Evidence for mate‐encounter Allee effect in an invasive longhorn beetle (Coleoptera: Cerambycidae)

1. Limited empirical support is available for mate‐encounter Allee effects in invasive insects due to the logistical challenges of studying demographic trends in low‐density populations. 2. Traps baited with pheromone and spruce volatiles were used to monitor the abundance of female Tetropium fuscum F. (Coleoptera: Cerambycidae) at multiple sites in Nova Scotia in 2011 and 2012. Each female was dissected to determine the presence or absence of sperm in its spermatheca (mated or virgin female, respectively). 3. Both male and total T. fuscum abundance declined with increasing distance to the focal point of T. fuscum's invasion. Female mating probability declined with male abundance and with distance from the invasion focus, and mating probabilities were very low at the most peripheral sites. Difficulty in encountering mates may thus contribute to limiting the spread of T. fuscum. 4. The approach outlined here could be integrated into existing surveys of wood borers using traps baited with semiochemicals to improve our understanding of the role of the mate‐encounter Allee effect in invasion dynamics.     

Residence Probability and Population Size of Red Knots During Spring Stopover in the Mid-Atlantic Region of the United States

ABSTRACT Weekly counts of western Atlantic red knots (Calidris canutus rufa) at their Delaware Bay migration stopover site have suggested a major decline since the 1980s. We estimated red knot spring passage population size in the New Jersey Coast-Delaware Bay region (DENJ; 2004 and 2006) and Virginia (VA; 2006 and 2007), USA, by correcting weekly aerial counts for mean daily residence probability between counts in a Monte-Carlo simulation. We used daily telemetry relocations in mark-resight models to estimate mean daily residence probability. Average daily residence probability was approximately 1.0 in mid-May, 0.96–0.97 in the week of 22 May, and 0.64–0.77 after May 28 in DENJ in 2004 and 2006 and in VA in 2006. Average daily residency was approximately 0.88 in VA in 2007 from 22 May to 5 June. No birds moved from VA to DENJ in 2006 and only 2 birds (5.5%) moved in 2007. Stopover population sizes (±SE) in DENJ were 17,108 ± 1,322 in 2004 and 19,555 ± 831 in 2006, and in VA were 7,224 ± 389 in 2006 and 8,332 ± 718 in 2007, significantly greater than peak aerial counts. Years with similar peak counts had different residence probabilities; hence, adjustments for turnover should be used in the future to assess annual population changes. Our results suggest that VA can support a significant portion of this red knot subspecies during migration in at least some years. Managing red knots for recovery should entail improving our understanding of the use of other Atlantic Coast sites and protecting key coastal habitat from disturbance and development.     

The use of discriminant analysis for the estimation of sampling biases for female tsetse

ABSTRACT.

• 1 In this paper we investigate whether the technique of discriminant analysis can be used to estimate sampling biases for female tsetse.
• 2 Discriminant analysis was first applied to laboratory samples of female tsetse, Glossina morshans morsitans Westwood, to test whether flies of known history could be assigned to the correct day of the pregnancy cycle on the basis of their fat, haematin and corrected residual dry weight.
• 3 Following the satisfactory results from the laboratory samples, the same technique was applied to field samples of G.m. centralis Machado captured by electric traps and hand nets in Zambia and of G.palpalis palpalis (Robineau-Desvoidy) captured in biconical traps at five sites in Ivory Coast. The results show that flies on day 1 of the pregnancy cycle were most likely to be caught, with a second peak of day-6 and day-7 flies, while very few day-8 or day-9 flies were caught.
• 4 These major peaks in fly trappability coincide with the known feeding habits of female tsetse, and indicate synchrony of feeding by many members of the population immediately after larviposition and again as the larva in utero moults from the second to third instar. G.palpalis is relatively more available at this later stage of its pregnancy cycle to the capture methods used than is G.morsitans. A third feed may be taken at a more variable point in the pregnancy cycle.
• 5 This method of estimating the sampling biases of female tsetse could allow an estimate of total population size, as long as the absolute sampling efficiency of flies on any one day of the pregnancy cycle could be established by, for example, mark-release-recapture experiments.

