Allen C Cohen

Geometric relationships between whitefly feeding behavior and vascular bundle arrangements

This study revealed strong evidence that nymphs of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, are obligate feeders on vascular bundles and that there are large differences between different host plants as to the availability of vascular bundles to silverleaf whitefly nymphs. The relationship between nymphs and leaf vascular bundles was studied using 1) leaf sectioning and 2) techniques of leaf clearing of intact leaves. A geometric model is presented of the feeding relationship of vascular bundle‐using homopterans. The relative abundance of vascular bundles was examined in six species of host plants that varied from highly preferred to tolerably acceptable. Included in order of acceptance were cantaloupe, cotton, hibiscus, broccoli, lantana and lettuce. The length of vascular bundle per 1.0 mm2 of leaf surface ranged from about 10 mm in cantaloupe to 2.8 mm in lettuce. Salivary sheaths were found to connect with vascular bundles in 100% of the intact nymphs examined by the staining and clearing technique. However only 64% of those examined by the sectioning technique appeared to be connected to vascular bundles. This indicates that the sectioning technique leads to a high rate of error, causing an underestimation of the importance of direct contact with vascular bundles. About 50% of epidermal stylet penetrations were through epidermal cells; the remaining 50% went through intercellular junctions. On cotton leaves, the distance between the point of labial contact with the leaf surface and the nearest point of the vascular bundle rarely exceeded 60 μm. Our studies show that while 50% of lettuce leaf‐surface was beyond 60 μm of a vascular bundle, only 10% of cantaloupe leaf surface area was outside of the 60 μm range. In cotton, mean distance from labium to the nearest point of the vascular bundle was 40.9 μm (SEM = 2.66, N = 50, range 0–80 μm). Over 98% of all salivary sheaths went to minor veins (78% to single‐filament vascular bundles, nearly 20% to double filament bundles). Fewer than 2% went to bundles with 3 or more filaments.

Prey selection by in vitro- and field-reared Geocoris punctipes

The patterns of prey selection of Geocoris punctipes (Say) (Hemiptera: Lygaeidae), reared continously on artificial diet for six years, were almost identical with patterns shown by their field‐derived counterparts.

Effects of water stress and rehydration on hemolymph volume and amino acid content in the blister beetle, Cysteodemus armatus

1. 1. Hemolymph volume, osmolality, amino acid concentrations and fecal amino acid concentrations were measured in a desert blister beetle, Cysteodemus armatus LeConte, which were not desiccated, 10% desiccated (% of body mass), or rehydrated. 2. 2. Desiccation and rehydration had significant effects on the hemolymph volume in this species but not hemolymph osmolality. 3. 3. Total amino acid concentrations were significantly affected by hydration state. 4. 4. Hemolymph urea, asparagine, methionine and histidine were significantly affected by hydration state, but other ninhydrin positive substances (NFS) were not affected. 5. 5. While production of fecal material (frass) decreased with desiccation, the concentration of most amino acids increased, indicating excretion as an avenue of hemolymph osmoregulation.

Effect of Antifungal Agents on Biological Fitness of Lygus hesperus (Heteroptera: Miridae)

Abstract Artificial diets have become important components of rearing systems for insects that are used for research purposes and in commercial production. Because the rearing conditions for insects also provide ideal settings for mold growth, antifungal additives are often used to reduce diet contamination. However, the antifungal agents must not only be effective in mold suppression, they must also be safe to the target insects of the rearing programs. The toxicity of five commonly used antifungal agents (benzoic acid, formalin, methyl paraben, propionic acid, and sorbic acid) was tested using diet bioassays on Lygus hesperus Knight, and the effect on biological fitness was measured. Biological fitness was defined as total number of survivors, mean biomass (dry weight) accumulated per cage over the total treatment period, egg production, time to adult emergence, and time to start of egg laying. Methyl paraben and formalin were found to have significant negative effects on these measurements of biological fitness. Challenge tests to determine the ability of the antifungal agents to suppress mold growth when inoculated into the diet medium are currently in progress.

Demonstration and preliminary characterization of α-amylase in the sweetpotato whitefly, Bemisia tabaci (Aleyrodidae: Homoptera)☆

Abstract An α-amylase that hydrolyzes unmodified starch or amylopectin azure was demonstrated in crude and partially purified extracts prepared from whole carcasses of sweetpotato whiteflies (SPW) ( Bemisia tabaci Genn.). All nymphal instars and adult SPW, including newly eclosed crawlers that had not yet fed on plant materials, were found to have active α-amylase. α-Amylase activity per mg protein was greatest in 1st instars and decreased with age up to the “pupal” stage, with a very slight increase in activity in adults. However, activity per individual did not differ substantially as a function of age. The α-amylase had an apparent molecular weight of about 70 kDa, an isoelectric point of 6.32 and eluted with about 250 mM NaCl from a strongly basic anion-exchange column. The enzyme activity was inhibited by EDTA and not activated by either NaCl or KNO 3 . CaCl 2 strongly enhanced activity. α-Amylase activity was greatest at pH 7.0, but there was considerable activity at pHs above 7.0. The K m of the α-amylase was 1.47 Mm with p -nitrophenyl α- d -malto-heptaoside as substrate. The presence of an amylolytic enzyme in a phloem-feeding insect is unexpected and raises questions about current assumptions of feeding behavior of this species.

