Carmine A. Lanciani

Resource Partitioning in Species of the Water Mite Genus Eylais

Resource partitioning was studied in 20 species of the water mite genus Eylais, the larvae of which parasitize adult Coleoptera and Hemiptera living in shallow ponds. Co—existence of sympatric species is possible because the mites exploit host resources in different ways. Most commonly they parasitize different species, but when hosts are identical, the mites remain segregated by differences in the precise site of attachment, biotope, or season of parasitism. Mite biology, host dispersal, and competition for attachment sites from other water mite species may restrict further subdivision of host resources. See full-text article at JSTOR

Demonstrating parasitic water mite-induced mortality in natural host populations

The truncated negative binomial distribution is used to demonstrate water mite-induced mortality in a field population of the mosquito host Anopheles crucians . Consistent changes in the parameters of this distribution and in the number of hosts expected in higher mite load classes as truncation is applied to successively lower mite load classes suggest that many heavily parasitized individuals were missing from field samples. These changes are not observed in distributions derived from an association between parasitic larvae of another water mite, Hydrachna conjecta , and the insect Sigara ornata , which is apparently immune to this parasite. Although the method discloses parasite-induced mortality that is non-linearly related to parasite load, it fails to reveal linear parasite-induced mortality in a hypothetical example.

Pesticide Resistance and Metabolic Rate in German Cockroaches (Dictyoptera: Blattellidae)

Although physiological resistance mechanisms to most pesticides have developed in insects, costs may be associated with these mechanisms. For example, a reproductive cost is shown by resistant tobacco budworms, Heliothis virescens , which produce significantly fewer fertile eggs (Plapp et al. 1990), and a behavioral cost is shown by resistant Anopheles mosquitoes, which spend less time searching for hosts (Rowland 1987). An energetic cost may also be associated with resistance. For example, a common mechanism of pesticide detoxification is enzymatic breakdown of ingested or ab-

Larval Photoperiod and Metabolic Rate in Drosophila Melanogaster

The metabolic rate of adult Drosophila melanogaster Meigen is partially determined by larval photoperiod. Generally, flies reared in a short-day environment have higher whole-animal and weight-specific metabolic rates than do flies reared under long-day conditions. The effect of photoperiod on metabolic rate may help explain why short-day flies develop faster and have higher Malthusian fitness than do long-day flies. The photoperiod effect may also facilitate the maintenance of viable populations in seasonally variable environments.

The effect of photoperiod on cold tolerance in Drosophila melanogaster.

Abstract 1. 1.|Descendents of Florida and Ithaca, U.S.A. populations of Drosophila melanogaster were reared under short (10 h light: 14 h dark) or long (14 h light: 10 h dark) photoperiods. 2. 2.|Flies were chilled for 8, 16, 32, or 64 min and the time to recovery was recorded. 3. 3.|Recovery time increased as chilling time increased. 4. 4.|Recovery time was also related to photoperiod; short-photoperiod flies recovered faster than did long-photoperiod flies. 5. 5.|These results together with earlier observations of higher metabolic rates of short-day flies indicate the importance of photoperiod in adaptively modifying physiological features.

The influence of parasitic water mites on the instantaneous death rate of their hosts

SummaryThe effect of 2 species of water mites on the instantaneous death rate of their hosts was measured on the basis of laboratory experiments. In both parasite-host association — the parasitic water mite Hydryphantes tenuabilis on the aquatic insect host Hydrometra australis and the parasitic water mite Arrenurus pseudotenuicollis on the mosquito Anopheles crucians — the effect of mite load on the instantaneous death rate of the host appeared to be linear. Also, the impact of a single parasite on the hosts death rate was apparently related to the ratio of parasite to host body weight. The results of this study are in general agreement with recent theoretical investigations of the regulation of host populations by parasites.

Diel cycles and measurement of metabolic rates in Drosophila

Abstract 1. 1. Increasing incubation time over which metabolism is measured can provide reasonable estimates of metabolic rates in species with diel cycles. 2. 2. The rates of metabolism of Drosophila melanogaster and D. simulons were measured over consecutive 1-hr intervals to confirm the existence of diel variation. 3. 3. These hourly measurements were integrated over 4- to 9-hr intervals to simulate long incubation times. 4. 4. The estimates of metabolic rate obtained from the 4- to 9-hr intervals closely agreed with the average hourly measurements in both species. 5. 5. Consequently, experiments requiring long measurement intervals that may include periods of fluctuating metabolic rates can provide valid comparative estimates of energy expenditures.