     

Detrimental effects of recent ocean surface warming on growth condition of Atlantic salmon

Ocean climate impacts on survivorship and growth of Atlantic salmon are complex, but still poorly understood. Stock abundances have declined over the past three decades and 1992–2006 has seen widespread sea surface temperature (SST) warming of the NE Atlantic, including the foraging areas exploited by salmon of southern European origin. Salmon cease feeding on return migration, and here we express the final growth condition of year‐classes of one‐sea winter adults at, or just before, freshwater re‐entry as the predicted weight at standard length. Two independent 14‐year time series for a single river stock and for mixed, multiple stocks revealed almost identical temporal patterns in growth condition variation, and an overall trend decrease of 11–14% over the past decade. Growth condition has fallen as SST anomaly has risen, and for each year‐class the midwinter (January) SST anomalies they experienced at sea correlated negatively with their final condition on migratory return during the subsequent summer months. Stored lipids are crucial for survival and for the prespawning provisioning of eggs in freshwater, and we show that under‐weight individuals have disproportionately low reserves. The poorest condition fish (～30% under‐weight) returned with lipid stores reduced by ～80%. This study concurs with previous analyses of other North Atlantic top consumers (e.g. somatic condition of tuna, reproductive failure of seabirds) showing evidence of major, recent climate‐driven changes in the eastern North Atlantic pelagic ecosystem, and the likely importance of bottom‐up control processes. Because salmon abundances presently remain at historical lows, fecundity of recent year‐classes will have been increasingly compromised. Measures of year‐class growth condition should therefore be incorporated in the analysis and setting of numerical spawning escapements for threatened stocks, and conservation limits should be revised upwards conservatively during periods of excessive ocean climate warming.     

Testing the nutrition hypothesis for the adaptive nature of insect galls: does a non‐adapted herbivore perform better in galls?

Abstract.  1. The nutrition hypothesis for the adaptive nature of galls states that gall-inducing insects control the nutrient levels in galls to their own benefit. Although the nutrition hypothesis is widely accepted, there have been few empirical tests of this idea.
2. A novel method is presented for testing the nutrition hypothesis that links manipulation of gall nutrient levels by the gall inducer to herbivore performance. The effects of adaptation and nutritional advantage are separated by using a herbivore that is adapted to a host plant susceptible to galling but one which never enters the gall environment.
3.  Hellinsia glenni (Cashatt), a plume moth (Pterophoridae) and one of its host plants provide an excellent system for testing the nutrition hypothesis because H. glenni larvae feed internally on the relatively nutrient-poor stems of a goldenrod, Solidago gigantea , but do not venture into the nutrient-rich galls induced on that plant by a tephritid fly, Eurosta solidaginis . The nutrition hypothesis was tested by transplanting early-instar H. glenni larvae into galls and stems of S. gigantea to determine if the larvae transplanted to galls would perform better compared with those larvae transplanted to stems.
4. The results support the nutrition hypothesis for the adaptive nature of galls. Hellinsia glenni achieved greater final mass in the gall environment compared with the final mass larvae achieved in the stem environment. There was also evidence that the quality of gall tissue is controlled by the gall inducer, which has not been previously demonstrated for mature E. solidaginis galls.     

Pathogenic variability of downy mildew (Sclerospora graminicola) on pearl millet. II. Statistical techniques for analysis of data

Different cultivars of pearl millet were exposed to infection by asexual propagules of Sclerospora graminicola in Polythene tunnels. Subsequent incidence of disease was measured on one-month old seedlings. The data consisted of binomial proportions based on differing total numbers of seedlings. It is shown how to utilise the logit link in the GLIM statistical package for analysis to compare variety performances. In addition the possibilities of interplot interference and intraplot variation were investigated using GLIM. Interplot interference occurred infrequently and did not affect the rank order of the cultivars in terms of their response to the fungus infection. Intraplot variation was also shown to be non significant in spite of proximity of some plants to the disease spreader plants. Once these potentially confounding phenomena were eliminated the cultivars could be compared directly with impunity. GLIM was also used to confirm that the type of symptom expression was a stable feature of each host genotype.