lines) and one insectary‐reared population was compared using fertility life tables. Of the composite populations, three were created with maximal and identical genetic variation as a mixture of all 26 inbred lines, but these were then reared for a different number of generations (2, 6 or 17) before their performance was measured. The remaining two composite populations were created based on the performance of the individual inbred lines: one was a combination of two inbred lines with a high intrinsic rate of natural increase (rm), ‘high rm’; and the other was a combination of two lines with a ‘low rm’. High and low rm populations were reared for two generations prior to testing. Parameters measured were fertility, longevity and sex ratio. We found no difference between the maximally variable population reared for two generations and the ‘high rm’ population (rm = 0.285 and 0.282, respectively). ‘Low rm’ was the population with the lower performance (rm = 0.255). Genetically variable population reared for two generations for 48 h produced significantly more offspring than the populations reared for 6 and 17 generations. Hybrid population derived from the high‐rm lines did significantly better than that derived from the low‐rm lines. Low‐performance populations become more male based than high performance at 48 h. The potential benefits to improve population's performance using inbred lines for mass rearing are discussed.     

Sequentially Rejective Test Procedures for Detecting Outlying Cells in One- and Two-Sample Multinomial Experiments

For multiple testing of multinomial models in the case of one or two samples we propose using test procedures based on the principle described by MARCUS, PERITZ and GABRIEL (1976). These methods are based in each step of the sequentially rejective strategy on tests which exhaust the full α level (i.e. which are not conservative). The tests can be performed in a finite or asymptotic version.     

Field population biology of citrus whitefly, Dialeurodes citri (Ashmead) (Heteroptera: Aleyrodidae), on oranges in California

Populations of Dialeurodes citri (Ashmead) on oranges were studied in two orange orchards in southern California, USA, to quantify developmental times and mortalities affecting this species. Four populations were followed in detail for three generations over 2 years, by monitoring the development and survival of 200 individuals in each population. Overall, preimaginal mortality among the generation studied varied from 56 to 94%. No evidence of disease or parasitism was present in the populations, and mortality was likely due to generalist predators. Weather records for the period were typical for the region, and periods of rainfall or elevated temperatures did not show any correlation with periods of mortality in the populations. Overall, the populations have high survival rates for whitefly populations, and this high survival is likely a major contributing factor to their pest status in California orchards. Addition of natural enemies to reduce the survival rates of these populations is proposed as the next course of action in suppressing populations below damaging levels.     

Impact of natural enemies on coffee leafminer Leucoptera coffeella (Lepidoptera: Lyonetiidae) population dynamics in Chiapas, Mexico

Coffee leafminer, Leucoptera coffeella, is a pest in many New World coffee growing areas. Previous studies suggested that its population dynamics were strongly affected by natural enemies, particularly of larvae, and physical environmental conditions. Our study documented through field surveys and life table analyses (i) the natural enemy complex associated with coffee leafminer and (ii) the impacts of natural enemies on the population dynamics of coffee leafminer, on coffee (Coffea arabica) at two elevations and two rainfall levels in the Soconusco region of Chiapas, Mexico. Twenty-two larval parasitoid species (including 14 morphospecies) were collected. Egg and pupal parasitoids were not recovered. Life table analyses showed that parasitism contributed 10% of real mortality, and parasitism rates were 8–10-fold higher at the low (<550 m) versus high (>950 m) elevation; parasitism rates were similar under low (<100 mm) and high (>400 mm) rainfall. Seventeen predator species (including five morphospecies) were collected, of which most were ants (Formicidae, 14 species) that contributed >58% of real mortality. Life table analyses showed that predation rates were higher at high versus low elevation and under high versus low rainfall. Independently of elevation and rainfall, egg predation (likely by ants) was the most important source of indispensable mortality (range = 0.13–0.30), except at low elevation and high rainfall where pupal predation (=0.14) was similarly important. Also, predation was the main source of coffee leafminer larval and pupal mortality during a 13-month period in a low elevation coffee farm and was highest during the rainy season (>400 mm rainfall/month), when coffee leafminer prevalence was highest. Overall, predation of eggs and pupae (the latter particularly at low elevation), mostly by ants, were the most important sources of coffee leafminer mortality. Because ants were the main source of coffee leafminer egg and pupal mortality, their importance and potential role in coffee pest management strategies were discussed.     

Patterns of context-dependent codon biases

The association of codon context and codon usage was studied in seven bacteria as well as Schizosaccharomyces pombe and Encephalitozoon cuniculi. The association is strongest in magnitude closest to the codons of interest but there is apparently no rule about which of the two contexts is generally strongest associated to codon usage. In all bacterial species and in the intron-rich Sch. pombe it was furthermore observed from plots of chi2 versus N that the wobble positions of codons in the proximity cause regular peaks both upstream and downstream. This observation is discussed in relation to a possible effect of mutational pressure on the association of codon usage and codon context. Absence of peaks corresponding to the wobble positions in the intron-poor En. cuniculi, and presence in Sch. pombe, may indicate that the role of introns in the context-dependent codon bias is negligible.     

Comparison of life table parameters for Maconellicoccus hirsutus, Anagyrus kamali, Cryptolaemus montrouzieri and Scymnus coccivora

The pink mealybug Maconellicoccushirsutus Green (Homoptera: Pseudococcidae) wasrecently introduced to Trinidad. M.hirsutus almost immediately attained peststatus and despite the implementation ofcultural and chemical control measures, thepopulation increased above the economic injurylevel. Three natural enemies, Anagyruskamali Moursi (Hymenoptera: Encyrtidae), Cryptolaemus montrouzieri Mulsant (Coleoptera:Coccinellidae) and Scymnus coccivoraAyyar (Coleoptera: Coccinellidae) were introduced.Life fecundity tables were constructed for thepest-natural enemies complex in the hope ofunderstanding the interaction of each naturalenemy with its host, and, in so doing, form acomparative approach to assessing theeffectiveness of each natural enemy. Thestudies were carried out in the laboratory at27.0 ± 3.0 °C and 58.0 ± 3.0%RH, which is within the average field conditions in Trinidad.The net reproductive rates (R_o), theinnate capacity for increase (r_m) and thefinite rate of increase () were found to behigher for the natural enemies compared to thepest. The doubling time for M. hirsutuswas 8.83 days, while A. kamali, C.montrouzieri and S. coccivora populationsdoubled in 2.09, 5.13 and 4.45 daysrespectively. The significantly higherpopulation parameters of the natural enemies,coupled with their shorter doubling times, meanthat their populations can grow faster and thusexert a controlling effect on pest numbers.     

Unconditional small-sample confidence intervals for the odds ratio

The traditional approach to 'exact' small-sample interval estimation of the odds ratio for binomial, Poisson, or multinomial samples uses the conditional distribution to eliminate nuisance parameters. This approach can be very conservative. For two independent binomial samples, we study an unconditional approach with overall confidence level guaranteed to equal at least the nominal level. With small samples this interval tends to be shorter and have coverage probabilities nearer the nominal level.