EARLY ABSCISSION IN HACKBERRY LEAVES BEARING PACHYPSYLLA GALLS (HOMOPTERA: PSYLLIDAE)

Early leaf abscission has been reported in several species of plants attacked by insects, e.g., leaf miners (Faeth et al. 1981), gall aphids (Williams & Whitham 1986), and psyllids that do not form galls (Clarke 1962, 1963). In northern Florida, the leaves of hackberry ( Celtis leavigata Willd.) are commonly exploited by the glabrous nipple gall Pachypsylla sp. (possibly Pachypsylla celtidiscucurbita Riley, Yang & Mitter 1994). Observations of very early leaf fall from hackberry trees on the University of Florida campus in Gainesville, Florida, in late August revealed that most fallen leaves bore galls of this psyllid. Accordingly, we sampled leaf fall from hackberry trees throughout the autumn of 1995 to determine whether galled leaves represented a greater proportion in early than in late leaf falls. We chose 3 widely separated sites on the University of Florida campus. Site 1 was a large, solitary hackberry tree near Keys Residential Complex, site 2 was a small patch of hackberry trees of various sizes on the northwest edge of campus, and site 3 was a large, solitary hackberry tree near the Psychology Building. At each site on 8-IX-95, we delineated a sample area (1.5 m by 1.0 m) where we cleared all leaves. On 29-IX-95, 6-XI-95, 21-XI-95, 29-XI-95, and 6-XII-95, we collected all leaves in each sample area. We later inspected the leaves for galls and calculated the percent of leaves bearing galls. We analyzed the changes in percent galled leaves over time at each site with an ANCOVA model after arcsine transforming percent data. Our analysis of the data presented in Table 1 revealed that as autumn progressed, leaves bearing galls represented a significantly decreasing percent of fallen leaves ( P = 0.0009). The percent of fallen, galled leaves averaged over all 3 sites showed the expected trend: 50.55% (29-IX-95), 44.90% (6-XI-95), 40.97% (21-XI-95), 31.27% (29XI-95), and 30.60% (6-XII-95). Early abscission of exploited leaves may be an induced plant defense because it can kill exploiters by preventing them from completing development (Williams & Whitham 1986; Prezler & Price 1993). However, leaf abscission may more often be viewed as a plant response to leaf damage, especially if the attacker emerges before leaf abscission or completes development even in abscised leaves (Stiling & Simberloff 1989). Whether adults of P. sp. emerge before leaf abscission or nymphs complete development in abscised leaves is not known. But, adults of the closely related Pachypsylla celtidismamma (Fletcher) do emerge from galls in Celtis occidentalis L. before leaf fall (Lill 1998). Thus, early leaf abscission in trees attacked by gall-making psyllids could be simply a response to leaf damage. We thank Susan Halbert of the Florida Division of Plant Industry for taxonomic information on Pachypsylla species.

Comparative energetics of a northern and southern population of Drosophila melanogaster

Abstract 1. 1. Weight-adjusted metabolic rates of laboratory-reared, female descendents of Drosophila melanogaster collected from northern New York and northern Florida were compared at 18,21, and 25°C. 2. 2. New York flies had significantly higher rates of metabolism at incubation temperatures of 21 and 25°C but not at 18°C. 3. 3. A nested analysis of variance showed that at 2PC, 29% of the total variance in metabolic rate was due to between-population differences and 27% was due to line differences within populations. 4. 4. The metabolic rate characteristics of both groups of flies are consistent with their patterns of fecundity and seasonal abundance.

Metabolic rate and sexual activity in Drosophila simulans

Abstract The metabolic rates of 4-day-old Drosophila simulans females are affected by sexual activity. Virgin females have the lowest rates of metabolism, inseminated females that were separated from males had higher rates of metabolism, and females that were kept continuously in contact with males had the highest rates of metabolism. Differences between the metabolic rates of the latter two classes of females are unrelated to differences in their rates of egg laying.