Chemical composition of tobacco budworm eggs during development

Abstract 1. 1. The protein, carbohydrate, and lipid composition were analyzed in eggs of Heliothis virescens during four developmental periods: 0, 24, 48 and 65 hr (pre-eclosion). Dry weights of individual eggs decreased from 24.6 μg to 15.7 μg/egg during the 65 hr period. 2. 2. Protein did not decrease significantly while carbohydrates (largely glycogen) decreased from 10.6 to 3.1% of the dry weight and lipids decreased from 16.6% of the dry weight to 8.1%. Glycerophospholipids did not change significantly while triacylglycerols decreased dramatically. 3. 3. The fatty acyl composition did not follow the same compositional profile as the diet. 4. 4. The major fatty acyls were C16:0, C18:1 and C18:2, while those in the diets were C16:0, C18:0, C18:2 and C18:3. 5. 5. Each egg utilized for catabolism 0.7 μg protein, 2.13 μg carbohydrate and 2.57 μg of lipid which account, respectively, for 8.3, 24.8 and 66.9% of the eggs energy expenditure.

Effects of water stress on hemolymph volume, osmotic potential and chemical composition in Megetra cancellata

Abstract 1. 1. Rates of water loss in Megetra cancellata were very high compared to those reported for other xeric arthropods. 2. 2. Hemolymph weight in hydrated animals was 43.0% of the total body weight while it was 24.7% in desiccated animals that had lost 16.1% of their body weight as water. 3. 3. Hemolymph osmotic potential increased from 417 to 447 mOsm/kg in desiccated beetles, but osmotic regulation was evident. 4. 4. Total hemolymph protein mass and concentration decreased in desiccated beetles while amino acid concentrations remained constant (at about 70 mM). 5. 5. Na+ and −PO4 concentrations increased in desiccated beetles. 6. 6. Cl− and K+ concentrations in desiccated beetles were equal to those in undesiccated beetles.

Fatty acid and amino acid composition of teratocytes from Lygus hesperus (miridae: hemiptera) parasitized by two species of parasites, Leiophron uniformis (braconidae: hymenoptera) and Peristenus stygicus (Braconidae: Hymenoptera)

Abstract 1. 1. Teratocytes (dissociated trophamnion cells liberated from eggs of certain hymenopteran endoparasites into host hemolymph upon hatch) from Lygus hesperus parasitized by Peristenus stygicus or Leiophron uniformis were analyzed and compared. 2. 2. Fatty acid profiles were similar in the 2 types of teratocytes except for myristic acid (C14:0) which was found in higher concentrations in P. stygicus and linolenic acid (C18:3) which was found in higher concentrations in L. uniformis . 3. 3. Of 22 amino acids found in both species, there were 12 that differed significantly between the 2 species (aspartic acid, threonine, α-aminoadipic acid, alanine, valine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, and arginine). Most of these were essential amino acids, and in every case, concentrations were higher in P. stygicus than in L. uniformis associated teratocytes.

Temperature and water relations of a parasitic wasp in its free-living adult stage and its phytophagous host☆

Abstract 1. 1. Temperature and water relations in the parasitic wasp Anaphes ovijentatus (Crosby and Leonard) (Mymaridae: Hymenoptera), one of the smallest of insects, and its host Lygus hesperus Knight (Miridae: Heteroptera) were studied. 2. 2. LT50s for the free living adult female wasps were higher (20.63 hr) than those of male wasps (14.68 hr) and 1st instar Lygus nymphs (7.07 hr) at 30°C with an RH of 3. 3. Critical thermal maxima were significantly higher in the parasitic wasp (47.6°C) than in its host (45.7°C). 4. 4. Rates of water loss were dependent upon temperature and saturation deficit with evidence of an ability of both species to exercise some control over loss rates under increasingly stressful conditions. 5. 5. Rates of water loss of both species were comparable to those of other xeric-adapted insects on a loss per unit of surface area-specific basis. On a weight-specific basis, rates of water loss for these insects which weigh less than 100 μg were higher than those of larger, xeric-adapted species.